Evaluation of the mobility of Fe, Zn, Pb, Cd and As from tailings by sequential extraction and experiments under imposed physicochemical conditions

Tailings constitute an important source of potentially toxic metals and metalloids (PTMM) to the environment. Determining PTMM mobilization potential is relevant for estimating their hazard. The release of Pb, Zn, Fe, Cd and As from oxidized and less oxidized tailings situated at the mining town of Zimapan, Mexico, was evaluated by applying various extraction schemes: 'geoavailable', the scheme of the Community Bureau of Reference (BCR), and experiments at distinct pH and redox conditions. Total concentrations varied as: Fe (10.6-19.4%), As (8397-107,649 mg/kg), Zn (1325-30,635 mg/kg), Pb (3810-10,000 mg/kg), and Cd(16-1425 mg/kg). Geoavailability (proportion of elements released with a solution simulating rainwater) in oxidized tailings reached 79.1% for Zn, 69% for Cd, 7.3% for Fe, 5.1% for As, 1% for Pb. Cadmium was the most geoavailable element (1%) in less oxidized tailings. BCR fractionation showed different mobilities among elements and samples from each deposit. Less oxidized tailings could become more hazardous with time, mobilizing mainly Zn, Cd and As. Geoavailable As, Fe and Cd surpass irrigation water standards. In spite of its low mobile proportion, the high total As concentrations may produce hazardous levels in soils. The geoavailable procedure constitutes an easy to apply and economic method that may be used to perform a first evaluation of the tailings' pollution potential to the nearby soils.