A novel reaction system is introduced for direct leaching of zinc sulphide concentrates. The system was tested in a semi-batch mode and found competitive to conventional technology. A detailed mathematical model of the new reaction system was developed to facilitate the optimal design. The model was validated with pilot-scale semi-batch experiments. The system and the model can be applied, after minor modifications, in continuous mode as well. (c) 2007 Elsevier Ltd. All rights reserved.