Mechanisms of bioleaching of a refractory mineral of gold with Thiobacillus ferrooxidans

A quick, simple and reproducible method for the indirect determination of t he population of the absorbed and suspended bacterias in the cultivation me dia is the Bradford's method. It has been used to evaluate the fraction of bacteria adhered to the mineral during the bioleaching process and the susp ended fraction. It was observed that a significant fraction of the bacteria is adhered to the mineral surface. This proportion varies with the environ mental conditions, mainly pH, the presence of ferric ions and the way to su pply the mineral sulphide. It has also been observed that the fraction adhe red to the solid shows a progressive loss of its oxidative activity. The re sults can help demonstrate that the sulphides leaching is due to the combin ation of the direct bacterial action on the sulphide mineral surface with t he indirect leaching by the ferric ion produced by the bacteria into the so lution. (C) 2001 Elsevier Science B.V. All rights reserved.