Integration of ion-exchange and nanofiltration processes for recovering Cr(III) salts from synthetic tannery wastewater

Abstract

This study aims to investigate the possibility of integrating both ion-exchange (IX) and nanofiltration (NF) processes for the recovery of Cr(III) salts from a synthetic solution prepared with concentrations of Cr(III), and Cl− in the range of industrial effluents of tanneries. Ion exchange should be used as a pre-treatment for uptaking Cl− ions from the effluent, and thereafter the treated solution is fed to an NF unit to recover chromium sulphate salt for reuse in the tanning bath. The strong anionic resin Diaion PA316 was selected for evaluating chloride–sulphate ion-exchange equilibrium, with respect to mass of resin, NaCl concentration, temperature and ratio . It was observed that the separation factor, , depends on the total electrolyte concentration and the ratio plays a role as well. Moreover, it was determined that the resin prefers sulphate over chloride since is less than 1. The performance of the NF process is dependent on and the rejection of Cr(III) may decrease from 90% to 70% as the ratio increases from 0.5 to 2. Regarding the integration of both IX and NF, the feed solution after treatement with the resin was fed to NF where the ratio of led to the best operating conditions for this process (90% of Cr(III) rejection and up to 77% for ions). This strategy may be considered as a sustainable approach since it permits to obtain a solution enriched in Cr(III) salt for reuse in the tanning process, thus contributing to environmental protection.