Arsenic phase distribution in Zimapán mine tailings, Mexico

Abstract

Arsenic contamination of groundwater has been linked to natural and anthropogenic sources in Zimapán, Mexico. Leaching of mine tailings was identified as one of the man-made causes of environmental arsenic pollution. Arsenic mobility from four tailing piles was studied by chemical procedures. Conductivity, concentration of sulfates, and pH in aqueous leachates were used as indicators of the physico-chemical conditions influencing arsenic mobility. Arsenic geochemical fractionation was determined through sequential extraction from the tailings. High arsenic contents from 2550 mg/kg to 21 400 mg/kg were found in all the tailings. Most arsenic was contained in the residual considered more stable, and in iron and aluminium oxyhydroxides fractions. Arsenic found in the soluble and exchangeable fractions (up to 1560 mg/kg) may mobilize easily and pollute the environment. On the other hand, presence of calcite in the tailings may decrease arsenic leaching. Arsenic and sulfate contents, speciation, and pH, indicate that the recent pile is a major source of pollution. This shows that even stable forms of arsenic may mobilize and may represent an environmental risk. Higher pH is observed to prevent the dissolution of arsenic bound to carbonates. Hence, addition of calcium oxide or calcite to the tailings is recommended.