Mobility and attenuation of arsenic in sulfide-rich mining wastes from the Czech Republic

The mineralogical composition of mining wastes deposited in countless dumps around the world is the key factor that controls retention and release of pollutants. Here we report a multi-method data set combining mineralogical (X-ray diffraction, electron microprobe and Raman microspectrometry) and geochemical (sequential extraction and pore water analysis) methods to resolve As mobility in two 50-years-old mining waste dumps. Originally, all of the As in the mining wastes selected for the study was present as arsenopyrite and with time it has been replaced by secondary As phases. At Jedova jama mining area, the most of As precipitated as X-ray amorphous ferric arsenate (HFA). Arsenic is also accumulated in the scorodite and Fe (hydr) oxide (with up to 3.2 wt.% As2O5) that is particularly represented by hematite. Mining wastes at Dlouha Ves contain only trace amount of scorodite. Arsenic is primarily bound to Pb-jarosite and Fe (hydr) oxides (especially goethite) with up to 1.6 and 1.8wt.% As2O5, respectively. The porewater collected after rainfall events indicated high concentrations of As (similar to 4600 mu g.L-1) at Jedova jama, whereas aqueous As at Dlouha Ves was negligible (up to 1.5 mu g.L-1). Highly mobile As at Jedova jama is attributed to the dissolution of HFA and simultaneous precipitation of Fe (hydr) oxides under mildly acidic conditions (pH similar to 4.4); immobile As at Dlouha Ves is due to the efficient adsorption on the Fe (hydr) oxides and hydroxosulfates under acidic pH of similar to 2.8. Taken together, As mobility in the ferric arsenates-containing mining wastes may significantly vary. These wastes must be kept under acidic conditions or with high aqueous Fe(III) concentrations to prevent the release of As from incongruent dissolution of ferric arsenates. (C) 2016 Elsevier B.V. All rights reserved.