A sequential two-step process using moderately and extremely thermophilic cultures for biooxidation of refractory gold concentrates

Abstract

In many cases, the use of extreme thermophiles, like the archeon Sulfolobus metallicus, in a continuous bioleaching process of gold concentrates is limited by the arsenic content in the feed. In this work, a sequential two-step bioleaching process for gold-containing refractory pyrite/arsenopyrite concentrates has been investigated for the possibility of lowering the toxicity of arsenic with respect to the extremely thermophilic culture. In the first stage, a moderately thermophilic culture was used followed by the extremely thermophilic S. metallicus in the second stage. It was found that the S. metallicus culture survives higher arsenic concentrations than expected when the concentrate was pre-oxidized at a lower temperature. Thus, with this sequential two-step bioleaching process, it is possible to reduce the toxicity of the released arsenic. Therefore, the use of higher pulp densities of arsenic-containing minerals is enabled. When the leached mineral residues were subjected to cyanidation, cyanide consumption and thiocyanate formation were significantly lower after the second stage. In addition, a somewhat higher gold and silver grade was found in the residue from the concentrate ultimately oxidized by S. metallicus.