Papers by Author: Mariekie Gericke

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Authors: Inez J.T. Dinkla, Mariekie Gericke, B.K. Geurkink, Kevin B. Hallberg
Abstract: Bioleaching test work was performed in continuously operated multi-stage reactor systems at 70°C using a thermophilic culture treating an Aguablanca Ni-Cu concentrate from Spain and a blend of Cu concentrates from Bor, Serbia. The copper in both these concentrates occurs as chalcopyrite and therefore the use of thermophiles was applied, which resulted in copper recoveries of over 95%. Qualitative assessment of the microbial community in the bioreactors was performed by terminal restriction enzyme fragment length polymorphism (T-RFLP) and clone library analysis of the 16S rRNA genes amplified by PCR. T-RFLP analysis revealed that only archaea were present, and that the communities in both the Aguablanca and Bor systems consisted of two different microorganisms. A 16S rRNA gene clone library using DNA from the Aguablanca system was constructed and screened. Again, two archaea were detected in similar relative abundance in the population as found by T-RFLP analyses. The sequences of these two cloned genes revealed that the dominant archaeon (up to 98% of the total archaea detected) was Acidianus brierleyi, and the other was Metallosphaera sedula. Quantitative assessment of the microbial community was performed by Q-PCR and confirmed the dominance of archaea in the system with Acidianus being the dominant strain (98-99% of the total population) and a minor part of the population (1-2%) consisted of Metallosphaera. Additionally, very small amounts of Sulfolobus spp. were detected. This study, along with other recent studies on the diversity of thermoacidophiles involved in the solubilization of copper from chalcopyrite concentrates, revealed that a wider variety of thermoacidophiles are involved in bioprocessing of metal sulfides, and showed that A. brierleyi should be considered an important biomining acidophile.
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Authors: Mariekie Gericke, Y. Govender, A. Pinches
Abstract: The focus of this paper is on the treatment of low-grade chalcopyrite-pyrite containing concentrates. The bioleaching of chalcopyrite is a major challenge due to slow copper leach kinetics and poor copper extractions. Bioleaching tests were carried out in bench-scale piloting facilities, comprising fully controlled multi-stage continuously operated reactor systems using moderate thermophile and thermophile consortia under both uncontrolled and controlled redox potential conditions. Bioleaching operating conditions and control strategies have been identified, which have the potential to significantly increase the rate of Cu leaching and to reduce process costs by allowing control of the amount of pyrite oxidised.
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Authors: Mariekie Gericke, Byron Benvie, Leon Krüger
Abstract: The weathering of kimberlite ores leads to the weakening of the kimberlite structure, which allows the use of less intensive comminution procedures during the liberation of diamonds from the ore, resulting in a decrease in potential damage to the diamonds. The possibility to use iron- and sulphur-oxidising chemolithotrophic microorganisms as a way to accelerate the weathering of kimberlite ores was evaluated. It was demonstrated that the presence of sulphuric acid as well as ferric iron could result in changes in the clay component of these ores. The results provided promising evidence that weathering can be successfully accelerated, but showed that the degree of transformation varies between different kimberlite types with different mineralogical characteristics.
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Authors: Mariekie Gericke, Heinrich H. Muller, P.J. van Staden, A. Pinches
Abstract: The focus of this paper is on the development of a bioleaching process for the treatment of complex polymetallic concentrates, containing chalcopyrite, sphalerite, galena and silver, using a moderately thermophilic culture operating around 45°C. Initial development R&D work and subsequent research for process improvements carried out in bench-scale piloting facilities will be discussed.
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Authors: Sehliselo Ndlovu, Geoffrey S. Simate, Mariekie Gericke
Abstract: Nickel laterite contains metal values but is not capable of participating in the primary chemolithotrophic bacterial oxidation because it contains neither Fe2+ iron nor substantial amount of reduced sulphur. Its metal value can, however, be recovered by allowing the primary oxidation of FeS2, or similar iron/sulphur minerals to provide H2SO4 acid solutions, which solubilise the metal content. This study investigated the possibility of treating nickel laterites using chemolithotrophic microorganisms. Preliminary studies conducted using H2SO4 acid, citric acid and acidified Fe2(SO4)3 gave an insight on the use of chemolithotrophic bacteria in this process,. Results showed that H2SO4 acid performed better, in terms of nickel recovery, than citric acid or acidified Fe2(SO4)3. In the bacterial leaching test works, mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferrooxidans were used in the presence of elemental sulphur and FeS2 as energy sources. The sulphur substrate exhibited better effects in terms of bacterial growth, acidification and nickel recovery than the FeS2 substrate. Using response surface methodology, the theoretical optimum conditions for maximum nickel recovery (79.8%) within the conditions studied was an initial pH of 2.0, 63μm particle size and 2.6% pulp density.
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