A steady-state, axi-symmetric, numerical model was developed to investigate the agglomeration of molten particles of sulphide ore in the reaction shaft of a flash smelting process used for extracting copper. The turbulent, particle-laden, gas flow was simulated in conjunction with a population balance model to account for agglomeration. The agglomeration was found to depend primarily on the particle to gas mass loading ratio, and the particle size and turbulence intensity at the shaft inlet. Predictions compared well with the limited experimental data in the literature. Increasing the angle at which the flow enters the shaft from the burner was found to increase agglomeration up to a critical angle at which the flow behaviour changes. The results have implications for the control and reduction of dust levels in the waste gas stream. (C) 2009 Elsevier Ltd. All rights reserved.