Resource recovery from acid mine drainage using dispersed alkaline substrate: A geochemical assessment

Acid mine drainage is a global environmental problem due to the release of acid and metal(loid)s into surrounding waters, requiring treatment. However, these leachates also represent an important opportunity for waste valorization, as many of the metals they contain are of economic interest and could be retained in the treatment residues. This study focuses on the geochemical features of precipitates from a Dispersed Alkaline Substrate passive remediation system located at the Esperanza mine, as a first step in assessing the valorization potential. The geochemical profile of the precipitates was analyzed using X-ray diffraction, scanning electron microscope and inductively coupled plasma techniques. The findings reveal preferential fronts of precipitation and the concentration of elements, including Fe, Al, Cu, Zn, and rare earth elements across the profile. These fronts correspond to the dissolution of the alkaline reagent, calcite, and the consequent precipitation of sulfate mineral phases. Correlation analyses showed patterns of co-precipitation among elements, especially concerning fronts of Fe oxyhydroxysulfates, basaluminite, and the varying behaviour of Zn and Rare earth elements. The economic assessment revealed significant concentrations of economically valuable elements within specific depth intervals (i.e. Al: 4.3 tons, Zn: 670 kg, Cu: 370 kg, REE: 35 kg, Co: 16 kg, Y: 1 kg, or Sc: 0.6 kg), indicating areas with substantial potential for element recovery. While the value of the waste ($24,000) from passive treatment may not match that of active mining, its revaluation could help reduce the environmental impact of Acid Mine Drainage by partially offsetting the maintenance costs of passive treatment plants. • Economic potential of waste from passive acid mine drainage treatment assessed. • Most of undesirable elements (e.g. Fe, As, V, Sb) remain in a thin surface layer. • Valuable elements (Cu, Zn, Rare Earths, Sc, Co) precipitated on preferential fronts. • Basaluminite fronts concentrate 80 % of the total economic potential of precipitates. • Passive treatment precipitates hold potential for partial cost recovery.