Effect of physicochemical conditions on the growth and activity of Acidithiobacillus ferrooxidans in a simulated heap bioleaching environment

摘要

Recent understanding of the microbial retention within heap bioleaching systems has highlighted the importance of quantifying microbial growth and activity in both the bulk flowing solution and in the ore-associated phase. Typically, industrial heap bioleaching operations report variations in process conditions, such as inoculum concentration and the copper concentration in the recycled irrigation solution. In this paper, a mini-heap reactor system of low-grade ore inoculated with Acidithiobacillus ferwoxidans was used to investigate the effect of a selection of physicochemical conditions on microbial growth, colonisation and substrate utilisation kinetics of both the planktonic and sessile populations. The factors studied included inoculum size, availability of ferrous iron in the bulk flowing solution, copper concentration in the bulk flowing solution and inoculum cultivation conditions. A smaller inoculum size led to a longer lag in iron oxidation rates and colonisation, but apparent specific growth rates were similar. However, there was an observable difference in the localisation of the cells between the interstitial and attached phases. Growth of the inoculum on pyrite led to greater iron oxidation rates, but did not increase colonisation or specific growth rates. The ferrous iron grown inoculum appeared to exhibit a lower specific iron oxidation rates during the exponential growth phase. The introduction of 6 g L~(-1) cupric ions into the feed solution containing 0.2 g L~(-1) ferric iron decreased the microbial growth rate in the bulk flowing solution (PLS) and interstitial phase but not that of the attached phase, irrespective of prior exposure of the inoculum to cupric ion. There was no observable benefit in pre-exposure of the inoculum to copper. The microbial population in the interstitial phase remained the most abundant population in the heap under all physicochemical conditions considered.