A comparison of the bacterial and chemical leaching of sphalerite at the same solution conditions

In this work we describe the use of a novel experiment to study the bacteri al leaching of sphalerite (ZnS). We have constructed an experiment in which the conditions in a leaching reactor without bacteria are forced by a cont rol system to follow the conditions in a leaching reactor with bacteria. Th e leaching with bacteria takes place in a batch reactor where the redox pot ential is measured continuously. These measurements serve as the setpoint v alue for a leaching experiment without bacteria in which the solution redox potential is controlled by the application of an electrolytic current. Iu this manner, the solution conditions of the chemical leaching experiment em ulate the conditions found in the bacterial leaching experiment. The results obtained for sphalerite show that the amount of zinc dissolved is initially the same for both chemical and bacterial leaching. After appro ximately 10 hours, the conversion obtained in the bacterial leaching experi ment is higher than that obtained in the chemical leaching experiment. This may be due to the formation a product layer of sulphur that is formed on t he unreacted sphalerite in the chemical leaching reaction. Although this su lphur is porous, it limits the rate of leaching under certain conditions. I n the bacterial leaching experiments, this product layer is not present, si nce sulphur is oxidised by the bacteria. The rate of leaching of sphalerite is therefore higher in the bacterial leaching experiment because the produ ct layer has been removed.