Some aspects of the effect of pH and acid stress in heap bioleaching

The chemical and physical conditions in sulphide heaps provide a complex environment for micro-organisms, with differences in redox potential, acidity, temperature, oxygen and solution chemistry conditions being experienced both temporally and spatially. One of the most important parameters for successful microbial colonisation and active microbial metabolism is suitable pH conditions in the heap. Typically heaps reach tens of metres high and the pH of irrigation solution travelling through heap changes significantly.In this study, we investigated the effect of pH and acid stress for moderately thermophilic and thermophilic mixed cultures, operating at 50–60 °C in a heap bioleaching environment. Results collected from laboratory scale column reactors packed with the low grade whole ore and irrigated with different pH solutions during a temperature shift from moderately thermophilic conditions to thermophilic conditions are discussed.

► The effect of pH on microbial populations was investigated at 50–60 °C in a bio-heap environment.
► At 60 °C, effective thermophilic colonisation occurred with feed pH between pH 1.1 and 2.0.
► After colonisation at 60 °C, a decrease in feed pH below pH 0.9 compromised microbial activity.
► An irrigant pH greater than pH 0.9 is recommended for bioleaching at 60 °C.