The Influence of Secondary Mineral Phase Crystallization on Antimony and Arsenic Mobility in Mine Drainage

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Borcinova Radkova, Anezka
Antimony , Arsenic , Tailings , Antimony Secondary Minerals
Mine waste containing high concentrations of the potentially toxic metalloids antimony (Sb) and arsenic (As) poses a risk for the natural environment since they are toxic to various organisms. To assess this risk, it is necessary to understand the role of mineralogy, particularly the influences of solubility and variable chemical composition of minerals. The sites selected for this study allow an insight into the Sb behaviour in three different systems: freshly deposited stibnite-containing tailings at Beaverbrook Sb mine (Newfoundland), historical mine waste at Špania Dolina-Piesky (Slovakia) where tetrahedrite is the main Sb host, and several historical Sb deposits in Slovakia where the Sb association with colloids was investigated. Water analyses using ICP-AS-OS, HG -AAS were combined with mineralogical analyses conducted using a combination of SEM, EMPA, MLA and synchrotron-based μXRD, μXRF and μXANES (see the list of abbreviations). The study of tetrahedrite weathering reveals that after being released from primary tetrahedrite, Sb becomes a part of a structure of secondary Sb minerals tripuhyite and pyrochlore which are stable in near-surface conditions, whereas As and Cu are contained in µXRD-amorphous phase. It is concluded that Sb is not very mobile when tetrahedrite is weathering under oxidizing, near-neutral conditions. At Beaverbrook, Sb is rapidly released from stibnite in tailings deposits to the pore water in an oxic environment where it transforms to highest oxidation state Sb5+. Arsenopyrite oxidizes less rapidly, and the formation of oxidation rims contributes to its slower dissolution. The formation of less soluble Sb-Fe secondary phases, and formation and dissolution of easily soluble brandholzite contribute to Sb cycling in the environment of freshly deposited tailings. In mine drainage from several historical mine sites, it was determined that colloids influence As mobility more than Sb mobility. At the sites where As is the main contaminant, abundant Fe-As-Si-O colloids were detected on the surface of 0.01 µm filters. Only very high Sb concentration (above 6600 µg/L) promoted precipitation of low amounts of Fe-Sb-Si-O±S colloids. Secondary Sb minerals with different stability are formed in mine waste environment. Understanding the conditions of their formation and their characteristics allow the prediction of potential environmental issues.
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