Nanofiltration to Improve Process Efficiency of Hexavalent Chromium Treatment Using Ion Exchange

Abstract

Managing waste brine from strong base anion exchange processes used for hexavalent chromium removal is an important operational, environmental, and economic consideration. This study investigates the use of nanofiltration to recover excess regenerant salt and reduce the waste volume using brine collected from full‐ and pilot‐scale installations. Using a 2 N sodium chloride regeneration solution, divalent anions (i.e., sulfate and chromate) exhibited high rejections (>0.97), and monovalent anions (i.e., chloride and nitrate) exhibited low to negative rejections (−0.2 to 0.05), allowing preferential passage of excess regenerant salt. A batch concentration model was developed for a case study. Waste can be concentrated to 0.6 bed volume and a significant fraction of the regenerant salt can be recovered. This process would require about 20 m 2 of membrane area per 1,000 L of resin to treat waste in 8 h, which could be implemented in a mobile treatment unit serving multiple decentralized systems.