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 μg 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.