Effect of flocculating agents on solubility behavior of calcium sulfate dihydrate (gypsum) in aqueous sodium chloride system and solution properties at 35 degrees C

Abstract

The effect of addition of flocculating agents, viz., alum (KAl(SO4)(2)center dot 12H(2)O) (up to 10 wt%) and polyaluminum chloride ([Al(OH)(a)Cl-b](n), a >1.05; n similar to 15) (up to 6 wt%) on the solubility behavior of calcium sulfate dihydrate (gypsum, CaSO4 center dot 2H(2)O) in aqueous NaCl solutions has been examined at 35 degrees C. The solubility of CaSO4-2H(2)O decreases with the addition of alum while it increases with the addition of polyaluminum chloride without any significant shift in solubility maximum. Density (rho) and speed of sound (u) have also been determined for the quaternary systems (CaSO4 center dot 2H(2)O+NaCl+alum/PAC+H2O) at 35 degrees C and used to estimate solution isentropic compressibility (kappa(S)) and ion-hydration (n(h)) characteristics. Empirical equations describing the s, rho, u and kappa(S) as a function of solution composition are presented.