Arsenic mineralogy of near-neutral soils and mining waste at the Smolotely-Líšnice historical gold district, Czech Republic

The mineralogical composition of mining wastes and contaminated soils is the key factor that controls the retention and release of pollutants. Herein, we used bulk analyses, selective extractions, X-ray diffraction, electron microprobe, and Raman microspectrometry to determine the distribution and speciation of As as a function of depth in four slightly acidic to near-neutral soil and mining waste profiles at the Smolotely-Líšnice historical Au district (Czech Republic). The soils there, which have developed from long-term weathering, exhibit As levels as high as 1.87 wt% in the richest area; the 80-90 year old mining waste contains up to 0.87 wt% As. In the soils and mining waste, the primary As ore (arsenopyrite) has almost completely oxidized to secondary As minerals such as arseniosiderite, bariopharmacosiderite, yukonite, and Fe (hydr)oxides (ferrihydrite, goethite, and hematite), with variable As2O5 and CaO concentrations (up to 27.5 and 3.8 wt%, respectively). Arsenic distribution and speciation were found to vary with depth and soil type. Whereas the presence of multiple As-hosting phases that occurred in the mining waste and cambisol developed over a granodiorite, bariopharmacosiderite was absent in the cambisol overlying gabbrodiorite. Poorly-crystalline phases such as yukonite and As-bearing ferrihydrite were not detected in the gleysol. These differences in the secondary As mineralogy were attributed to the different redox conditions and variations in the prevailing chemical systems in the saprolites/soils. The variable solubility of the secondary As-bearing phases influences the mobility of As in shallow soils and near-surface mining wastes.