A Bauxsol™-based Permeable Reactive Barrier for the Treatment of Acid Rock Drainage

Permeable reactive barriers (PRBs) have generally been used to treat low flow and/or low contaminant loads of acid rock drainage (ARD). Bauxsol™, a product made from seawater-neutralized red mud (a by-product of alumina refining) buffers pH at 8.8 and has been shown to remove >99% of heavy metals loadings at >1000 meq/kg, which would make it an ideal medium for PRBs. Unfortunately, Bauxsol™ is very fine-grained (>90% of the material 90% species protection.The metal binding preference of Cu>Pb>Zn>Mn displayed by the PRB is consistent with the pKa of hydration values and it appears that MOH+ formation dominates the removal of these metals. However, other removal processes appear to apply for Fe, Al, and Cd. Overall metal removal efficiencies ranged from 91.22% for Mn to >99.99% for Cu. Analysis of dried spent Bauxsol™ indicates that bound metals are not readily leachable, allowing the spent media to be disposed safely in a landfill.