International journal of mine water

Microbial heavy metal retention was studied using seepage water sampled from a former uranium mining site in Eastern Thuringia, Germany. The seepage water has a low pH and contains high concentrations of metals, including uranium, rare earth elements (REE), and other heavy metals. Microbial influence on sorption and/or active uptake of heavy metals was studied using REE patterns. Incubation of seepage water with the bacterium Escherichia coli caused sorption of heavy metals to biomass. Incubation with the fungus Schizophyllum commune, however, had a much more pronounced effect, including significant fractionation of REE, pointing to the possibility of a specific active uptake mechanism. Extraction factors and fractionation coefficients are given to show the capacity of the presented bioextraction for future applications.

This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO3), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.