Investigating the Effect of Acid Stress on Selected Mesophilic Micro-organisms implicated in Bioleaching

摘要

During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may stress the bioleaching inocula, particularly on inoculation during agglomeration. The acid addition for agglomeration varies across operations and ore types, with limited information available on recommended concentrations. The initial pH in the agglomeration mix may be as low as pH 0.5 and is typically below pH 1.This paper investigates the effect of acid stress on mesophilic species, typically implicated in mineral sulphide bioleaching and critical for heap colonisation at start-up, as a function of acid concentration (and resulting acidity) and duration of exposure in submerged culture. Following acid stress, cultures were returned to standard operating conditions in batch stirred tanks and their performance assessed in terms of ferrous oxidation and microbial growth rates. The increasing acid stress resulted in an increase in the lag period before onset of microbial growth and iron oxidation, whereafter typical performance was observed under low stress conditions while reduction in rate and extent of ferrous iron oxidation persisted at extreme conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed with increased acid concentration. Microbial speciation indicated a substantial decrease in the number of surviving bacterial species.