The availability of freshwater is one of the major development challenges that South Africa faces. South Africa is a water-scarce (semi-arid) country with rainfall distributed unevenly and away from the centres of major developments. The rainfall is tied to seasonal cycles that drive us repeatedly between floods and droughts. This paper serves to study the groundwater chemistry in light of the uranium mining that precedes shale gas fracking in the Karoo Uranium Province. The aim is to have groundwater baseline chemistry assessment before mining commence in order to be able to track mining effect on groundwater in the future. A total of 128 samples are dealt with in this work, 112 collected from groundwater, 9 collected from springs and 7 extracted from a database. The samples were analysed for physical parameters, cations, anions and metals. Redox potential was also determined as it plays a pivotal role because it controls the availability and form of uranium in a solution. Uranium is a radioactive actinide naturally occurring in the area. Therefore, this assessment will be crucial in order to understand how changing redox and pH conditions affect uranium solubility and to estimate the extent of uranium transport by water during and after mining. The effects of the redox potential and pH on uranium mobility have been examined in this work by means of computer modelling by using the Geochemist’s Workbench (GWB) 11.0. The composition of the water used for modelling resembled that of a typical bedrock groundwater of Karoo Uranium Province. The simulations were carried out under different redox potentials at different pH levels in the presence of ferrihydrite, dissolved organic matter and carbonates/bicarbonates to include the effects of uranium adsorption. The results show that the redox potential at which the uranium mineral (uraninite) dissolves varies depending on the pH of the groundwater.
Analysis of the simulation results indicated that the dissolution of uraninite takes place at a lower Redox condition with increasing pH (alkaline pH condition). This means higher redox conditions are needed for the dissolution of uraninite at low pH. Moreover, it is further concluded that the adsorption of uranium to ferrihydrite and carbonates is important at pH 6-10 and pH 5-8 respectively, which therefore play an important role in controlling the mobility of uranium in the modelled groundwater.