Solubility of FeSO4·7H2O in the H2SO4–Ti(SO4)2–H2O, H2SO4–MgSO4–H2O, and HCl–H2O Systems from 278 to 313 K

The solubilities of FeSO 4 ·7H 2 O in the H 2 SO 4 –Ti(SO 4 ) 2 –H 2 O and H 2 SO 4 –MgSO 4 –H 2 O systems were measured with a dynamic method from 278.15 to 308.15 K. Due to the hydrolysis property of Ti(IV), it was found that the common ion effect of Ti(SO 4 ) 2 was not so obvious as that of MgSO 4 for the solubility of FeSO 4 ·7H 2 O. The solubility of FeSO 4 ·7H 2 O in the HCl–H 2 O system was also measured by same method. The solubility did not change much at first, yet substantially increased when more HCl was added into the solution. New interaction parameters of ions for the mixed-solvent electrolyte (MSE) model were regressed by the experimental solubility data, with the average relative deviations of less than 5.0%. The speciation and the activity coefficients of species in the FeSO 4 –HCl–H 2 O system with an FeSO 4 concentration of 1.0 mol·kg –1 were predicted by the MSE model with the newly regressed parameters at 303.15 K.