A recently developed mixed-solvent electrolyte (MSE) model to describe the chemistry of calcium sulphate in aqueous multi-component sulphate solutions has been extended to complex mixed chloride-sulphate solutions. The model accurately represents the solubility of calcium sulphate solid phases, namely dihydrate, hemihydrate and anhydrite, in mixed chloride-sulphate solutions containing H2SO4, Fe-2(SO4)(3), HCl, NaCl, Na2SO4, MgO2, MgSO4, CaCl2, etc., over a wide range of temperatures and ionic strengths. It predicted the solubility of calcium sulphate from 20 to 95 degrees C in simulated nickel processing solutions containing NiSO4, H2SO4, Fe-2(SO4)(3), Na2SO4 and LiCl. It was found that increasing Na2SO4 or LiCl concentrations in NiSO4-H2SO4 solutions do not have a significant effect on the calcium sulphate solubility. The model was shown to be a practical tool for assessing the scaling potential of calcium sulphate over a wide range of temperatures and concentrations where experimental data are not available. (C) 2008 Elsevier B.V. All rights reserved.