Browsing by Subject "Heap bioleaching"

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    Determining the effect of acid stress on the persistence and growth of thermophilic microbial species after mesophilic colonisation of low grade ore in a heap leach environment
    (Elsevier, 2013) Tupikina, O V; Minnaar, S H; van Hille, R P; van Wyk, N; Dew, D; Harrison S T L; Rautenbach, G F
    The microorganisms involved in the bioleaching of sulphidic mineral ores are acidophilic. Generally, a pH in the range of pH 1–2.5 is applied for optimal growth in these systems. In operating heaps, perturbation of conditions could result in changes in the pH outside this “safe” window, so an understanding of the effect of changes in pH on growth and activity of bioleaching microbes is needed. Previous work has shown that some microorganisms e.g. Acidithiobacillus thiooxidans, Leptospirillum ferriphilum and Leptospirillum ferrooxidans are able to adapt to low pH environments (∼pH 0.9). However, most studies on the response of micro-organisms implicated in mineral bioleaching to pH have been conducted under submerged, aerated culture conditions, with limited performance-based studies conducted under conditions mimicking a heap environment. In this study, the effect of acid stress on the persistence of the thermophilic micro-organisms in the ore bed inoculated at mesophilic conditions and their subsequent growth on reaching thermophilic conditions is considered. Following inoculation, five columns loaded with a low grade chalcopyrite ore were irrigated at a feed pH of 1.7 at 25 °C. After a few days, the temperature was sequentially increased from 25 °C through 37 °C to 50 °C, resulting in an Eh above 850 mV across all columns. The irrigation feed pH was then varied across the range pH 1.0 to 1.7 at 50 °C. Eh values greater than 800 mV could be attained in the columns with feed pH values between pH 1.2 and pH 1.7 at 50 °C. The Eh of the column receiving feed solution at a pH of 1.0 at 50 °C dropped to below 700 mV and did not recover. The temperature was then increased gradually to 60 °C. All the columns with feed pH of 1.2 and higher achieved Eh values above 800 mV. Quantitative analyses of the microbial community on selected PLS and ore samples indicated that lower pH affected the persistence of the thermophilic micro-organisms in the ore bed and their subsequent growth on reaching thermophilic conditions. The microbial population detached from the ore sample after 120 days decreased by a factor of 5–15 and 25–100 fold on decreasing the operating pH from 1.5–1.7 to 1.4 and 1.2 respectively. Poor microbial activity was found at pH 1.0, suggesting ineffective growth or persistence of the archaea.
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    Development of a method to assay the microbial population in heap bioleaching operations
    (Elsevier, 2005) Coram-Uliana, Nicolette J; van Hille, Robert P; Kohr, William J; Harrison, Susan T L
    Heap bioleaching is an economically viable approach to the mining of low-grade ores. Oxidation is microbially assisted, involving a consortium of microorganisms that together span the mesophilic to extreme thermophilic range of temperatures (25–80 °C). Temperatures inside the heap are not externally regulated, making the microbial interactions difficult to predict. In order to gain insight into these interactions, a qualitative and quantitative assay of the microorganisms that colonise the ore surface or are present in the liquid phase between the ore clusters at different levels within a heap has been developed. This method was developed using crude ore and liquid samples obtained from the GeoBiotics temperature controlled mesophilic heap operation at the Agnes Gold Mine in Barberton, South Africa, and the high temperature test columns at SGS Lakefield Research, Johannesburg, South Africa. This method of sample analysis may be applied to bioheap leach operations with and without temperature control. Ease of application, reproducibility and turn around time influenced technique design in order to provide a useful assay for commercial bioleaching operations. Following microbial removal from the solid phase using successive washes with detergent and acidified water, the cells were enumerated and genetic DNA was isolated. Microbial identification was achieved via restriction endonuclease analysis of the 16S rRNA genes, as well as 16S rRNA gene sequencing where necessary. Quantification was achieved using species-and genus-specific probes through fluorescent in situ hybridisation (FISH).
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    Microbial colonisation in heaps for mineral bioleaching and the influence of irrigation rate
    (Elsevier, 2012) Chiume, R; Minnaar, S H; Ngoma, I E; Bryan, C G; Harrison, S T L
    Microbial colonisation is important for mineral dissolution in heap bioleaching of low grade ore. Colonisation studies to date have focused on the microbial attachment of single species to mineral concentrates in batch and flow systems. Hydrology and soil engineering studies suggest interaction between microbial colonisation and fluid flow in porous systems that result from solution-ore and microbe-mineral contacting (Wan et al., 1994 and Yarwood et al., 2006). The effect of the irrigation rate on microbial colonisation was assessed using columns packed with acid agglomerated low grade copper-containing ore. Continuous flow, unsaturated, aerated bed reactors were inoculated by pulse irrigation with iron and sulphur oxidising mesophilic microorganisms (1012 cells/ton ore), followed by operation at irrigation rates of 2, 6 and 18 l/m2/h. A novel in-bed sampling technique allowed the extraction of ore samples from the bed during the leaching process. Novel insights regarding microbial growth, interstitial and weakly and strongly attached microbial populations were obtained. Bacterial adherence and cell number retained in the ore bed increased over the 32 day leaching period. Average specific growth rates of ore-associated micro-organisms of 0.161 ± 0.0045, 0.155 ± 0.026 and 0.120 (± 0.00) 1/h were obtained at 2, 6 and 18 L/m2/h respectively. Faster colonisation occurred at lower irrigation rates. At higher irrigation rates, higher detachment and cell removal were apparent, based on PLS cell numbers. The interstitial cells from the stagnant fluid in the ore bed formed the dominant contribution to the microbial population within all the heap systems.