Keywords: arsenic mobility, mining, mineralogy, metals, oxidised tailings, Mexico, water leachates, secondary minerals, arsenopyrite oxidation, arsenic concentrations, sorption, chemistry, environmental pollution
Arsenic mobility was studied in tailings from Zimapan, a mining zone of Mexico. Primary mineral phases are quartz, calcite, pyrite, pyrrhotite, sphalerite and arsenopyrite. Secondary minerals in oxidised tailings include gypsum, K-jarosite, lepidocrocite, goethite, beudantite and kaolinite. The highest levels of As (up to 3.95 ± 2.29 weight %), Zn (up to 3.26 ± 2.21 weight %) and Pb (up to 0.93 ± 0.83 weight %) were measured in unoxidised tailings located at the edge of the town. Concentrations in water leachates from oxidised tailings were: As (0.41–48.68 mg/L), Zn (1.5–400 mg/L), Pb (<1.0–1.8 mg/L) and Fe (1.9–897.5 mg/L). Mineralogy, pH, and heterogeneity of tailings, explain these concentration ranges. Arsenopyrite oxidation releases arsenic that is then partly incorporated in secondary minerals like beudantite and K-jarosite. Arsenic is also immobilised by sorption onto positively charged surfaces of hydrous ferric oxides.