Dissertations / Theses on the topic 'Platinum group metals (PGEs)'

In this study, a reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed to separate and determine Pt and Pd after formation of their chelates with N,N-diethyl-N'
-benzoylthiourea (DEBT). With the aim of reducing the number of steps in treating the samples, the method developed does not require the elimination of excess chelating reagent before the analysis of metal chelates. The different physical and chemical parameters affecting separation were examined in details. The whole analysis was completed on a C18 column in 16 min at 280 nm, with the mobile phase of acetonitrile-methanol-water (80:10:10, v:v:v) containing 0.20 mol l-1 pH 5.0 acetate buffer at a flow rate of 0.8 ml min-1. Detection limits of the method, based on 3s, were found as 14.2 ug l-1 for Pd and 0.77 mg l-1 for Pt using a 20-ul sample loop. Reproducibility of the method for ten repeated measurements was found as 2.36 % for 0.60 mg l-1 Pd and 2.58 % for 10.0 mg l-1 Pt as % RSD. The proposed method is a rapid, simple and highly selective method for the simultaneous determination of Pt and Pd by HPLC without the need for any interference elimination process.

Ni laterites are considered worthy targets for critical metals (CM) exploration as rare earth elements (REE), Sc and platinum group elements (PGE) can be concentrated during weathering as a result of residual and secondary enrichment. In this investigation geochemical and mineralogical data of CM from two different nickel laterite types (i) from the Moa Bay mining area in Cuba (oxide type) and (ii) from the Falcondo mining area in the Dominican Republic (hydrous Mg silicate type) are presented. Emphasis is given on examining their potential to accumulate CM and on processes involved. Results show that CM are concentrated towards the surface in specific zones: (i) REE in clay minerals rich horizons and within zones composed of secondary Mn oxide(s) (ii) Sc within zones rich in secondary Fe and Mn bearing oxide(s) and (iii) PGE in zones with high concentrations of residual chromian spinel and secondary Fe and Mn bearing oxide(s) at upper levels of the Ni laterite profiles. Concentration factors involve (i) residual enrichment by intense weathering (ii) mobilization of CM during changing Eh and pH conditions with subsequent reprecipitation at favourable geochemical barriers (iii) interactions between biosphere and limonitic soils at highest levels of the profile (critical zone) with involved neoformation processes. Total contents of CM in both Ni laterite types are low when compared with conventional CM ore deposits but are of economic significance as CM have to be seen as cost inexpensive by-products during the Ni (+Co) production. Innovative extraction methods currently under development are believed to boost the significance of Ni laterites as future unconventional CM ore deposits. Two Ni laterite profiles from the Falcondo mining area have been compared for their platinum group element (PGE) geochemistry and mineralogy. One profile (Loma Peguera) is characterized by PGE-enriched (up to 3.5 ppm total PGE) chromitite bodies incorporated within the saprolite, whereas the second profile is chromitite-free (Loma Caribe). Total PGE contents of both profiles slightly increase from parent rocks (36 and 30 ppb, respectively) to saprolite (-50 ppb) and reach highest levels within the limonite zone (640 and 264 ppb, respectively). Chondrite-normalized PGE patterns of saprolite and limonite reveal rather flat shapes with positive peaks of Ru and Pd. Three types of platinum group minerals (PGM) were found by using an innovative hydroseparation technique: (i) primary PGM inclusions in fresh Cr-spinel (laurite and bowieite), (ii) secondary PGM (e.g., Ru-Fe-Os-Ir compounds) from weathering of preexisting PGM (e.g., serpentinization and/or laterization), and (iii) PGM precipitated after PGE mobilization within the laterite (neoformation). Results provide evidence that (i) PGM occurrence and PGE enrichment in the laterite profiles is independent of chromitite incorporation; (ii) PGE enrichment is residual on the profile scale; and (iii) PGE are mobile on a local scale leading to in situ growth of PGM within limonite, probably by bioreduction and/or electrochemical metal accretion. Free grains of PGM with delicate morphologies were discovered in limonite hosted chromitite samples (“floating chromitites”) from highest levels in the Falcondo Ni laterite deposit (Dominican Republic). Textural and chemical evidence obtained via SEM and EMP analysis points to a multistage formation: (i) primary PGM formation at magmatic stage; (ii) transformation to highly porous secondary Os-Ru PGM during serpentinization; (iii) neoformation of Ir-Fe-Ni-(Pt) mineral phases during early stages of lateritization; (iv) neoformation of Pt-(Ir) mineral phases within the critical zone of the profile resulting in nugget shaped accumulation of rounded particulates during late stages of lateritization. The observation of accumulations of most likely biogenic mediated in situ growth of Pt rich nanoparticles in supergene environments could help to explain (i) why Pt bearing nuggets are the most abundant PGM found in surface environments, (ii) why Pt nuggets from placer deposits generally surpass the grain sizes of Pt grains found in parent rocks by several orders of magnitude (few micrometers vs. several millimeters) and (iii) how anthropogenic PGE contamination may affect our biosphere. Osmium chromitite, saprolite and limonite (Falcondo mining area), suggest that serpentinization of the Loma Caribe peridotite has not significantly affected the Re-Os system in Os-rich PGM. This is noted by the fact, that primary PGM formed at magmatic stage and secondary Ru-Os-Mg- isotope characteristics from primary and secondary PGM, separated from Si PGM formed due desulphurization of primary PGM with significant incorporation of Mg silicates, have almost identical Os isotope characteristics, typical of the mantle. However, the Re-Os system can be significantly disturbed during stages of lateritization when porous secondary PGM react with Fe-rich fluids, thus forming hexaferrum and magnetite in the 187 188 interstices of secondary PGM. Here presented data indicate that more radiogenic ratios in higher levels of the weathering profile are linked to steady mobilization of PGE within secondary PGM resulting in subsequent loss of Os counterbalanced by the incorporation of Fe. Os/ Os In this investigation presented data clearly states that PGE are neither noble nor inert in surface environments, at least in those related to tropical Ni laterites from the Northern Caribbean.

Philosophiae Doctor - PhD
Nowadays, the pollution of surface waters with chemical contaminants is one of the most crucial environmental problems. These chemical contaminants enter rivers and streams resulting in tremendous amount of destruction, so the detection and monitoring of these chemical contaminants results in an ever-increasing demand. This thesis describes the search for a suitable method for the determination of platinum group metals (PGMs) in environmental samples due to the toxicity of mercury films and the limitations with methods other than electroanalytical methods. This study focuses on the development of a novel bismuth-silver bimetallic nanosensor for the determination of PGMs in roadside dust and soil samples. Firstly, individual silver, bismuth and novel bismuth-silver bimetallic nanoparticles were chemically synthesised. The synthesised nanoparticles was compared and characterised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy, and transmission electron microscopy (TEM) analysis to interrogate the electrochemical, optical, structural, and morphological properties of the nanomaterials. The individual silver, bismuth, and bismuth-silver bimetallic nanoparticles in the high resolution transmission electron microscopy results exhibited an average particle size of 10-30 nm. The electrochemical results obtained have shown that the bismuth-silver bimetallic nanoparticles exhibit good electro-catalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible spectroscopy, Fourier-transformed infrared spectroscopy, and Raman spectroscopy results confirmed the structural properties of the novel bismuth-silver bimetallic nanoparticles. In addition the transmission electron microscopy and selected area electron diffraction morphological characterisation confirmed the nanoscale nature of the bismuth-silver bimetallic nanoparticles. Secondly, a sensitive adsorptive stripping voltammetric procedure for palladium, platinum and rhodium determination was developed in the presence of dimethylglyoxime (DMG) as the chelating agent at a glassy carbon electrode coated with a bismuth-silver bimetallic nanofilm. The nanosensor further allowed the adsorptive stripping voltammetric detection of PGMs without oxygen removal in solution. In this study the factors that influence the stripping performance such as composition of supporting electrolyte, DMG concentration, deposition potential and time studies, and pH have been investigated and optimised. The bismuth-silver bimetallic nanosensor was used as the working electrode with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. The differential pulse adsorptive stripping peak current signal was linear from 0.2 to 1.0 ng/L range (60 s deposition), with limit of detections for Pd (0.19 ng/L), Pt (0.20 ng/L), Rh (0.22 ng/L), respectively. Good precision for the sensor application was also obtained with a reproducibility of 4.61% for Pd(II), 5.16% for Pt(II) and 5.27% for Rh(III), for three measurements. Investigations of the possible interferences from co-existing ions with PGMs were also done in this study. The results obtained for the study of interferences have shown that Ni(II) and Co(II) interfere with Pd(II), Pt(II) and Rh(III) at high concentrations. The interference studies of Cd(II), Pb(II), Cu(II) and Fe(III) showed that these metal ions only interfere with Pd(II) and Pt(II) at high concentrations, with no interferences observed for Rh(III). Phosphate and sulphate only interfere at high concentrations with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. Based on the experimental results, this bismuth-silver bimetallic nanosensor can be considered as an alternative to common mercury electrodes, carbon paste and bismuth film electrodes for electrochemical detection of PGMs in environmental samples. Thirdly, this study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry (DPAdSV) of PGMs in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the SPCEs. Optimisation parameters such as pH, DMG concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng/L. The detection limit for Pd(II), Pt(II) and Rh(III) was found to be 0.07 ng/L, 0.06 ng/L and 0.2 ng/L, respectively. Good precision for the sensor application was also obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II) and 5.37% for Rh(III), for three measurements. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42- and PO43- does not interfere with Pd(II) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. These possible interference ions only interfere with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) as the supporting electrolyte solution.

The aim of this thesis is the elaboration of a detailed literature review on the use of ion exchangers for the preconcentration of platinum group metals. This work contains an actual literature review on this issue. In this work you will find information about the current occurrence of platinum metals in the environment, their impact on health, properties, resources and the use. There are also described ways of decomposition, extraction and use of ion exchangers. In the experimental part this thesis deals with optimization of ion exchangers and following application of real samples from the city of Brno.

A series of half-sandwich complexes, [M([9]aneS₃)*XY]ⁿ+ have been synthesised from MCl₂ [M = Pd, Pt,X = Y = Cl^-(n = 0), PPh₃0.5dppm, 0.5dppe,0.5x2, 2'-bipy(n = 2), X = Cl^-, Y = PPh₃(n&61 1); M = Pd, X = Y = 0.5oxytriphos, 0.5x1, 10-phen(n = 2), X = Cl^-, Y = PCy₃(n = 1)]. All but one of the crystal structures [M = Pd, X = Y = Cl^-, PPh₃, 0.5dppm, 0.5oxytriphos, 0.5x2,2'-bipy, 0.5x1,10-phen, X = Cl^-, Y&61 PPh₃; M = Pt, X = Y&61 PPh₃, 0.5dppm] solved show the metal in a square-planar, S₂XY co-ordination set, with a long-range apical interaction to the remaining S-atom of [9]aneS₃; [Pt([9]aneS₃)(PPh₃)₂]²+ is trigonal bipyramidal. The reductive electrochemistry of the Pd complexes shows the stabilisation of Pd(I) species by bidentate, π-acceptor X,Y ligands. A series of complexes [Ru([9]aneS_3)XYZ]^+ (X-Cl^-, Y = CO or PCy_3, Z&61 H or MeCN; X = H, Y = Z = 0.5x1,5-COD) and [Ru([n]aneS_4)*XY]^m+ (X = Cl^-, Y = PPh_3, n = 12,14,16, m&61 1; X = McCN, Y = PPh_3, n = 12,14, m&61 2; X = Y = McCN, n = 16, m = 2) have also been prepared. The crystral structures of [Ru([9]aneS_3)XYZ]^+ (X = Cl^-, Y = CO, Z&61 McCN; X = H, Y = Z = 0.5x1,5-COD) show the metal to be octahedrally co-ordinated. Such is also the case for [Ru([n]aneS_4)XY]^m+ (n = 14,16, X = Cl^-, Y&61 PPh_3; n = 16, X = Y = MeCN), with the non-macrocyclic ligands mutually cis. A study by nmr spectroscopy of the mechanism of formation of [Ru([9]aneS_3)Cl(PPh_3)(C_4H_3O)H^+ ]^- from [Ru([9]aneS_3)Cl_2(PPh_3)] and Et_2O/THF was undertaken. The former complex, and the dimeric intermediates [Ru([9]aneS_3)(PPh_3)Cl]_2^2+ and [Ru([9]aneS_3(PPh_3)(μ2-Cl)Tl(μ3-Cl)]_2^2+ were characterised by X-ray crystallography. Finally, the novel agostic species [Pd(H[9]aneN_3)Cl_2]_2(PF_6)_2.2([Pd(H[9]aneN_3)Cl_2]_2) is described. The X-ray structure of the dimer shows an unsupported Pd-Pd bond with mutally cis-Cl^- ligands. Only one of the two metal ions in the dimer forms an agostic M-H-N bond. The metal in each of the monomers also forms on M-H-N agostic bond. *[9]aneS_3 = 1,4,7-trithiacyclononane, [14]aneS_4 = 1,4,8,11-tetrathiacyclotetradecane [12]aneS_4 = 1,4,7,10-tetrathiacyclododecane, [16]aneS_4 = 1,5,9,13-tetrathiacyclohexadecane.

In this thesis, a series of symmetrical and unsymmetrical pincer ligands are synthesised and explored as supports for platinum group metals, such as palladium, platinum and ruthenium. In Chapters 2 and 3, the synthesis and characterisation of novel pyridine-based dianionic aryl-containing [C,NPy,O] and phenol-containing [O,NPy,O] pincer pro-ligands and their reactivity towards palladium(II) and ruthenium(II) metal precursors is described. [C,NPy,O]-type pincer pro-ligands have been shown to promote sp2 C-H activations upon reaction with palladium(II) and ruthenium(II) metal salts. Phenol-containing [O,NPy,O] pincer pro-ligands demonstrated deprotonation of the phenolic oxygen, resulting in a tridentate coordination upon binding to palladium(II) and ruthenium(III) metal centres. In Chapter 4, six novel paramagnetic ruthenium(III) pincer complexes developed from aryl-containing [C,NPy,O] and phenol-containing [O,NPy,O] pincer pro-ligands, have been employed as efficient catalysts for the transfer hydrogenation of ketones. Chapter 5 describes the synthesis of mono(imino)pyridyl [N,NPy,O] pincer pro-ligands incorporating an ethyl ester group at 6-position and their ability to undergo hydrolysis to a carboxylic acid upon coordination to palladium. Use of platinum(II) metal precursor, on the contrary, did not promote hydrolysis resulting in a bidentate coordination mode in the corresponding complexes. Chapter 6 explores the reactivity of two dien [N,N,N] pincer pro-ligands towards palladium(II) salts. Preliminary investigations demonstrated the ability of the amine-NH donor moieties to promote NH···A (acceptor) hydrogen bond interactions with the acceptor atoms on their corresponding anions in the solid state.

Very little information exists on the marine biogeochemistry of Rh, Pd and Pt, or the platinum group elements (PGE), an emerging group of contaminants whose principal emissions are associated with the abrasion of the catalytic converter in motor vehicles and chemotherapy drugs discharged in hospital wastes. In this study, Rh(III), Pd(II) and Pt(IV) were added individually and in combination to cultures of the marine microalga, Chlorella stigmatophora, maintained in coastal seawater at 15oC and under fluorescence lighting both in the presence and absence of trace nutrients (e.g. Fe, Co, Zn and EDTA). The accumulation of PGE was established under varying conditions (pH, algal biomass, PGE concentration, time) by ICP-MS analysis of seawater and nitric acid digests and EDTA washes of the alga, the latter giving a measure of PGE adsorption by C. stigmatophora. Under all conditions the extent of accumulation was in the order: Rh > Pd >> Pt. In short-term (24-h) exposures, accumulation isotherms were quasi-linear up to PGE concentrations of 30 ug L-1, although Pd displayed convexity, hence saturation of available binding sites, at greater concentrations. The pH, adjusted between about 5.5 and 9.5 by addition of acid or base, did not have a great impact on PGE accumulation, with Rh displaying a moderate increase in accumulation and Pd a moderate reduction with increasing pH. More important, all PGE displayed a significant reduction in accumulation on a weight-normalized basis with increasing concentration of algae, an effect not reported for metal-marine algal interactions previously in the literature. Longer-term experiments showed that the rates of both overall accumulation and internalization were greatest for Pd and least for Pt. Consistent with this observation, the toxicity to C. stigmatophora evaluated by both pigment content and growth rate, was significantly greater for Pd than for Pt. Differences in the biogeochemical behaviours among the PGE are attributed to differences in their aqueous speciation in seawater, different affinities for the algal surface, different tendencies to cross the cell membrane, and especially with regard to Pd and Pt, differences in the rates of these interactions. Thus, although the equilibrium chemistries of Pd and Pt are very similar, their differential biogeochemistries are the result of kinetic constraints on reactions involving the latter. Because the environmental concentrations of PGE are predicted to increase with increasing emissions from vehicles and hospitals, the results of this study make an important contribution to an improved understanding of the likely effects and fates of these emerging contaminants in the marine environment. The results are also more generally important to an improved understanding of the interactions of trace metals with microalgae in seawater.

Includes abstract.
Includes bibliographical references (leaves 74-79).
Historically the platinum group metals (PGMs) have been, and are still being dissolved by means of rather aggressive methods, e.g. aqua regia. Limited research has been conducted into the dissolution of the PGMs using different oxidizing agents. The dissolution of gold on the other hand has been afforded extensive research, and numerous papers and review articles have been published on the subject. The last number of years has seen the biggest application by volume of the PGMs as part of autocatalysts towards the degradation of harmful motor vehicle exhaust gases. This has subsequently sparked research into the recovery of specifically platinum, palladium, and rhodium from spent autocatalysts. Currently pyrometallurgical recovery of PGMs is being employed predominantly. A hydrometallurgical process on the other hand is, based on current technology, still a rather aggressive process that makes for high maintenance costs and an unpleasant environment. Gold has traditionally been dissolved by making use of cyanide, which is still the major route for gold dissolution. Due to environmental concerns lixiviants such as thiosulphate (S2O3 2-), thiourea (H2NCSNH2), and thiocyanate (SCN-) are gaining acceptance due to them being more environmentally friendly and giving good recoveries. These ‘softer’ alternatives have however not been tested on the PGMs. It is therefore the aim of this study to obtain an improved understanding of the leaching of the PGMs using lixiviants less aggressive than aqua-regia. These lixiviants include (i) SCN-, (ii) S2O3 2-, (iii) H2NCSNH2, and (iv) AlCl3/HCl. A thermodynamic study highlighted the fact that thermodynamic data for platinum-, palladium- and rhodium complexes are basically non-existent. To therefore obtain a clearer thermodynamic understanding of the leaching of the platinum group metals by means of these alternative lixiviants, future detailed speciation and thermodynamic investigations need to be conducted. An exploratory electrochemical investigation focusing on open circuit potentials and potentiodynamic scans, showed AlCl3 / HCl / NaOCl to be a good candidate for the leaching of the platinum group metals followed by SCN- / Fe3+ and CS(NH2)2 / Fe3+. Actual leach results, employing virgin autocatalysts as sample material, again highlighted the potential of AlCl3 / HCl / NaOCl as being a good lixiviant system. The surprise package, however, has been SCN- / Fe3+ that rendered very good results for Pd and Pt.

Includes bibliographical references.
To date the principle methods for the determination of the platinum-group metals (PGMs) use an "off-line" assay with flame-atomic absorption spectrometry and visible spectrometry. Both suffer numerous interferences and involve time-consuming and arduous laboratory separation methods prior to analysis. An "on-line" method for the rapid assay of the PGMs is indeed a lacking component in the analysts' repertoire of methods. This study describes the development of spectrophotometric methods for the determination of the PGMs using flow-injection analysis (FIA). The principle of exploiting the remarkably specific and selective reaction of stannous halides with the PGMs to yield a series of intensely coloured complexes in acidic solutions forms the basis of these methods. The reaction is subject to relatively few interferences from other transition metals. A high speed scanning spectrophotometer is employed to obtain second order data. The successful manipulation of the data enables the determination of PGMs as single components and also simultaneously in mixtures. Attention is focused on the establishment of principles for successful multi-component analysis of PGMs. The development of a software program for multi-wavelength data manipulation was mandatory and is described. Criteria for successful selection of analytical wavelengths are discussed. The usefulness of multi-dimensional graphical data representation is demonstrated in a stop-flow study of the palladium reaction with tin (II) chloride. Qualitative information is provided regarding the nature of complexes and their interactions. Correlation of spectrophotometric data with complex solution colour changes is made. The requirements for future progress in multi-component FIA determinations as well as the direction for future research conclude the study.

Environmental concerns and more stringent regulations have stimulated the development of new cleaner technologies to decrease the emissions of greenhouse gases and other hazardous gas emissions. In this study, the steam reforming of biooil as well as NOx storage and reduction catalysts were investigated. The production of hydrogen by steam reforming of bio-oils obtained from the fast pyrolysis of biomass requires the development of efficient catalysts able to cope with the complex chemical nature of the reactant. Steam reforming of a few model compounds and that of an actual bio-oil was investigated in the temperature range 650-900°C over Pt, Pd and Rh supported on alumina and a ceria-zirconia sample. The use of ceria-zirconia led to higher H2 yields. The supported Rh and Pt catalysts were the most active, while palladium-based catalysts performed poorly. Temperatures close to, or higher than, 800°C were required to achieve significant conversions to COx and H2 (e.g., H2 yields around 70%) ofthe bio-oil. NOx Storage and Reduction (NSR) catalysts are considered to be one of the most promising solutions to meet the upcoming NOx exhaust emission regulations. However, despite the high level of activity in this area, it is surprising that most studies have been conducted under conditions that are far from realistic. A fast transient apparatus has been developed to study these catalysts under realistic temporal conditions. The performance of a typical Pt/Ba/y-Ah03 NSR catalyst was studied as a function ofthe temperature, rich phase duration, reductant concentration, the type of reductant and the space velocity and the importance of the regeneration step in the NSR process was highlighted. The regeneration step was further investigated over Pt and/or Rh based catalysts by coupling of fast transient kinetic switching and the use of 15NO. An unexpected double peak in the evolution of nitrogen was revealed. The first peak occurred immediately on switching from lean to rich conditions, while the second peak started at the point at which the gases switched from rich to lean. Rh/Ba/Ah03 trap was found to be dependent on the rate of NOx storage, since the rate of regeneration was sufficient to remove the NOx stored in the lean phase. pt/Ba/Al203 was found to be limited by the rate of regeneration.

In pressurised water reactors (PWRs), hydrogen overpressure is used to keep the corrosion potential below the threshold for onset of intergranular stress corrosion cracking (IGSCC) in type 304 SS. However, some regions may contain higher oxygen levels resulting in an increase in the potential. These 'dead space' regions are difficult to access and during refuelling; oxygen may become trapped in these locations. The objective of this study was to investigate the influence of PGM additions on IGSCC susceptibility of type 304 stainless steels (SS) in the sensitised state within PWRs. The work presented herein investigates several aspects of the IGSCC problem. Virgin and platinum group metal (PGM)-modified (Ru and Pd) 304 SS have been studied. Material characterisation, including microstructural, tensile properties, hardness and grain size measurements, has been conducted. Crack initiation studies using U-bend samples in autoclaves simulating PWR environments have also been performed. In addition, crack propagation studies using circumferential cracked bar (CCB) specimens under constant extension in potassium tetrathionate solutions, a well-known medium to promote IGSCC on sensitised stainless steels, have been conducted in order to evaluate cracking resistance. Electrochemical studies using model solutions for PWR chemistry (containing boric acid and lithium hydroxide) and also potassium tetrathionate were carried out to look at the influence of the PGM on the kinetics of the main electrochemical reactions. The results revealed that PGM additions appeared to reduce crack initiation on sensitised type 304 SS under oxygenated conditions in high temperature water containing sulphate and chloride. PGM-doped and standard sensitised type 304 stainless steels revealed susceptibility to IGSCC propagation in 0.01 M K2S4O6, at pH=1.5 and 25°C. Electrochemical studies in potassium tetrathionate media showed smaller anodic dissolution peaks with PGM additions and metallography indicated less intergranular attack with PGM additions. In PWR model electrolytes, PGM additions, particularly 1 wt% Ru, were shown to catalyse the oxygen reduction reaction or hydrogen oxidation reaction, depending on the oxygen /hydrogen level. Overall findings showed that Ru additions can improve the IGSCC resistance of sensitised type 304 SS in PWR, while Pd additions are less effective.

The enantioselective hydrogenation of a-ketoesters over a platinum surface modified by cinchona alkaloids has been studied using accurate computational modelling. A series of small prototype compounds were used to interact with the metal surface, leading to the study of acetone adsorption on a platinum surface. It was found that the enol and enolate isomers of acetone may play a crucial role in the surface chemistry. The enol form of acetone was significantly more stable than the keto-form, and the enolate form was also more stable. Vibrational frequency analysis suggests that the enolate form may prove to be a better fit to some of the experimental data than the commonly-accepted ketone form. The interaction of an a-ketoester, methyl pyruvate, with a platinum surface was then studied using the same techniques. The enol form was again the most stable surface species compared to the enolate and ketone forms. Additionally, the cis form of methyl pyruvate was generally more stable than the trans form. A full vibrational analysis was performed, allowing comparison with future experimental work. In order to investigate the conversion between the different types of isomer, an eigenvector following scheme is under development to find reaction barriers and transition states. To date, this has been applied to simpler systems with success and is in the process of being extended to more complicated applications. Concurrently, a technique to study the whole enantioselective reaction system was also being developed. This involves a modified simple QM/MM scheme containing a model for the surface, the substrate and modifier. This was successfully applied to a simple system (methyl pyruvate interacting with the surface and modifier) and yielded predicted ees in agreement with experimental observation. This was extended to a more complex system under study at Cardiff University and reproduced the experimental enantioselectivity this was then used to suggest possible improvements to enhance the ee of this system.

The interest in biosensors can be attributed to the first described enzyme containing sensor used to detect levels of glucose in 1962. Although research into biosensors was initially slow to pick up, the field has become increasingly popular and research has been widespread for the last 20 years. The continuing research into biosensors is crucial as this will improve current devices to become smaller, faster and more economical and yield new biosensors. This thesis is mostly concerned with the development of an integral component of a biosensor, the redox mediator. Complexes of ruthenium incorporating electron rich sulfur-donor ligands such as naphthalenedithiol should possess interesting redox qualities which could be used to produce better mediators. A second area covered in this thesis is in the structural studies of a series of iridium and rhodium complexes. Two classes of ruthenium complexes with sulfur-donor ligands have been prepared. The first class incorporates the ruthenium bis-bipyridine moiety while the second contains pentamethylcyclopentadienyl ruthenium. Most complexes synthesised exhibited reversible oxidation waves in the region of -0.1 to 0.2 V vs. Ag/Ag⁺. Their possible use as redox mediators was hindered by several factors, particularly difficulties in purification. They also exhibited oxygen sensitivity and low stability when in solution.The second area covered in this thesis is to further understand the bonding of the ligands used in the above study. A series of pentamethylcyclopentadienyl iridium and rhodium complexes were synthesised with three different dithiolato ligands. Two of the three ligands studies produced structures that included more than one metal centre leading to straining of the ligand. In order to study the monomeric form, the clusters were opened with a neutral phosphine ligand. Both the Ir…S and Rh…S bond lengths of all the complexes were within expected parameters.

This work aims to develop solvent extractants to recover platinum and palladium from highly acidic chloride solutions bearing other platinum group metals (PGMs). In general, metal values can be recovered by solvent extraction through three different mechanisms: metal cation extraction (1); metalate anion extraction (2); or metal salt extraction (3). Mn- + n(LH)(org) ⇌ [M(L)n](org) + nH+ (1) MClx n- + nL(org) + nH+ ⇌ [MClx(LH)n](org) (2) MClx + nL(org) ⇌ [MClxLn](org) (3) The main objective of this thesis is to establish whether ditopic extractants can be developed which have chemical functionalities that allow both mechanisms (2) and (3) to operate, co-extracting Pt(IV) and Pd(II) as their chloridometalates in an outer sphere binding site (2) and allowing their separation by raising pH to transfer the more kinetically labile Pd(II) to an inner sphere binding site (3) and releasing H2PtCl6 to the aqueous strip solution. A review of the literature is presented in Chapter 1, noting current commercially available extractants and the processes in which they are, or have been, applied. Particular attention is paid to the mode of action of the reported extractants and whether they extract metal cations, anions or metal salts. This chapter also outlines the proposed solvent extraction circuit in which new reagents developed in this thesis would be incorporated and the methods applied during the screening of candidate extractants. Chapter 2 deals exclusively with the use of reagents with inner-sphere binding sites for the selective extraction of palladium over platinum. Work on a series of oxime reagents synthesised for palladium extraction as part of preliminary MSci research (Andrew M. Wilson, MSci Thesis, University of Edinburgh, 2011) is reviewed. Studies of the hydrolytic stability of oximes indicate that they are unsuitable for incorporation into ditopic reagents for use in a circuit with a highly acidic feed solution. Thioethers were studied as alternatives as they show high kinetic selectivity for palladium over platinum and are more stable under acidic conditions. The synthesis and extraction properties of model reagents (largely arylalkyl thioethers) are reported and compared with those of the commercially available di-n-hexylsulfide. Incorporation of a polar group such as an amide provides phase transfer catalysis, accelerating the rate of transport of Pd(II) into the organic phase, but reducing selectivity over Pt(IV). The identification of functionalities that operate as receptors for chloridometalates by forming outer-sphere assemblies is explored in Chapter 3. The synthesis of amine, amide and amino-amide extractants from acid chloride streams and the effects of variations of functional groups on the extraction of PtCl6 2− are described. Secondary amides were found to be stronger extractants than tertiary amides, and aliphatic amides also show better metalate extraction than aromatic amides. The interactions between protonated aminoamide reagents and PtCl6 2− werre analysed by X-ray crystallography, noting that C-H∙∙∙Cl interactions with the “soft” chloridometalate anion are more common than with the “hard” chloride ion which shows a preference for more conventional N-H∙∙∙Cl interactions. Chapter 4 combines the reagent types explored in Chapters 2 and 3, in ditopic extractants that have both inner- and outer sphere binding sites. The synthesis and characterisation of a series of thioether amide reagents are reported and the selective extraction of platinum and palladium over other PGMs are discussed. In-house screenings of aryl- and alkylthioetheramide extractants showed selective co-extraction of Pd(II) and Pt(IV), rejecting Ir(III). Pt(IV) can be selectively water-stripped followed by ammonia-stripping of Pd(II). Industrial screenings at Johnson Matthey Technology Centre further exemplified the selectivity of these extractants over Ru(III) and Rh(III), although third phases were formed when the reagents were used for recovery from highly concentrated metal-feed solutions. The mode of action of the ditopic extractants is discussed, based on DFT calculations, crystal structure determinations and NMR studies, which support the formation of outersphere metalate assemblies and inner-sphere palladium complexes. Chapter 5 describes new difunctional (inner + outer sphere complexation) extraction by a single chemical entity, in this case an unsaturated N-heterocycle (an azole). The synthesis and characterisation of a series of hydrophobic azoles are described. These have basicities which allow protonation when contacted with strongly acidic solutions (2), but can be deprotonated in contact with water to allow their neutral forms to form inner-sphere complexes with Pd(II). Triazole-based reagents show the selective co-extraction of Pt(IV) and Pd(II) and, as with the ditopic thioetheramide reagents reported in Chapter 4, allow the selective water stripping of Pt(IV) and subsequent ammonia stripping of Pd(II).

This research describes a two-dimensional modelling effort of heat and mass transport in simplified intrusive models of sills and their feeder dykes. These simplified models resembled a complex intrusive system such as the Great Dyke of Zimbabwe. This study investigated the impact of variable geometry to transport processes in two ways. First the time evolution of heat and mass transport during cooling was investigated. Then emphasis was placed on the application of convective scavenging as a mechanism that leads to the formation of minerals of economic interest, in particular the Platinum Group Elements (PGEs). The Navier-Stokes equations employed generated regions of high shear within the magma where we expected enhanced collisions between the immiscible sulphide liquid particles and PGEs. These collisions scavenge PGEs from the primary melt, aggregate and concentrate it to form PGEs enrichment in zero shear zones. The PGEs scavenge; concentrate and 'glue' in zero shear zones in the early history of convection because of viscosity and dispersive pressure (Bagnold effect). The effect of increasing the geometry size enhances scavenging, creates bigger zero shear zones with dilute concentrate of PGEs but you get high shear near the roots of the dyke/sill where the concentration will not be dilute. The time evolution calculations show that increasing the size of the magma chamber results in stronger initial convection currents for large magma models than for small ones. However, convection takes, approximately the same time to cease for both models. The research concludes that the time evolution for convective heat transfer is dependent on the viscosity rather than on geometry size. However, conductive heat transfer to the e-folding temperature was almost six times as long for the large model (M4) than the small one (M2). Variable viscosity as a physical property was applied to models 2 and 4 only. Video animations that simulate the cooling process for these models are enclosed in a CD at the back of this thesis. These simulations provide information with regard to the emplacement history and distribution of PGEs ore bodies. This will assist the reserve estimation and the location of economic minerals.

Centrifugal Partition Chromatography (CPC) is a multistage liquid-liquid countercurrent distribution technique which utilizes rotating teflon cartridges to hold a liquid phase stationary while the other liquid phase is pumped at a constant flow rate. It has been demonstrated to be a valuable technique for the base line separations of families of metal ions such as the platinum group metals (PGM)--Pt, Pd, Rh and Ir. The separations of these metals as their anionic chloro complexes were achieved using the heptane-water phase pair with a stable and relatively inexpensive extractant trioctylphosphine oxide (TOPO) functioning as a ligand in its neutral form and as a cation in its protonated form. A striking feature of the chromatograms of the complexes and ion pairs were their much poorer efficiencies compared to the efficiency of an organic analyte like 3-picoline under identical distribution rations. The inefficiencies of the PGM separations were also a function of the concentrations of the aqueous and organic phase components. These inefficiencies could be attributed to slow kinetics of the back extraction of the complexes and ion pairs and could be used to derive the mechanisms of these slow chemical kinetic steps. A correlation was established for the Pd(II) system between the CPC inefficiencies and the half lives of the slow reactions measured independently by stopped flow in micelles. This correlation was utilized to derive the rate constants for the back extraction of the TOPO complexes and ion pairs of Pt and Ir. The mechanisms of the extraction reactions were derived using the principle of microscopic reversibility based on the mechanisms of the back extraction reactions. This was then used to obtain estimates for the rate constants for the extraction reactions as well. The PGM were thus separated and their equilibrium and kinetics (extraction and back extraction) completely characterized using CPC. This is a significant development with CPC because such complete equilibrium and kinetic characterizations are hard to achieve with conventional liquid chromatographic techniques.

>Magister Scientiae - MSc
The purpose of this study was to develop a high performance-lower cost catalyst to be applied in Direct Methanol Fuel Cells (DMFC). The study also aimed to prepare plurimetallic supported platinum (Pt), platinum-ruthenium (PtRu), platinum-ruthenium-vanadium (PtRuV) and platinum ruthenium-vanadium-iron (PtRuVFe) upon multi-walled carbon nanotube (MWCNT) as well as upon multiwalled carbon nanotube-titanium oxide (MWCNT/TiO2) supports. Platinum is very active but prone to poisoning by carbon monoxide (CO), which may be present in the fuel used in fuel cells. The focus on the use of methanol was because of its better reaction kinetics, and better performance in direct methanol fuel cells (DMFC) better than proton exchange membrane fuel cell (PEMFC). When Pt is alloyed with another platinum group metals (PGM) the alloying decreases the over-potential for reactions critical in the fuel cells. Proton exchange membrane fuel cell (PEMFC) performance may be improved at low metal loading, when supported pluri-metallic catalysts are applied since the trimetallic catalysts may promote high catalyst utilisation. In practice, DMFC require electrodes with a Pt loading to achieve acceptance fuel cell (FC) power performance. The aim of this study was therefore the reduction of the catalyst loading through further improvement of mass activity of Pt based catalysts by partial substitution of the noble metal/metals, and the use of a carbon support that will provide high surface area, good electrical conductivity and high stability. MWCNT supported pluri-metallic (PtRuVFe,) and bimetallic (PtRu) nanoparticles possessed characteristic of increased surface area, improved electron transfer rate, enhance electro-catalytic activity and promoted stability.

Includes bibliographical references.
Steam methane reforming is a well-established industrial process used for generating hydrogen and synthesis gas. By performing this reaction in micro-channel reactors it is possible to take advantage of increased heat and mass transfer rates, allowing equipment size and residence times to be decreased by an order of magnitude which, in turn, leads to the possible utilisation of small scale steam reformers for portable fuel cell power systems. In this study, two commercial steam reforming catalysts, namely catalysts YR and XR, and a single in-house synthesised Rh/Al2O3 catalyst were studied in both packed bed and microchannel reactor configurations. All these catalysts exhibited stable activity in the packed bed reactor experiments.

Phytomining is suggested as a novel technology to obtain platinum group metals (PGMs) nanoparticles from plants grown on the mineralized soil, rock, or on mine wastes. The primary determinant of metal uptake by a plant is the bioavailability of the metal in the soil-plant system. In this thesis project, the bioavailability of PGMs of several PGM-rich materials is assessed with respect to phytomining. Notably, feed, concentrate and tailings from North American Palladium (NAP) in Canada, and two gossan samples from Broken Hill (BH) mineral complex in Australia are assessed in the context of phytomining. Geochemical techniques are used to obtain the mineralogy, the total concentration of PGMs, and concentrations of PGMs extracted by chemicals. These methods assess the bioavailability of PGMs in the samples and enable the estimation regarding the available concentrations of Pd, Pt, Au and Cu to plants. Soil-associated factors such as pH, salinity (EC), and cation exchange capacity (CEC) have been shown to influence indirectly the bioavailability of PGMs. Thus, soil-associated factors were analyzed. Additionally, a selection model for the substrate of phytomining is proposed. The criteria for choosing substrate for the phytomining of Pd include available Pd concentration, pH, EC, CEC and available Cu concentration. This thesis concludes that the PGM species that can be extracted by ammonium acetate are the best indicators of their natural availability to plants. Those PGMs that can be extracted by fulvic acid and citrate-dithionite are good indicators as they can be soluble in soils. According to the selection model, the available Pd concentration of BH gossan 1 is higher than 2 mg/kg. Its low EC, high CEC, and proper pH make it a suitable substrate for plant growth. It is the best “one” of the five samples for phytomining of Pd. One thing to note is that high Cu-tolerant plant species should be chosen to grow on BH gossan 1 due to its high Cu concentration available to plants.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

This thesis is concerned with the electrochemistry and spectroscopy of redox-active late transition metal complexes of the 2,2'-bipyridine ligand (bpy) and their reduction products. Complexes of general formula [Ph(4,4'-X₂-bby)L₂] (where L is a non redox-active ligand and X = NH₂, OEt, Me, H, Ph, C1, CO₂Me) undergo two one-electron reductions as revealed by cyclic voltammetry. The absorption spectra of the one-electron reduction products reveal the first of these reductions to be localised on the bpy ligand giving rise to radical anion ligand complexes of Pt(II). Epr spectra of the reduced, seventeen-electron species indicate a significant (ca. 10%) admixture of metal 5d orbitals in the SOMO, in good agreement with EHMO calculations. Both the E_1/2 value of the first reduction process and the MLCT ν_max value vary linearly with the Hammett parameter of the substituent X. The second reduction electron spin-pairs with the first in the same π* orbital. The LUMO of [Pd(4,4'-X₂-bpy)C1₂] is Pd 4d based and these complexes undergo irreversible two-electron reductions. Complexes of the 4,4'-(NO₂)₂-bpy ligand undergo up to four one-electron reductions. Epr spectroscopy of the di-reduction products of [M(4,4'-(NO₂)₂-bpy)L₂] (M = Pd, Pt, L = C1; M = Rh, L₂ = 1,5-cod) shows that spin-triplet species are formed on di-reduction and consequently that the LUMO-SLUMO gap is smaller than the spin-pairing energy for these complexes. The redox-active orbitals are highly localised on the nitro-groups. EHMO calculations are in good agreement. [Pt)bpy)₂]²⁺ undergoes a redox-induced dimerisation reaction at room temperature. Low-temperature cyclic voltammetry reveals the redox-active orbital to be bpy-based. The single-crystal structures of [Pt(4,4'-(NO₂)₂-bpy)C1₂] and [Au(bpy)C1₂]BF₄ are reported.

Includes bibliographical references (leaves 143-153).
The aim of this study is to investigate the economic and technical feasibility of processing platinum group metals (PGMs) and base metals (BMs) from a low-grade ore concentrate produced in the concentrator plant at Lonmin Pic. The PGMs of particular interest are platinum, palladium, ruthenium and rhodium, while the BMs of interest are copper and nickel. The ore concentrate, as a by-product, represents only 5 % of the total PGM value but as much as 70 % of the total tonnage of material processed in the concentrator plant. Further upgrading this material is not considered a viable route. However, even this low PGM content in the concentrate material accumulates to appreciable value on an annual basis motivating the need to develop alternative methods of extracting value from it. Initial estimates indicate that extraction levels of at least 50 % of the PGMs and 50 % of the BMs would need to be achieved, using low cost hydrometallurgical processes, to make the venture economically viable. These methods would exclude treatment via the smelter and pressure leaching: which are costly. energy intensive and result in leaching of large quantities of non-valuable elements. Previous studies revealed that organic acids had the potential to economically extract the PGMs under alkaline conditions, and BMs under acidic conditions, from various ores and concentrate materials. A literature survey confirmed that certain organic acids can be used to leach metals from ores and concentrates via chemical complexation. It further revealed that other chemical agents. namely cyanide, thiosulphate and bisulphide, were similarly capable of strongly complexing PGMs under various conditions of pH and temperature. The survey also revealed industrially established methods for extracting BMs from low-grade ores and concentrates. Based on this material, this study experimentally evaluated these options with the intent to propose a flowsheet to treat the concentrate material. This was conducted in two phases of experimental work.

The availability of finite resources is uncertain due to the worldwide increase in population growth and global industrialisation. Consequently, there is a pressing need for substitutive replacements and methods of replenishing stocks by recycling. The platinum group metals (PGMs) are rare, expensive elements with an unpredictable supply chain and a wide range of industrial applications for which there are often no substitutes. Mining from primary ores is environmentally damaging; hence recycling is vital to minimise losses and maintain stock at sustainable levels. This work investigates the feasibility of recovering PGMs from secondary waste sources and bioconverting them into new catalysts, circumventing the current environmentally polluting and energy expensive pyrometallurgical processing. Two secondary sources of PGMs were examined: scrap automotive catalysts and spent furnace refractory lining. This study shows a route to improve PGM recycling from secondary waste sources and, further, the potential to produce a catalytically active end product without the need for traditional refining.

A range of low-valent late transition-metal triarylphosphine complexes have been prepared and characterised by a combination of 1H, 31P and 19F (as appropriate) NMR and IR spectroscopies and mass spectrometry. Some of these complexes have been isolated as single crystals and characterised by X-ray diffraction. The triarylphosphine ligands used in this study were P(4-CH3OC6H4)3, P(4-HOC6H4)3, P(2-CH3OC6H4)3, PPh2(2-CH3OC6H4), P(2-HOC6H4)3 and PPh2(2-C2H3C6H4) whilst the transition-metals were platinum(II), palladium(II), rhodium(I), rhodium(III), osmium(II) and ruthenium(II). This work has shown that the former four phosphine ligands act as monodentate ligands whilst the last two ligands act as hybrid multidentate ligands. The metal complexes of the ortho-hydroxy substituted ligand exhibit fluxional behaviour in solution, where the phosphine is interchanging between mono- and bi-dentate modes of coordination. In contrast, fluxionality has not been observed in the case of the ortho-vinyl substituted ligand. A set of platinum(II)-, osmium(II)- and ruthenium(II)-fluoride triarylphosphine complexes have been prepared and characterised. The electron-donating substituents in the phosphine strengthen the metal-phosphine and metal fluoride bonds as compared to those for the non-substituted triarylphosphine ligand, PPh3. Furthermore, these substituents affect the geometry at the metal centre in these complexes. In the reactions of P(2-HOC6H4)3 with [Pt(-F){P(4-CH3OC6H4)3}2]2 or [M(-F)F(CO)3]4 (M = Os, Ru), metal chelates are formed by the displacement of fluoride by phenoxide and liberation of HF, whereas, in the related reactions, the ortho-vinyl substituted ligand acted in a monodentate mode.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: In Base Metal Refineries (BMRs), the copper sulphate leach solution produced during the final pressure leaching stage contains impurities such as selenium and tellurium, as well as other precious metals (OPMs, namely Rh, Ru, and Ir). Se and Te are removed by precipitation with sulphur dioxide prior to electrowinning of Cu. While a small percentage of the dissolved OPMs precipitate with the Se and Te, the largest portion remains in solution and is recycled to the first stage leach. If a larger portion of the OPMs in solution can be recovered in the Se/Te precipitation stage, OPM losses and the OPM inventory of the plant can be reduced. The aim of this project was to determine operating conditions that would allow maximum OPM recovery with minimal Cu and Ni co-precipitation in the Se/Te removal section of a BMR. The effects that the operating temperature, pressure, stirring rate, reagent type, and reagent quantity have on the metal precipitation behavior and precipitate characteristics were determined experimentally. Thio-urea and sulphurous acid were evaluated as precipitation reagents for temperatures of 80°C and 160°C, stirring rates of 250 rpm and 500 rpm, and pressures equal to ambient pressure and 7 bar. 200 % and 320 % excess thio-urea and 720 % and 960 % excess sulphur dioxide were used. The precipitation of OPMs with sulphur dioxide was generally poor; the maximum percentage Rh, Ru, and Ir precipitated were 35 %, 18 %, and 20 %, respectively. It was, however, found that the OPM precipitation increased as the reagent amount was increased. Increasing the temperature further increased Rh and Ir precipitation but affected the Ru precipitation negatively. Thio-urea precipitated virtually all of the Rh contained in the solution irrespective of the values of the process variables studied. As was the case with sulphur dioxide, increasing the amount of thio-urea added resulted in increased Ru and Ir precipitation, while higher temperatures favored Ir precipitation but not Ru precipitation. The maximum percentage Ru and Ir precipitation achieved with thio-urea were 87 % and 60 %, respectively. Complete Se precipitation was observed at all process conditions, while Te precipitation increased as the operating temperature and the reagent quantity were increased. Maximum Te precipitation of 98 % and 90 % were achieved when using 320 % excess thio-urea and 960 % sulphurous acid quantities, respectively, at 160°C and a stirring rate of 250 rpm. Increasing the reagent quantity and temperature did, however, also result in increased copper and nickel precipitation. The statistical analysis of the results allowed regression models to be fitted to predict the percentage metal precipitation as a function of the investigated process variables. These models were used to define an objective function to determine the optimal operating conditions. A temperature of 80oC, a pressure of 7 bar, and 200 % excess thio-urea were proposed as the optimum operating conditions that would yield 98 % Rh, 75 % Ru, and 48 % Ir precipitation with less than 5 % Cu and Ni co-precipitation. Experimental validation tests confirmed the model predicted values and proved repeatability of the experimental data.
AFRIKAANSE OPSOMMING: Die kopersulfaat logingsoplossing wat tydens die finale drukloging stadium in Basis Metaal Raffinaderye (BMRe) produseer word, bevat onsuiwerhede soos selenium en tellurium sowel as ander edelmetale (AEMe, naamlik Rh, Ru, en Ir). Se en Te word voor Cu elektrowinning verwyder deur middel van presipitasie met swaweldioksied. Alhoewel ʼn klein persentasie van die opgeloste AEMe saam met die Se en Te presipiteer, bly die grootste gedeelte in oplossing en word gevolglik na die eerste loging stadium hersirkuleer. AEM verliese en die AEM inventaris van die aanleg kan verminder word indien ʼn groter gedeelte van die AEMe in die Se/Te presipitasie stadium herwin kan word. Die doel van hierdie projek was om bedryfstoestande te bepaal om maksimum AEM herwinning met minimale Cu en Ni kopresipitasie in die Se/Te verwyderingseksie van ʼn BMR te behaal. Die effekte wat bedryfstoestande soos temperatuur, druk, roerder tempo, tipe reagens, en hoeveelheid reagens op die metaal presipitasiegedrag en presipitaat eienskappe het, is eksperimenteel bepaal. Tio-ureum en swaweligsuur is evalueer as presipitasie reagense vir temperature van 80°C en 160°C, roerder tempo’s van 250 rpm en 500 rpm, en drukke gelyk aan omgewingsdruk en 7 bar. 200 % en 320 % oormaat tio-ureum en 720 % en 960 % oormaat swaweldioksied is gebruik. Die presipitasie van AEMe met swaweldioksied was swak in die algemeen; die maksimum persentasie Rh, Ru, en Ir presipitasie wat behaal is, is 35 %, 18 %, en 20 %, onderskeidelik. Daar is egter gevind dat die AEM presipitasie toeneem indien die hoeveelheid reagens toeneem. ʼn Toename in die temperatuur het verder tot ʼn toename in Rh en Ir presipitasie gelei, maar dit het Ru presipitasie negatief affekteer. Tio-ureum het basies al die Rh in oplossing laat presipiteer, ongeag die waardes van die ander prosesveranderlikes wat ondersoek is. Soos wat die geval vir swaweldioksied was, het ʼn toename in die hoeveelheid tio-ureum ʼn toename in die Ru en Ir presipitasie tot gevolg gehad, terwyl hoër temperature Ir presipitasie bevoordeel en Ru presipitasie benadeel het. Die maksimum persentasie Ru en Ir presipitasie wat met tio-ureum behaal is, is 87 % en 60 %, onderskeidelik. Volledige Se presipitasie is by alle proses toestande waargeneem, terwyl Te presipitasie toegeneem het soos wat die temperatuur en die hoeveelheid reagens toegeneem het. Maksimum Te presipitasie van 98 % en 90 % is behaal toe 320 % oormaat tio-ureum en 960 % oormaat swaweligsuur, onderskeidelik, by 160°C en ʼn roerder tempo van 250 rpm gebruik is. ʼn Toename in die hoeveelheid reagens en die temperatuur het egter ook meer koper en nikkel presipitasie tot gevolg gehad. Die statistiese analise van die resultate het dit moontlik gemaak om regressie modelle te pas om die persentasie metaal presipitasie as ʼn funksie van die ondersoekte veranderlikes te voorspel. Hierdie modelle is gebruik om ʼn doelfunksie te definieer ten einde die optimale bedryfstoestande te bepaal. ʼn Temperatuur van 80°C, ʼn druk van 7 bar, en 200 % oormaat tioureum is voorgestel as die optimale bedryfstoestande wat 98 % Rh, 75 % Ru, en 48 % Ir presipitasie met minder as 5 % Cu en Ni kopresipitasie tot gevolg sal hê. Eksperimentele geldigheidsbepalingtoetse het die waardes wat deur die modelle voorspel is bevestig en die herhaalbaarheid van die eksperimentele data bewys.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 71-77).
by Jingshu Zhang.
S.M.

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.

Thesis (MEng) -- Stellenbosch University, 2014.
ENGLISH ABSTRACT: In this study, SiC reduction of Rowland and Easterns LG (Low Grade) concentrates was investigated. The purpose of the study was to investigate the feasibility of SiC as reductant with respect to metal fall, PGM grade in the alloy, slag composition, Cr solubility and overall PGM recovery. The integration of such process in the current matte-based collection process was also investigated. Currently, the matted-based collection process is most widely used for PGM recovery, but because PGM containing concentrates are becoming more enriched with UG2 (Upper Group 2) LG concentrates, it is expected to be integrated or replaced with an alloy collection process. This kind of process offers greater flexibility to the different types of ore that could be used. The process is chromium tolerant and environmentally friendly. For this purpose Rowland and Easterns UG2 LG Concentrate samples from Lonmin Western Platinum Limited were analysed with XRD, XRF and ICP-MS and it was found that SiO2 and MgO are the most abundant oxides and Pd is the most abundant element from the PGMs. Sulphide bearing minerals such as chalcopyrite were detected in low concentrations (below 1 %) and Cr2O3 concentrations are between 2 – 4 %. The FeO/SiO2 ratio was lower in Rowland LG concentrate. SiC reduction of Rowland and Easterns concentrate was done at 1600℃. Reductant to concentrate ratios for laboratory scale experiments were ranged from 2.5 to 3.5 kg SiC / 100 kg concentrate. SiC reduction of Rowland concentrate had different reduction times. The duration of reduction experiments ranged from 30 - 180 min. PGM recoveries from SiC reduction of Rowland concentrate were very poor (below 10 %) and Fe recoveries were lower than 50 %. A slag viscosity at the end of the melt of more than 4 poise was responsible for poor phase separation. SEM images revealed metal prills entrained in the slag phase instead of settling and combining to the alloy globule at the bottom of the crucible. However, PGM recoveries from SiC reduction of Easterns concentrate was significantly better. More than 85 % of Ir and Pd and almost 60 % of Pt were recovered in a test with a reductant to concentrate ratio of 3.5 kg SiC / 100 kg Easterns concentrate. Fe recovery was also the highest at 66%. Cr and Si concentrations were below 5 % in total. The slag viscosity at the end of melt was calculated to be less than 4 poise and a SEM image of a slag sample revealed few entrained metal prills. After the above findings on the importance of viscosity, it was decided to increase the FeO content in the initial concentrate charge in order to decrease slag viscosity, increase metal fall (PGM collecting phase) and further increase PGM recovery. Peirce-Smith converter slag was used for this purpose. A test was conducted with the addition of 10 kg converter slag / 100 kg Easterns concentrate. The reductant to concentrate ratio was kept at 3.5 kg SiC / 100 kg Easterns concentrate. The results revealed that Ir and Pd recoveries were more than 95%, while Pt recovery was almost 70%. Fe recovery increased to 76 %. On the basis of the results from the test, an optimum feed ratio between Easterns LG concentrate, Rowland concentrate and Peirce-Smith converter slag was calculated. Thermodynamic phase equilibrium calculations predicted that the concentrate charge should consist of 60 - 80% Easterns concentrate with a slag addition of 30 – 40 kg converter slag / 100 kg LG concentrate. SiC reduction of this optimum LG concentrate charge is expected to recover more than 90% of all PGMs. Cr and Si concentrations in the alloy will be below 1 % in total. The amount of converter slag as an addition will be however limited by final PGM grade in the alloy, furnace slag quantities recycled and slag resistivity required in the alloy furnace. The effectiveness of SiC as reductant was also compared to C reduction. C reduction of an optimum concentrate charge had a marginally higher metal fall at the same reductant to concentrate ratio than SiC reduction of an optimum concentrate charge. However, gas emissions are on average 3 times higher for C reduction of a concentrate charge and C reduction requires at least 300 MJ more to smelt 1 ton of LG concentrate than SiC reduction. This is mostly due to C reacting endothermically with FeO to produce Fe(l) and CO(g) in contrast to SiC reacting exothermically with FeO to produce Fe(l), SiO2(l) and CO(g). Integrating SiC reduction of LG concentrates into the existing smelting route at Lonmin was also proposed through a process flow diagram. From an economic point of view, it was found that SiC reduction of 1 ton of LG concentrate charge with a converter slag addition requires almost 700 MJ more than the smelting of a UG2 blended concentrate to produce a matte phase. However it must be taken into account that the sulphide rich layers in the Bushveld complex are being depleted rapidly and alternative processes such as SiC reduction and alloy collection process will be utilized faster than expected. Moreover, gas emissions from reductive smelting is considerably lower, hence it is a more environmentally friendly process. Finally, from the findings of this study, it could be said that base metals and PGMs could be recovered in an iron alloy from SiC reduction of LG concentrate with converter slag additions. Therefore integrating such a process into the matte-based collection process could be considered as a future alternative to smelting UG2 LG concentrates.
AFRIKAANSE OPSOMMING: In hierdie studie, word SiC reduksie met Rowland en Oostelikes LG (Lae Graad) konsentrate ondersoek. Die doel van die studie was om die doeltreffendheid van SiC as reduktant te ondersoek met betrekking tot metaalval, PGM graad in die allooi, slaksamestelling (spesifiek word daar gekyk na Cr oplosbaarheid) en algehele PGM herwinning. Die integrasie van die proses in die huidige mat-gebaseerde versamelingproses word ook ondersoek. Tans word die mat-gebaseerde versamelingproses die algemeenste gebruik om PGM'e te kollekteer, maar omdat PGM konsentrate al hoe meer verryk word met UG2 (Upper Group 2) LG konsentrate, word daar verwag dat dit geïntegreer of vervang gaan word met 'n allooi-versamelingproses. Hierdie tipe proses bied groter buigsaamheid om die verskillende reekse van erts wat gebruik kan word. Die proses kan ook chroom hanteer en is omgewingsvriendelik. Vir hierdie doel was Rowland en Oostelikes UG2 LG konsentraatmonsters van Lonmin Western Platinum Limited ontleed met XRD, XRF en ICP -MS en met die ontleding was daar gevind dat SiO2 en MgO die volopste oksides was en dat Pd die volopste elemente van die PGMe was. Sulfiedminerale soos chalkopiriet is in lae konsentrasies opgespoor (minder as 1%) en Cr2O3 konsentrasies is tussen 2-4 %. Die FeO/SiO2 verhouding was laer in Rowland konsentraat. SiC reduksie van Rowland en Oostelikes konsentrate is teen 1600 ℃ uitgevoer. Die reduktant tot konsentraat verhouding vir laboratoriumskaal eksperimente het gewissel van 2.5 – 3.5 kg SiC / 100 kg konsentraat. SiC reduksie van Rowland LG konsentraat het verskillende reduksie tye gehad. Die duur van die reduksie eksperimente het gewissel van 30-180 min. PGM herwinning van SiC reduksie met Rowland konsentreer was baie laag (onder 10 %) en Fe herwinning was minder as 50%. 'n Slakviskositeit aan die einde van die smelt was hoër as 4 poise en was verantwoordelik vir die swak skeiding van fases. SEM beelde het gewys dat fyn metaalstukkies opgehou was in die slakfase in plaas daarvan dat dit vestig en kombineer met die allooibolletjie aan die onderkant van die smeltkroes. In teenstelling was die PGM herwinning van SiC reduksie met Oostelikes konsentraat aansienlik beter. Meer as 85 % van Ir en Pd was herwin en byna 60% van Pt was herwin tydens 'n toets met 'n reduktant tot konsentraat verhouding van 3.5 kg SiC / 100 kg Oostelikes konsentraat. Fe herwinning was 66% en was ook die hoogste van al die eksperimente. Cr en Si konsentrasies was minder as 5 % in totaal. Die slakviskositeit aan die einde van smelt was bereken en is minder as 4 posie. 'n SEM beeld van 'n slakmonster het baie min vasgevangde metaalstukkies getoon. Na afloop van die bogenoemde bevindinge oor die belangrikheid van viskositeit, was daar besluit om die FeO inhoud van die aanvanklike konsentraat te verhoog. Dit was gedoen om die slakviskositeit te verminder, die metaalval (PGM kollektering fase) te verhoog en sodoende die PGM herwinning verder te verbeter. Vir die doel was Peirce -Smith omskakelaarslak gebruik. ʼn Toets was uitgevoer met die toevoeging van 10 kg omskakelaarslak / 100 kg Oostelikes konsentraat. Die reduktant tot konsentraat verhouding was behou by 3.5 kg SiC / 100 kg Oostelikes konsentraat. Die resultate het getoon dat meer as 95 % van Ir en Pd herwin was, terwyl byna 70 % Pt herwin was. Die Fe herwinning het toegeneem tot 76%. Op grond van die resultate van die toets, is 'n optimale verhouding tussen Oostelikes konsentraat, Rowland konsentraat en Peirce -Smith omskakelaarslak bereken. Termodinamiese modellering voorspel dat die begin LG konsentraat voer uit 60 – 80 % Oostelikes konsentraat moet bestaan, met 'n slak toevoeging van 30 – 40 kg omskakelaarslak / 100 kg LG konsentraat. Daar word verwag dat meer as 90 % van PGM'e herwin sal word vanaf SiC reduksie met ʼn optimum LG konsentraat voer. Cr en Si konsentrasies in die allooi sal minder as 1% in totaal wees. Die hoeveelheid slak wat bygevoeg kan word sal egter beperk word deur die finale PGM graad in die allooi, oond-slak hoeveelhede wat herwin kan word en slakweerstand wat benodig word in die allooi-oond. Die effektiwiteit van SiC as reduktant is ook vergelyk met C reduksie. C reduksie van ʼn optimale konsentraatvoer het 'n effens hoër metaalval wanneer dieselde reduktant tot konsentraat verhouding behou was vir SiC reduksie van 'n optimale konsentraatvoer. Gas hoeveelhede van C reduksie is gemiddeld 3 keer meer en vereis te minste 300 MJ meer om 1 ton LG konsentraat te smelt. Dit is hoofsaaklik te wydte aan C wat endotermies reageer met FeO om Fe (l) en CO (g) te produseer, in teenstelling met SiC wat eksotermies reageer met FeO om Fe (l), SiO2(l) en CO (g) te produseer. Integrasie van SiC reduksie met LG konsentrate in die bestaande smeltroete by Lonmin Western Platinum Limited is ook voorgestel deur 'n proses vloeidiagram. Uit 'n ekonomiese oogpunt, is daar gevind dat SiC reduksie van 1 ton LG konsentraatvoer met 'n omskakelaarslak byvoeging ongeveer 700 MJ meer benodig as om 1 ton UG2 gemengde konsentraat te smelt en 'n mat-fase te produseer. Dit moet wel in ag geneem word dat die sulfied ryk lae in die Bosveld-kompleks vinnig uitgeput word en dat hierdie alternatiewe prosesse soos SiC reduksie en ʼn allooiversameling proses vinniger as verwagtend benut sal word. Verder, gas hoeveelhede van SiC reduksie is laer en daarom is dit 'n meer omgewingsvriendelik proses. Ten slotte, vanaf die bevindinge van hierdie studie, kan dit gesê word dat basismetale en PGM'e in 'n ysterallooi herwin kan word deur middel van SiC reduksie met LG konsentrate en die toevoeging van omskakelaarslak. Daarom kan die integrasie van so 'n proses in die huidige mat-gebaseerde versameling proses beskou word as 'n alternatief vir die toekoms om UG2 LG konsentrate te smelt.

Masters of Science
The electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.