OpenUCT :: Browsing by Author "Petersen, Jochen"

Browsing by Author "Petersen, Jochen"

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Open Access
A study of alternative techniques to mercury amalgamation for gold extraction in artisanal and small-scale gold mining
(2022) Manzila, Archippe Ngwey; Petersen, Jochen; Moyo, Thandazile
Artisanal and small-scale gold mining (ASGM) has many definitions depending on the context. However, the common theme that characterises gold mining operations that fall within this category is that they make use of rudimentary methods to mine and process gold. The ASGM sector is a source of livelihood for millions of people worldwide and continues to grow due to the ever-rising demand for gold, and high unemployment rates which have been exacerbated by the Covid-19 pandemic, particularly in developing countries. Mercury amalgamation is the method of choice to recover gold in ASGM. This method consists of contacting the gold found within an ore with mercury to form an alloy i.e., the mercury-gold amalgam and subsequently burning off mercury to recover the gold in a form known as sponge gold. The popularity of this method has to do with its simplicity of application, low cost, and quick returns. However, mercury is a highly toxic substance; therefore, its use presents serious health risks for artisanal miners and their communities, and environmental risks for the ecosystems surrounding their operations. These risks arise primarily from the amalgam burning stage, whereby mercury is vapourised, and the dumping of mercury-rich tailings into local rivers. This mercury release affects human health by causing serious diseases that may lead to death. From an environmental perspective, mercury has been reported to severely pollute river ecosystems, inevitably finding its way to food chains. Due to these issues, alternative technologies such as borax smelting, the Gemini table, thiosulphate, cyanide, chlorine, and urea leaching, to name a few, have been developed or adapted over the years to substitute mercury. However, most of these technologies have not been successfully implemented in artisanal mining operations. This lack of success is primarily due to their complexity and high cost, making them unattractive to artisanal miners. This study investigates the application of cyanide and thiosulphate leaching as alternatives to mercury amalgamation for the recovery of gold in ASGM operations. Although cyanidation is practiced in ASGM, in some regions, it is only employed to treat tailings from the mercury amalgamation process. This is undesirable due to the fact that exposing mercury to cyanide results in the mobilisation of elemental mercury found in the tailings as mercury cyanide. This project investigates gold extractions that can be achieved with cyanide and alkaline thiosulphate systems and compares the results to those of mercury amalgamation. This investigation was undertaken by conducting leach experiments using cyanide at 1 g/L, 3 g/L and 5 g/L, and ammonium thiosulphate at 0.1 M and 0.5 M, on 3 ore samples originating from artisanal mining locations. The experiments were conducted using batch stirred tanks reactors and the operating conditions (T= 26°C, solids loading: 30%, particle size: --300 +150 µm) were selected to mimic as closely as possible the conditions of artisanal mining processes. The findings of the study revealed that cyanide leaching was the better performing technology compared to thiosulphate leaching as it achieved gold extractions of 71.6%, 69.7% and 67.8% for the 3 ores samples (Sample 1, Sample 2, and Sample 3, respectively) while thiosulphate leaching achieved gold extractions of 54.1%, 35.6% and 38.0% for the 3 ores, respectively. Studying the minerology of the ores, using XRF, XRD, QEMSCAN, SEM-EDS and diagnostic leach, revealed the presence of sulphide minerals hosting refractory gold which contributed to the low gold extractions observed. Cyanide leaching proved to be a system that is easier to control compared to thiosulphate leaching, making it much more attractive to artisanal miners. It is recognised that cyanide is a toxic chemical, however, the method is already practiced in ASGM and cannot be simply wished away. Instead, steps must be taken for its safe and responsible use. Hence, this research makes recommendations on avenues that can be explored to reduce the risks associated with cyanide use. It was also found that cyanide leaching outperformed mercury amalgamation which typically achieves gold recoveries of 30-50%. Thiosulphate leaching may be capable of achieving better gold recoveries than mercury amalgamation as well, as one of the ore samples achieved a gold extraction of 54.1%. However, this would depend on the ore type and reagent conditions as it was found that the 3 ore samples responded differently to leaching.
Open Access
A Study on the Applicability of Agitated Cyanide Leaching and Thiosulphate Leaching for Gold Extraction in Artisanal and Small-Scale Gold Mining
(Multidisciplinary Digital Publishing Institute, 2022-10-14) Manzila, Archippe Ngwey; Moyo, Thandazile; Petersen, Jochen
Mercury amalgamation is the method of choice to recover gold in artisanal and small-scale gold mining (ASGM). However, despite the low cost and simplicity of this method, the use of mercury presents serious health and environmental risks, as well as low efficiency in gold extraction. This study investigates the application of cyanide and thiosulphate leaching as alternatives to mercury amalgamation. This investigation was undertaken by conducting leach experiments using cyanide at 1 g/L, 3 g/L, and 5 g/L, and ammonium thiosulphate at 0.1 M and 0.5 M, on three ore samples originating from an artisanal mining area in Zimbabwe. The operating conditions (T = 26 °C, solids loading: 30%, particle size: −300 + 150 µm) were selected to mimic as closely as possible the conditions of artisanal mining processes. It was found that cyanide leaching was the better performing technology compared to thiosulphate leaching, as it achieved gold extractions of 71.6%, 69.7%, and 67.8% for the three ore samples (Sample 1, Sample 2, and Sample 3, respectively), whereas thiosulphate leaching achieved gold extractions of 54.1%, 35.6%, and 38.0% for the three ores, respectively. Both methods outperformed mercury amalgamation, which typically achieves gold recoveries of 30%–50%. Studying the minerology of the ores, using XRF, XRD, QEMSCAN, SEM-EDS, and a diagnostic leach, revealed the presence of sulphide minerals hosting refractory gold which contributed to the low gold extractions observed. Besides achieving higher gold extraction, cyanide leaching proved to be a system that is easier to control compared to thiosulphate leaching, making it much more attractive to artisanal miners.
Open Access
Ammonia leaching as a pre-treatment for the processing of oxidised PGM ores
(2015) Musonda, Kabwe Julianna; Petersen, Jochen
The exploitation of near-surface deposits has resulted in the need to adjust current conventional mineral processing technologies for the treatment of low grade oxidised PGM ores. The exposure of the ore to the atmosphere leads to the formation of an oxidation layer (consisting of base metal oxides) which inhibits the flotation process that requires a clean mineral surface to be effective. Previous studies have shown that an acid pre-treatment could lead to a 20% PGM recovery increase. Due to the corrosive nature of acid, such treatment would require additional equipment and a pre-wash. Therefore, this project investigates the use of ammonia as a pre-treatment of oxidised low grade PGM ores. Ammonia leaching has shown success in the extraction of base metals (94% and 91% Cu and Ni extraction) and is used as a wash reagent in an attempt to dissolve the oxidation layer and expose a cleaner mineral surface. Both column leaching of whole ore and batch stirred tank reactor leaching of milled ore were investigated as pre-treatment methods for varying length of process times, and the material was subsequently tested for its flotation behaviour. The total solids, base metal and PGM recoveries were monitored in order to determine the effect of the treatment.
Open Access
Ammonium hexachlororuthenate precipitation
(2011) De Klerk, Frederick Jacobus; Westra, Arjan; Hagemann, Justin; Petersen, Jochen
Ammonium hexachlororuthenate (ACR) is a salt precipitated during a substitution reaction between ammonium and ruthenate dissolved in a strong hydrochloric acid medium. This precipitation reaction is used within the platinum industry as a means of recovering and purifying ruthenium. Application of this process at the Precious Metals Refinery of Anglo Platinum has brought to light certain inefficiencies. In recent years, volatility in the Ru market price occurred, indicating a potential to benefit financially from an improved Ru recovery. Consequently, this study was conducted to understand the effect of certain parameters on the process of precipitating ammonium hexachlororuthenate.
Open Access
The anodic dissolution of covellite in acidic, chloride solutions
(2010) Basson, Petrus; Petersen, Jochen
An electrochemical study was conducted on a stationary, synthetically produced, covellite electrode in acidic, chloride solutions at ambient conditions to investigate the dissolution behaviour of the mineral over a surface potential range from the open circuit potential (OCP) to about 0.62 V (vs. SHE). The electrode was mounted in an apparatus, which was designed to resemble leaching of the mineral under conditions applicable to heap leaching of whole ores, where the mineral occurs in cracks or pores in the gangue matrix or is covered (or partially covered) by reaction products.
Open Access
Application of HPGR and X-Ray CT to investigate the potential of Witwatersrand gold ore for heap leaching : a process mineralogy approach
(2014) Nwaila, Glen; Becker, Megan; Petersen, Jochen
Auriferous conglomerates of the Archaean Witwatersrand Basin in South Africa host one of the largest known gold resources and rate as the worldâ€™s most outstanding example of a fossil megaplacer deposit. For the past 40 years, Witwatersrand gold production in South Africa has been progressively declining due to problems related to high energy costs, decreasing grade, accessibility to greater depths, health and safety issues, labour union unrest and economic uncertainties: thus the overall viability of current gold production is questionable. Ultimately, the future of Witwatersrand gold mining relies on devising smarter strategies across the entire industry, but in particular critical areas such as comminution and extraction. With the continuous increase in mining depth, dominance of low-grade gold ores and strict safety regulations, metallurgical processing options have become limited. Heap leaching is a well-established technology which continues to grow in use and provides several benefits to solve some of these problems. High pressure grinding rolls (HPGR) is another technology with significant potential, especially for its application in coarse particle heap leaching due to its ability to induce micro-cracks as well as its high grinding efficiency and low energy requirements. This study explores the use of these two technologies in a process mineralogical framework using novel 3D X-ray computed tomography mineralogical analysis in order to assess a potential of the Witwatersrand gold ore for heap leaching.
Open Access
Assessment of a Shredding Technology of Waste Printed Circuit Boards in preparation for Ammonia-based Copper leaching
(2020) Prestele, Marc Patrick; Petersen, Jochen; Moyo, Thandazile
The electronic waste (e-waste) stream grows at a global annual rate of 3-5%, with an expected 50 Mt to be discarded worldwide in 2020 alone. These large amounts of e-waste pose considerable environmental and health problems while also presenting socio-economic opportunities to most nations, especially to developing countries such as South Africa. E-waste presents a specifically unique challenge to developing nations as they suffer the challenges associated with e-waste, but do not have sufficient waste volumes to adopt business models used in developed countries to harness the economic opportunities presented by the growth of this waste streams. Recycling of e-waste requires huge capital and operating costs to run integrated recycling facilities and developing countries generally lack this funding. Furthermore, developing countries suffer from inadequate infrastructure, absent legislation and lacking capital investment which are necessary for the processing of e-waste regardless of it being regarded as a secondary resource or waste. Printed circuit boards (PCBs) are a valuable fraction of e-waste, made up of tightly laminated metal-polymer composites containing several base and precious metals which makes them attractive to recyclers. Hydrometallurgy is a widely explored technology that allows for scalable operations for recovering metals from PCBs. However, for it to be effectively employed, the metals in PCBs need to be liberated or be accessible to leach agents. To date, this still heavily relies on energy-intensive pulverisation prior to the leaching and subsequent metal recovery stages. This paper explores the structure of the PCB, developing an understanding of how the structural design of the board translates to the difficulty in liberating or exposing the metals for leaching. The paper goes further to test and compare metal liberation techniques as well as compares energy consumption and costs associated with the techniques; with the view to identify a low energy and low capital investment method that would be suitable for adoption by small scale recyclers typical of those operating in South Africa. The structural design of the PCBs was explored through an intensive literature survey and conducting a case study of the PCB manufacturing process of a local company as well as running tensile tests, drop weight impact tests and three-point bending tests on a batch of custom-made PCBs supplied by the local company. The metal liberation methods tested included the use of an industrial grab shredder to size reduce and delaminate the PCBs, use of a planetary ball mill and some instances including precursors such as freezing the PCBs in liquid nitrogen or soaking the boards in NaOH to remove the upper- and lowermost epoxy layers. The effectiveness of each method was then evaluated using a diagnostic ammoniacal leach test in which the extent of copper dissolution from the PCB is used as an indicator of the performance of the liberation method. Results on the structural design of the PCBs showed that it would be suitable to use size reduction mechanisms that are based on impact stresses as the fibreglass and epoxy could absorb all other stresses at high intensity without failing. In general, all treated or untreated PCBs underwent a maximum of six shredding passes, with results generally producing poor recoveries, not exceeding 27.5%. “Untreated” PCBs, referring to PCBs that only have undergone shredding in the industrial grab shredder, showed increasingly iv higher copper recoveries with consecutively shredding cycles. The 6th cycle produced the highest copper recoveries of 6.80g (23.5%) after 72 hrs. PCBs that had been soaked in NaOH and undergone six passes through the industrial grab shredder recovered a maximum of 27.5%. Interestingly, using a similar process but only shredding the PCBs in four passes showed similar results at 26.14% Cu recovery. Shredding the PCBs in four passes and subsequently milling them for 60 min (without NaOH treatment) showed lower Cu recoveries at 13.29% and this was not improved by extending the milling time to 120 min. This showed that the NaOH treatment was more effective in exposing the outer layers of copper relative to the shredding and milling. It can be seen that apart from size reduction there is delamination of some of the shredded PCB pieces. However, this delamination is not always complete and Cu metal can still be seen covered by fibreglass and hence inaccessible to leach agents. It is concluded that the combination of the shredding and NaOH method has potential and it is recommended to incorporate a 2nd NaOH stage to further delaminate the inner layers of the PCB exposing the copper
Open Access
Assessment of the potential carbon footprint of engineered processes for the mineral carbonation of PGM tailings
(2016) Ncongwane, Mpendulo S; Broadhurst, Jennifer; Petersen, Jochen
Mineral carbonation is a carbon sequestration technology that entails the reaction of CO2 with oxides or silicates of magnesium, calcium or iron to produce stable carbonate compounds. Magnesium-rich tailings from the platinum industry in South Africa have been identified as a potentially viable and attractive feedstock for CO2 sequestration through mineral carbonation. Many of the strategies proposed to enhance the dissolution kinetics of silicate minerals, such as the use of elevated temperatures and pressures and chemical additives, as well as pretreatment through mechanical and thermal activation, are energy intensive and will thus reduce the net CO2 sequestration capacity of the overall mineral carbonation process. As a result, there is growing recognition of the need to evaluate the processes using life-cycle based approaches and tools to ensure they result in net CO2 reduction. However, to date, research and development has focused primarily on the optimisation of extraction and/or carbonation efficiencies, with specific emphasis on the relatively reactive silicate minerals, such as olivine and serpentine. This project seeks to investigate the viability of using pyroxene-rich PGM tailings for the sequestration of CO2, with specific emphasis on net carbon neutrality. Promising mineral carbonation processes have been identified on the basis of an extensive literature review, and include the: ammonium salts pH swing, Lackner's HCl multi-stage, gas-solid Abo Akademi University process, direct aqueous process, and mineral acid pH swing. Material and energy balances were then conducted for these processes on the basis of the sequestration of 1 ton of carbon dioxide, using Aspen Plus v8 simulation software package. The material and energy data were then used to determine the total carbon footprint contributions, through the use of SimaPro v 7.7.3. life cycle assessment software.
Open Access
Base metal heap and tank leaching of a platreef flotation concentrate using ammoniacal solutions
(2013) Muzawazi, Caroline; Petersen, Jochen
The technical feasibility of the ammonia leaching process of a Platreef flotation concentrate was investigated in different reactor settings i.e. shake flasks, columns and batch stirred tank reactors, respectively. The process investigated aims to use either a heap leaching environment or tank leaching of untreated low-grade concentrates under ambient conditions and mild temperatures. This process is proposed as an alternative primary treatment method for the recovery of base metal sulphides from a PGM containing concentrate that cannot be extracted economically by conventional milling, smelting and refining methods.
Open Access
Biooxidation kinetics of Leptospirillum Ferriphilum attached to a defined solid substrate
(2011) Duku, Porogo; Petersen, Jochen; Minnaar, Sanet; Harrison, STL
Bioleaching can be categorized as being either stirred tank type (i.e. bio-oxidation) or irrigation type (i.e. heap/dump bioleaching) yet studies investigating the kinetics of bioleaching systems mostly use empirical data determined from stirred tank type and initial rate experiments in batch cultures or using iso-potential devices. Rate equations deduced from such empirical data is then used to model both the stirred tank type and irrigation type bioleaching systems overlooking the possibility that there may be significant differences in their environments and therefore the kinetics. Tank bioleaching systems are well mixed suspension systems dominated by planktonic microorganisms (freely suspended in the liquid medium). Heap bioleaching systems on the contrary, are heterogeneous in nature with chemical and physical conditions changing over time and are dominated by sessile microorganisms (attached microorganisms to the surface of a solid). The heap bioleaching system is therefore highly complex compared to the stirred tank-type systems. Microbial growth in bioleaching systems significantly influence the overall bioleaching kinetics yet biological kinetic effects in sessile/ attached environments are not well understood. Heap and dump leaching account for about 20% of the world’s copper production and are becoming popular methods of copper production from leaching low grade ores. It is therefore important that the kinetics of irrigation type bioleaching systems are well understood. A strategy to determine the microbial kinetics of a sessile microbial population is enforced in this study. From this, empirical data determined from irrigation type environments can then be used to derive equations which can be used to accurately model heap bioleaching systems. Three sets of experiments were conducted to try and achieve this: i. planktonic experiments - investigating the microbial kinetics of a planktonic microbial population ii. attachment experiments - investigating the nature of growth of the microbial population to the surface of a solid substrate during attachment to create a sessile microbial population iii. sessile experiments - investigating the microbial kinetics of the sessile microbial population A pure culture of Leptospirillum ferriphilum (a mesophilic, ferrous iron oxidizing bioleachingmicroorganism) was used in this study. Planktonic experiments were conducted in a completely mixed, well aerated continuous stirred tank reactor (CSTR) with a 1 litre working volume, operating at a pH of about 1.3 and temperature of 37oC. Attachment and sessile experiments were conducted using a CSTR with similar conditions to the planktonic experimental, however the system was modified by introducing a packed bed vessel (PBR) attached as a closed loop to the CSTR. Solution drawn from the CSTR was then continuously pumped through the PBR and back to the CSTR.
Open Access
Characterisation of the effect of alteration on the PPM platinum ore and evaluation of selected strategies to improve metallurgical performance
(2011) Ramonotsi, Mpho; Petersen, Jochen; Becker, Megan
The aim of this study is in two parts; the first part focuses on mineralogical quantification of the extent of weathering at PPM by profiling the flotation behaviour and host rock density with spatial depth.
Restricted
Competitive Bioleaching of Pyrite and Chalcopyrite
(Elsevier, 2006) Petersen, Jochen; Dixon, David G
An experimental study was conducted to investigate the heap bioleaching of a copper-gold concentrate using the Geocoat™ technique. Small-scale columns were operated at selected temperatures using bacterial consortia suited to these temperatures. In all experiments secondary copper sulfides would leach more rapidly than pyrite. Chalcopyrite, however, appeared to leach only in the presence of extremely thermophile microbes and selectivity towards chalcopyrite decreased with leach time. Analysis of the leach tailings showed that, surprisingly, the overall rate of bio-oxidation did not significantly increase with temperature. Further, analysis of ferric demand for mineral oxidation vs. ferric supply by microbial oxidation suggests that chalcopyrite leaching is promoted by extreme thermophiles due to a favourable interplay between reaction kinetics, solution potential and chalcopyrite ‘passivation’ phenomena, whereas pyrite leaching is favoured at lower temperatures. This analysis also explains why selectivity towards chalcopyrite decreases with time. The results are of some significance for the development of a high temperature whole ore chalcopyrite heap bioleach process.
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Conventional and electrochemical bioleaching of chalcopyrite concentrates by moderately thermophilic bacteria at high pulp density
(Elsevier, 2011) Ahmadi, Ali; Schaffi, Mahine; Petersen, Jochen; Schippers, Axel; Ranjbar, Mohammad
Conventional and electrochemical bioleaching were investigated to extract copper from Sarcheshmeh chalcopyrite concentrate at high pulp densities. Experiments were conducted in the presence and absence of a mixed culture of moderately thermophilic iron- and sulphur oxidizing bacteria using a 2-L stirred electro-bioreactor at 20% (w/v) pulp density, an initial pH of 1.4–1.6, a temperature of 50 °C, a stirring rate of 600 rpm and Norris nutrient medium with 0.02% (w/w) yeast extract addition. The results of 10 day leaches showed that, when using electrochemical bioleaching in an ORP range of 400 to 430 mV, copper recovery reaches about 80% which is 3.9, 1.5 and 1.17 times higher than that achieved in abiotic electrochemical leaching, conventional bioleaching, and electrochemical bioleaching at 440–480 mV ORP, respectively. It appears that applying current directly to the slurry optimises both, the biological and chemical subsystems, leading to an increase in both, the dissolution rate and the final recovery of copper from the concentrate. Mineralogical analysis of the solid residues of electrochemical leaching in both, biotic and abiotic media, showed the formation of chalcocite and covellite minerals on the surface of not leached chalcopyrite. It is postulated that the reduction of refractory chalcopyrite to more soluble minerals such as chalcocite and covellite is achieved through both, electron transfer upon electrode contact and by ferrous reduction at the low ORP of the slurry. These secondary minerals are then rapidly dissolved through bioleaching, while at the same time a formation of a passive layer of jarosites is minimised. This process also appears to promote an increased bacteria–solid ratio due to favourable growth conditions.
Open Access
The development of an online amperometric technique to measure free and WAD cyanide in gold plant leach liquors and effluent streams
(2012) Van der Merwe, Wendy A M; Petersen, Jochen
In 2004, Mintek recognised the gold mining industry‘s need for an online free and WAD cyanide measurement device and went about extending the existing free cyanide analyser,the Cynoprobe to include WAD cyanide measurement. The WAD cyanide analysis technique was to be based on ligand exchange, which required the selection of an appropriate reagent,with amperometric finish. Thereafter, the technique was validated in the laboratory to include the capabilities of the prototype instrument in terms of accuracy and precision (0.5-100 ppm WAD CN). Various local trials were conducted in order to validate the measurement and the robustness of the instrument in an industrial environment. Successful trials (<10% error with respect to laboratory analysis) led to international application and exposure to complex ore types and process solutions.
Open Access
The effect of carbon dioxide on the growth and activity of leptospirillum ferriphilum
(2010) Naik, Linus; Harrison, STL; Petersen, Jochen
Microbial oxidation rates catalysed by the acidophilic micro-organisms mediating mesophilic and thermophilic bioleaching of mineral sulphides have been well characterised under conditions typical of active tank leaching processes in the mineral industry. However, with the increasing need to beneficiate low grade ores, heap bioleaching processes are increasingly of interest. The physicochemical conditions within the heap bioleach differ considerably from the tank leaching system in terms of typical iron concentration, presence of dissolved salts and dissolved gases. This study focuses particularly on the kinetic description of the microbial ferrous oxidation rate and the microbial growth rate of the Leptospirillum species under conditions where the supply of carbon dioxide is limited.
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The effect of dissolved cations on microbial ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture
(Elsevier, 2008) Ojumu, Tunde V; Petersen, Jochen; Hansford, Geoffrey S
In heap bioleaching the dissolution of gangue minerals from igneous ore materials can lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the target minerals. In the present study the effect of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g•dm− 3 and combined concentrations 0 to 16 g•dm− 3each (or total ionic strength from 0.2 to 1.3 M) has been investigated in continuous culture using Leptospirillum ferriphilum. Increasing the concentrations of the salts increasingly depresses the specific rate of ferrous iron oxidation and also shifts the viable range more and more into the low potential region. Aluminium significantly reduces the amount of carbon biomass maintained in the reactor, whereas magnesium actually enhances it at low concentrations. The experimental data was correlated using the Pirt equation and a simplified substrate utilisation model. The results suggest that the maximum microbial growth rate and growth yield decline significantly only at total ionic strengths above about 1 mol•dm−3. The implications of this study are that heap cultures are likely to perform sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.
Open Access
Effect of HPGR on platinum bearing ores and the flotation response as compared to the conventional ball mill
(2011) Solomon, Nomonde; Mainza, Aubrey; Becker, Megan; Petersen, Jochen; Franzidis, Jean-Paul
This thesis focuses on the application of the high pressure grinding rolls (HPGR) on platinum bearing ores Merensky, UG2 and Platreef. Conventional tumbling mills such as the ball mill that are typically applied on these ore types are highly energy intensive with a small percentage of the input energy being used for actual breakage. Rapidly increasing energy costs have contributed to the rising interest of the HPGR in the platinum industry, particularly in plants processing UG2 and Platreef ores. Therefore, this thesis seeks to determine if the HPGR can be used as an alternative to the ball mill. Key aspects of interest are throughput, energy efficiency, PGE grade and recovery and PGM liberation.
Open Access
Effect of scale of operation on heap leaching performance
(2019) Van Staden, Petrus Johannes; Petersen, Jochen
The extent to which differences in bulk density and in irrigation geometry contribute towards the differences observed in leaching performance between laboratory-scale columns versus commercial-scale heaps was investigated. Furthermore, the contributions of segregation and stratification, which are absent from columns but unavoidable in heaps, were also investigated. Four case studies provided data whereby the column and heap leaching of the respective sample materials could be directly compared. The first involved gold-bearing ore, the second gold-bearing sand, a third was conducted on oxide-copper ore and the fourth case study was performed on sulphidic copper ore. The first case study was published by others, while the other three were conducted by the author himself. Furthermore, custom-designed boxes were constructed whereby the segregation and stratification of ore could be simulated. Tests were performed to observe the leaching performance of segregated and stratified ore samples, compared to unsegregated and unstratified ore samples. The leaching characteristics of each case was quantified in terms of the parameters of a mathematical model, based on dual-porosity hydrology and diffusion with chemical reaction, which provided optimised fits to the experimental data. Furthermore, fundamental relations were derived for the impact that changes in bulk density and changes in drip-irrigation spacing are theoretically expected to have on the same model parameters. These relations were tested against the actual trends observed in the model parameters that best fitted the data of the four case studies and of the segregation/stratification experiments. It was found that the diffusional distance, which places a mass-transfer limitation on the over-all rate of leaching, can be governed by either the ore bulk density, or by the irrigation dripper spacing. The relations derived under this study can be used to estimate the maximum dripper spacing that can be permitted to prevent dripper spacing from becoming the rate-limiting parameter. Estimates of the impact of dripper spacing on the ultimate extent of extraction are also provided. However, neither segregation nor stratification exhibited significant or reproducible effects on leaching kinetics. These findings can place the drafting of heap leaching design parameters on a more fundamental footing.
Open Access
The effects of solution conditions on the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture
(2008) Ojumu, Tunde Victor; Petersen, Jochen; Hansford, Geoffrey Spearing
The objective of this work was to investigate the effects of a wide range of solution conditions,namely: temperature, pH, dissolved Al and Mg, and the effect of total iron concentration on the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphilum, with a view to developing a comprehensive rate equation.
Open Access
An electrochemical reduction process for the recovery of copper powder from a refinery effluent stream
(2014) Bezuidenhout, Chandon; Petersen, Jochen
In recent years a significant amount of research has gone into the development of a feed pretreatment process for the concentrate refined at Anglo American Platinum's Precious Metals Refiners (PMR). Such a process has the potential to significantly simplify the downstream refining process and reduce the number of unit processes required for purification. One of the considered options involves a high temperature oxidative roast process followed by a high temperature hydrochlorination process to volatilise base metal chlorides and other impurities. The resulting precious group metal (PGM) concentrate is cleaner and thus requires significantly less process steps to final product. The off-gas from hydrochlorination contains predominantly silver, copper, nickel and iron. This off-gas undergoes a quench-scrub to condense the base metal chlorides. The quench-scrub liquor undergoes a dechlorination process with sulfuric acid to precipitate AgCl(s). The filtrate from this process then undergoes an electrochemical reduction process to recover copper metal concentrate. The objectives of this study were to: i. Determine the operating conditions for an electrochemical reduction process aimed at recovering copper as a copper powder from a sulfuric acid stream containing copper, nickel and iron. ii. Develop a conceptual flowsheet for a batch electrochemical process and estimate the capital cost and operating cost.