Modelling of bioleaching copper sulphide ores in heaps or dumps

The effects of variable permeability and number of bacteria on bioleaching of copper sulphide in dumps and heaps were studied. The calculations were p erformed using a two dimensional model for heaps or dumps containing mainly chalcocite and pyrite. The rate of mineral dissolution was related to the rate of oxidation by bacteria attached onto the ore surface. Oxygen transpo rt through the ore bed is caused by natural convection. The results show th at variations of bed permeability with depth may have a great influence on the aeration of the bed. In wide ore beds of uniform permeability, aeration of the central parts is deficient and in most of the cases, oxygen is tota lly depleted at the centre. In ore beds where permeability increases with t he depth, aeration is substantially improved. It suggests that dumps and he aps should be built with coarse materials at the bottom to improve aeration . The impact of the number of bacteria, on the other hand, is small. This i s explained by the control exerted by the availability of oxygen on the rea ction rate. A high concentration of oxygen results in a large number of bac teria and in a high reaction rate. If the concentration of oxygen is small or oxygen is completely depleted the reaction rate is negligible; thus the number of bacteria is not crucial.