Geochemical characterization and modeling of arsenic behavior in a highly contaminated mining soil

The environmental assessment and management of historical mining sites contaminated with various inorganic species require a better knowledge of pollutant-bearing phases. Among elements present in mining soils, arsenic is a toxic metalloid with potential high content and high mobility capacity into the environment. The objective of this paper was to investigate the mobility and fractionation of arsenic (As) in a highly As contaminated soil (ca. 3 wt%). The soil was collected from an old gold mining site in France, where mining activities and smelting processes of gold ores took place. Single and sequential chemical extraction procedures were firstly conducted. These leaching tests were used to assess the potential mobility of As depending on its fractionation in the contaminated soil, and also on the portion of As sorbed onto soil particles. Additionally numerical simulations were performed using the USGS software PHREEQC-3 in order to evaluate the role of adsorption on As mobilization. This multidisciplinary approach provided information on the nature of As fixation in this mining soil. Moreover the role of adsorption in the control of dissolved As was evidenced by geochemical modeling. Results showed that As appeared to be mainly (ca. 72 wt%) reversibly sorbed to iron (Fe) compounds in the soil, in particular Fe oxyhydroxides. Consequently a potential risk of As mobilization exists especially under acidic and/or reducing conditions, which frequently occurs in mining environments.