Selective ion exchange recovery for enabling passive wetland treatment of bauxite processing residue leachates

Bauxite residue disposal can give rise to alkaline leachate that requires long-term treatment. Results are presented trialling a mesocosm-scale system integrating selective metal(loid) recovery with passive treatment technologies for application to high pH bauxite processing residue leachates. This system, combining ion exchange resin adsorbents for targeted removal of potentially ecotoxic metal(loid)s (e.g. vanadium [V], arsenic [As]) with aerobic wetland polishing beds, aims to treat alkaline leachates to meet effluent targets with reduced energy and chemical demands compared to conventional acid dosing and high-density sludge processes. Commercially available ion exchange resins were tested for their ability to selectively remove metal(loid)s from bauxite processing residue leachates sourced from a legacy disposal area in Western Europe. Results indicated fast and efficient removal of V (88%) and As (93%) from solution, with removal efficiency remaining high after repeated treatment cycles (V:85%, As:75% after 11 cycles). Recovery efficiency during resin elution using sodium hydroxide (NaOH) remained above 90% after repeated cycles for both target metal(loid)s, indicating effective re-use of adsorbent materials. Aerobic wetland mesocosms containing common reeds (Phragmites australis) were assessed for their suitability as a final polishing step for leachates post-ion exchange treatment. Bauxite residue leachates of varying ionic strength were used as influent, with effluent water quality monitored over a period of >100 days to determine treatment efficiency. Wetland mesocosms were effective in buffering effluent pH to within environmentally acceptable limits (pH <9) under all leachate scenarios, and wetland soils inhibited residual aqueous metal(loid) content, with efficient removal efficiencies for V (up to ~94%), As (up to ~48%) and aluminium (up to ~87%).