Dissertations / Theses on the topic 'Ferric sulphate'

This thesis presents the results of an investigation on the impact of continuous circuit and solution parameters on coprecipitation of arsenic with ferric iron from acidic sulphate solution. The techniques employed were selected, or developed, to emulate industrial practice. The concept behind the work was to better understand the link between the process of precipitation and the stability of arsenic in the resultant coprecipitates. This was performed by examining the role of circuit design and co-ions on both arsenic removal during coprecipitation and arsenic retention during ageing. The parameters/factors investigated included continuous versus batch operation, number of stages (pH profile), recycling and Ca2+, Ni2+ and Al3+ as co-ions. Arsenic removal was found to be greatly improved by continuous rather than batch coprecipitation. In addition, the presence of calcium (introduced as slaked lime) was found to be instrumental in the removal and retention of arsenic. Arsenic retention during ageing (up to 300 days) at various temperatures (3, 22, 40 and 70°C) was observed to reach an "equilibrium" that was strongly affected by the continuous circuit design, as well as the co-ions present during coprecipitation. Evidence is presented of the partitioning of arsenic within the coprecipitates in two principal phases, namely ferric arsenate (FeAsO4•xH2O) and arsenic adsorbed ferrihydrite. Continuous circuit design parameters, such as staging, that resulted in enhanced stability appear to yield coprecipitates with higher ferric arsenate content. Analysis of the kinetic and "equilibrium" arsenic retention data yielded activation energy (~ 60 kJ/mol) and enthalpy (~ -38.5 kJ/mol) values that suggest a reaction controlled exothermic dissolution mechanism.
Ce mémoire de maîtrise présente les résultats d'une étude portée sur la co-précipitation de l'arsenic et des ions ferriques en solution aqueuse sulfatée. L'utilisation d'un procédé continu et les paramètres de la solution ont été considérés comme cibles d'étude. Les techniques employées ont été sélectionnées ou développées afin de simuler les méthodes opératoires industrielles. L'idée directrice de ce travail était d'aboutir à une meilleure compréhension sur les liens entre les mécanismes de précipitation et la stabilité de l'arsenic dans les co-précipités formés. Aussi, le rôle du design du procédé ainsi que celui des co-ions sur l'extraction, respectivement la stabilisation de l'arsenic ont fait l'objet d'un examen approfondi à court terme soit au stade de co-precipitation, respectivement à long terme durant le vieillissement de la solution. Les paramètres/facteurs étudiés incluaient le caractère continu du procédé (en comparaison avec un procédé discontinu), le nombre d'étapes (le profile pH), le recyclage des produits solides et la nature (Ca2+, Ni2+ et Al3+) des co-ions introduits dans le système. Cette étude a montré que l'utilisation d'un procédé continu (en comparaison avec un procédé discontinu) améliorait considérablement l'extraction de l'arsenic à partir de solutions aqueuses sulfatées. Aussi, la présence de calcium (introduit sous forme de chaux hydratée) s'est avérée profitable à l'extraction de l'arsenic à court et à long terme. Il a été observé que la stabilisation de l'arsenic dans le cas des expériences de vieillissement (d'une durée de 300 jours) performées à différentes températures (3, 22, 40 et 70°C) atteignait un état d'équilibre fortement influencé par le design du procédé continu ainsi que par les co-ions présents lors de la co-précipitation. Il a été mis en évidence que lors de la phase de co-précipitation, l'arsenic était réparti sous forme de de

This study (between August 1992-May 1994) of the impact of ferric sulphate dosing, examined phosphorous and nitrogen inputs and outputs, nutrient fluxes within the water column, and phosphorus sediment-water interactions in Rutland Water. Rutland Water, a lowland, eutrophic pumped-storage reservoir in the UK experienced severe cyanobacterial blooms and scums during the late summer of 1989 which received national media attention. In response to this, from June 1990, ferric sulphate was added to the reservoir with the pumped input from the rivers Nene and Welland to attempt to precipitate phosphorus to the sediments to limit phytoplankton abundance. The seasonality of phosphorus and nitrogen loadings influenced in-lake nutrient concentrations and subsequent phytoplankton biomass. The pumped input was the dominant source; the natural inflows were insignificant. Ferric sulphate did not influence nutrient temporal and spatial patterns, although the decline in in-lake phosphorus concentrations between 1990 and 1991 was related primarily to the decline in the annual phosphorus loading during drought conditions and also to the large quantities dosed. Wind-generated mixing, together with the effect of the jetted input were sufficient to prevent the development of full stratification, although at the deepest site slight dissolved oxygen stratification developed during summer. Nutrient depth variation was attributed to sedimentation and subsequent decomposition of organic matter in the bottom waters. Ferric sulphate increased phosphorus sedimentation, which was the dominant downward flux. Ferric sulphate floc increased the sediment redox potential, lowered pH and increased the phosphorus-binding capacity of the sediments, although the high ratio of total iron:total phosphorus already present was inferred as governing the strong phosphorus-binding capacity. Although no sediment phosphorus release was detected under the redox-driven mechanism, any potentially released phosphorus influenced by microbiological actions was reprecipitated to the sediments due to the maintenance of relatively aerobic conditions in the water column.

Mestrado em Engenharia do Ambiente - Instituto Superior de Agronomia
Given the growing food requirements, mainly due to the increase of the world population, the global livestock sector is more intensive. The pig production, an important sector follows this trend yielding large quantities of slurry, rich in nutrients, organic matter and higher amount of metals in the livestock effluents. Physico-chemical processes procedures are effective in the treatment of effluents, which includes coagulation / flocculation. This tecnhology was selected for the development of an experimental study on a raw effluent to simulate reality, where the nutrient removals were analyzed by coagulation / flocculation. In this study the effectiveness of conventional coagulants and polymers was compared, after optimization of the dose, agitation time and speed and volume of sludge produced. The biopolymer used was chitosan, because it is abundant and natural. Aluminum sulphate (Al2(SO4)3) was found to be more effective than ferric chloride (FeCl3), two of the most commonly used coagulant in the treatment of waste water. Comparing the results with the ones obtained by natural sedimentation, it is shown that the coagulation / flocculation is effective in removing turbidity and COD, and especially in the removal of metals analyzed. These removals exceed 60% and reduce the sludge volume by about 38%. The phosphorus, element which can cause eutrophization of the water is removed almost entirely (around 70%-94%).

Sludge treatment and disposal are one of the most important parts of sewage treatment. These are economically challenging parts, and therefore emphasis is placed on effective dosing. The dose should be as small as possible but also the highest dry matter output. The main target of this diploma thesis is therefore to show that it is possible to achieve the same or better degree of drainage of the sludge if different flocculant/coagulant ratio is applied to the sludge. Diploma thesis deals with determination of the optimal combination of chemical doses during sludge dewatering. The thesis contains two parts, practical and theoretical. The theoretical part consists of research, overview of processed research and works in the area of sludge dewatering. The second part is a description of laboratory measurements and evaluation of results.

Abstract Chemical treatment is considered best available technology for purification of peat extraction runoff in Finland, due to its capability to remove dissolved organic carbon (DOC), suspended solids and nutrients. However, lack of optimisation and adaptation of this method for purification of diffuse pollution sources, e.g., peat extraction runoff, has led to significant fluctuations in purification efficiency. This thesis evaluated the suitability of commercially available coagulants for the treatment of typically humic water. Inorganic (ferric sulphate, aluminium sulphate and a mixed product) and organic (polyDADMAC, polyamine, chitosan and tannin products) coagulants were studied. Investigations included assessment of required dosage and the influence of process parameters (pollutant concentration, mixing, water pH and temperature) on coagulant performance. In addition, the process conditions in existing treatment systems were examined in field experiments aimed at identifying possible factors affecting purification. Ferric sulphate (FS) was the most effective of the coagulants tested. It produced excellent flocs and achieved higher removal efficiency, particularly for DOC, than the other coagulants. However, the dosage required for FS was significantly higher than for e.g., polyDADMAC and chitosan. Moreover, samples treated with FS displayed high iron concentration and acidic pH. The organic polymers achieved satisfactory results, but further research is needed before they can become viable alternatives to metal salts. The quality of peat extraction runoff water was found to vary significantly. It was also observed that variations in DOC concentration, even for particulate rich samples, controlled coagulant dosage and, consequently, treatment efficiency. For inorganic coagulants, mixing provided during flocculation had a more significant influence on purification than mixing provided during coagulation. This is relevant hence in now existing treatment facilities no mixing is employed during flocculation. Based on the research conducted, suggestions were formulated for process optimisation aimed at reducing variations in purification efficiency, thus increasing the reliability of the method and reducing related environmental impacts
Tiivistelmä Turvetuotannon valumavesien käsittelyssä yksi parhaista käyttökelpoisistatekniikoista on kemiallinen käsittely, koska se pystyy poistamaan valumavedestä liukoista orgaanista hiiltä (DOC), kiintoainetta ja ravinteita. Tästä huolimatta kemiallisen käsittelyn optimointia ei ole tehty hajakuormitukselle, kuten turvetuotannon valumavesille, minkä seurauksena valumavesien puhdistustuloksissa on suurta vaihtelua. Tässä väitöstyössä tutkittiin markkinoilla saatavilla olevien kemikaalien sopivuutta turvetuotannon humuspitoisille valumavesille. Tutkimuksessa testattiin epäorgaanisia (ferrisulfaatti, alumiinisulfaatti ja näiden sekoitus) ja orgaanisia (polyDADMAC, polyamiini, kitosaani ja tanniinipohjaisia polymeerejä) koagulanttikemikaaleja. Tutkimuksessa selvitettiin koagulanttien annostarpeet sekä erilaisten prosessiparametrien (vedenlaatu, sekoittaminen, pH ja lämpötila) vaikutus koagulanttien toimintaan. Laboratoriotutkimusten lisäksi väitöstyö sisälsi kenttämittauksia turvetuotannon valumavesien tyypillisten kemiallisen vesienkäsittelyn prosessiparametrien selvittämiseksi. Tutkituista koagulanteista rautasulfaatti oli tehokkain. Se tuotti hyvin laskeutuvaa flokkia ja poisti parhaiten valumavesien orgaanista ainesta. Rautasulfaatti vaati kuitenkin selkeästi suuremman annostuksen kuin esimerkiksi polyDADMAC ja kitosaani. Lisäksi puhdistettuun veteen jäi paljon rautaa ja vesi oli hapanta. Orgaanisilla kemikaaleilla saavutettiin myös kohtalainen/melko hyvä puhdistustulos, mutta lisää tutkimusta tarvitaan ennen kuin ne voivat olla vaihtoehtona epäorgaanisille kemikaaleille. Turvetuotannon valumaveden laatu vaihteli paljon. Valumaveden orgaanisen aineen määrän vaihtelulla oli suurin vaikutus kemikaalin annostukseen ja puhdistustulokseen. Sekoituksista kemiallisen käsittelyn flokkulaatiovaiheen sekoituksella oli suurempi vaikutus puhdistustulokseen kuin koagulaatiovaiheen sekoituksella. Tutkituilla turvetuotantoalueilla ei kuitenkaan ollut tällä hetkellä riittävää sekoitusta flokkulaatiovaiheessa. Tässä väitöstyössä esitetään parannuksia kemiallisen käsittelyn optimointiin paremman ja vakaamman puhdistustuloksen aikaansaamiseksi humuspitoisille vesille

Increasing freshwater scarcity across the world means that wastewater reclamation is being considered as a key method in which to meet the growing demand. Evolution of water reuse schemes where high quality product is required such as for indirect potable reuse has led to the adoption in recent years of the integrated membrane scheme using a combination of microfiltration or ultrafiltration with reverse osmosis membrane. However, despite technological advancements, these membranes are still prone to fouling resulting in increased costs through cleaning or replacement. This thesis aims to look at pretreatment to reduce the fouling propensity of the microfiltration membranes via a 600m3 /d pilot plant which was commissioned to investigate indirect potable reuse. A range of pretreatments including pre-screening, pre-coagulation, powdered activated carbon and granular activated carbon were assessed based on fouling amelioration, water quality improvement and cost analysis. Results showed that ferric sulphate dosing was the most effective in terms of reducing the reversible fouling rate especially at high turbidity loads enabling higher flux to be realised leading to a small cost benefit. Activated carbon proved the most effective pretreatment in terms of organic removal and a significant reduction in the irreversible fouling rate. However, the cost involved in using this as a pretreatment is significant compared to possible cost savings through reduced requirement for chemical cleaning. This pretreatment is only viable if it obviates the need for a separate organic removal process.

Bibliography: pages 98-105.
The work presented in this dissertation is an investigation of-the ferric leaching of zinc from sphalerite. A further aspect of this study was an investigation of the influence of pyrite on the dissolution rate of sphalerite due to possible galvanic interactions. This study is one component of a larger study of the sub-processes involved in the bioleaching of sulphide minerals in which the ferric leaching of the sulphide mineral is assumed to be a chemical step with the bacteria oxidising ferrous iron to ferric iron and elemental sulphur, if formed, to sulphate. The literature showed that two types of model have been used to describe the ferric leaching of the sphalerite. The first type was a shrinking-particle model in which there action was described by first order kinetics or an electrochemical mechanism. The second type included a mass transfer resistance in terms of a shrinking-core model described by half-order kinetics or a decaying diffusion coefficient. All four of these models were tested for their ability to predict published data for the ferric leaching of sphalerite. It was found that the models fitted the data for the initial period of a leach up to conversions of about 50%. However, no one of the models was found to be successful in predicting the data for prolonged leaching to high conversions.

Bibliography: leaves 63-68.
This thesis is part of the greater study and looks into understanding the ferric leaching sub-process by establishing an effective way of measuring the rate of the chemical leach process.

The oxidative dissolution of chalcopyrite in ferric media often produces incomplete copper recoveries. The incomplete recoveries have been attributed to inhibition caused by the formation of a metal deficient sulphide and the deposition of elemental sulphur and jarosite. Although these phases have been qualitatively identified on the surface of chalcopyrite, none have been quantitatively identified. The aim of the project was to quantitatively analyse the surface before and after oxidative dissolution, with X-ray photoelectron spectroscopy (XPS), and to use the phases identified as the basis for mechanisms of dissolution and inhibition.
XPS analysis was performed on chalcopyrite massive fractured under anaerobic atmosphere and chalcopyrite massive and concentrate oxidised in 0.1 M ferric sulphate (pH 1.9) and 0.2 M ferric chloride (pH 1.6) at 50, 65 and 80ºC. Quantitative XPS analysis of the chalcopyrite surfaces required the development of programs that accounted for the observed XPS spectra. The output of these programs was used to construct profiles of the chalcopyrite surfaces and the deposited phases. These surface profiles were correlated with copper recoveries determined for chalcopyrite concentrate dissolution under the same conditions.
The surface of chalcopyrite before oxidative dissolution reconstructs to form a `pyritic' disulphide phase. This phase is oxidised in ferric media to form thiosulphate via the incorporation of oxygen atoms from the hydration sphere. The thiosulphate reacts in the oxidising conditions of low pH to form elemental sulphur, sulphite and sulphate. The sulphate complexes with ferric to produce hydronium jarosite. This reaction occurs at the surface during the initial stages of dissolution and in the bulk solution during the latter stages. This precipitation of hydronium jarosite during the latter stages of dissolution corresponds to inhibition of the dissolution reaction. It is therefore concluded hydronium jarosite is responsible for inhibiting the oxidative dissolution of chalcopyrite in ferric media.
The identification of hydronium jarosite as the inhibiting phase is consistent with the industrial practice of removing `excess' iron from the ferric solution before oxidative dissolution. However, additional iron and sulphate are generated at the chalcopyrite surface during oxidative dissolution. These high iron and sulphate concentrations combine with the low pH and high temperatures favoured for the oxidative dissolution of chalcopyrite to produce ideal conditions for jarosite precipitation. Therefore, pH must be lowered further to prevent jarosite precipitation and enhance copper recoveries from chalcopyrite in ferric media.

Luminescence measurements have been applied to three different structures namely, sulphate, fluorides and YAG. In all cases the RE doping suppresses the intrinsic emission and results in intense luminescence characteristic of the RE dopant. Additionally, in double doped samples, or contaminated ones, the TL data show that each dopant defines a glow peak, which is displaced in temperature relative to the others. Examples of this were discussed for CaS04:Ce,Mn; YAG:Nd,Tb,Cr,Mn; BaF2:Ho,Ce and BaF2:Tm,Ce. The data are discussed in terms of an energy transfer model between different parts of extended defect complexes which encompass the RE ion and the lattice defects. Calcium sulphate doped with Dy define a TL peak near 200°C suitable for radiation measurements, but when co-doped with Ag the TL peak move to higher temperatures with minor effects on the peak sensitivity. In Ce,Mn double doped samples, the peak temperatures differ by -7°C between the Ce and Mn sites. The TL glow curves from alkaline earth fluorides are complex and contain several overlapping peaks. Curve fitting show that the peak maxima below room temperature are insensitive to the RE dopant. Additionally the host material has a modest effect on the peak positions. Above room temperature each dopant provides a TL curve specific to the added RE ion and do not show common peaks. Concentration has many effects on the resultant glow curve, and even at the lowest concentration used here (0.01%) there is evidence of cluster formation. Samples with high RE content show low values of the frequency factor consistent with the energy transfer model in that the emission from RE-RE cluster dominates over the emission from direct charge recombination within the defect complex. The effect of concentration and the TL mechanism operating below room temperature are also discussed. Luminescence signals from the near surface of YAG:Nd (via CL) were contrasted with those from the bulk material via RL. Results indicate that the outer few micron layers differ significantly in luminescence response from the bulk crystal. The differences were ascribed to result from solvents that enter the YAG lattice during the growth stage or subsequently from cleaning treatments via the dislocations caused by cutting and polishing. Additionally, the growth stage may include gases from the residual air in the growth furnace trapped into the YAG lattice. In each case there is a discontinuity in luminescence intensity and/or emission wavelengths at temperatures which mach the phase transitions of the contaminants. At the transition temperature there will be a sudden pressure change and this will induce surface expansion or bulk compression. The differences between the two cases were detected by the alternatives of CL and RL excitation, where the Nd or Er lines have moved in opposite directions. The detection of such low concentrations of solvents/trapped gases by luminescence is extremely difficult due to experimental limitations. Hence their role in luminescence generation is normally ignored.