NATURAL RELEASE OF COPPER AND ZINC INTO THE AQUATIC ENVIRONMENT

The disposition of base metal ionic species in the aquatic environment is presented. The entry of these ions from natural leaching processes is discussed. Natural leaching processes include biological and chemical aqueous oxidation of sulphidic waste rock and tailings. The effects of biological and non-biological oxidation of pyrite on the solubilization process and the mobility of dissolved copper and zinc were evaluated using experimental data and mathematical modelling. The diffusion and convection of atmospheric oxygen through unsaturated but moist pyrite deposits are shown to be rate-limited for establishing the acidity and metal ion flux in the groundwater regime. The evolution of acidic water conditions may take several years to develop, depending on the inherent kinetics and neutralizing capacity of the calciferous components of the waste rock or tailings. Chemical and biochemical reactions play an important role during the onset of acidic conditions, while diffusive and convective transport are important later. The results of this evaluation were used to construct a practical model to predict acid mine drainage problems and suggest covers as a method of abatement to reduce oxygen and hydraulic transport.