Mobility potential of metals in acid mine drainage occurring in the Highveld area of Mpumalanga Province in South Africa: Implication of sediments and efflorescent crusts

Abstract

Prediction of the dispersion of pollutants from the acid mine drainage is an important step toward the development of remediation strategy and mitigation of environmental impact. Geochemical studies are often carried out to determine the speciation and mobility of metal pollutants in sediments and water. In the present study sequential leaching and humidity cell tests were carried out on the sediments from acid mine drainage (AMD) basin for the determination of the susceptibility of metal release. The X-ray diffraction (XRD) and Mössbauer analyses were carried on the efflorescent salts from the stream bank to determine the secondary minerals that could further contribute to AMD pollution impact; while speciation of metals in AMD solution was done using the geochemical model PHREEQC. The results show that metals such as Fe, Ni and U are bioavailable from the exchangeable fraction F1 of the sediments in the range of 1.1–81%; while secondary minerals contribute to higher release of Fe and SO42− in solution. The sediments studied were found to have a relatively higher acidity potential (36 and 73) versus a negligible neutralization potential. Species prediction of dissolved metals showed dominance of free metal ion species in water. Secondary minerals such as goethite and iron sulfate which have been reported to contribute to further acidification of water were found in the efflorescent crusts. The findings in this study therefore predict higher mobility and sustainable occurrence of metals in the effluent considered, prompting intervention for preservation of the environment and scarce water resources.