Exploring sulfate and metals removal from Andean acid mine drainage using CaCO3-rich residues from agri-food industries and witherite (BaCO3)

Abstract

Dispersed alkaline substrate (DAS) is a matured passive remediation technology that has shown very high performances treating acid mine drainages (AMD). However, this remediation approach needs to improve its environmental footprint as well as to ensure almost complete water sulfate removals for longs periods of time. The present study improves the use of witherite (BaCO3) as a reagent on DAS-type treatments to induce highwater sulfate removals in the context of Andean AMD. Also, three CaCO3-rich residues from the agri-food industry were tested as alternatives to the current use of limestone. Two sets of column experiments were developed with various flow rates (1.5-5.4 L/day), net acidities (202 and 404 mg/L as CaCO3 eq.) and reactive agents (calcite, eggshells, seashells and witherite). Seashells were validated as a perfect limestone substitutes on the CaCO3-DAS stages. Malachite was observed, for the first time within these columns, as a mineral phase actively involved in Cu water removal. The BaCO3-DAS columns achieved values under 500 mg/L of sulfate at the output of the system for up to 6 months (initial sulfate concentration ranged 1234-2468 mg/L). Upscaling calculations of the present results support the feasibility of using this technology at a full field scale, especially as a wastewater treatment for abandoned mine sites, although some strategies to reduce witherite costs are recommended.