Effective passive treatment of high-strength acid mine drainage and raw municipal wastewater in Potosí, Bolivia using simple mutual incubations and limestone

Abstract

To assess the viability of passive approaches for treating acid mine drainage (AMD) at Cerro Rico de Potosí, Bolivia, alkalinity production, acidity neutralization and metals removal were tracked for incubations of AMD in the presence of limestone (LS), a 1:1 mix of AMD and raw municipal wastewater (WW), and a 1:1 mix of AMD and WW in the presence of LS. Three AMD sources from abandoned adits on Cerro Rico, raw WW from the city of Potosí and locally available LS were incubated in-situ for 72 h in 1-L cubitainers. Although locally sourced LS can increase final alkalinity up to 397 mg/L as CaCO 3, it is a potential source for Mn and a few other possibly undesirable elements. Results indicated that in lieu of substrate analysis, AMD and LS cubitainer incubations reveal the quality and chemical composition of potential calcareous passive treatment substrate. Relevant to the prospects of AMD and WW passive co-treatment, mixing AMD with WW had relatively little effect on the final alkalinity achieved by LS dissolution. Accounting for dilution, dissolved concentrations of Ag, Al, As, Cd, Cr, Fe, Pb, Sb, Se, Sn, V and Zn decreased by AMD and WW incubation. Especially efficient As removal was noted, with WW incubation driving mixed concentrations from 19.4 to 0.34 and 3.58 to 0.28 mg/L with the two higher strength AMD source waters. Rare earth element (REE) results were varied. Although AMD mixed and unmixed with WW then incubated with LS generally decreased REE concentrations, Pr and Nd concentrations increased under some LS exposures. Incubation with WW alone generally decreased dissolved concentrations of REE, however La, Pr, Eu and Nd concentrations increased with WW exposure. Overall, results indicate that cubitainer incubations have broader utility than has been previously taken advantage of, passive treatment can be expanded to target more constituents of interest than it has been traditionally applied, and that the co-treatment of AMD with WW is a promising new application of passive treatment that merits further investigation.