Arsenopyrite Weathering and Leaching of Arsenic in an Austrian Soil

Abstract

The extent of arsenopyrite weathering in relation to co-existing minerals in an Austrian soil and the leaching of arsenic from the soil has been investigated. Soil and underlying bedrock samples were collected and characterized by chemical and mineralogical analyses. The solubility of the soil arsenic under anaerobic conditions was studied by incubating the soil sample in distilled water for different periods of time using a customized lycimeter. The solubility of arsenic from pure arsenopyrite mineral and mixtures of arsenopyrite with chalcopyrite or pyrite was studied by incubating the pulverized minerals. Speciation of arsenic in the incubated and non-incubated soil samples was carried out by sequential leaching, solvent-extraction, and ion exchange chromatographic techniques.

Results of SEM analysis indicated that arsenopyite (FeAsS), the most common mineral in the area, occurs in paragenesis with pyrite (FeS₂) and chalcopyrite (CuFeS₂). The existence of these minerals with arsenopyrite was found to enhance its solubilization. From the speciation study it was found that nearly all (92%) of the arsenic in the soil exists in the inorganic form. Out of the total inorganic arsenic, the trivalent inorganic species accounted for only 3% and the remaining 89% was found to be the pentavalent form. The low solubility of As in the Graz soil is attributed to the prevalence of this pentavalent inorganic species.

Keywords:

• Mobility
• speciation
• extraction
• incubation
• pyrite
• chalcopyrite