Dissertations / Theses on the topic 'Precious metals'

The world population reached 7.5 billion inhabitants in April 2017. The number of mobile phones will reach 4.77 billion by the end of this year. Mobile phones are made of more than 50 elements. Discoveries of economically viable gold mines in the main producing countries have been slowing down significantly since the 1800s. The global surface temperature of the planet is warming at 0.17⁰C per decade relative to pre-industrial levels. The mobile phone was chosen for this thesis because it is a comprehensive unit of hazardous waste and e-waste. Mobile phones are a municipal solid waste and public health concern. The low energy and low barrier to entry recycling business this thesis envisions recycles precious metals from end of life mobile phones close to where the devices are discarded. This thesis uses system dynamics to model the exponential adoption of mobile phones and its impact in mining and CO₂e emissions. The model is the basis to calculate the return of new precious metal recycling businesses. Climate change is one of the hardest problem men has ever faced because it requires many countries to work together to establish climate centric governance and policies. Businesses are reviewing their supply chain and energy sources. This work focuses on disruptive low energy and low barrier to entry technologies to recycle precious metals from mobile phones. Local recycling businesses will create jobs and stimulate the economy in B.C., Canada, and the world.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

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Using regression and correlation approaches covering the last twenty years of daily data for seven countries, this thesis investigates safe haven and hedge abilities of precious metals against international equities over a given state of the economy. Furthermore, this thesis examines different portfolios performance in-samples and out-of-samples with the aim to observe whether investing in precious metals can help to mitigate investor risk management. The key results are: (i) Gold is the finest precious metal for international hedging against equities (ii) Gold provides valuable portfolio risk management benefits (iii) 60/40 portfolios allocated with gold proffer good investor outcomes.
Recorrendo a duas abordagens diferentes, regressão e correlação, e cobrindo os últimos vinte anos de dados diários para sete países, esta tese investiga as propriedades "safe haven" e "hedge" dos metais preciosos, em comparação com acções internacionais para um dado estado da economia. Adicionalmente, esta tese avalia o desempenho de diferentes portfolios, dentro e fora da amostra, com o objectivo de verificar se o investimento em metais preciosos poderá ajudar a atenuar a gestao do risco por parte do investidor. Os principais resultados são os que se seguem: (i) O ouro é o melhor metal precioso para um "hedging" internacional em oposição às acções (ii) O ouro permite obter valiosos benefícios de gestão de risco do portfolio (iii) 60/40 dos portofios atribuidos com ouro permitem ao investidor obter bons resultados.

The increasing demand for precious metals such as palladium and gold for industrial applications has led to the exploration of sustainable environmental-friendly technologies to capture and recycle these metals from mine wastes. Phytomining is an emerging technology that makes use of the ability of plants to extract and accumulate metals from soil and water. Chapter 3 discusses the potential of phytomining to recover palladium from mine waste materials. These studies determined that willow (Salix sp.) and miscanthus (Miscanthus giganteus) were able to accumulate high levels of palladium in the aerial tissues when grown on synthetic media containing palladium as well as on mine waste materials. The use of chemical lixiviants improved the uptake and translocation of palladium in both willow and miscanthus. The potential of palladium nanoparticle formation in plants as plant-based catalysts was investigated but no palladium nanoparticles were detected when the plants were grown on synthetic mine waste. Chapter 4 evaluates the potential of merA gene for mercuric reductase in Arabidopsis as a genetic engineering approach to improve tolerance to gold and palladium in plants. In contrast to previously published findings merA expression did not increase tolerance of the transgenic plants to toxic levels of gold and palladium. Inhibition studies on purified mercuric reductase further revealed that gold and palladium inhibited the activity of MerA with ionic mercury. In Chapter 5, the potential of synthetic biology strategy was also investigated where the expression of synthetic short peptides, which are shown to be responsible in the formation of various sizes of metal nanoparticles in vitro, were found to increase the formation of smaller sized gold nanoparticles (< 10 nm diameter) compared to wild type plants when expressed in Arabidopsis. Chapter 6 describes the transcriptional response of Arabidopsis to precious metals and investigates the potential involvement of heavy metal transporter 5 (AtHMA5) in the detoxification mechanism for gold and palladium. AtHMA5 was found to be strongly up regulated in response to gold and palladium. However, studies with Arabidopsis hma5-1 mutant knockout lines and yeast heterologous expression studies demonstrated that gold and palladium is not a substrate for AtHMA5 suggesting that AtHMA5 is not involved in gold and palladium detoxification. Overall, this work is the first to describe a holistic approach in searching for suitable field applicable plant candidates for phytomining of precious metals such as palladium and gold as well as strategies to improve its uptake, tolerance and nanoparticle formation in plants.

The project aim is to develop recyclable systems based on ionic liquids (ILs) or deep eutectic solvents (DESs), in combination with ligands and/or oxidants, for the recovery of Pd and Pt from catalytic converters and of Au from electronics using non-toxic reagents. The synthesis of dione and dithione ligands (1,4-dimethyl-2,3-piperazinedione, 1,4-dimethyl- 2,3-perhydrodiazepinedione, 1,4-dimethyl- 2,3-piperazinedithione, and 1,4-dimethyl-2,3- perhydrodiazepinedithione) and their iodine adducts (1,4-dimethyl-2,3-piperazinedithione/ triiodide, 1,4-dimethyl-2,3-perhydrodiazepinedithione/ bisdiiodine), for the dissolution of Pd and Pt was investigated. 1,4-dimethyl-2,3-piperazinedione, 1,4-dimethyl-2,3-perhydrodiazepinedione, and 1,4-dimethyl-2,3-piperazinedithione were successfully synthesised using conventional methods. 1,4-dimethyl-2,3-piperazinedione and 1,4-dimethyl-2,3- perhydrodiazepinedione were also synthesised mechanochemically while 1,4-dimethyl-2,3- piperazinedithione can be synthesised sonochemically. The adduct 1,4-dimethyl-2,3- piperazinedithione/triiodide was also successfully synthesised. The mild conditions which would lead to the dissolution of Pd, Pt, and Au were examined. The best results were achieved in DESs, where metal solutions up to 200 mM (Reline 200) and 300 mM (Ethaline 200) were obtained, using a Pd:iodine ratio of 1:4. The highest Au concentration (57.1 mM) was obtained in [BMIM]OTf using a triphenylphosphine:iodine ratio of 1:1. Mixed chloride/iodide square-planar Pd(II) complexes are believed to form in the DESs. Solutions of Pd and iodine in either DES produce CVs that are similar to each other. Dissolved Pd was recovered by electrodeposition from Reline 200 and the mixture could be recycled at least twice. Pd was also successfully recovered from a used catalytic converter as proven by cyclic voltammetry, SEM, and EDX spectroscopy. A triphenylphosphine:iodine mixture in [BMIM]OTf was able to dissolve Au at room temperature without the need of anhydrous/anaerobic conditions. The Au complex formed has not been confirmed but appears to be a unique, stable product. Approximately 53% of Au was successfully recovered via electrodeposition and the remaining solution successfully re-used for further Au dissolution.

This thesis investigates the presence of speculative bubbles in the prices of precious metals. The investigation develops in three stages. First, we present the theoretical framework. Second, we carry out an institutional analysis of the gold market. Third, we conduct an econometric investigation using a comprehensive new data set of the prices of gold, silver and platinum. Speculation is a phenomenon strictly related to expectations. Hence, the natural theoretical framework for the study of speculative bubbles begins with a theory of expectations. The theory of speculative bubbles emerges from the non-uniqueness of solutions to rational expectations models. We present the theoretical background on the problem of multiple solutions to rational expectations models. We then critically examine the theoretical and empirical literature on speculative bubbles, pointing out the questions still unanswered in the field. The high volatility and the presumed speculative attacks in the 1970's and 1980's make the prices of gold, silver and platinum a natural choice for investigating the presence of speculative bubbles. An institutional analysis of the gold market show the complexity of the factors determining its price. This thesis adopts two empirical approaches. The first concerns tests of the restrictions that the presence of speculative bubbles impose on the prices of precious metals. In particular, it applies non-parametric tests in the spirit of the Blanchard and Watson (1982) approach to test for bubbles in the price of gold. Their results are contradictory and overall show little evidence of bubbles in the price of gold. In contrast, our results indicate the presence of speculative bubbles in the prices not only of gold, but also of silver and platinum. The second approach which, to our knowledge, has not previously been explored, consists of inferring the presence of bubbles through a comparison of the market fundamentals and the price movements of the three metals. The results provide evidence of the presence of speculative bubbles.

Thesis (MSc. (Physics)) -- University of Limpopo, 2016
The stabilities of PtS to PdS and PdS to PtS were investigated using density functional theory within the generalized gradient approximation. Their structural, electronic and mechanical properties were determined to show their stability and the effect of pressure on different compositions. We found good correlation of calculations with available ex-perimental data. The lattice parameters were observed to fluctuate with increasing con-centration for both systems. Furthermore, heats of formation were calculated to deter-mine the relative structural stability of the systems. They predict that the most stable structure is Pd50S50 P42/mmc and Pt25Pd25S50 P42/mmc being the least stable. Pd12.5Pt37.5S50 P42/m is the most stable and Pd50S50 P42/m being the least stable struc-ture. The Pt37.5Pd12.5S50 P1 was said to be the most stable structure and Pd50S50 P1 be-ing the least stable. The phonon dispersion calculations show that Pt50S50 P42/mmc, Pd50S50 P42/mmc, Pd12.5Pt37.5S50 P42/m and Pt50S50 P1 (derived from P42/mmc) are me-chanically stable, consistent with calculated elastic constants. The Pt25Pd25S50 P42/mmc show soft modes, which are due to vibrations of Pt and Pd atoms in the x - y plane which suggests the instability of the structure, in agreement with C66 being negative, and consistent with heats of formation. The lattice parameters decreased steadily with increasing pressure. An anomaly was observed in Pt50S50 P1 (derived from P42/mmc), where the c lattice parameter was found to increase with increasing pressure. The elec-tronic density of states (DOS) were performed on all compositions. The DOS were sub-jected to pressure and it was generally noted that the band gap increases with increas-ing pressure. It was observed that the smaller the band gap, the more stable the struc-ture. Furthermore, phonon dispersions under pressure show that compounds with the P42/mmc and P1 (from P42/mmc) symmetries display the mixing of lower and upper en-ergy bands at pressures above 30 GPa.
National Research Foundation

Aim of this work is the analysis of the materials and parameters related to the investment casting process,mainly focusing on peculiarities and criticisms of the casting of precious metals in jewelry production.Precious metals casting is traditionally and historically targeted to overcoming limitations in terms of geometries and final quality of the cast part. Moreover, an increasing interest rises concerning the use of new technologies and the industrializations of typical handcraft skills. New materials are therefore introduced into the process, in order to be able to get thin and intricate shapes, hollow parts and innovative design features. This is leading to a substantial rearranging of the process, with a constant innovation regarding technologies and medication of traditional materials. Considering the whole process, nvestment casting is dealing with a wide range of materials, from metallic, polymeric and ceramic classes. All these materials cannot be considered as single identities, but their synergetic behavior has to be studied, not just meaning that all of them contribute to the final quality of the cast part, but taking into account possible mutual interdependencies. The research work has been divided in a preliminary analysis of the process, in order to deepen the knowledge about material features, and in a extended study on the application of competences deriving from other sectors to the specific one. In fact it’s almost impossible to find sector boundaries between jewelry and fashion accessories both in terms of process and in terms of market. Therefore the analysis of the state of the art has been widened to other processes and applications, in particular focusing on fashion accessories and eyewear component production. Market analysis clearly show a high interest of jewelry towards innovative processes/materials, often deriving from completely different fields of application. For this reason, an analysis of the investment casting process applied in the automotive and biomedical sectors can give valuable hints for the jewelry production optimization. Particular attention has also been paid to fluid dynamic analysis of the casting system, considering metal flow into the flask and following cooling and solidification. For this purpose, computational fluid dynamic has been applied to the process. Material analysis, needed for both the simulation and for a complete understanding of the process, has been carried out. Physical and thermal properties of metals and investment materials have been analyzed in order to get a proper database for casting simulation. Waxes and resins have been tested both in terms of thermal, mechanical and chemical characteristic, in order to understand their respective roles into the process and try to optimize them. Following the analysis, process implementation has been performed in order to apply information deriving from experimental tests to the process. Many parameters can be taken into account when optimizing precious metal casting; in order to focus the research activity, some limitation in terms of process have been applied. Casting trails were conducted using a static vacuum casting machine on sterling silver and 18 kt. Gold alloys, referring to traditional investment casting process.

ABSTRACT PRECONCENTRATION OF SOME PRECIOUS METALS USING DEBT IMPREGNATED RESIN Refiker, Hü
rmü
s M. Sc., Department of Chemistry Supervisor: Prof. Dr. R. Sezer Aygü
n Co-supervisor: Assoc. Prof. Dr. Melek Merdivan August 2005, 107 pages In this thesis, trace amounts of gold and silver have been determined by flame absorption spectrometry (FAAS) after preconcentration by N,N-diethyl-N'
-benzoylthiourea (DEBT) impregnated resin (Amberlite XAD-16). In the first part of the thesis, sorption behaviours of gold and silver with DEBT impregnated resin under optimized conditions
stirring time, pH, desorption of metals and metal ion capacities of the resin have been studied in batch process. Metal ion capacity of resin is calculated as 0.17 mmol/g resin and 0.104 mmol/g resin for silver and for gold, respectively. In the second part of the thesis, preconcentration of gold and silver was tried by DEBT impregnated resin using column process under optimized conditions
pH, flow rate and volume of sample solution, nature of eluent, flow rate and volume of eluent However, due to partial leaching of DEBT by time, no satisfactory and reproducible results could be obtained. In the final part of the study, metal chelates prepared in aqueous solutions were passed through the column under optimized conditions and satisfactory sorption-desorption and selective preconcentration could be achieved. Under optimized conditions, silver and gold ions at the concentrations of 0.05 &
#61549
g/mL and 0.015 &
#61549
g/mL with preconcentration factors of 7.7 and 6.7, respectively could be determined by FAAS. The proposed method is highly selective without the need for any interference elimination process. Keywords: Precious metals, Solid-phase extraction, DEBT, Amberlite XAD-16

In 1992, several thousand residents from northern Bosnia's Prijedor region were detained in the Omarska concentration camp, which was created and run on the site of an iron mine by the mine's own engineers, labourers and management. Often overlooked in discussions about the ethnoreligious nature of the Balkan conflict is the fact that Omarska's workers relied heavily on their technical knowledge (of organic compounds, geology and terrain, machinery) to generate new ways of concentrating and executing prisoners.
Anthropology

Epithermal deposits include a broad range of precious metal, base metal, mercury, and stibnite deposits. These deposits exhibit a low temperature of formation (180-280°C) at pressures of less than a few hundred bars (equivalent to depths of 1.5 - 2.0lkm). Epithermal gold deposits are the product of large-scale hydrothermal systems which mostly occur in convergent plate margin settings. Associated volcanism is largely of andesitic arc (calcalkaline to alkaline), or rhyolitic back-arc type. Porphyry Cu-Mo-Au deposits form deeper in the same systems. Genetic processes within individual deposits take place in an extremely complex manner. The resultant mineral associations, alteration styles and metal deposition patterns are even more complicated. Many attempts have been made to classify epithermal deposits based on mineralogy and alteration, host rocks, deposit form, genetic models, and standard deposits. For the explorationist, the most useful classification schemes should be brief, simple, descriptive, observationally based, and informative. Ultimately, two distinct styles of epithermal gold deposits are readily recognised: high-sulphidation, acid sulphate and low-sulphidation, adularia-sericite types. The terms high-sulphidation (HS) and low-sulphidation (IS) are based on the sulphidation state of associated sulphide minerals, which, along with characteristic hydrothermal alteration, reflect fundamental chemical differences in the epithermal environment. Highsulphidation-type deposits form in the root zones of volcanic domes from acid waters that contain residual magmatic volatiles. The low-sulphidation-type deposits form in geothermal systems where surficial waters mix with deeper, heated saline waters in a lateral flow regime, where neutral to weakly acidic, alkali chloride waters are dominant. The HSILS classification, combined with a simple description of the form of the deposit, conveys a large amount of information on mineralogy, alteration, and spatial characteristics of the mineralisation, and allows inferences to be drawn regarding likely regional controls, and the characteristics of the ore-forming fluids. The modern understanding of these environments allows us to quite effectively identify the most probable foci of mineral deposition in any given district. Current knowledge of these deposits has been derived from studies of active geothermal systems. Through comparison with alteration zones within these systems, the exploration geologist may determine the potential distribution and types of ore in a fossil geothermal system. Alteration zoning specifically can be used as a guide towards the most prospective part of the system. Epithermal gold deposits of both HS- and LS-styles are nevertheless profoundly difficult exploration targets. Successful exploration must rely on the integration of a variety of exploration techniques, guided by an understanding of the characteristics of the deposits and the processes that form them. There are no simple formulae for success in epithermal exploration: what works best must be determined for each terrain and each prospect. On a regional scale tectonic, igneous and structural settings can be used, together with assessment of the depth of erosion, to select areas for project area scale exploration. Integrated geological-geophysical interpretation derived from airborne geophysics providesa basis of targeting potential ore environments for follow-up. Geology, geochemistry and surface geophysics localise mineral concentrations within these target areas

The present study focuses on the characterization of solid-liquid extraction techniques for the separation and preconcentration of rare-earth elements and precious metals. We developed an impregnated resin with di (2-ethylhexyl)phosphoric acid (D2EHPA) in order to separate rare-earth elements
Els treballs realitzats es centren en la caracterització de sistemes d’extracció sòlid-líquid per a la separació i preconcentració de terres rares i metalls preciosos. Amb aquest objectiu es varen avaluar diferents resines quelants, majoritàriament disponibles comercialment, per a la separació i recuperació de metalls preciosos, així com la seva aplicació a processos en columna utilitzant llits de resina fixos. També s’inclou la caracterització del procés de separació d’itri i neodimi mitjançant una resina impregnada amb dissolvent

The Wolf and Capoose prospects represent two distinctly different types of precious metal deposits in volcanic rocks of the Stikinia terrane, central British Columbia. At the Wolf prospect, auriferous and argeniferous metallic minerals are in bladed quartz-carbonate veins and heterolithic breccias within Lutetian calc-alkaline rhyolite of the Ootsa Lake Group. Electrum, native silver, and silver sulphosalts occur as inclusions in and adjacent to pyrite in five silicic zones which have eight recognisable phases of veining and brecciation and are bordered by argillic and sericitic altered rhyolite. Fluid inclusions define growth zones in precious metal-bearing quartz-carbonate veins and precious metal-poor drusy quartz veins. The inclusions are primary, two-phase, liquid-rich, low salinity, and low C0₂. Homogenization temperatures of quartz-carbonate veins are 270°C and 170°C and in the late drusy quartz veins, 250°C. Oxygen and hydrogen isotope compositions of vein quartz, rhyolite, and alkali feldspar phenocrysts indicate that depositional fluids were ¹⁸0 depleted by 4 to 9 0/00. Ootsa Lake Group rocks at Wolf are formed by explosive eruptions and flows, related to a ring fault. Flat-lying rhyolite tuffs and flows are intruded by cogenetic stocks and dykes in a caldera collapse setting. Precious metal deposition occurred as one event related to quartz-carbonate veins. Later drusy quartz veins precipitated from a different fluid. Primary fluid inclusion homogenization temperatures show that fluids which deposited quartz-carbonate were boiling and existed under both hydrostatic and near lithostatic pressures at depths of about 100 m. Oxygen and hydrogen isotope compositions indicate a high degree of isotopic exchange between rhyolite and large volumes of low ¹⁸0 content meteoric fluids. The fluids evolved to a non-boiling, lower salinity, extremely ¹⁸0 depleted, precious metal-poor variety which precipitated late drusy quartz veins. Geological setting, vein and breccia textures, alteration, metal distribution and depositional fluid evolution at Wolf resemble a low sulphur, epithermal hot spring or silicified stockwork deposit. At the Capoose prospect, auriferous and argeniferous metallic minerals occur as inclusions within disseminated galena and sphalerite in calc-alkaline Maastrichtian rhyolite sills intrusive into Lower and Middle Jurassic Hazelton Group volcanic and sedimentary rocks. Flow-banded, spherulitic rhyolite sills are preserved within a minor horst. Spessartines in the sills are similar in composition to plutonic garnets with less than 5% change in end member composition from rim to core. They occur adjacent to disseminated, aggregate and vein galena, sphalerite, pyrite, arsenopyrite and chalcopyrite. Sulphide and spessartine accummulations are commonly surrounded by muscovite and quartz coronas. Sulphide poor quartz and calcite veining is in hornfelsed Hazelton Group rocks peripheral to the sills. Phyllic alteration is restricted to the sills and overprints mineralized zones. Primary two-phase, liquid-rich, low salinity, low C0₂ fluid inclusions from late silicate veins homogenize from 285°C to 335°C. Rhyolite sills are not depleted in ¹⁸0 whereas sericite, quartz and calcite are. Spessartine in rhyolite sills at Capoose crystallized as late phenocrysts stabilized by high manganese content. They provided a nucleus for sulphide deposition shortly after sill emplacement in groundwater saturated, permeable Hazelton Group rocks. Cooling, crystallization and fracture development in the sills initiated hydrothermal circulation and phyllic alteration with late quartz and calcite veins related to collapse of the hydrothermal system. Lead-zinc mineralization occurred as two events, with only one related to precious metal and copper deposition. Oxygen isotope compositions of quartz-garnet mineral separate pairs indicate crystallization of garnets and sulphides from magmatic fluids at temperatures from 528°C to 725°C. Sericite, quartz and calcite precipitated from meteoric fluids. In summary, hydrothermal fluids at the Capoose prospect evolved from early, high temperature magmatic fluids to late lower temperature, low salinity, meteoric fluids. The geological setting, silicate and sulphide mineralogy, alteration, metal distribution and depositional fluid compositions at Capoose resemble a low-grade, epigenetic, intrusion-related, porphyry-style deposit.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The biosorption of copper, nickel, gold and platinum from single metal aqueous solutions by the nickel hyperaccumulator Berkheya coddii plant biomass was investigated. Potentiometric titrations of the biomass and determination of optimal sorption pH for each metal showed that nickel ions were released from the biomass into solution. The presence of free nickel ions interfered with the uptake of the other three metals and further biosorption investigations were discontinued. Three fungal isolates found colonising metal solutions were cultured and screened for their ability to remove 50 mg.l⁻¹ of copper, nickel, gold and platinum from solution and to survive and grow in precious metal refinery wastewaters. One isolate was selected for further studies based on its superior metal uptake capabilities (35 and 39 mg.l⁻¹ of gold and platinum, respectively) and was identified as Phoma glomerata. Copper, nickel, gold and platinum uptake studies revealed that nickel and gold were the most toxic metal ions, however, toxicity was dependent on pH. At pH 6 more biomass growth was achieved than at lower pH values and metal uptake increased by 51 and 17 % for copper and nickel, respectively. In addition, the production of extracellular polymeric substances played a role in base metal interaction. Precious metals were observed to be preferentially removed from solution, complete removal of gold and platinum was observed at all initial pH values, 89 % of copper was bioaccumulated at an initial metal concentration of 55 mg.l⁻¹ (pH 6) and only 23 % of nickel was removed from solution under the same conditions. Metal bioaccumulation was confirmed through transmission electron microscopy and micro particle induced X-ray emission. The effect of P. glomerata immobilised in a packed bed reactor on precious metal refinery wastewaters was investigated. It was found that the fungal isolate was not able to remove the high salt and chemical oxygen demand concentrations found in the wastewaters, however due to its ability to survive and grow in undiluted wastewater and remove metal ions from solution it may be utilised as a metal detoxification step in the treatment process train.
PDFCreator Version 0.9.0
AFPL Ghostscript 8.53

The selective recovery of rhodium from wastewaters, in which the metal would be otherwise lost, would be highly profitable if the process were suitably low-cost. Current recovery processes are generally high maintenance and high-cost, whereas biological processes can be engineered to run with little external input in terms of cost and maintenance. Three emerging technologies were chosen based on their reported efficiency when removing base metals from wastewaters. The first technology screened, the sulphide-extraction membrane bioreactor (SEMB), consists of a sulphate-reducing prokaryote (SRP) anaerobic digester, in which a silicone membrane is submerged. Wastewater is passed through the membrane and metal ions are precipitated as metal sulphides by the hydrogen sulphide gas, which is capable of permeating the membrane. The second technology screened was a fluidized sand bed reactor in which metal ions are removed from solution via induction of nucleated precipitation by sodium carbonate onto the sand grains. The third, and most well established removal technology screened was a biosorption system using immobilized Saccharomyces cerevisiae biomass as the biosorbent. Experimental trials with each technology highlighted drawbacks with each; the SEMB system proved to be largely ineffective when challenged with the removal of rhodium from the wastewater as the rhodium precipitate fouled the membrane within hours, the fluidized bed system seemed unable to overcome the acidity of the wastewater and thus could not precipitate out the rhodium metal, and the efficiency of the biosorption process was hampered by the diversity of rhodium species present in the wastewater, which reduced the amount recovered. The outcomes of the trials with each technology indicated that further optimization of the technology or pretreatment of the wastewater is necessary before any of these options can be implemented. It could be concluded, however, that despite further optimization, both the SEMB and the fluidized bed system were not applicable in this case as precipitation would be non-specific, resulting in the necessity for further steps in order to purify the rhodium ions. Hence, the biosorption system was shown to be most applicable, and further optimization of the system could yield a highly efficient rhodium recovery process.

The process of precious metal refining can be up to 99.99% efficient at best, and although it may seem small, the amount of valuable metal lost to waste streams is appreciable enough to warrant recovery. The method currently used to remove entrained metal ions from refinery wastewaters, chemical precipitation, is not an effective means for selective recovery of precious metals from a wastewater. Biosorption, the ability of certain types of biomass to bind and concentrate metals from even very dilute aqueous solutions, may be an effective point-source metal recovery strategy. The yeast, Saccharomyces cerevisiae, has been found capable of sorbing numerous precious and base metals, and is a cheap and abundant source of biomass. As such, it represents a possible precious metal sorbent for application to refining wastewaters. In this investigation, S. cerevisiae biomass was immobilized, using polyethyleneimine and glutaraldehyde, to produce a suitable sorbent, which was found to be capable of high platinum uptake (150 to 170 mg/g) at low pH (< 2). The sorption mechanism was elucidated and found to be a chemical reaction, which made effective desorption impossible. The sorption process was investigated in a packed bed column conformation, the results of which showed that the diameter and height of the column require further optimization in order to attain the metal uptake values achieved in the batch studies. When applied to a refinery wastewater, two key wastewater characteristics limited the success of the sorption process; the high inorganic ion content and the complex speciation of the platinum ions. The results proved the concept principle of platinum recovery by immobilized yeast biosorption and indicated that a more detailed understanding of the platinum speciation within the wastewater is required before the biosorption process can be applied. Overall, the sorption of platinum by the S. cerevisiae sorbent was demonstrated to be highly effective in principle, but the complexity of the wastewater requires that pretreatment steps be taken before the successful application of this process to an industrial wastewater.

This research emphasizes on the use of seeded growth in synthesis of noble metal nanocrystals with precise control over the size, shape, and composition. In the first part of this work, I have produced Au nanocrystals with single-crystal structure and truly spherical profiles and investigated their optical properties and self-assembly as induced by dilution with water. These Au nanospheres were generated in high yield and purity, together with controllable sizes continually increased from 5 to 150 nm. I also found these Au nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires, respectively, as diluted with water. In the second part of this work, I demonstrate the kinetic control can be implemented to control the shape of mono- and bi-metallic nanocrystals in seeded growth. The as-prepared single-crystal nanospheres of Au were employed as seeds to synthesize of tetrahedral Au nanocrystals and Au@Pd core-shell nanocrystals with six distinct shapes. The success of the two demonstrations relies on manipulation of reaction kinetics to achieve different product shapes. The reaction kinetics was controlled by varying a set of reaction parameters, including the type and concentration of capping agent, the amount of reductant, and the injection rate of metal precursor solution. In the final part of this work, I will discuss an unusual change in crystallinity observed in seeded growth of Au nanocrystals on Au seeds. In particular, single-crystal Au seeds treated with a chemical species could develop twin defects during the seed-mediated growth process to yield multiply twinned products.

Removal of nitrogenous compounds from precious metal refinery (PMR) wastewater is important in terms of avoiding eutrophication (environmental protection), metal recovery (increased overall process efficiency and value recovery) and reuse of treated water (maximum use of natural resources). Extreme pH conditions (4 to 13 depending on the wastewater stream), high chemical oxygen demand (> 10,000 mg/I), numerous metals and high concentrations of those metals (> 20 mg/l of platinum group metals) in the wastewater are the main challenges for biological removal of nitrogenous compounds from PMR wastewater. Nitrogenous compounds such as NH₄⁺-N and N0₃-N are strong metal ligands, which make it difficult to recover metals from the wastewater. Therefore, a bioprocess was developed for removal of nitrogenous compounds from carefully simulated PMR wastewater. A preliminary investigation of metal wastewater was carried out to determine its composition and physico-chemical properties, the ability to nitrify and denitrify under different pH conditions and denitrification with different carbon Source compounds and amounts. Even at pH 4, nitrification could be carried out. A suitable hydraulic retention time was found to be 72 hours. There was no significant difference between sodium acetate and sodium lactate as carbon sources for denitrification. Based on these results, a reactor comparison study was carried out using simulated PMR wastewater in three types of reactors: continuously stirred tank reactor (CSTR), packed-bed reactor (PBR) and airlift suspension reactor (ALSR). These reactors were fed with 30 mg/l of Rh bound in an NH₄⁺ based compound (Claus salt: pentaaminechlororhodium (III) dichloride). Total nitrogen removal efficiencies of > 68 % , > 79 % and > 45 % were obtained in the CSTR, PBR and ALSR, respectively. Serially connected CSTR-PBR and PBR-CSTR reactor configurations were then studied to determine the best configuration for maximum removal of nitrogenous compounds from the wastewater. The PBR-CSTR configuration gave consistent biomass retention and automatic pH control in the CSTR. Ammonium removal efficiencies > 95 % were achieved in both reactors. As poor nitrate removal was observed a toxicity study was carried out using respirometry and the half saturation inhibition coefficients for Pt, Pd, Rh and Ru were found to be 15.81, 25.00, 33.34 and 39.25 mg/l, respectively. A mathematical model was developed to describe the nitrogen removal in PMR wastewater using activated sludge model number 1 (ASMl), two step nitrification and metal toxicity. An operational protocol was developed based on the literature review, experimental work and simulation results. The optimum reactor configuration under the set conditions (20 mg/I of Rh and < 100 mg/I of NH₄⁺-N) was found to be PBR-CSTR-PBR process, which achieved overall NH₄⁺-N and N0₃⁻-N removal efficiencies of > 90 % and 95 %, respectively. Finally, a rudimentary microbial characterisation was carried out on subsamples from the CSTR and PBRsecondary. It was found that the CSTR biomass consisted of both rods and cocci while PBRsecondary consisted of rods only. Based on these experimental works, further research needs and recommendations were made for optimisation of the developed bioprocess for removal of nitrogenous compounds from PMR wastewater.

Aquest treball contribueix a l'estudi de la sorció de metalls preciosos en chitosan, presentant-lo com una futura alternativa a nivell industrial en front dels altres processos ja utilitzats actualment. Concretament el nostre estudi esta centrat en la recuperació de metalls preciosos provenint de solucions clorhídriques a baixes concentracions.

Degut a l'alt valor i poca abundància d'aquests metalls, es necessari desenvolupar i consolidar nous processos de recuperació i separació per aquests metalls.

El treball presentat en aquesta tesi ha estat planificat basant-se en la contribució entre l'estudi de les propietats del chitosan realitzada en el "Laboratoire Gènie de l'Environnement Industrial de l?Ecole des Mines d?Alès" i per la investigació del comportament dels metalls preciosos en solució realitzada en el Departament de Enginyeria Química de la Universitat Politècnica de Catalunya.

Per portar els nostres objectius a terme, el primer treball va consistir en el estudi de les condicions d'equilibri i en les cinètiques d'adsorció del pal·ladi utilitzant flocs de chitosan. Aquest estudi es va realitzar en reactor tancat i obert.

Un cop aquesta part del treball va ser realitzada el nostre interès es va centrar en l'obtenció de nous derivats del chitosan que milloressin la seva capacitat d'adsorció, insertant derivats de sofre a la cadena de chitosan. Aquests nous derivats van ser utilitzats per l'estudi de la capacitat de sorció del platí i pal·ladi.

Per altre part degut als problemes generats per el alt contingut d'aigua en les perles de chitosan fabricades, es va realitzar un estudi amb perles prèviament secades i posteriorment rehidratades.

Finalment les nostres investigacions per tal de completar el nostre treball es van ampliar per l'estudi del osmi, iridi, rodi, ruteni.

Aquesta Tesi Doctoral resumeix el treball presentat en els següents articles:

I. Palladium Sorption on Glutaradehyde Crosslinked ChitosanM. Ruiz, A. M. Sastre i E. GuibalReactive & Functional Polymers, 45, 155-173 (2000)
II. Palladium Sorption on Glutaraldehyde-Crosslinked Chitosan in Fixed-Bed SystemsM. Ruiz, A. M. Sastre, M. C. Zikan i E. GuibalJournal of Applied Polymer Science, 81, 153-165 (2001)
III. Platinum and Palladium Sorption on Chitosan DerivativesE. Guibal, M. Ruiz, T. Vincent, A. M. Sastre i R. Navarro MendozaSeparation Science and Technology, 36 (5 & 6), 1017-1040 (2001)
IV. Palladium Sorption Using Chitosan DerivativesM. Ruiz, A. M. Sastre, J. R. Degorce-Dumas i E. GuibalTexts of textes des affiche posters. International Water Association (2000). ISBN: 2-9515416-0-0
V. Pd and Pt Recovery Using Chitosan Gel Beads. I. Influence of Drying Process on Diffusion PropertiesM. Ruiz, A. M. Sastre, E. GuibalSeparation Science and Technology (2002), en premsa
VI. Pd and Pt Recovery Using Chitosan Gel Beads. II. Influence of Chemical Modification on Sorption PropertiesM. Ruiz, A. M. Sastre, E. GuibalSeparation Science and Technology (2002), en premsa
VII. Influence of Drying Process of Chitosan Beads on the Sorption of Platinum and PalladiumM. Ruiz. A. M. Sastre i E. GuibalAdvances in Chitin Sciences, VI, (2002), en premsa
VIII. Osmium and Iridium Sorption on Glutaraldehyde Crosslinked Chitosan Gel BeadsM. Ruiz, A. M. Sastre i E. GuibalSolvent Extraction Ion Exchange, sotmès per a publicació
This work contributes to the study of the sorption of precious metals on chitosan, presenting it as a future alternative at an industrial level to the various existing processes.

This study is focused on the recovery of precious metals from hydrochloric acid solutions by techniques based in sorption on natural polymers.

Due to the high value and scarcity of precious metals, the need of developing and consolidating new separation and concentration processes is very important.

The work presented in this thesis has been planified and based on the contribution given by the research of the properties of chitosan in the sorption of metals, realized in the "Laboratoire Gènie de l'Environnement Industrial de l'Ecole des Mines d'Alès" and by the research of the behaviour of the precious metals in solution, realized in the Department of Chemical Engineering, Universitat Politècnica de Catalunya.
To get this investigation under way and to be able to develop it, the first work consisted of the study of the equilibrium conditions and the adsorption kinetics of Pd in chitosan in the form or flakes. This study was carried out using a closed and open reactor system.

Once this part of the work had been carried out, the specific interest of this investigation focused on obtaining chitosan derivatives that might improve the sorption capacity for Pd and Pt, by grafting sulphur compounds onto the chitosan, and also including desorption studies for Pd.

Owing to the possible transport problems which the high water content of the pearls of chitosan might cause, a drying process was used, comparing the results with those previously obtained (paper V). At the same time the sorption capacity of Pd and Pt was improved, introducing more amino groups in the chitosan chains

Finally, owing to the fact that the main part of the work was dedicated to the sorption of Pd and Pt, it was decided to complete this study by extending it to the metals Rh, Ru, Os, Ir and Re.

The results obtained are shown in the following papers:

I. Palladium Sorption on Glutaradehyde Crosslinked ChitosanN. Ruiz, A. M. Sastre i E. GuibalReactive & Functional Polymers, 45, 155-173 (2000)
II. Palladium Sorption on Glutaraldehyde-Crosslinked Chitosan in Fixed-Bed SystemsN. Ruiz, A. M. Sastre, M. C. Zikan i E. GuibalJournal of Applied Polymer Science, 81, 153-165 (2001)
III. Platinum and Palladium Sorption on Chitosan DerivativesF. Guibal, M. Ruiz, T. Vincent, A. M. Sastre i R. Navarro MendozaSeparation Science and Technology, 36 (5 & 6), 1017-1040 (2001)
IV. Palladium Sorption Using Chitosan DerivativesN. Ruiz, A. M. Sastre, J. R. Degorce-Dumas i E. GuibalTexts of textes des affiche posters. International Water Association (2000). ISBN: 2-9515416-0-0
V. Pd and Pt Recovery Using Chitosan Gel Beads. I. Influence of Drying Process on Diffusion PropertiesN. Ruiz, A. M. Sastre, E. GuibalSeparation Science and Technology (2002), en premsa
VI. Pd and Pt Recovery Using Chitosan Gel Beads. II. Influence of Chemical Modification on Sorption PropertiesN. Ruiz, A. M. Sastre, E. GuibalSeparation Science and Technology (2002), en premsa
VII. Influence of Drying Process of Chitosan Beads on the Sorption of Platinum and PalladiumN. Ruiz. A. M. Sastre i E. GuibalAdvances in Chitin Sciences, VI, (2002), en premsa
VIII. Osmium and Iridium Sorption on Glutaraldehyde Crosslinked Chitosan Gel BeadsN. Ruiz, A. M. Sastre i E. GuibalSolvent Extraction Ion Exchange, sotmès per a publicació

Adsorption mechanisms of modified thiol collectors on gold, silver, and gold-silver alloys have been studied and compared with those of ethyl xanthate (EX). The modified thiol collectors include dicresyl monothiophosphate (DCMTP), dialkyl dithiophosphinate (DTPI) and monothiophosphinate (MTPI). In general, the adsorption mechanisms on silver and gold-silver alloys can be explained by the EC-mechanism involving an electron transfer step and a chemical reaction step. Thus, the adsorption should be controlled by the Eh of the electrochemical oxidation of the electrode involved and the pK of the metal collector complex. According to this mechanism, DCMTP should adsorb on silver and gold-silver alloys at a lower potential than DTPI and MTPI since the pK of silver-DCMTP complex is larger than those of silver-DTPI and silver-MTPI. This has been verified to be the case by voltammetry, FTIR and contact angle studies. Likewise, EX adsorbs on silver at a lower potential than the modified thiol collectors because the pK of silver-EX is larger than those of the silver-modified thiol collectors. Both EX and the modified thiol collectors adsorb on silver at lower potentials than on the gold-silver alloys, which can be attributed to the lower activity of silver on the alloy surface. For the same reason, the potential for the onset of collector adsorption on alloys decreases with increasing silver content.
Ph. D.

In this study, the effect of Pt particle size on the reaction rate and selectivity of preferential oxidation of CO (PROX) reaction was investigated on Pt/Al2O3. 2% Pt/&
#947
-Al2O3 catalysts were prepared by incipient wetness method
the particle size of the catalysts was modified by calcination temperature and duration. Therefore, the relative amounts of low and high coordination atoms on the metal particle surface can be changed. Over these catalysts, first, the CO oxidation reaction was studied in the absence of hydrogen. The catalyst having the highest dispersion, i.e., lowest metal particle sizes, had the highest activity as indicated by its lowest light-off temperature. On the other hand, the turnover frequencies (TOF) of the catalysts were increasing with decreasing dispersion. The activation energy of the catalysts were also compared and examined: as the particle size increased, the activation energy decreased. In the second part, preferential oxidation of CO reaction in the presence of hydrogen was studied. Both CO conversion and selectivity first increased with increasing reaction temperature, then exhibited a maximum, and finally decreased. Both CO conversion and selectivity did not show any trend for different dispersed catalysts for &
#955
(2PO2/PCO) was 1. In order to reach a definite conclusion about the structure sensitivity of selective CO oxidation, the experiments with different &
#955
&rsquo
s and space times over the same catalysts should be performed.

Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: A 2 stage heap leach process to extract base and precious metals from the Platreef ore is currently being investigated industrially. A first stage bioleach is used to extract the base metals. In the 2nd stage, cyanide is used as the lixiviant at high pH to extract the platinum group metals and gold. By analogy with current gold recovery practices, the present study investigates the preferential and quantitative adsorption of precious metals (Pt, Pd, Rh and Au) over base metals (Cu, Ni and Fe) from an alkaline cyanide medium, by means of granular activated carbon. Experiments were designed statistically to optimise the process parameters using synthetic alkaline cyanide solutions close in composition to those expected from plant leach solutions. The statistical approach allowed the development of a reliable quantitative approach to express adsorption as a response variable on the basis of a number of experiments. A 2IV(7-2) fractional factorial design approach was carried out in a batch adsorption study to identify significant experimental variables along with their combined effects for the simultaneous adsorption of Pt(II), Pd(II), Rh(III) and Au(I). The adsorbent was characterized using SEM-EDX, and XRF. Precious metals adsorption efficiency was studied in terms of process recovery as a function of different adsorption parameters such as solution pH, copper, nickel, free cyanide ion, thiocyanate, initial precious metal (Pt, Pd, Rh and Au) ion and activated carbon concentrations. It was shown that adsorption rates within the first 60 minutes were very high (giving more than 90% extraction of precious metals) and thereafter the adsorption proceeds at a slower rate until pseudo-equilibrium was reached. Among the different adsorption parameters, at 95% confidence interval, nickel concentration had the most influential effect on the adsorption process followed by the adsorbent concentration. Adsorption of Ni was found to proceed at approximately the same rate and with the same recovery as the precious metals, showing a recovery of approximately 90% in two hours. The kinetics of Cu adsorption were slower, with less than 30% being recovered at the 120 minute period. This suggests that the co-adsorption of Cu can be minimised by shortening the residence time. Adsorption of Fe was found to be less than 5%, while the recovery of Rh was negligibly small. The effect of thiocyanate ion concentration was not as important as the effect of free cyanide ion concentration but still had some influence. The correlation among different adsorption parameters was studied using multivariate analysis. The optimum experimental conditions resulted in a solution with pH of 9.5, [Cu(I)] of 10 ppm, [Ni(II)] of 10 ppm, [CN ] of 132.44 ppm, [SCN ] of 98.95 ppm, [PMs] of 2.03 ppm and [AC] of 10 g/L. Under these conditions, predicted adsorption percentages of Pt, Pd and Au were approximately 98, 92 and 100%, at the level of 95% probability within two hours as an effective loading time. The negative values of ΔG° for all ions under optimum conditions indicate the feasibility and spontaneous nature of the adsorption process. Chemisorption was found to be the predominant mechanism in the adsorption process of Pt(II), Pd(II) and Au(I). Based on their distribution coefficients, the affinity of activated carbon for metal ions follows the selectivity sequence expressed below. Au(CN) > Pt(CN) > Pd(CN) > Ni(CN) > Cu(CN) Finally, it is important that additional research and development activities in the future should prove the economic viability of the process. Future work is also needed to investigate the adsorption of precious metals (PMs) by comparing the efficiencies and kinetics of adsorption when using sodium hydroxide (in this study) or lime, respectively, in order to control the pH.
AFRIKAANSE OPSOMMING: ʼn Tweefasige hooploogproses vir die ontginning van basis- en edelmetale van die Platrif-erts word tans industrieel ondersoek. ʼn Eerstefase-bioloog word gebruik om die basismetale te ontgin. In die 2de fase word sianied gebruik as die uitloog by hoë pH om die platinum-groepmetale en goud te ontgin. Na analogie van hedendaagse goudherwinningspraktyke het die huidige studie die voorkeur- en kwantitatiewe adsorpsie van edelmetale (Pt, Pd, Rh en Au) bo basismetale (Cu, Ni en Fe) vanuit ʼn alkaliese sianiedmedium met behulp van korrelrige geaktiveerde koolstof ondersoek. Eksperimente is op statistiese wyse ontwerp om die parameters van die proses te optimaliseer deur van sintetiese alkaliese sianiedoplossings wat in hulle samestelling nou ooreenstem met dié wat van oplossings van plant-loog verwag word, gebruik te maak. Die statistiese benadering het die ontwikkeling van ʼn betroubare kwantitatiewe benadering om adsorpsie as ʼn responsveranderlike op grond van ʼn aantal eksperimente uit te druk, moontlik gemaak. ʼn 2IV(7-2) -Fraksionele faktoriale ontwerp-benadering is tydens ʼn lot-adsorpsiestudie gevolg om beduidende eksperimentele veranderlikes tesame met hulle gekombineerde uitwerkings vir die gelyktydige adsorpsie van Pt(II), Pd(II), Rh(III) en Au(I) te identifiseer. Die adsorbeermiddel is met behulp van SEM-EDX en XRF gekenmerk. Adsorpsiedoeltreffendheid van edelmetale is bestudeer ten opsigte van proseskinetika en herwinning as ʼn funksie van verskillende adsorpsieparameters soos oplossing-pH, koper, nikkel, vry sianiedioon, tiosianaat, aanvanklike edelmetaal (Pt, Pd, Rh en Au)-ioon en geaktiveerde koolstofkonsentrasies. Daar is aangetoon dat adsorpsietempo‟s binne die eerste 60 minute baie hoog was (het meer as 90% ekstraksie van edelmetale opgelewer) en daarna het die adsorpsie teen ʼn stadiger tempo voortgegaan totdat pseudo-ekwilibrium bereik is. Onder die verskillende adsorpsieparameters, by 95%-vertroubaarheidsinterval, het nikkel-konsentrasie die grootste invloed op die adsorpsieproses gehad, gevolg deur konsentrasie van die adsorbeermiddel. Daar is bevind dat die adsorpsie van Ni teen nagenoeg dieselfde tempo en met dieselfde herwinning as die edelmetale voortgegaan het, wat ná twee uur ʼn herwinning van nagenoeg 90% getoon het. Die kinetika van Cu-adsorpsie was stadiger, met minder as 30% wat teen die 120-minute-tydperk herwin is. Dit dui daarop dat die ko-adsorpsie van Cu tot die minimum beperk kan word deur verkorting van die verblyftyd. Daar is bevind dat die adsorpsie van Fe minder as 5% is, terwyl die herwinning van Rh onbeduidend klein was. Die uitwerking van die konsentrasie van die tiosianaatione was nie so belangrik as die uitwerking van die konsentrasie van vry sianiedione nie maar het steeds ʼn mate van invloed gehad. Die korrelasie tussen verskillende adsorpsieparameters is met behulp van meerveranderlike analise bestudeer. Die optimale eksperimentele toestande het gelei tot ʼn oplossing met ʼn pH van 9.5, [Cu(I)] van 10 dpm, [Ni(II)] van 10 dpm, [CN] van 132.44 dpm, [SCN] van 98.95 dpm, [EM‟e] van 2.03 dpm en [AC] van 10 g/L. Onder hierdie toestande was die voorspelde adsorpsiepersentasies van Pt, Pd en Au nagenoeg 98, 92 en 100%, op die vlak van 95%-waarskynlikheid binne twee uur as ʼn doeltreffende laaityd. Die negatiewe waardes van ΔG° vir alle ione onder optimale toestande dui op die uitvoerbaarheid en spontane aard van die adsorpsieproses. Daar is bevind dat chemiesorpsie die deurslaggewende meganisme by die adsorpsieproses van Pt(II), Pd(II) en Au(I) is. Gebaseer op hulle distribusiekoeffisiënte volg die affiniteit van geaktiveerde koolstof vir metaalione die selektiwiteitsvolgorde soos hieronder voorgestel. Au(CN) > Pt(CN) > Pd(CN) > Ni(CN) > Cu(CN) Laastens, dit is belangrik dat addisionele navorsing en ontwikkelingsaktiwiteite in die toekoms die ekonomiese haalbaarheid van die proses bewys. Werk in die toekoms is nodig om die adsorpsie van edelmetale (EM‟e) te ondersoek deur vergelyking van die doeltreffendhede en kinetika van adsorpsie wanneer natriumhidroksied (in hierdie studie) of kalk, onderskeidelik, gebruik word ten einde die pH te beheer

Thesis (M. S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Mostafa A. El-Sayed; Committee Member: Adegboyega K. Oyelere; Committee Member: Bridgette Barry; Committee Member: Joseph W. Perry; Committee Member: Mark R. Prausnitz.

In this thesis the relationship between Brent oil prices, LME copper prices, Turkish gold and silver spot prices, XU100 index, interest rate and exchange rate is examined. Their long run Granger causality relationship is investigated by looking at Wald statistics. The short run relationship between them is examined by using generalized impulse responses. The data range is from January 2, 2002 to February 24, 2011. Due to the oil crisis in 2008, we divide the data into three periods: January 2, 2002 to December 31 as first period, 2007, from January 1, 2008 to December 31 as second period, 2008 and January 1, 2009 and February 24, 2011 as third period. We conduct each test separately for these periods but in third period we use Toda-Yamamoto procedure since maximum order of integration is 1.

Dissertation PhD--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: Adsorption tests were conducted with four different ion-exchange resins to determine the equilibrium adsorption of a range of precious and base metals. The adsorption characteristics were determined for synthetic single metal, as well as for multicomponent and base metal solutions. The effect of the el- concentration on the equilibrium adsorption was established for three different Hel concentrations in the above solutions. From the ion-exchange characteristics determined, a selective adsorption sequence is proposed for the separation of precious and base metals. Pure platinum, palladium and gold were dissolved in aqua regia and diluted to 2000 ppm (as metal) in 4M Hel. Ruthenium, rhodium and iridium were dissolved from pure salts in Hel. A 2000 ppm base metal solution was prepared by dissolving all the required components, including precious metals, to match an in-plant industrial basemetals solution composition. For each precious metal the equilibrium adsorption was determined for a couple of solution concentrations. Data points for adsorption curves were established by varying the amount of resin added to the test solution of a specific concentration. The equilibrium solution concentrations were determined by Iep analysis after 24 hours of exposure, using the bottle-roll technique. The experimental results obtained indicate a possible process route for the separation of precious metals with ion-exchange resin. The XAD7 resin is highly selective for gold from mixed solutions containing precious and base metals. It is also evident that, with the gold removed from the solution, the A22 resin adsorbs only palladium. IR200 resin adsorbs only the base metals from the solution. With all other precious metals removed from the solution (platinum and ruthenium must be extracted by other means), iridium can be adsorbed from the solution by IRA900 resin which is highly selective for iridium over rhodium. For all of the anion resins, XAD7, IRA900, and A22, the chloride concentration of the solution did not have a big effect on the adsorption capacity. However, the adsorption of base metals on IR200 is sensitive to chloride concentration, with a rapid reduction in adsorption at higher chloride concentrations. Statistical models were developed for the adsorption of each of the precious metals, as well as for the base metal solution. All adsorption data, obtained for a resin (typically 250 equilibrium data points), was used in the development of the model. The SPSS statistical software package was used to develop linear regression models. The interaction between all the input parameters, e.g. the interaction of gold and chloride ions, was modelled by specifying the product of the gold and the chloride concentrations as an input variable. The variables that determine the adsorption quantities were identified. High solution concentrations of the target adsorption component increase the adsorption quantity. It has been established that a higher platinum concentration increases the adsorption quantity of gold on XAD7 resin. However, the adsorption quantity is reduced at higher ruthenium concentrations. The adsorption quantity of iridium on IRA900 is reduced with increased rhodium concentration. The adsorption quantity of palladium on A22 is increased by the presence of rhodium and decreased by larger concentrations of iridium and platinum. The adsorption of base metals on IR200 is decreased at higher acid concentrations. Higher concentrations of gold in the base metal solution also decrease the adsorption quantity of base metals. The model predicted adsorption of each component compares well with the actual measured values. In batch adsorption tests the counter ion is not removed from the resin. The resin capacity for a specific ion concentration could therefore not be determined. As such, the adsorption models are only valid for the initial part of the ion-exchange process. The effect of kinetics on the adsorption was not determined.
AFRIKAANSE OPSOMMING: Adsorpsietoetse is gedoen met vier verskillende ioonuitruilharse om die ewewig adsorpsie van edelmetale en basismetale te bepaal. Die adsorpsie karakteristieke is bepaal vir sintetiese enkelmetaal-, meermetaal-, en basismetaaloplossings. Die effek van die Cl konsentrasie op die ewewigadsorpsie is bepaal vir drie soutsuurkonsentrasies in al die bogenoemde oplossings. 'n Prosesvloeidiagram vir die selektiewe adsorpsie van edelmetale en basismetale met behulp van die vier verskillende ioonuitruilharse word voorgestel. Suiwer platinum, palladium en goud is opgelos in koningswater en verdun na 2000 dpm (uitgedruk as metaal) in 4 molaar HCl. Rutenium-, rodium- en iridiumoplossings is verkry deur die oplos van suiwer edelmetaalsoute in HCl. 'n Basismetaaloplossing van 2000 dpm is voorberei deur die individuele komponente, wat die edelmetale ingesluit het, in die regte verhouding te kombineer om die samestelling van 'n industriële basismetaaloplossing te verkry. Vir elke edelmetaal is die ewewigadsorpsie bepaal vir tipies twee konsentrasies van edelmetaaloplossings. Verskillende data punte by 'n spesifieke edelmetaalkonsentrasie is bepaal deur die hoeveelheid hars wat by die toets oplossing gevoeg word te varieer. Die oplossingkonsentrasies by ewewig is bepaal deur IGP analise na 24 uur blootstelling met die roterende botteltegniek. Die resultate wat verkry is dui op 'n moontlike ioonuitruiigebaseerde proses vir die skeiding van edelmetale. Die XAD hars is selektief vir goudadsorpsie uit gemengde oplossings wat al die edelmetale, asook basismetale bevat. Dit is ook bevind dat indien goud uit die gemengde oplossing verwyder word, die A22 hars slegs palladium adsorbeer uit die oplossing. Die IR200 hars adsorbeer slegs basismetale. Wanneer al die ander edelmetale uit die oplossing verwyder is (platinum en rutenium moet met alternatiewe prosesse verwyder word) kan iridium geadsorbeer word met !RA900 hars vanuit 'n iridium- en rodium- gemengde oplossing. Vir al drie die anioonharse wat getoets is, naamlik, XAD7, !RA900 en A22, het die chloriedkonsentrasie nie 'n groot effek op die adsorpsie gehad nie. Die hoeveelheid basismetale wat op IR200 hars geadsorbeer word is egter baie sensitief vir die chloriedkonsentrasie, met 'n vinmge afname In adsorpsie by hoër chloriedkonsentrasies. Statistiese modelle is ontwikkel vir elke hars en vir elk van die edelmetale, asook die basismetaaloplossing. Al die eksperimentele data wat vir elke hars verkry is, tipies 250 ewewigspunte, is gebruik in die ontwikkeling van lineêre regressie modelle vir die primêre absorberende spesie op die hars. Hoër konsentrasies van die teiken adsorpsie komponent verhoog die adsorpsie daarvan. Hoër platinumkonsentrasies verhoog die adsorpsie van goud op XAD7, maar die teenwoordigheid van rutenium verlaag adsorpsie. Die adsorpsie van iridium op IRA900 word verlaag met hoër rodiumkonsentrasies. Die adsorpsie van palladium op A22 verhoog met die teenwoordigheid van rodium, maar neem af met hoër konsentrasies van iridium en platinum. Die adsorpsie van basismetale op IR200 neem af by hoër suurkonsentrasies. 'n Hoër goudkonsentrasie verlaag ook die adsorpsie van basismetale. Die gemodelleerde adsorpsie hoeveelhede vergelyk goed met die gemete waardes. Aangesien die uitgeruilde ioon nie verwyder word uit die toetsoplossing nie, kon die harskapasiteit vir 'n spesifieke ioonkonsentrasie nie bepaal word nie. Die modelle is derhalwe slegs getoets vir die aanvanklike deel van die ewewigsdata en die kinetika van adsorpsie is nie in ag geneem nie.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The Platreef ore deposit, situated in the Bushveld Igneous Complex, is one of the world’s largest platinum group metal (PGM) resources. The mineralogy of this resource is, however, unique as it consists of complex PGM mineralization with mainly copper and nickel, at very low PGM grades. The PGMs are mainly present in the ore as slow floating refractory minerals resulting in marginal process economics when processing via traditional mill-float-smelt processes. A new process is currently being investigated to extract PGMs from low grade Platreef ore and concentrate using a sequential heap leach process entailing heap bioleaching and high temperature cyanide leaching. The heap bioleach extracts the base metals in an acidic sulphate medium using a mixed culture of mesophiles and thermophiles. After heap bioleaching, the heap will be reclaimed, rinsed and restacked for high temperature cyanide leaching where the cyanide liquor is directly heated via solar energy in panels. Platinum, palladium and gold are extracted during the cyanide leaching stage and then recovered from the pregnant liquor either by adsorption onto activated carbon or ion exchange resins. Final metal recovery will proceed by techniques such as electrowinning and precipitation. In this thesis, process options for the recovery of platinum group metals from cyanide solutions were identified with different flowsheet alternatives developed utilizing these options. Simulations were made for the different processing alternatives with the objective of finding the alternative flowsheet to maximise net present value. The various processing options were simulated, combining data from concurrent experimental studies and data reported in literature with kinetic adsorption models. This was combined with economic models to arrive at an optimum design for each flowsheet alternative. Seven different processing alternatives for the recovery of platinum group metals from cyanide solutions were developed and investigated. These included two different activated carbon flowsheets as well as five different ion exchange resin flowsheets. The flowsheets differ in the elution procedures as well as the use of single or multiple resins. The well-known Merrill Crowe precipitation process was investigated but was found to yield unsatisfactory results. In each alternative, the cyanide solution is sent to a SART (sulphidization, acidification, recycling and thickening) plant to remove copper, nickel and zinc from solution prior to upgrading by means of adsorption onto activated carbon or ion exchange resins and subsequent elution. The platinum group metals are recovered from the eluate by precipitation using an autoclave, producing a solid product consisting of base and precious metals, while gold is recovered by electrowinning. It was found that the overall performance of the resin-in-solution (RIS) flowsheets were superior to that of the carbon-in-solution (CIS) flowsheets, from an overall PGM recovery perspective and product grades. The superior adsorption kinetics and high selectivity of the resins for the PGMs resulted in excellent overall plant performances, with PGM extractions in excess of 97%. Gold extraction efficiencies with resins were found to be lower than those achieved in the CIS flowsheets, mainly due to the higher selectivity of the resins for the divalent platinum and palladium cyanide complexes and poor gold elution efficiencies. The gold concentrations in the feed streams to these processes were, however, very low, at only 8.5% of the total precious metal content. The overall precious metal recoveries of the RIS flowsheets were thus higher than the CIS flowsheets due to the superior PGM extractions. From the cost analyses performed it was found that the RIS flowsheets requires lower initial capital costs, almost 28% lower than that require for the CIS flowsheets, while the operating cost requirements were found to be ±10% lower. This, combined with the high overall precious metal extractions, resulted in the RIS flowsheets to achieve higher net present values than those of the CIS flowsheets over an assumed project life of 15 years. The optimum flowsheet proposed for the recovery of precious metals from cyanide leach solutions was a RIS flowsheet option that employed the Amberlite PWA 5 resin, capable of extracting platinum, palladium and gold from solution, with elution being performed with a zinc cyanide solution. This process option had the lowest capital and operating cost requirements while achieving similar overall precious metal recoveries as the other flowsheets. Economic analysis of this process yielded the highest net present value, with a 31% increase in the overall return on investment compared to the optimal CIS flowsheet. Based on this, it was concluded that resin technology would be the best process option for recovering precious metals from cyanide leach solutions, however, additional research is required as the current level of process development is only at a concept phase.
AFRIKAANSE OPSOMMING: Die Platrif-erts, geleë in die Bosveld Kompleks, is een van die wêreld se grootste platinum groep metaal (PGM) reserwes. Die mineralogie van hierdie reserwe is uniek en bestaan uit komplekse PGM mineralisasie met hoofsaaklik koper en nikkel, teen baie lae PGM inhoud. Die PGMe is hoofsaaklik teenwoordig in die erts as stadig drywende minerale en dit lei tot marginale ekonomiese uitsigte wanneer hierdie reserwe deur tradisionele metodes verwerk word. Tans word ʼn nuwe proses ondersoek om die PGMe vanuit lae graad Platrif-erts en konsentraat te ontgin deur gebruik te maak van ʼn sekwensiële hooploogproses wat uit ʼn bio-loog en hoë temperatuur sianied loog stappe bestaan. Die bio-loog stap is verantwoordelik vir die ontginning van die basis metale deur gebruik te maak van ʼn suur sulfaat medium bestaande uit ʼn gemengde kultuur van mesofiele en termofiele. Nadat die bio-hooploog stap voltooi is, word die hoop herwin, gewas en herpak vir die daaropvolgende hoë temperatuur sianied loog, waar die sianied oplossing direk verhit word deur die gebruik van son panele. Platinum, palladium en goud word tydens hierdie stap ontgin en kan dan herwin word vanuit die loog oplossing deur gebruik te maak van adsorpsie deur geaktiveerde koolstof of ioon-uitruilings harse. Finale metaal herwinning kan deur elektroplatering en presipitasie vermag word. In hierdie tesis word verskeie proses opsies vir die ontginning en herwinning van PGMe vanuit sianied loog oplossings ondersoek waarna verskeie proses vloei diagram alternatiewe ontwikkel is met die doel om die opsie te vind wat die hoogste netto ekonomiese waarde sal oplewer. Die verskillende opsies is gesimuleer deur gebruik te maak van eksperimentele data gepubliseer in die literatuur en dit te kombineer met kinetiese adsorpsie modelle. Dit was dan gekombineer met ekonomiese modelle om ʼn optimum ontwerp van elke proses te verkry. Sewe verskillende proses vloei diagramme vir die herwinning en ontginning van PGMe vanuit sianied loog oplossings is ontwikkel en ondersoek. Hierdie het twee verkillende geaktiveerde koolstof prosesse en vyf verskillende ioon-uitruilings hars prosesse beslaan. Die opsies het verskil van eluerings metodes en adsorpsie medium. Die alombekende Merrill Crowe presipitasie proses is ook ondersoek, maar daar is gevind dat hierdie proses oneffektiewe resultate oplewer met betrekking tot die herwinning van die drie edel metale. In elke alternatief word die sianied oplossing in ʼn SART proses verwerk, waar die basis metale herwin word, gevolg deur die opgradering van die edel metale d.m.v. geaktiveerde koolstof adsorpsie of ekstraksie m.b.v. ioon-uitruilings harse, gevolg deur eluering. Die PGMe word dan herwin vanuit die eluerings oplossing deur termiese degradering van die metaal sianied komplekse, wat ʼn hoë graad presipitaat lewer bestaande uit die basis en edel metale. Goud word herwin d.m.v. elektroplatering. Daar is bevind dat die algehele verrigting van die ioon-uitruilings hars opsies beter was as die van die geaktiveerde koolstof opsies, beide van ʼn algehele edel metaal herwinnings en produk suiwerheid perspektief. Die verhoogde adsorpsie kinetika en hoër PGM selektiwiteit van die harse het daartoe gelei dat uitstekende algehele PGM herwinning verkry is in hierdie opsies, meer as 97%. Goud ekstraksie deur die harse was laer as wat verkry was deur die geaktiveerde koolstof opsies, weens die hoër selektiwiteit van die harse vir die divalente platinum en palladium sianied komplekse en laer hars eluering effektiwiteit. Die goud konsentrasies in die voer strome na die prosesse was laag, en het sowat 8.5% van die totale edel metale uitgemaak, wat bygedra het tot die lae goud herwinning. Algeheel was die edel metaal herwinning van die hars prosesse beter as die van die koolstof prosesse a.g.v. die hoër PGM adsorpsie. Koste evaluerings van die verskillende vloeidiagramme het getoon dat die hars opsies laer kapitaal kostes benodig, omtrent 28% minder as die koolstof opsies, terwyl bedryfskostes omtrent 10% minder was. Dit het bygedra tot die feit dat die ioon-uitruiling hars opsies ʼn hoër algehele netto ekonomiese waarde oor ʼn projek leeftyd van 15 jaar sal hê, aangesien de PGM ekstraksie, en dus die jaarlikse inkomste, ook hoër was. Die algehele proses vloei diagram wat voorgestel is vir die herwinning van edel metale vanuit sianied loog oplossings is die hars opsie wat gebruik maak van die Amberlite PWA 5 hars, wat in staat is om platinum, palladium en goud terselfdertyd te absorbeer, gevolg deur die eluering van die hars deur die gebruik van ʼn sink sianied oplossing. Hierdie proses het die laagste kapitaal en bedryfskostes getoon terwyl algehele PGM herwinning om en by dieselfde was as al die ander opsies. Hierdie proses sal verder ʼn 31% verhoging in die opbrengs op belegging lewer in vergelyking met die optimum geaktiveerde koolstof opsie. Die algehele gevolgtrekking is dat hars tegnologie die beter opsie sal wees vir die herwinning van edel metale vanuit sianied loog oplossings. Addisionele navorsing is dus nodig om resultate te verbeter aangesien hierdie studie slegs op ʼn konsep fase benadering was.

Fluid inclusion and mineralogical features indicative of boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Features associated with boiling that have been identified at Guanajuato include colloform texture silica, plumose texture silica, moss texture silica, ghost-sphere texture silica, lattice-bladed calcite, lattice-bladed calcite replaced by quartz and pseudo-acicular quartz after calcite and coexisting liquid-rich and vapor-rich fluid inclusions. Most samples were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into high-grade and low-grade samples based on the gold and silver concentrations. For silver, the cutoff for high grade was 100 ppm Ag, and for gold the cutoff was 1 ppm Au. The feature that is most closely associated with high grades of both gold and silver is colloform texture silica, and this feature also shows the largest difference in grade between the presence or absence of that feature (178.8 ppm Ag versus 17.2 ppm Ag, and 1.1 ppm Au versus 0.2 ppm Au). For both Ag and Au, there is no significant difference in average grade as a function of whether or not coexisting liquid-rich and vapor-rich fluid inclusions are present.

The textural and fluid inclusion data obtained in this study were analyzed using the binary classifier within SPSS Clementine. The models that correctly predicted high versus low grade samples most consistently (â 70-75% of the tests) for both Ag and Au were the neural network, the C5 decision tree and Quest decision tree models. For both Au and Ag, the presence of colloform silica texture was the variable with the greatest importance, i.e., the variable that has the greatest predictive power.

Boiling features are absent or rare in samples collected along a traverse perpendicular to the Veta Madre. This suggests that if an explorationist observes these features in samples collected during exploration that an environment favorable to precious metal mineralization is nearby. Similarly, good evidence for boiling is observed in the deepest levels of the Veta Madre that have been sampled in the mines and drill cores, suggesting that additional precious metal reserves are likely beneath the deepest levels sampled.

Master of Science

Cyanide heap leaching had been proposed as an alternative to the classic crush-mill-loatsmelt-refine route for processing platinum group metals (PGMs) from the Platreef ore body. Overall the process includes two stages of leaching. The first stage involves the thermophile bioleaching of the base metal (BM) sulphide minerals and acts as a form of pre-treatment to oxidise sulphur compounds and recovery valuable metals such as Cu, Ni and Co. The second stage focuses on cyanide-based heap leaching for the recovery of precious metals (PGMs +gold) from the solid residue of the first stage. Exploration and optimisation of this second stage in the context of a whole ore Platreef material is the focus of the present study. The first part of the study used a series of laboratory tests simulating heap leaching, conducted on coarse ore. The initial tests showed high recoveries of base metals (Cu, Ni and Co) could be achieved in a pre-treatment bioleach process, while in the second stage cyanide leach high levels of Pd and Au were extracted, but only 58% of the Pt after 60 days from the whole ore. It was observed that during the 60 day leaching period the rate of Pt leaching decreased considerably after 35 days. From the trajectory of the Pt leach curve from the 35 day mark onwards, it was observed that the leaching would not cease even after 60 days but would likely proceed but at that slow pace which indicated further Pt extraction would not be commercially viable in the long run. Mineralogical analysis has indicated that a significant component of the Pt in the ore is in the form a mineral sperrylite (PtAs2), which appears to leach slowly in cyanide as compared to other mineral forms such as certain tellurides and sulphides in the ore. Subsequently, efforts were made to investigate methods to improve the second stage leach process, in terms of Pt leaching from sperrylite, through further work on a pure mineral sample. The key focus was on finding a suitable oxidant that can be used in cyanide solutions, from among air, oxygen and ferricyanide, to facilitate the dissolution. Various tests using sperrylite mineral samples micronized to 5 μm in batch stirred tank reactors (BSTR) at 50°C were conducted. It was found that a combination of ferricyanide with cyanide extracted as much as 16 times more Pt than tests using only cyanide. The presence of air or pure oxygen did not contribute significantly to the amount of Pt leached in this system and made no difference at all in the leach tests using only cyanide. Further bench-scale studies focused on characterising the leaching mechanism of sperrylite in cyanide-ferricyanide solutions. It was found that the reaction, after proceeding at appreciable rates initially, tended to cease after 1 day, indicating some form of surface passivation, tentatively related to some form of solution equilibrium being achieved. However after re-leaching the sample with fresh solution, the Pt dissolution improved tremendously. This was further investigated in continuous leaching of a sample of the mineral using a small bed of sperrylite fixed in mini-columns. The results from the minicolumns showed the same leaching pattern as the experiments using BSTRs. It was eventually revealed that a suitable wash of the sperrylite sample using water removes the inhibiting layer and facilitates further and improved leaching. Unlike the cyanide-only system where the passivation was attributed to As build-up at the surface, in the cyanide-ferricyanide system it was attributed to adsorption of unknown reaction products on the mineral surface. Residual samples from batch leach experiments were analysed using X-ray photoelectron spectroscopy and showed samples from the cyanide-ferricyanide tests had less As on the surface than the untreated sample and the sample leached in cyanide. To some degree this supported the hypothesis that Pt leaching is eventually hindered by As passivation in a cyanide system. The presence of ferricyanide serves to oxidise As and thereby release more Pt in solution. Additionally, electrochemical techniques using a sperrylite electrode were employed to further understand the redox reaction under varying oxidation conditions. While the tests indicated a weak current under mildly oxidising conditions in cyanide solutions, this became rapidly limiting at potentials expected in a ferricyanide solution, indicating a form of surface passivation. An attempt was made to determine the number of electrons transferred during Pt dissolution to indicate the primary reaction mechanism through a long-term test held at constant potential, but dissolution rates were too small to be conclusive. Hence the study has shown that the cyanide-based heap leaching of PGMs from Platreef type ores is feasible in principle, but the dissolution of PtAs2 remains limited. While the study has given valuable pointers to understanding this observation, the conclusion is that PtAs2 is refractory in the given context and further development of this process remains promising through further investigation into the use of the cyanide-ferricyanide combination.

Aquesta Tesi Doctoral es centra en la recuperació de metalls precisos presents en dissolucions d'àcid clorhñidric, per mitjà de tècnqiues tant emergents com ben establertes basades en els principis de la tecnologia d'extracció líquid-líquid. La importància d'aquesta temàtica radica en el gran valor i l'escassetat d'aquests metalls. Les principals conclusions extretes d'aquest treball són:
- L'extracció liquid-liquid permet una ràpida extracció i stripping de Pd(II) quan s'empra l'extractant DEHTPA dissolt en querosè. El Pd(II) es pot extreure selectivament en presènica d'altres metalls com ara Cu(II), Fe(III), Pt(IV), Rh(III) i Zn(II).
- DEHTPA i Alamine 336 són extractants que han estat emprats en la preparació de resines impregnades que permeten extreure selectivament el Pd(II) així com la co-extracció de Pd(II) i Pt(IV) en presència de Rh(III). Les resines impregnates presenten les avantatges de la tecnologia de bescanvi iònic i mantenen la selectivitat dels extractants. Tot i això, s'ha vist que els processos tant d'extracció com d'stripping presenten cinètiques més lentes en relació amb d'altres tecnologies.. Les resines impregnades també s'han combinat amb la tecnologia de llit fluiditzat permetent el treball en continu.
- Les membranes líquides suportades (MLS) presenten l'atractiu que combinen els processos d'ectracció i stripping en una sola fase. El sistema SLM/DEHTPA permet el transport selectiu de Pd(II), que es troba controlat per fenòmens de difusió. La presència d'impureses en la solució d'alimentació és important donat que pot provocar fenòmens d'obturació en la membrana.
- L'extracció selectiva cloud point (CP) d'Au(III) emprant el surfactant PONPE7.5 s'ha aconseguit a temperatura ambient de forma similar a l'extracció líquid-líquid amb l'avantatge que no es requereix la utilització de dissolvents orgànics. L'aplicació d'aquesta tècnica es va aplicar amjb èxit a la recuperació d'Au provinent de circuits impresos, si bé cal esmentar que en l'etapa d'stripping va ésser necessària la utilització de cloroform.
This thesis is focused on the recovery of precious metals from hydrochloric acid solutions through emergent or well established metal recovery techniques based or on the principles of solvent extraction technology. This subject is of a great importance due to the high value and scarcity of precious metals, consequently the need of developing and consolidating new separation and concentration processes is imperative.
The main conclusions derived from this work are:
- Liquid-liquid extraction allow fast Pd(II) extraction and stripping when the extractant DEHTPA dissolved in kerosene is used as organic phase. Pd(II) can be selectively extracted by DEHTPA over Cu(II), Fe(III), Pt(IV), Rh(III) and Zn(II).
- DEHTPA and Alamine 336 are appropiate extractants for preparation of impregnated resins suitable for selective extraction of Pd(II) over metal impurities and co-extraction of Pd(II) and Pt(IV) against Rh(III). Impregnated resins maintain the advantages of ion-exchange technology, and also keep the selective characteristics of the extractants. However, the extraction and stripping kinetics of impregnated resins are slow compared to solvent extraction. Impregnated resins have also benn combined with fluidized bed technology allowing continuous operation.
- Supported liquid membranes (SLM) are very attractive since they combine the processes of extraction and stripping in a single stage. SLM/DEHTPA system permits selective Pd(II) transport on a diffusion controlled process. The presence of impurities inn the feed solution may cause blockage of the membrane.
- Selective cloud point (CP) extraction of Au(III) using the surfactant PONPE7.5 is achieved at ambient temperature in a similar manner as in solvent extraction not requiring the use of organic solvents. The application of CP extraction is demonstrated for the recovery of Au from a printed substrate, although the usage of an organic solvent, chloroform, is necessary in the stripping step.

Thesis (PhD)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: The objective of this work was to achieve a completely automated fire assay system for the analysis of process control samples on a flotation plant in less than 120 minutes. With this in mind, a systems engineering approach was undertaken. The physical and chemical characteristics of the technology for each subsystem were investigated in turn and the critical factors that influenced accuracy, precision and analysis time were identified and optimised. Some of the key developments achieved during this work were: · Existing technology for the sampling, filtering, drying and grinding of flotation plant samples were evaluated and where necessary, modified for this application. · The fusion system was totally re-designed with a bottom-loading configuration called FIFA (Fast In-line Fire Assay) to make automation with a central robot possible. With the fast fusing flux developed, a quantitative collection of the platinum group elements with a fifteen-minute fusion was achieved compared to an hour for the classical method. · A robust automated separator system was developed to isolate the lead collector from the fusion in the molten state thereby separating it quantitatively from the slag. This allowed the automation of the entire fire assay process. · Methods to prepare lead standards for calibration were developed. These were used to optimise analytical protocols for the analysis of platinum group elements in lead using a spark optical emission spectrometer. This made it possible to accurately determine the quantities of platinum group elements in lead samples prepared by the automated fire assay system. · A fully automated system was developed that could meet the accuracy and precision requirements for the analysis of tailings and feed grade samples in concentrator slurry streams in less than one hour compared with the 24-72 hours required when using classical methods. The new fire assay technology including flux, FIFA system, oxygen lance and separator were all patented along with the automation vendor. This technology has made the first fully automated fire assay system a reality.
AFRIKAANSE OPSOMMING: Die hoofoogmerk van die studie was om ‘n totale geoutomatiseerde vuuressaieering stelsel te ontwerp vir die ontleding van prosesbeheermonsters van ‘n flotasieaanleg in ‘n bestek van 120 minute. Gedurende die ontwerp is ‘n ingeneursstelselbenadering gebruik. Die fisiese en chemiese kenmerke van elke deel van die tegnologie is eers afsonderlik en dan as ‘n geheel ondersoek. Die bepalende faktore wat akkuraatheid, presisie en ontledingstyd beinvloed het was geidentifiseer en geoptimeer. Die hoofpunte van die werk behels onder andere die volgende: · Bestaande tegnologie vir monsterneming, filtrasie, droging en vermaling van flotasiemonsters was ondersoek en is, waar nodig, aangepas vir die finale stelsel. · Die smeltingsisteem was in geheel herontwerp om monsters van onder in die FIFA (Fast In-line Fire Assay) sisteem te laai en sodoende die outomatisering met ‘n sentrale robot te vergemaklik. ‘n Vinnig smeltende vloeimiddel was ontwikkel wat ‘n kwantitatiewe versameling van die platinum groep elemente binne ‘n tydsduur van vyftien minute moontlik gemaak het, in vergelyke met die oorspronklike duur van die klassieke smelt metode van een uur. · ‘n Outomatiese skeier was ontwikkel waarmee die gesmelte loodversamelaar geskei kon word van die slakfase. Met die nuwe stelsel kon die hele vuuressaieerproses outomaties verloop. · Metodes is ontwikkel om loodstandaarde vir kalibrasie doeleindes te berei. Die standaarde is op hulle beurt weer gebruik om ‘n ontleding protokol daar te stel vir die analiese van die platinum groep elemente in lood, met behulp van ‘n vonkontlading-optiese-uitstraling-spektrometriese instrument. Ten einde was dit moontlik om outomaties klein hoeveelhede van die platinum groep elemente in monsters akkuraat te bepaal, na voorbereiding met behulp van die geoutomatiseerde vuuressaieering stelsel. · Die volle geoutimatiseerde stelsel was ontwikkel wat aan die akkurate en noukeurige vereistes voldoen het vir die ontleding van flotasie-uitskot-envoergraad monsters van die konsentraataanleg binne die bestek van ‘n uur. Die nuwe vuuressaieer tegnologie, insluitend die vinnig smeltende vloeimiddel, FIFA en skeier stelsels, asook die suurstof lanset is gepatenteer met die vervaardiger. Die studie het gelei tot die eerste volle geoutomatiseerde vuuressaieering stelsel wat tans gebruik word in die industrie.

This paper aims to model and forecast the volatility of gold price with the help of other precious metals. The data applied for application part in the article involves three financial time series which are gold, silver and platinum daily spot prices. The volatility is modeled by univariate Generalized Autoregressive Conditional Heteroskedasticity (GARCH) models including GARCH and EGARCH with different distributions such as normal distribution and student-t distribution. At the same time, comparisons of estimation and forecasting the volatility between GARCH family models have been done.

Dissertation presented to obtain the Ph.D degree in Biology
Enterococcus faecalis is a commensal bacterium able to colonize different sites in the human host, such as the gastrointestinal tract, the genito-urinary tract and the oral cavity. It can also be found in numerous other environments, including soil, sand, water, food products and plants. These bacteria show a dual behavior: they can behave quite harmlessly as commensals, but are able to become opportunistic pathogens and cause serious infections, such as urinary tract infections and endocarditis, in hospital settings. The question as to how these bacteria are able to change from commensalism to pathogenicity has directed many recent studies to focus on the environmental host conditions that may trigger this transition as well as on the underlying molecular mechanisms. Metals are very important elements in the host environment, as they are key components of many proteins and are involved in numerous cell processes in both the host and the invading pathogen. The maintenance of metal homeostasis is fundamental to both to ensure that metabolism and cell functions are functioning properly. Variations in this homeostasis must be tightly regulated. In several Gram positive pathogens, metal homeostasis and regulation has been linked to their pathogenicity. The lack of knowledge on this subject in E. faecalis motivated the work presented in this thesis.(...)
Apoio financeiro da FCT e do FSE no âmbito do Quadro Comunitário de apoio BD nº SFRH/BD/30362/2006

The thesis employs glycine processes to recover base and precious metals from waste printed circuit boards. Different alkaline glycine-based leaching systems were proposed and investigated in-depth. Leaching behaviour of various metals was discussed. Different options for copper recovery from leachates have also been evaluated. The thesis provides a sustainable and de-centralised hydrometallurgical approach to treat the problematic e-waste, particularly in countries like Australia where the e-waste volume is limited and the geography is vast.

Le polissage électrochimique aussi appelé électropolissage (EP) est un procédé électrolytique de parachèvement des objets métalliques qui vise à améliorer leurs propriétés esthétiques et fonctionnelles. Sa spécificité réside dans la dissolution anodique contrôlée d’une fine couche de surface, dirigée préférentiellement sur les micro-aspérités, qui permet d’aboutir en une seule étape non seulement au nivellement de la pièce traitée mais aussi à son brillantage. C’est donc un procédé que l’on peut qualifier de super-finition permettant, en quelques minutes, d’atteindre une rugosité sub-micrométrique associée à la brillance de la pièce. Contrairement aux techniques de finition mécaniques traditionnelles (usinage, rodage, polissage…) c’est un procédé sans contact et donc sans perturbation métallurgique de la couche superficielle obtenue après enlèvement de matière. Il ne nécessite pas d’outils et s’adapte facilement aux pièces de géométrie complexes et aux structures fines en treillis.Connu depuis près d’un siècle, son application au traitement des métaux précieux est en revanche assez marginale et la bibliographie dédiée à l’électropolissage de l’or et de ses alliages est extrêmement pauvre. Ceci s’explique par le fait que les mécanismes mis en jeux ne sont pas complètement investigués et qu’en l’absence de modélisation prédictive, il est nécessaire de déterminer expérimentalement, pour chaque alliage, une formulation d’électrolyte adaptée et des paramètres électriques de traitement (en tension ou courant). Les électrolytes de polissage sont en général constitués de composés dangereux ou toxiques (fluorure, perchlorate, cyanure, cyanate, thiourée …). Ainsi la dangerosité des bains et la complexité apparente de la technique sont un frein au développement d’opérations industrielles dans les secteurs de l’horlogerie, de la joaillerie ou du luxe en général, pourtant désireux d’automatiser les procédés de finitions, en particulier pour les designs complexes. Le projet de recherche aura donc pour objectif d’étudier et de proposer un procédé soutenable d’électropolissage pour l’or et ses alliages (jaune, rose, gris, …) en rupture avec les travaux précédents du laboratoire sur l’électropolissage de métaux à haute résistance mécanique réalisé par dissolution dans des mélanges acides. Une attention particulière sera portée à la compréhension des mécanismes au regard des caractéristiques métallurgiques, topographiques et géométriques des substrats, avec une étude de la densité spectrale de puissance des motifs de rugosité. L’un des verrous scientifiques majeur à lever sera la recherche de solutions de polissage ayant un impact environnemental le plus réduit possible (exemptes de composés dangereux ou pathogènes tels que fluorure, cyanure, thiourée, …) en utilisant une large gamme de complexants combinés à l’emploi d’ondes de polarisation pulsées, de fréquence et amplitude variables. Cette analyse de la réponse du système constituera un enjeu majeur dans le potentiel d’exploitation futur des procédés développés
Electrochemical polishing, commonly referred to as electropolishing (EP), is an electrolytic process used to enhance the aesthetic and functional properties of metallic surfaces. This process involves the controlled anodic dissolution of a thin surface layer, with a focus on removing micro-asperities, resulting in simultaneous surface leveling and brightening. Within just a few minutes, electropolishing achieves sub-micrometric roughness and a bright, smooth finish. Unlike traditional mechanical finishing methods such as machining, lapping, or polishing, EP is a non-contact process that preserves the metallurgical integrity of the surface. Additionally, it can be easily applied to parts with intricate geometries or delicate lattice structures, making it highly adaptable for complex applications.Known for almost a century, its application to the treatment of precious metals is however rather marginal, with very limited research dedicated to the electropolishing of gold and its alloys. This gap in literature stems from the incomplete understanding of the underlying mechanisms and the lack of predictive models. As a result, optimizing the electrolyte composition and electrical parameters (such as voltage or current) for each specific alloy requires extensive experimental work. Furthermore, the electrolytes commonly used in electropolishing often contain toxic or hazardous chemicals—such as fluoride, perchlorate, cyanide, cyanate, and thiourea—posing significant safety and environmental concerns. These factors, combined with the perceived complexity of the technique, have hindered its widespread industrial adoption, particularly in sectors like watchmaking, jewelry, and luxury goods, where gold and its alloys are prevalent.The objective of the research project will therefore be to study and propose a sustainable electropolishing process for gold and its alloys (yellow, pink, gray, etc.). Particular attention will be paid to understanding the underlying mechanisms of electropolishing in relation to the metallurgical, topographic, and geometric characteristics of the substrates. This will involve studying the power spectral density (PSD) of the surface roughness patterns to gain deeper insights. One of the major scientific obstacles will be the development of environmentally friendly polishing electrolytes. The goal is to eliminate hazardous compounds commonly found in traditional electrolytes, such as fluoride, cyanide, and thiourea, and replace them with more sustainable complexing agents. In tandem, the project will explore the use of pulsed polarization waves with variable frequency and amplitude to optimize the polishing process. This analysis of the system response will be a major issue in the future potential exploitation of the developed processes

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Rina Tannenbaum; Committee Co-Chair: Rosario A. Gerhardt; Committee Member: E. Kent Barefield; Committee Member: Karl I. Jacob; Committee Member: Preet Singh; Committee Member: R. Bruce King. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The aim of this research is to investigate the price discovery, market efficiency and the temporal dynamic price relationships between financial prices (futures and index) and spot price, for three of the most important precious metals, namely gold, silver and platinum. When people are concerned about the economy, prudent investors switch their investment into precious metals rather than other asset classes. Precious metals futures, thus, are used by commercial producers and users and investors of precious metals to hedge risk or to make profit on the price fluctuations. Understanding the relationship between markets should foster sensible investment decisions and improve the statistical hedging properties of precious metals. Inspired by consideration of the unique status of precious metals in the economy and limited existing empirical evidence of price relationship regarding these metals, this research attempts to contribute to the space literature on market efficiency and causality cross three categories of markets—index, futures and spot. Further it will extend the research on price relationships and interactional impacts of precious metals markets based on non-synchronous trading that connects all the major markets around the world. The findings confirm long-term equilibrium relationships between US futures/index markets and special spot markets of all three precious metals by Cointegration tests. Via VECMs, the findings also revealed that futures prices and indexes of all the tested precious metals played a dominant role in the long run, but not all of them could be the unbiased estimators of the future spot price. On the other hand, mixed results of short-term causality suggested that US futures and indices led spot prices in the majority of cases. The results from this research supported the hypothesis that futures/indices functioned in the price discovery role in both the long- and short-term, and more importantly, the findings had value implications for market users in decision-making and improving their portfolio performance on precious metal markets.

Lead-lag relationships among precious-metals prices and their early-warning potential of shifts in exchange rates and inflation is debated. By examining a suite of precious-metals prices by multivariate State-Space analysis, this research goes beyond previous studies that focus upon gold, and avoids ad-hoc lag-length specification that plagues other methods. Precious-metals prices and structural economic variables are selected in accord with economic theory from a reduced-form model that recognizes both stock and flow components of precious-metals markets. Structure of the ARMA equations corresponding to the resulting State-Space models allows for testing lead-lag relationships among the variables. With monthly first-differenced real price and rate data, current prices of gold, silver, and platinum are sensitive to not only the interest-rate component of the cost of carry but also to expected future own-prices. But among these precious metals, only gold prices lead platinum prices, which suggests precious-metals are traded in more separable markets and are less substitutable as assets in a monthly time-frame than commonly perceived and that speculative activity from the gold market spills over into silver before platinum. Precious-metals prices do not lead exchange rates but exchange rates do lead platinum prices which suggests that exchange-rate disequilibria impacts gold and silver more quickly than the less-liquid platinum market. Furthermore, gold prices, with monthly first-differenced data in both nominal and real terms, do not lead interest rates, exchange rates, or inflation, and hypotheses that gold prices exhibit leading relationships to these structural economic variables are rejected. Likewise, the potential of precious-metals prices as early-warning indicators of shifts in economic determinants of capital flows is questioned.