Investigating Microbial Colonisation in Bioheaps with Varying Irrigation Rate

摘要

Microbial colonisation plays an important role in mineral dissolution in heap bioleaching of low grade ore. To date, colonisation studies have focused on microbial attachment of single species to mineral concentrate under batch conditions, not representative of the heap leaching environments, with recent extension to flow systems (Africa et al. 2010, Minerals Engineering, 23, 486; Bromfield et al. 2010, Bio- & Hydrometallurgy conference proceedings). Hydrology and soil engineering investigations have suggested significant interactions between microbial colonisation and fluid flow in porous systems. Therefore, heap hydrology is expected to affect microbial colonisation through solution-ore and microbe-mineral contacting. The influence of the irrigation rate on microbial colonisation was assessed using columns packed with acid agglomerated low grade copper-containing ore. The systems were inoculated via irrigation with iron and sulphur oxidising mesophilic microorganisms (10~(12) cells/ton ore), whilst operating under continuous flow through the unsaturated, aerated bed, using three different irrigation rates (2, 6 and 18 l/m~2/h). A novel in-bed sampling technique allowed for the extraction of ore samples at intervals during the leaching process to give novel insight into the microbial growth and the interstitial, weakly and strongly attached microbial population. Increasing bacterial adherence and cell number retained in the ore bed was clearly seen over the 32 day leaching period. Average specific growth rates of ore-associated micro-organisms of 0.0053, 0.0052 and 0.0043 h~(-1) were found for 2, 6 and 18 L/m~2.hr, showing faster colonisation under low flow regimes. At higher irrigation rates, higher detachment and cell removal are postulated, as the total number of cells exported from the ore bed was 2.2x10~(10), 6.5x10~(10) and 7x10~(10) cells for irrigation rates of 2, 6 and 18 L/m~2.hr respectively. For all conditions, the interstitial cells from the stagnant zone of the ore bed were the most dominant form of cells accumulated within the heap systems.