Acid mine drainage prediction techniques and geochemical modelling: case study on gold tailing dams, West Rand, Witwatersrand basin area, South Africa

• Main Author: Wu, Changhong
• Other Authors: Khotseng, Lindiwe
• Language: en
• Published: University of the Western Cape 2021
• Subjects: Acid Mine Drainage; Gold Tailings; Geochemical; Mineralogical
• Online Access: http://hdl.handle.net/11394/8401

Doctor Scientiae === Acid Mine Drainage (AMD) is identified as one of the contributors to environmental hazard in the gold mining region of South Africa, as caused by the mining operational activities performed by mining industries in South Africa. This effect motivates the development of AMD prediction techniques application and geochemistry modelling using gold tailing dams located in West Rand area, Witwatersrand Basin as a case study. Control strategies are devised to assess, understand and measure the acidic potential generation of waste materials in ensuring the right method required to analyse risks caused by AMD to environment. The method encompasses mineralogical and geochemical analysis of 93 samples collected, AMD prediction, test modification and geochemical modelling. This method was appropriately applied to understand the basic mechanisms involved in controlling acid generation, assessing prediction procedure and selecting the right prediction tools. Study objectives are attained by performing a series of experimental lab tests on the samples collected from the two major tailing dams (Mogale and Gold One_1 tailings). Results derived from the lab experiments (XRD and SEM-EDS) show presence of mineral phases characterised with the surface feature of samples, and unknown substances of samples were identified. Geochemical characterisation was performed by XRF and ICP-MS to determine the major oxides elements and trace elements, respectively. Leco test generate total sulphur and total carbon. Multistatistical analysis is used to interpret the data derived from geochemical characterisation process to explicate the metal and trace elements distribution and occurrence. Initial samples were screened and categorised based on paste pH and EC using kinetic tests to determine acid-forming and neutralising minerals in samples and static tests to determine acid generation potential in samples. Net Acid Producing (NAPP) was mathematically calculated from Acid Neutralising Capacity (ANC), Maximum Potential Acidity (MPA) and total Sulphur. Results obtained from the Paste pH demonstrate that samples collected from 1 meter downward the holes to 10 meters, with a few meters samples in hole T003 at Gold One_1 are non-acidic while the remaining tailing samples are acidic. ANC/MPA ratio was applied to assess the risk of acid generation from mine waste materials. Graphical illustrations of the Acid Base Account (ABA) are plotted to demonstrate the net acidic generation potential trends of samples, which were classified into non-acid forming, potential acid forming and uncertain categories. Results integration between ANC, Single Addition Net Acid Generation (NAG) test and NAPP were used to classify acid generation potential of the samples. Leachate collected from leaching column test were analysed for pH, EC and chemical element by ICP-MS. The leaching column test used to analyse samples (T004) and (T001) collected from the two major tailings was set up for a 4-month experiment. Study findings present environmental assessment report on the two investigated gold tailing dams in Witwatersrand Basin area. Other findings are improved understanding of the application and limitations of various existing AMD prediction methods for assessment of gold mine waste and conceptual geochemical modelling developed to test appropriate methodology for AMD potential at a given gold mine site.