Environmental impact of leach water from selected mine tailings materials in South Africa

Abstract

Background and objective: Mine tailings materials pose severe impacts to the environment (soils, water and ecosystem). A variety of processes such as erosion or sedimentation and leaching disperse trace elements to the natural environment. The environmental impact of leach water from selected mine tailings materials in South Africa was studied. Methods and materials: Sampling was done at sixteen different mine tailings materials, and detailed analysis was accomplished. Laboratory leaching for trace elements (TEs) was performed with the use of humidity cells as outlined in Chapter 3. The ICP-MS analysis method was further used to determine the concentrations of U, Cr, Co, Ni, Pb, Cu, As, Mn, Zn and Cd TEs. The level of TEs in soils was measured against the South African soil screening values (SSV) for all land-uses protective of the water resources to indirectly protect the ecosystem (NEMWA Act NO 59 of 2008). Uranium, As, Cu, Ni, Cr and Cd levels at sampling sites TJ3, TJ9, TJ15 and TJ20 were above the threshold limits. Results: To classify soils and other fines i.e. tailings according to texture, particle size distribution analyses were performed. The size of tailings ranged from very coarse sand to clay. This contributed to understanding the mobility of TEs under study. Cation exchanged capacity (CEC) and anions analyses were also performed to support the results. Conclusion: The pH of leached water ranged between 2.19 (TJ20) and 10.12 (TJ2), whereas EC ranged between 0.51 mS/cm (TJ23) and 60.7 (TJ1) respectively. Revegetation to hinder TEs from leaching was recommended. The addition of gypsum was also recommended to reduce the level of Na in mine tailings materials.