The interfacial reactivity between green rust sulfate (GRSO4) and arsenic (As) species were investigated using batch adsorption experiments. GRSO4 is capable of adsorbing up to 155 and 88 mg g−1 of As(III) and As(V), respectively. The value of pH greatly affects adsorption, with As(III) removal 2.5 times higher at alkaline pH, while As(V) removal higher at circum-neutral conditions. Competing groundwater species such as magnesium (Mg2+) or phosphate ( PO 4 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq133.tif"/> ) reduce removal efficiency. Our results show that GRSO4 is a stable, efficient and environmentally-relevant mineral substrate for As sequestration in anoxic groundwater systems.