A laboratory study was undertaken using mine tailings and soil columns to evaluate some of the natural processes that can control the mobility of metals at Pb–Ag mine tailings impoundments. The effects of buffering, pH, and salinity were examined with tailings from the El Arteal deposit. Al, Ba, Cd, Cu, Fe, Mn, Ni, Pb, Sr, and Zn were mobilized when the tailings were leached. However, when the mine tailings were placed above alluvial soils, Al, Ba, Cd, Cu, Mn, Pb, and Zn were retained, although Fe and Sr clearly remained mobile. Most of the metal retention appears to be associated with the increase in pH caused by 18 calcite dissolution. The sorption of some metals (Cu, Pb, and Zn) onto oxyhydroxides of Fe and Mn, sulphates, clay materials, and organic matter may also explain the removal of these metals from the leachate.

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