Bioleaching of cobalt from an arsenidic ore

Arsenic is one of the main contaminants in soil, especially in (former) mining areas, but arsenic can also be a source of exploitable metals, if present as arsenides. In the following paper we report the microbial leaching of an arsenide (e.g. safflorite (CoAs2)) for the first time. Bioleached cobalt yielded up to 92% in presence of citric acid, while the non-inoculated and chemical controls yielded in merely 4% and 10%, respectively. Even though high yields were achieved, the arsenide turned out to be a difficult leaching substrate, leading to a diverse activity. While the addition of citric acid improved the cobalt liberation and resulted in a more stable activity, the absence led to yields ranging from 35% to 82%, depending on the ability to cope with the arsenide. From the comparison of the leaching with 1% and 2% (w/v) ore, it can be concluded that the decreased activity resulted in an unfinished leaching. Furthermore, the typestrains of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum were not able to grow in presence of the arsenide.