Enhancement of copper and molybdenum bioextraction from sulfide ore through nutrient balance and the addition of Thiobacillus cuprinus

Abstract

To enhance bioleaching of copper sulfide dumps, optimal nutrient and pH conditions for the native iron-oxidizing bacteria were determined. Biological activity was followed by monitoring rates of iron oxidation and enumerating T. ferrooxidans. The optimal ratios of N:P were 5:1 to 20:1. The optimal pH was between 1.8 and 2.4 as measured by rates of iron oxidation. When measured by bacterial enumeration, the optimal pH range was 1.4 to 1.6. Shake flask studies were conducted using: 1) raffinate; 2) raffinate with nutrients; or 3) bacterial growth medium. Initial rates of copper extraction were doubled when raffinate was supplemented with nutrients. Exogenous strains of Thiobacillus were able to oxidize iron more rapidly than the native strains. However, no greater concentrations of copper were extracted in the presence of the exogenous strains than when only native bacteria were present. The highest rates of molybdenum extraction were achieved using growth media rather than raffinate. Raffinate with nutrient amendments and growth medium were supplemented with T. cuprinus. More copper was extracted when conditions favored T. cuprinus than when they favored T. ferooxidans. This is the first study, to our knowledge, describing the use of T. cuprinus amendments to native bacterial populations for enhanced copper extraction from dump ore.