Hydrodynamics, temperature, pH and various other physico-chemical factors influence the morphology of nickel produced via hydrogen reduction. The focus of the current work is the effect on hydrodynamics of changing the impeller and reactor configurations in a 75 1 stirred vessel with draft tube and baffles. The aim was to determine which configuration resulted in maximum particle suspension and local gas hold-up while using the minimum impeller speed and power consumption. A response surface methodology of experimental design was employed. This ensured that the number of candidate variables to be tested was reduced to a minimum and that interactive effects between variables were taken into account. The impeller configurations tested were a single Rushton turbine, a single axial flow impeller, and a double impeller system consisting of a combination of the two. The reactor configurations, tested at different gas flow rates, were varied to test the effects with and without baffles. It was found that optimum mixing could be achieved using a baffled vessel with an upper axial flow impeller and a lower Rushton turbine, and by keeping a minimum impeller clearance from the vessel bottom. This is in agreement with [Mineral Processing, 1-2 August 2002]. (C) 2003 Elsevier Ltd. All rights reserved.