A hybrid anion exchanger with nanoscale zero valent iron for trace hexavalent chromium removal from drinking water

Hexavalent chromium, Cr(vi), is a human carcinogen that occurs in groundwater worldwide. While not federally regulated in the USA, the State of California has approved a new Cr(vi) maximum contaminant level at 10 mu g L-1, expected to go into effect fall 2024. This study synthesizes, characterizes, and verifies performance of a hybrid strong base anion exchanger with nanoscale zero valent iron (NZVI-resin) for trace Cr(vi) removal from drinking water. NZVI-resin was synthesized by exchanging tetrachloroferrate ion (FeCl4-) onto the resin prior to sodium borohydride (NaBH4) reduction. The impact of important synthesis variables was identified, including reagent concentrations and molar ratios, solvent selection, temperature, and drying procedure. Material characterization techniques (e.g. SEM-EDS and XPS) determined NZVI presence and elemental distribution on the resin surface. Our work showed a 360% increase in treated water throughput using NZVI-resin compared to unmodified resin for trace Cr(vi) removal in column experiments. This work presents a broad assessment of the material characteristics of NZVI-resin, discusses the limitations of batch tests, and describes operational challenges for Cr(vi) treatment. Hexavalent chromium is carcinogenic and can occur in groundwater worldwide. Modifying ion exchange resin with zero valent iron increases treatment efficiency in column experiments.