Treatment of a gold bearing arsenopyrite concentrate by ferric sulphate leaching

Biooxidation can be used as a pretreatment for gold-bearing sulphide ores; it has low reagent costs and is very interesting from an environmental point of view. However the kinetics of this process is slow. Long residence times (several days, even weeks) cause excessive operational costs. If biooxidation proceeds through an indirect contact mechanism, its kinetics may be improved by means of the physical separation of the two operations relating the two effects involved: the chemical attack of sulphides by ferric iron and the biological oxidation of the ferrous iron produced (chemical and biological effects). The separation of the two effects allows the individual enhancement of both stages. In this paper the ferric sulphate leaching of an arsenopyrite concentrate is studied as an example of the Indirect Biooxidation with Effects Separation Process. This method of chemical oxidation has been taken to represent the separation of the chemical and the biological effects within a biooxidation system. The results are very satisfactory. The kinetics of the chemical oxidation stage (ferric sulphate leaching) is enhanced by the use of silver as a catalyst and moderate high temperature. Taking into account that the kinetic activation of the biological ferrous iron oxidation (biological stage) has been already proved, the enhancement of the chemical oxidation stage leads to the whole process improvement.