Papers by Mariekie Gericke
SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated f... more SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated for the production of single-cell protein (SCP) on bagasse hydrolysates. However, the small cell volume of strain ESP-94 would complicate harvesting of the cells during a continuous fermentation process. Auxotrophic mutants of strain ESP-94 were generated and intraspecific protoplast fusion experiments performed in an attempt to increase the cell volume of strain ESP-94. The fusion products were characterised with respect to cell volume, DNA content and genetic stability. Six genetically stable fusants with bigger cell volumes and higher DNA contents were obtained. One such fusant, fnsant F 17, had a cell volume 3-times that of strain ESP-94, while exhibiting similar growth rates to strain ESP-94 on D-xylose as carbon source.
Springer eBooks, Nov 15, 2022
International Journal of Mineral Processing, 2001
The ability of an extreme thermophile to oxidise a concentrate comprising of chalcopyrite Ž. Ž. 6... more The ability of an extreme thermophile to oxidise a concentrate comprising of chalcopyrite Ž. Ž. 66% and pyrite 11% is described. A batch test at 708C showed that a copper extraction of) 98% was possible. A series of continuous tests were carried out in a three-stage pilot plant, employing standard-design mechanically agitated and aerated tanks. The effect of residence time, feed grind and the mass transfer supply of oxygen and carbon dioxide on bioleach performance were evaluated. The results showed that overall Cu extractions of 95% could be obtained. However, compared to mesophilic and moderately thermophilic bioleaching bacteria, the extreme thermophiles appeared to be more sensitive to the solids concentration employed, which may also be related to the particle size of the feed solids. Levels of oxygen consumption approaching the maximum rates currently being employed in commercial-scale bioleach tanks treating refractory gold pyritic concentrates could be achieved. To maintain these high oxidation rates, it was important to ensure that the supply rate of oxygen and carbon dioxide to the reactors was sufficient. The high copper extractions obtained in these tests showed that a process treating chalcopyrite concentrates using extreme thermophiles has the potential for further development and assessment for commercial applications.
Method for operating a bioleaching process with redox potential control. A method of operating a ... more Method for operating a bioleaching process with redox potential control. A method of operating a bioleaching process for leaching an ore or concentrate containing sulfur, which includes subjecting a suspension bioleaching including dissolved oxygen, dissolved carbon, sulfur and microorganisms to a stage bioleaching dioxide and controlling the redox potential bioleaching the slurry at a predetermined interval.
The microbial consortia in sulphate-reducing bioreactors with different operating conditions were... more The microbial consortia in sulphate-reducing bioreactors with different operating conditions were studied and compared to the sulphate reduction efficiencies. The results showed vast differences in microbial communities among the reactors. The fraction of sulphate-reducing bacteria correlated with the bioreactor performance. This study sheds new light to the biological sulphate-reducing process applied in bioreactors, which is traditionally seen as a black box.
The development of techniques for the synthesis of nanoparticles of well-defined size, shape and ... more The development of techniques for the synthesis of nanoparticles of well-defined size, shape and composition is a challenge and an important area of research in nanotechnology. Many microorganisms have the ability to produce inorganic nanostructures and metal nanoparticles with properties similar to chemically-synthesised materials, while exercising control over the size, shape and composition of the particles. This alternative approach to chemical synthesis procedures uses microbial systems for the production of nanosized materials. Intracellular synthesis of gold nanoparticles, as well as extracellular formation of nanoparticles in the presence of fungal cell extract has been successfully demonstrated. The possibility to manipulate the size and shape of gold nanoparticles by altering key growth parameters was investigated and the results have provided some understanding as to which parameters may have an effect on the formation of gold nanoparticles.
One of the major challenges confronting the mining and minerals processing industry in the 21st c... more One of the major challenges confronting the mining and minerals processing industry in the 21st century is the management of water in an environment of ever decreasing water resources. Especially polluted mine water, from both active and abandoned mines represent a major problem worldwide. Discharge from the latter has been recognised as the main cause of 7% of failures to achieve the goals of the Water Framework Directive (2000/60/EC).
Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) Abstract is paper d... more Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) Abstract is paper describes the commissioning and operation of a pilot-scale passive biological sulphate reduction (BSR) process, treating mine-impacted water from a South African coal mine. e pilot plant comprises three 7 m3 reactors, with a nominal feed rate of 245 L/d. e substrate comprises woodchips, wood shavings, hay, lucerne and cow manure. Process performance is evaluated relative to in uent pH level, hydraulic residence time (HRT), ambient temperature variations, and substrate replenishment rate. Early results demonstrate removal of su cient sulphate to meet regulatory requirements for discharge or agricultural use. Benchmark capital and operating cost estimates of the process are discussed.
Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) Abstract Mine impac... more Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) Abstract Mine impacted water includes all water impacted by mining activities, from process efuents to polluted water courses due to mining activities. In South Africa, mine impacted water has caused severe and long term degradation of the environment. As a result, much research is focused on treating mine impacted water, speci cally increasing or neutralising the pH of the water and decreasing the sulphate and metals concentrations. South African mine impacted water generally contains high levels of sulphate, o en in excess of 3g/L, and stringent regulations enforce low sulphate discharge limits of 200 600 mg/L. Biological sulphate reduction has been demonstrated as a feasible treatment technology for removal of sulphate and precipitation of metals from mine impacted water. Sulphate is biologically converted to sulphide in this process, which is either released as hydrogen sulphide gas, or remains in solu...
Journal- South African Institute of Mining and Metallurgy
Mintek was a leading participant in the BioMinE project between 2004 and 2008. This project, whic... more Mintek was a leading participant in the BioMinE project between 2004 and 2008. This project, which was funded in part by the European Commission, was aimed at the development of biotechnology for the minerals industry in Europe. Mintek’s research programme focused mainly on the development of integrated bioleach-based processes for the recovery of base metals from complex, low-grade sulphide concentrates. Specific European mineral resources were targeted and used in integrated piloting campaigns involving bioleaching, solution purification, and metals recovery. This paper describes the use of thermophilic bioleaching for the recovery of nickel and copper from a low-grade nickel-copper concentrate produced at the Aguablanca Mine in southern Spain. Currently, the Aguablanca Mine produces a bulk nickel-copper concentrate for sale to a smelter, and the proposition is to increase the profitability of the operation by the on-site production of metal or metal intermediate. Initially, bench...
Hydrometallurgy, 2008
... The development of a bioleaching process for the treatment of complex Cu-polymetallic concent... more ... The development of a bioleaching process for the treatment of complex Cu-polymetallic concentrates, containing chalcopyrite, sphalerite, galena and silver, using a moderately ... Keywords:Bioleaching; Copper polymetallics; Moderate thermophiles. ... Batch bioleach tests 2.4. ...
Enzyme and Microbial Technology, 2009
A mixed consortium of sulphate-reducing bacteria was used to investigate the enzymatic mechanism ... more A mixed consortium of sulphate-reducing bacteria was used to investigate the enzymatic mechanism for the total bioreduction of platinum (IV) into platinum (0) nanoparticles. It was established that two different hydrogenase enzymes were involved. First the platinum (IV) was reduced to platinum (II) by a two-electron bioreduction using an oxygen-sensitive novel cytoplasmic hydrogenase. Second the platinum (II) ion was reduced to platinum (0) nanoparticle by another two-electron bioreduction involving an oxygen-tolerant/protected periplasmic hydrogenase. The enzyme was identified from its reaction with Cu(II), an active inhibitor of periplasmic hydrogenases. No exogenous electron donors were necessary as endogenous production of hydrogen/electrons, via the oxidation of metabolites, was generated in situ by the cytoplasmic hydrogenase. The hydrogen then dispersed through the cell to the periplasm where it became available for use by the periplasmic hydrogenase. The endogenous electrons were used, in the absence of sulphate, for the reduction of platinum (II) by the periplasmic hydrogenase. It was found that the Pt(IV) ion must be fully reduced before reduction of the Pt(II) ion would begin. Transmission electron microscopy and energy dispersive X-ray analysis confirmed the deposit of platinum particles into the periplasmic space.
Biotechnology Letters, 2008
A mechanism for the bioreduction of H2PtCl6 and PtCl2 into platinum nanoparticles by a hydrogenas... more A mechanism for the bioreduction of H2PtCl6 and PtCl2 into platinum nanoparticles by a hydrogenase enzyme from Fusarium oxysporum is proposed. Octahedral H2PtCl6 is too large to fit into the active region of the enzyme and, under conditions optimum for nanoparticle formation (pH 9, 65 degrees C), undergoes a two-electron reduction to PtCl2 on the molecular surface of the enzyme. This smaller molecule is transported through hydrophobic channels within the enzyme to the active region where, under conditions optimal for hydrogenase activity (pH 7.5, 38 degrees C) it undergoes a second two-electron reduction to Pt(0). H2PtCl6 was unreactive at pH 7.5, 38 degrees C; PtCl2 was unreactive at pH 9, 65 degrees C.
This paper describes the development of a passive biological sulphate reduction (BSR) process. La... more This paper describes the development of a passive biological sulphate reduction (BSR) process. Laboratory-scale test work was performed on a mine-impacted water from a South African coal mine. The substrate mix comprised wood chips, wood shavings, hay, lucerne and cow manure. Over 90 % sulphate removal was achieved, the pH level was raised to above 7, and metals were precipitated. Operating parameters were optimised to increase process kinetics. The results were used to design a pilot plant which will be operated at the coal mine, treating several hundred litres of water per day.
Journal of the Southern African Institute of Mining and Metallurgy, 2012
Solid State Phenomena
Mondo Minerals owns talc mines in Finland at Sotkamo and Vuonos. A by-product of their talc minin... more Mondo Minerals owns talc mines in Finland at Sotkamo and Vuonos. A by-product of their talc mining operations is a high-grade sulfide concentrate containing pyrrhotite, pentlandite, pyrite, gersdorffite and magnesite. Nickel is the main metal of economic interest, but the concentrate also contains a small amount of cobalt and a significant quantity of arsenic. Multiple processing options were evaluated before identifying Mintek’s bioleaching technology as the most suitable for the recovery of nickel and cobalt from this stream. This paper describes the technical development of the process, from laboratory test work to plant design and early plant operation.
Nanotechnology, 2006
Fusarium oxysporum fungal strain was screened and found to be successful for the inter- and extra... more Fusarium oxysporum fungal strain was screened and found to be successful for the inter- and extracellular production of platinum nanoparticles. Nanoparticle formation was visually observed, over time, by the colour of the extracellular solution and/or the fungal biomass turning from yellow to dark brown, and their concentration was determined from the amount of residual hexachloroplatinic acid measured from a standard curve at 456 nm. The extracellular nanoparticles were characterized by transmission electron microscopy. Nanoparticles of varying size (10-100 nm) and shape (hexagons, pentagons, circles, squares, rectangles) were produced at both extracellular and intercellular levels by the Fusarium oxysporum. The particles precipitate out of solution and bioaccumulate by nucleation either intercellularly, on the cell wall/membrane, or extracellularly in the surrounding medium. The importance of pH, temperature and hexachloroplatinic acid (H(2)PtCl(6)) concentration in nanoparticle formation was examined through the use of a statistical response surface methodology. Only the extracellular production of nanoparticles proved to be statistically significant, with a concentration yield of 4.85 mg l(-1) estimated by a first-order regression model. From a second-order polynomial regression, the predicted yield of nanoparticles increased to 5.66 mg l(-1) and, after a backward step, regression gave a final model with a yield of 6.59 mg l(-1).
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Papers by Mariekie Gericke