Arsenic removal from natural groundwater using 'green rust': Solid phase stability and contaminant fate

Arsenic (As) contamination in groundwater remains a pressing global challenge. In this study, we evaluated the potential of green rust (GR), a redox-active iron phase frequently occurring in anoxic environments, to treat As contamination at a former wood preservation site. We performed long-term batch experiments by exposing synthetic GR sulfate (GRso(4)) to As-free and As-spiked (6 mg L-1) natural groundwater at both 25 and 4 C. At 25 C, GRso4 was metastable in As-free groundwater and transformed to GlIcos, and then fully to magnetite within 120 days; however, GRso(4) stability increased 7-fold by lowering the temperature to 4 degrees C, and 8-fold by adding As to the groundwater at 25 degrees C. Highest GRso4 stability was observed when As was added to the groundwater at 4 C. This stabilizing effect is explained by GR solubility being lowered by adsorbed As and/or lower temperatures, inhibiting partial GR dissolution required for transformation to GlIcos, and ultimately to magnetite. Despite these mineral transformations, all added As was removed from As-spiked samples within 120 days at 25 C, while uptake was 2 times slower at 4 degrees C. Overall, we have successfully documented that GR is an important mineral substrate for As immobilization in anoxic subsurface environments.

Automated summary

This study demonstrates the potential of green rust (GR) in treating arsenic (As) contamination in groundwater. Lowering temperature or adding arsenic can increase the stability of GR, reducing the solubility of arsenic and effectively immobilizing it in the mineral. This ultimately improves the efficiency of arsenic remediation.