A rotating diffusion cell (RDC) has been used to study the kinetics of extraction of the transition metals cobalt (II), nickel (II), copper (II) and zinc (II) from sulphate solutions into either of two extractants held in n-heptane; di-(2-ethylhexyl) phosphoric acid (D2EHPA) or di-(2- ethylhexyl) dithiophosphoric acid (D2EHDTPA). The metal concentration was 10 mM and the aqueous pH was held at 4.5. The extractant concentration was varied between 0.015 to 0.4 M. In the case of cobalt extraction by D2EHPA, the metal concentration and the pH were varied Different diluents and modifiers were also studied.The rate of extraction by D2EHDTPA was found to be faster than D2EHPA. A comprehensive mathematical model, based upon established two film theory, was developed and used to describe the above experimental results. The model was also used to predict values of the important parameters. ... These values compared well with those found by other authors but using quite different experimental techniques. OS4 In the case of cobalt extraction by D2EHPA, the more polar diluents lowered the initial rate. The overall model predicts such behaviour where the rate is also dependent on the partition coefficients of the extractant. Finally, the theory of the RDC allows the prediction of the diffusion layer thicknesses, this information together with the reaction zone thickness is used to explore the influences of diffusion and chemical reaction on the overall transfer process. The diffusion processes are calculated to be the most important of the two. This is especially so for the D2EHDTPA systems.

The Twickenham Platinum Mine (TPM) Project is located in the north eastern limb of the Bushveld Complex, north west of Steelpoort in the Limpopo Province. The property hosts platinum group metals (PGM) mineralisation in the Merensky Reef (MR) and Upper Group 2 Chromitite (UG2). The two reefs are separated by 400 m of mafic and ultramafic rocks of the Rustenburg Layered Suite. The question that must be answered with this study relates to the economic viability of the MR compared to that of the UG2 at the TPM Project, as it stands in 2011. The assumption is that no mining has commenced on this project and that there is an equal opportunity to commence mining on one of the reefs. The study describes the ore body characteristic for each reef, focussing on the lithologies, structure, and resources available. The discounted cash flow (DCF) method was used to determine the economic value of each reef. The net present value (NPV) and internal rate of return (IRR) were calculated and used to compare the ore bodies. The input parameters to the DCF are the main limiting factors to this method, as the results are heavily dependent on the assumptions made. The input parameters used were based on actual published values and generally accepted and motivated assumptions. A sensitivity and risk analysis was completed to identify value ranges and potential risks to the projects. The outcome of the analysis has been compared to other projects as a benchmark to ensure the project assumptions were realistic. The world markets supply and demand for PGM is intricately related to exchange rates, metal prices, inflation, and investment risk. These have an influence on the strategic planning for a company as well as investment decisions through various project evaluation methods. South Africa has a long history of mining and metals extraction. Extensive mining legislation has been developed to ensure the country’s mineral wealth is protected and the health and safety of employees are high priority. Specific challenges related L! to mining on the Eastern Limb are discussed in order to justify the high risk assigned to the project for this evaluation. The DCF was calculated and the outcome indicated that neither the MR nor the UG2 is economically viable using these parameters in the 2011 economy. The MR evaluation produced a negative NPV (R -1,664,541,443.47) and an IRR of 9 %, which is well below the required discount rate of 12 %. The initial project capital will be repaid after 19 years of the 33 year life of mine. The sensitivity analysis showed that by reducing the initial capital by 30 %, the project produces a positive NPV. The other factor that produced a positive NPV was by reducing the operating cost by 50 %. This project will have to be re-evaluated after all parameters have been tested and some re-engineering has been done to optimise the extraction of the MR ore body. The UG2 evaluation produced a negative NPV (R -109,614,208.27) and an IRR of 12 %, equal to the required discount rate. The initial project capital will be repaid after 16 years of the 32 year life of mine. The sensitivity analysis showed encouraging results, as minor changes to the input parameters produced a positive NPV. The two parameters that were most significant were the recoveries and the capital requirements. By increasing the recovery percentage by 2 %, the project NPV becomes positive and a reduction of the initial capital by 10 %, also resulted in the NPV becoming positive. This indicates that with some refinement to the input parameters, the UG2 could be extracted as an economically viable project. The only concern is the sensitivity to changes in grade, which will have to be very well defined and controlled when mining commences. The risk assessment related closely to the challenges identified for a mining operation on the Eastern Limb, with the relationship with the local community and the build-up phase of the project emerging as the highest risks. The limited infrastructure development and high levels of poverty that exists in the area has a direct influence on the support structures and services available for the build-up phase of a mine. The build-up phase requires substantial development and services that will have to be sourced at high risk and cost from substantial distances, to ensure that steady state is reached. The socio-economic development of the local community is critical for the success of the mine. Upliftment of the local community in terms of education and training, job opportunities and health care will provide the foundation for a good relationship / Dissertation (MSc)--University of Pretoria, 2012. / Geology / Unrestricted

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

Les piles à combustible microbiennes (PCMs) sont une technologie convertissant l’énergie chimique stockée dans la matière organique en énergie électrique à l’anode à l’aide de bactéries dites électroactives. A l'inverse des bioanodes, l’intérêt porté aux cathodes biologiques dans les PCMs est récent et ces dernières sont encore peu étudiées. Les objectifs de ces recherches ont donc été d’identifier et de décrire des bactéries ainsi que les mécanismes permettant de catalyser une réduction cathodique notamment celle de l’oxygène. La première partie des travaux portant sur la réalisation d’un criblage pour la formation de biocathodes a révélé l’inefficacité du métabolisme hétérotrophe pour la conception de biocathodes performantes. De ce fait, la suite des travaux a porté sur la bactérie chimiolithoautotrophe acidophile Acidithiobacillus ferrooxidans. Deux mécanismes de transfert d’électrons dépendant du fer ont été mis en évidence générant un courant maximal de -3,8 A.m-2. Nous avons également abordé les mécanismes de transfert d’électrons en milieu neutre chez une bactérie hétérotrophe, Pseudomonas brassicacearum NFM421 bien que peu performante en terme de production de courant. Cette dernière permet une catalyse indirecte de la réduction de l’oxygène à la cathode à pH neutre via un métabolite secondaire le 2,4-diacéthylphloroglucinol associé au fer, mettant encore une fois en lumière l’importance du fer dans le transfert d’électrons. Ce travail a également porté sur la potentielle application des biopiles dans des environnements anthropisés en vue de l’extraction de métaux et plus particulièrement de terre rares qui s’avèrent être une voie de recherche prometteuse. / Microbial fuel cells (MFCs) are devices that convert chemical energy contained in organic matter into electrical energy using electroactive bacteria that act at the anode. Currently, MFCs performances are limited by the use of abiotic cathode. The interest in biological cathode has recently started and less is known about bacterial diversity and mechanism that catalyze cathodic reduction. The aims of the research work are therefor to identify and describe potential bacteria and mechanism involved in such catalysis. The first part of the work is the realization of a screening that did not show conclusive results and might indicate that heterotrophic metabolism was not an efficient choice. Next, Acidithiobacillus ferrooxidans had been used and shown two extracellular electron transfer mechanism depending on iron. A maximum current intensity of -3,8 A.m-2 had been reached. To be close to operational condition of MFC, Pseudomonas brassicacearum NFM 421 has also be use and shown capacity to indirectly catalyze the oxygen reduction at a neutral pH using the 2,4-diacethylphloroglucinol, a secondary metabolite, associated to iron. However, current reach remained weak. Considering difficulty to build efficiant biocathode at a neutral pH, the end of this work had been focused on a new application of the MFC: metal and rare earth extraction from soil and contaminated site that appeared to be a great research opportunity to follow.