Arsenic solid speciation in tailings of the abandoned Pan de Azucar mine, Northwestern Argentina

Abstract

In the Argentina Puna region there are several metal sulfide mines that ceased their activity twenty years ago without a proper closure plan. The exposure of the waste rocks and tailing impoundments to weathering led to sulfide oxidation and generation of highly acid solutions rich in metal(oid)s, that react with the unaltered waste rocks, partitioning into different solid phases. The As speciation along a 120 cm depth oxidation profile described in the Pan de Azucar mine tailings was studied by standarized sequential extraction procedures. Results show that the highest As concentration remain in the bottom unaltered layer mainly associated with primary and secondary sulfides. In the upper layers, the total As concentrations are ?î40 to 70% lower than that of the bottom layer, and most As is associated with amorphous and cristalline oxides. More bioavailable forms of As (exchangeable and soluble) account for less than 1.5% of the total As concentration.