CaSO 4 scale conditions of membranes predicted by a multi-ion thermodynamic model

Abstract

The increase of TDS concentration in RO process, due to the permeation and polarization effects, together with particular internal distributions of salts can create the conditions for Gypsum scaling at membrane interfacies. The analysis of such conditions is done by a Multi-ion interaction model that describes the Gypsum solubility taking into account the nature and the amount of each ion present in concentrated brines of sea water or brackish water to be treated. The model for the activity coefficients of salts is based on a theory which considers the excess Gibbs energy of the solution as a sum of three terms: a Debye-Huckel contribution; a Born term as correction factor for the change of the dielectric constant of the solvent due to the presence of ions and other indissociated species; and a short range contribution calculated according to NRTL equation. The parametrization of the model requires only parameters characteristic of the pure components and of the binary systems.