Predictions on the solubility and equiscale line of water content for the quaternary system (Li+Na+Cl+SO4+H2O) at 298.15 K

Abstract

Pitzer ion-interaction theory is widely used to calculate the solubilities of salt–water systems. In the paper, the solubilities and equiscale lines of water contents of the reciprocal quaternary system (Li+Na+Cl+SO4+H2O) at 298.15K were calculated using Pitzer theory and Harvie, Møller, Weare solubility modeling approach (HMW model). In this predictive calculation, the quasi-Newton and dichotomy methods were used to solve the system of simultaneous equations of the equilibrium expressions among solid and liquid phases, and to obtain the ionic molalities, Jänecke indices of phase diagram and the Jänecke indices of the equiscale lines of water contents in the reciprocal quaternary system. Based on the Jänecke indices, the dry-salt phase diagram and the equiscale lines of water-phase diagram were plotted. The predictive phase diagram via the theoretical calculation agrees well with the experimental phase diagram except for the phase region of double salt 2 (Li2SO4·Na2SO4, Db2). Distributions of equiscale lines of water-phase diagram on the dry-salt diagram of the reciprocal quaternary system reflect that phase areas of double salts of Db1 and Db2 bear maximal water contents. The predictive phase diagram and equiscale lines of water-phase diagram are often necessary in the technological design of chemical engineering for the utilization of inorganic salts in salt lake brines.