The IBES (Indirect Bioleaching with Effects Separation) process has been developed for the bioleaching of Cu-Zn sulphide concentrate, Zn concentrate, and as a pretreatment for refractory gold ores. In this work The influence of copper ion on the application of this process to a Zn sulphide concentrate was studied. A negative effect of Cu2+ ions on the rate of zinc dissolution was observed Kinetic curves of ferric leaching have been combined with the residence time distribution for n CSTRs (Continuous Stirred Tank Reactors) in series, in order to predict the mean residence time and the number of reactors required in the ferric sulphate leaching of this Zn concentrate for different copper concentrations. Results indicate that some modifications on the IBES process flowsheet are needed.