Regeneration of pilot-scale ion exchange columns for hexavalent chromium removal. (1st July 2017)

• Record Type: Journal Article
• Authors: Korak, Julie A.; Huggins, Richard; Arias-Paic, Miguel
• Is Part Of: Water research. Volume 118(2017)
• Page Start: 141
• Page End: 151
• Publication Date: 2017-07-01
• Subjects: Hexavalent chromium -- Strong base ion exchange -- Regeneration -- Uranium -- Vanadium -- Hazardous waste; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2017.03.018
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Due to stricter regulations, some drinking water utilities must implement additional treatment processes to meet potable water standards for hexavalent chromium (Cr(VI)), such as the California limit of 10 μg/L. Strong base anion exchange is effective for Cr(VI) removal, but efficient resin regeneration and waste minimization are important for operational, economic and environmental considerations. This study compared multiple regeneration methods on pilot-scale columns on the basis of regeneration efficiency, waste production and salt usage. A conventional 1-Stage regeneration using 2 N sodium chloride (NaCl) was compared to 1) a 2-Stage process with 0.2 N NaCl followed by 2 N NaCl and 2) a mixed regenerant solution with 2 N NaCl and 0.2 N sodium bicarbonate. All methods eluted similar cumulative amounts of chromium with 2 N NaCl. The 2-Stage process eluted an additional 20–30% of chromium in the 0.2 N fraction, but total resin capacity is unaffected if this fraction is recycled to the ion exchange headworks. The 2-Stage approach selectively eluted bicarbonate and sulfate with 0.2 N NaCl before regeneration using 2 N NaCl. Regeneration approach impacted the elution efficiency of both uranium and vanadium. Regeneration without co-eluting sulfate and bicarbonate led to incomplete uranium elution and potential formation of insoluble uranium hydroxides that could lead to long-term resin fouling, decreased capacity and render the resin a low-level radioactive solid waste. Partial vanadium elution occurred during regeneration due to co-eluting sulfate suppressing vanadium release. Waste production and salt usage were comparable for the 1- and 2-Stage regeneration processes with similar operational setpoints with respect to chromium or nitrate elution. Graphical abstract: Highlights: Three ion exchange regeneration approaches were compared for chromium removal. Regeneration approach did not impact net removal of chromium from system. Uranium was not fully eluted from resin without co-eluting sulfate and bicarbonate. Vanadium elution was incomplete with only NaCl and enhanced with NaHCO3 . Waste fractions and salt consumption were similar for regeneration techniques.