Enhancing the activity of iron-oxidising bacteria: A case study with process liquors from heap bioleaching of a complex sulphide ore

Causes of inhibition of bioleaching by Cu are also thermodynamic

“…Similar results were obtained with ferroxidant cells and [Cu 2+ ] = 20 g L −1 , indicating a severe impairment of microbial catalytic action, which is consistent with the information found in most of the consulted papers . Among these, Brahmaprakash et al .…”

“…In these cases, there are periods in which conversion rises exponentially, which is indicative of microbial catalysis. The times to reach them and their slopes suggest that the negative effect Cu 2+ has on bio‐oxidation is proportional to its own concentration, which is consistent with the consulted literature . Nevertheless, the bio‐oxidation curves that were obtained for 10 and 15 g L −1 of Cu 2+ are unusual; during the time before the exponential phase, Fe 2+ conversion is higher than expected, allowing that the biotic and abiotic curves may be superimposed.…”

“…Similar results were obtained with ferroxidant cells and [Cu 2+ ] = 20 g L −1 , indicating a severe impairment of microbial catalytic action, which is consistent with the information found in most of the consulted papers. [24][25][26][27][28][29][30][31] Among these, Brahmaprakash et al 26 reports that the impossibility of Acidithiobacillus ferrooxidans oxidising Fe 2+ under these conditions can be overcome through successive re-cultivation, adapting the cells to this environment. Li and Ke 30 describe Fe 2+ bio-oxidation with 20 g L −1 of Cu 2+ present in the medium after previously adapting the microorganisms by successive re-cultivation, a procedure which required over a year in order to be effective.…”

“…The times to reach them and their slopes suggest that the negative effect Cu 2+ has on bio-oxidation is proportional to its own concentration, which is consistent with the consulted literature. [24][25][26][27][28][29][30][31] Nevertheless, the bio-oxidation curves that were obtained for 10 and 15 g L −1 of Cu 2+ are unusual; during the time before the exponential phase, Fe 2+ conversion is higher than expected, allowing that the biotic and abiotic curves may be superimposed. One characteristic effect of bio-oxidation inhibition caused by Cu 2+ is a longer latency period, and one of the advantages of microorganism adaptation is that this period is shortened.…”

“…11 Regarding the interaction between Cu and iron-oxidising microorganisms, most of the consulted papers concur that cellular metabolism is inhibited when Cu concentration reaches 5 g L −1 , and that the biological tolerance limit is about 20 g L −1 . [24][25][26][27][28][29][30][31] However, when it comes to quantifying kinetic variations caused by Cu 2+ , little has been published and with varying results, despite using the same system; that is batch culture trials. Difficulty in processing data and interpreting results is inherent to this methodology, partly because cells are amidst a medium the composition of which is ever changing.…”