Ferrous sulfate heptahydrate FeSO47H(2)O is a major waste produced in titanium dioxide industry by the sulfate process and has caused heavy environmental problem. A new green process for the treatment of FeSO47H(2)O was proposed to make use of iron source and recycle sulfate source as H2SO4. It was found that by adding concentrated HCl to the FeSO4 solution, FeCl24H(2)O was crystallized out, which was subsequently calcined to produce Fe2O3 and HCl. Concentrated H2SO4 solution (about 65 wt %) was obtained by evaporating the FeCl24H(2)O-saturated filtrate. To facilitate the process development and design, the solubilities of FeCl24H(2)O in HCl, H2SO4, and HCl+H2SO4 solutions were measured and the experimental data were regressed with both the mixed-solvent electrolyte model and the electrolyte NRTL model. On the basis of the prediction of the optimum conditions for the crystallization of FeCl24H(2)O, material balance of the new process was calculated. FeCl24H(2)O and Fe2O3 were obtained from a laboratory-scale test with about 70% recovery of ferrous source for a single cycle, indicating the feasibility of the process. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 4549-4563, 2017