Microbial Community Composition on Lignite before and after the Addition of Phosphate Mining Wastes

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Abstract
Empirical field tests in which phosphate mining wastes (NPR) were added to various sulphidic mining wastes resulted in neutral drainage. A biofilm was documented on waste rock covering the pyrite. This was likely the cause of the improved effluents. NPR was added to sterile columns containing pyritic lignite and spiked with granulated pyrite. The biological columns were inoculated with 108 cells/g of lignite-cultured microbes from Rio Agrio, Argentina. The microbes were maintained at 30°C using pyrite as sole energy source. The microbial populations were monitored with MPN before NPR addition and 2, 4 and 10 weeks later. After 45 days strong bioleaching was evident, as measured by electrical conductivity. Concurrently, a shift in the microbial populations took place. In the presence of NPR about 90% of populations consisted of heterotrophic neutrophiles covering the pyrite surfaces with a 10 μm thick biofilm, whereas without NPR, 99% of the populations were iron oxidizing acidophiles in mono-layered biofilms. These results are relevant to controlling processes in heap leaching and acid rock drainage.