Geochemical characterisation of the Witbank coalfields, South Africa
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Date
2020-11
Authors
Thwala, Kedibone
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The Witbank Coalfield is one of the 19 coalfields found in South Africa and has been exploited for coal for more than a century. The coalfield is located in the Mpumalanga Province, roughly 100 km east of Johannesburg. The dissertation focuses on the Witbank Coalfield wherein Arnot, Goedehoop, Mafube, Zibulo, Landau and Greenside collieries, as well as Blaauwkrans and Greenside Discard Facilities were investigated. Coal mining in this area has proven to be problematic, has caused contamination of surface and groundwater resources, and changed the quality of the water over the years. The purpose of this study was to investigate the acid generating potential of the Witbank coalfield by examining the groundwater chemistry, acid-base-accounting predictions as well as sulphur contents of the coal seams and host rocks. The data obtained from the mines were processed using tools such as WISH, ABACUS and PHREEQC to create descriptive diagrams that aided in further understanding the acid generating properties of the study area. Arnot, Goedehoop, Greenside colliery and its discard dump are the most problematic due to their high sulphate concentrations. Sulphur contents of coal seams were compared to the groundwater sulphate concentrations. Although this was instrumental in understanding the relationship between sulphur and sulphate concentrations, sulphur is not evenly distributed amongst and within the different seams, leading to certain hotspots. Geochemical speciation showed hydrated metals and carbonates are likely to precipitate as secondary mineral phases. Overall, the results demonstrated that the groundwater of the investigated study sites was sulphate contaminated and that the majority of samples collected from the sites were potentially acid generating. ABA data was compared with the groundwater chemistry to evaluate whether the ABA predictions were reflected in the groundwater quality. Results of this study confirmed that ABA is a useful tool to predict potential constituents of concern in groundwater.
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Keywords
Dissertation (M.Sc. (Geohydrology))--University of the Free State, 2020, Acid base accounting, Groundwater chemistry, Water types, Sulphate concentrations, Sulphur contents