Evaluation of potential acid mine drainage: A case study of the Albert Silver Mine, Mpumalanga Province, South Africa

Abstract

Generally, mining produces mine wastes that contain sulfide minerals that have potential to produce acid mine drainage. Albert Silver Mine conducted mining of the silver-sulfide bearing ore from 1885 to 1914. However, at the time, little attention was being given to acid mine water generation. This study investigated the current status of acid mine drainage on the Moses river and the potential of the silver ore to produce acid mine drainage. This was achieved through investigating both sulfide and carbonate minerals in the silver ore. The sulfide and carbonate minerals were investigated using X-ray diffraction spectroscopy and petrographic studies. The current status of acid mine generation of the site was also studied through water quality analysis of the Moses River. Static and kinetic tests acid mine drainage prediction techniques were conducted to determine the acid generation potential of the silver ore. The sulfide minerals discovered within the silver ore are pyrite, arsenopyrite, chalcopyrite and galena, the carbonate mineral discovered was calcite (5.6 wt%). The neutralisation capacity of the rock samples was high as confirmed by the values of NNP and NPR, ranging from 20.75 to 80.65 kg CaCO3/t and 2.64 to 115.91 kg CaCO3/t, NAGpH ranged from 2.3 to 5.37 and the NAGpH7.0 ranged from 0.1976 to 12.378 kgH2SO4/t. The kinetic tests yielded neutral pH values ranging from 5.98 to 8.02, electrical conductivities from 13.85 to 147.5 µS/cm, acidity from 0.04 to 0.25 mmol/L, alkalinity from 0.01 to 0.704 mmol/L, sulfate concentrations from 0 to 8 mg/L and ferrous iron concentrations from 0 to 0.18 mg/L. The water chemistry results from the Moses River yielded pH values from 7.00 to 7.78, electrical conductivities from 240 to 520 µS/cm and very low metal concentrations; lower than WHO and S.A. water quality guidelines. Pyrite was framboidal in morphology, disseminated and with large surface areas. Mineralogically, the study discovered sulfide minerals and calcite was the only carbonate mineral. According to the water quality analysis there is no threat of acid mine drainage at the Moses river, the outcomes of the acid mine drainage prediction led to the conclusion that there is no potential acid mine drainage issue.