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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.

Oxide materials exhibit a wide variety of structures and properties. In particular, transition metal oxides tend to be highly stable while exhibiting a wide range of properties that can be used for numerous applications. This work focuses on investigating how the structures��� of 4d and 5d transition metal oxides influences their properties. Specifically oxides of Ru, Rh and Ir were investigated. A complete solid solution was found between isostructural Pb���Mn���O������ and Pb���Rh���O������. Pb���Rh���O������ shows a Verwey-type transition at 185 K. This transition remains with a 3 % substitution of Mn for Rh but disappears with a 4 % substitution of Mn for Rh. The structure was found to expand in the direction perpendicular to the layers of the structure, which is the c-axis, despite a contracting unit cell. Bi for Pb substitution in Pb���Mn���O������ was found to be limited as compared to in Pb���Rh���O������. Alkali metal substitution on the A-site of the orthorhombic perovskite SrRuO��� showed only low substitution levels were possible. Nonetheless, the substituted phases showed decreased ferromagnetic Curie temperatures, increased electrical resisitivity and relatively unchanged Seebeck coefficients. Thermoelectric studies of Sr[subscript 2-x]La[subscript x]CoRuO��� perovskite phases showed Sr���.���La���.���CoRuO��� with the best thermoelectric performance. This system showed possible correlations between cation ordering on the B-site and the charge carrier transport. A similar thermoelectric study of (RhV)[subscript 1+x]Ti[subscript 1-2x]O��� phases crystallizing in a disordered trirutile structure was done. Electron carriers were found to be dominant and dependent on Ti content. The electron carriers appear to become diminished at higher temperatures. Sr���IrO��� crystallizes in a K���NiF���-type structure. Effects of Ti, Fe and Co substitution for Ir were investigated. A complete Sr���Ir[subscript 1-x]Ti[subscript x]O��� solid solution was synthesized and characterized while limited solubility was found for Fe and Co substitutions. All substitutions showed a decrease in the c-cell parameter coupled with a decrease in octahedral tilting. All substitutions also showed a decrease in magnetic susceptibility and an increase in the paramagnetic effective moment was observed for Co and Fe doped samples. An incomplete solid solution was formed for Sr���Ti[subscript 1-x]Rh[subscript x]O��� phases; however effects of increased octahedral tilting with higher Rh content were observed. / Graduation date: 2013

This project investigates the optimisation of platinum-group metals recovery at the Mimosa Mine in Zimbabwe. The first part of this research investigates how collector performance can be improved by using collector combinations (mixtures) of the standard sodium iso-butyl xanthate with a secondary collector. The synergistic effect of the sodium-iso-butyl-xanthate (SIBX) combined with trithiocarbonates (TTCs) or dithiophosphates (DTP) was investigated. The short chain and the long chain TTCs were investigated. These collector combinations were studied at various molar percent ratios. The SIBX:DTP combination was studied at a 1:1 mass ratio or molar ratio of 1:1.3. Amongst all the collector combinations, it was established that the SIBX/DTP combination improved sulphur recoveries by 10% and subsequently the PGE+Au recovery by 10% compared to when the SIBX was used on its own. The C4-TTC showed poor performance in the sulphur recovery; however an improvement in PGE + Au recovery was noticeable. There was generally no significant metallurgical improvement with respect to final grades and recoveries with C10 and C12TTC mixtures with SIBX. However, the 6.25 molar per cent substitution of SIBX by C12TTC appeared to show some improvement on sulphur but not on PGM+Au recovery and grade. It was therefore concluded that the SIBX/DTP combination at 1:1 mass ratio (total moles of 0.64) showed a potential to improve the grades and recoveries of the Mimosa Mine. The Mimosa ore is characterised by an unusually large amount of talc, which often causes problems during the flotation of the PGM minerals due to the fact that talc consumes high amount of reagents. Therefore the purpose of the second part of this thesis was to investigate the possibility of removing talc prior to the flotation process by de-sliming. Two cyclones (36.9 mm and 76.0 mm) were used for de-sliming the flotation feed. De-sliming the ore was able to reduce the depressant dosage up to 300 g/t as opposed to 500 g/t that is used at Mimosa Mine. / Dissertation (MSc)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

This diploma thesis in the theoretical part analyses the characteristic feature of individual platinum group elements, their toxicity, anthropogenic sources and the presence of platinum group elements in the environment of the Czech Republic. In addition, there are specified types of bioindicators focusing mainly on lichens, mosses and needles. There are described individual bioindication techniques and pre-treatment of samples for platinum metals determination in bioindicators. The subject of the experimental part is to verify the sorption efficiency and ability of platinum and palladium using the SPE method and to determine the actual platinum metal contamination in selected localities in the city of Brno. There was also the additionally subject to verify the sorption potential of selected bioindicators and determination of the environmental pollution by platinum metals using the bag technique. In the experimental part, the bioindicators of moss Pleurozium schreberi, lichen Xanthoria parietina, lichen Flavoparmelia caperata and needles Pinus nigra were used.

Prague and Brno belong to one of the most contaminated cities of Czech Republic. The main objective of this study was to compare PGE contents and concentrations of risk elements (Zn, Cd, Pb, Cu, As, Sb, Hg) in the soils of both cities's municipal parks. Soil samples were taken from depths of 0-10 cm, 10-20 cm and 20-30 cm. Besides soil samples, the sand samples from children sandpits were taken from depth 0-30 cm. In 52 samples of soil and sand Pd, Pt and Rh contents were determinated by ICP- MS after Ni-S fire assay procedure. Soil samples were additionally analysed on Pb isotopic composition. Higher PGE contents were determined in Prague; the highest contents were measured at location of Ortenovo náměstí (50,5 μg·kg-1 Pt, 33,9 μg·kg-1 Pd a 11,3 μg·kg-1 Rh). Elevated PGE concentrations were found in the upper layers of most soils in both cities. Elevated contents of risk elements were determined at locations with high traffic density. Most of samples showed that contents of risk elements decrease with depth. The highest concentrations reached Zn (394 mg·kg-1 ), Pb (290 mg·kg-1 ) and Cu (181 mg·kg-1 ). In Prague, the isotopic ratios 206 Pb/207 Pb vary from 1,136 to 1,181; in Brno from 1,161 to 1,192. Measured isotopic ratios suggest contamination both from gasoline and ore combustion. Key words:...

The distribution of platinum group elements and increase of thein emissions in the environment are mostly related to the use of automobile catalyst. The antropogenic emissions of these noble metals accumulate aloung the roads. The methods such as ICP-OES and XRD were used for determinativ of phase and elemental composition of these samples. The matrix of the gasoline catalyst is composed of Al, Ce oxides with Pt-Pd-Rh coatings. Matrix of diesel catalyst is composed of cordierite with Pt coatings. ICP-MS was used for determination Pt, Pd and Rh. Before the analysis was performed such as pre-concetration fire assay fusion into a NiS button. The leaching characterization of Pt, Pd and Rh was examined during kinetic batch experiments in sodium chloride (1g/l, NaCl), 20 mM Na2P4O7 (NaPyr), fulvic acid (FK, DOC 50 mg/L) and 20 mM citric acid . The results show, that the dissolution of Pt and Pd is the fastest in citric acid and sodium pyrophosphate. Sodium chloride in the concentrations employed, which could be derived from melt waters formed during winter road treatment, does not have a substantiv impal on the speciation and mobilization of Pt and Pd. Organic acid does not have significantly impct on the release of Pt and Pd to the solution. The calculated normalized bulk released NRi values in the range 0,16...

This study described an alternative approach for flotation circuit optimization using a mathematical programming technique. Mathematical formulation resulted in mixed integer nonlinear programming problem. Experimental method was used to determine operating conditions of flotation circuit such as flotation circuit stream grades. These conditions were used as the basis for solving optimization problem formulated. The results of the optimization problem were obtaining by setting up the problem in MATLAB optimization toolbox. Performance of flotation circuit in terms of recovery with respect to operating conditions such as residence, number of cells and rate constant has been presented. Stage recoveries were presented as well as overall recovery of the entire flotation circuit. Optimization strategy used superstructure to compare and analyse different alternatives flotation circuits configurations on the basis of stage recoveries. Five circuit alternatives were evaluated are best performing were identified. The statistical analysis was carried out using Statistical Package for Social Sciences (SPSS) software for analysing data derived from mathematical formulation developed for three stages of flotation circuit. Statistically, alternatives A and B can be considered as the most efficient alternatives for the Rougher recovery since they have the same highest means relative to others. Alternative B has the highest mean of 0.995 followed by Alternative A with a mean of 0.991, the least being alternatives D, C and E, respectively. These results imply that Alternative B could be the most efficient alternatives for overall circuit recovery against all other alternatives. One of the key findings were that recovery rate at the rougher stage is higher than the one at the cleaner stage. This results also showed flotation circuits with recycle streams yield comparatively good performance in terms of recovery at rougher stage as compared to circuit without recycle stream. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

The world energy supply and demand, together with limited available resources have resulted in the need to develop alternative energy sources to ensure sustainable and expanding economies. Hydrogen is being considered a viable option with particular application to fuel cells. The Hybrid Sulphur cycle has been identified as a process to produce clean hydrogen (carbon free process) and can have economic benefits when coupled to nuclear reactors (High Temperature Gas Reactor) or solar heaters for the supply of the required process energy. The sulphur trioxide decomposition reactor producing sulphur dioxide for the electrolytic cells in a closed loop system has been examined, but it is clear that development with respect to a more durable active catalyst in a reactor operating under severe conditions needs to be investigated. A suitable sulphur trioxide reactor needs to operate at a high temperature with efficient heating in view of the endothermic reaction, and has to consist of special materials of construction to handle the very corrosive reactants and products. This investigation was undertaken to address (1) the synthesis, characterisation, reactivity and stability of a suitable catalyst (2), determination the reaction rate of the chosen catalyst with a suitable micro reactor (3) construction and evaluation of a packed bed reactor for the required reaction, and (4) the development and validation of a reactor model using computational fluid dynamics with associated chemical reactions. A supported catalyst consisting of 0.5 wt% platinum and 0.5 wt% palladium on rutile (TiO2, titania) was prepared by the sintering of an anatase/rutile supported catalyst with the same noble metal composition, synthesized according to an incipient impregnation procedure using cylindrical porous pellets (±1.7 mm diameter and ±5 mm long). Characterization involving: surface area, porosity, metal composition, - dispersion, - particle size, support phase and sulphur content was carried out and it was found from reactivity determinations that the sintered catalyst, which was very different from the synthesized catalyst, had an acceptable activity and stability which was suitable for further evaluation. A micro pellet reactor was constructed and operated and consisted of a small number of pellets (five) placed apart from each other in a two-stage quartz reactor with sulphur trioxide generated from sulphuric acid in the first stage and the conversion of sulphur trioxide in the second stage, respectively. Attention was only confined to the second stage involving the conversion of sulphur trioxide with the supported catalyst. The overall reaction kinetics of the pellets involving momentum, heat and mass transfer and chemical reaction was evaluated and validated with constants obtained from literature and with an unknown reaction rate equation for which constants were obtained by regression. As result of the complexity of the flow, mass and heat transfer fields in the micro pellet reactor it was necessary to use a CFD model with chemical reactions which was accomplished with a commercial code COMSOL MultiPhysics® 4.3b. A reversible reaction rate equation was used and a least squares regression procedure was used to evaluate the activation energy and pre-exponential factor. The activation energy obtained for the first order forward reaction was higher than values obtained from literature for a first order reaction rate (irreversible reaction) for the platinum group metals on titania catalysts. Detailed analyses of the velocity, temperature and concentration profile revealed the importance of using a complex model for determination of the reaction parameters. A fixed bed reactor system consisting of a sulphuric acid vaporizer, a single reactor tube (1 m length, 25 mm OD) heated with a surrounding electrical furnace followed, by a series of condensers for the analysis of the products was constructed and operated. Three process variables were investigated, which included the inlet temperature, the weight hourly velocity and the residence time in order to assess the performance of the reactor and generate results for developing a model. The results obtained included the wall and reactor centreline temperature profiles together with average conversion. As a result of the complexity of the chemistry and the phases present containing the products from the reactor a detailed calculation was done using vapour/liquid equilibrium with the accompanying mass balance (Aspen-Plus®) to determine the distribution of sulphur trioxide, sulphur dioxide, oxygen and steam. A mass balance was successfully completed with analyses including SO2 with a GC, O2 with a paramagnetic cell analyser, acid/base titrations with sodium hydroxide, SO2 titrations with iodine and measurement of condensables (mass and volume). The results obtained showed that a steady state (constant conversion) was obtained after approximately six hours and that it was possible to obtain sulphur trioxide conversion approaching equilibrium conditions for bed lengths of 100 mm with very low weight hourly space velocities. A heterogeneous 2D model consisting of the relevant continuity, momentum, heat transfer and mass transfer and the reaction rate equation determined in this investigation was developed and solved with the use of the commercial code COMSOL MultiPhysics® 4.3b with an appropriate mesh structure. The geometry of the packed bed (geometry) was accomplished by generating a randomly packed bed with a commercial package DigiPac™. The model predicted results that agreed with experimental results with conversions up to 56%, obtained over the following ranges: weight hourly space velocity equal to 15 h-1, temperatures between 903 K and 1053 K and residence times between 0.1 and 0.07 seconds. The post-processing results were most useful for assessing the effect of the controlling mechanisms and associated parameters. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2014