Metal/loid release from cyanidation wastes in response to rainfalls

Abstract

Cyanide heap leach operations developed in Tharsis (SW Spain) from 1982 to 2001 left the legacy of a huge amount of cyanidation wastes deposited over a total area of 47 ha without any type of isolation. The main goals of this work are to study the release of metals and metalloids under rainfall occurrence and the potential impact on the aquatic life. A vertical profile was sampled in the leaching heap and the chemical and mineralogical composition of these wastes was analyzed. In addition, the response of these wastes to rainfalls was studied by leaching with water at different solid-liquid ratios. The cyanidation wastes are mainly composed by Fe oxides/oxyhydroxides (i.e. goethite and hematite), oxyhydroxysulfates (i.e. jarosite), and quartz as well as gypsum in different levels. Although the alkaline conditions of the cyanidation wastes precluded the mobilization of most metals, some elements such as As, Zn, Ni and Pb showed concentrations which may pose a significant risk to aquatic life if chronic exposure is maintained. For this reason, a safe disposal of these wastes is needed in order to reduce the release of metals into the environment.