Geotechnical and geochemical impact assessment of Bamangwato Concessions Limited (BCL) mine waste dumps on Selebi-Phikwe environment, Botswana

Abstract

Mining activities produce significant amounts of wastes (tailings, slag and waste rock) which, with loss in material strength, could trigger slope instability while the wastes minerals’ chemical reactions also have the potential to produce acid mine drainage (AMD) contaminations. Plausible environmental impacts that could be caused by Bamangwato Concessions Limited (BCL) mine waste dumps was investigated through geotechnical, geochemical, and mineralogical studies. The mine wastes geotechnical properties were determined through laboratory testing and used to establish safe slope angles of the waste dumps based on the Simplified Bishop method using Rocscience Slide2 software Version 9.007. The geochemical and mineralogical studies to determine the influence of the mine wastes on the environment were through X-ray diffraction (XRD) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) on samples of tailings, slag, and soil from the mine, while Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was applied to water samples. Safe slope angles up to 20° were established for the tailings dam at slope heights of 40-60 m and water levels from 30-40 m height. The slag dump safe slope angle was 30° for water levels up to 20 m at slope heights of 40-60 m. The waste rock dump slopes were stable for slope heights up to 60 m and slope angles rising to 40°. The heavy metals in the tailings in order of concentrations (in ppm) was Iron(80000)>Nickel(1805.3)>Copper(1388.4)>Manganese(373.8)>Chromium(138.7)>Cobalt(97.3)>Zinc(53)>Lead(14). Statistical analysis suggested miscellaneous sources of pollution. Continuous monitoring of heavy metals concentrations around the waste dumps has been recommended.