Determining uranium activity distribution in water streams and sediment in three mining regions of South African

Abstract

Uranium is a by-product in the mining of gold in South African landscapes (Coetzee et al., 2006). Since these activities are done on land in different provinces of South Africa and near communities inhabited by people and animals, there is a risk of exposure from this uranium by-product during operations and after operations have ceased. It is therefore necessary to determine the levels of contamination at present to identify the potential risks posed to people and the environment. The purpose of this study was to determine the activity concentrations of uranium isotopes (238U, 235U, and 234U) in sediment and water and the 234U/238U activity ratios in the water around gold mining operations in Gauteng, North West, Free State, and Mpumalanga province. The concentration of uranium in water and sediment around the Witwatersrand Basin covering the mining regions of Gauteng (West Rand location), the North West (Klerksdorp location), the Free State (Welkom location), and Mpumalanga (East Rand location) provinces in South Africa was determined using alpha spectrometry and gamma spectrometry. Water and sediment samples were collected during different months of the year in these regions. The selected months were times when different seasons of the year started, i.e., September (the beginning of Spring), December (the beginning of Summer) and March (the beginning of Autumn). This selection was made to see whether the change in the season impacted the activity concentration levels. The samples were contained in plastic bottles and tubs and then transported to the laboratory for analysis. Alpha spectrometry was used to analyse water samples, and Gamma spectrometry was used to analyse sediment samples to determine the activity concentration of uranium and the concentration of uranium in water and sediment. The transfer coefficient of uranium in water was calculated from the concentration results. The highest uranium concentration in water and sediment was found in West Rand. The concentration in water and sediment, respectively, had a mean value of 7263,8 mBq/L and 1871,7 Bq/kg in West Rand; 2346 mBq/L and 186,7 Bq/kg in Welkom; 1887,7 mBq/L and 452,2 Bq/kg in Klerksdorp and 807,2 mBq/L and 260 Bq/kg in East Rand. The isotopic ratios of 234U/238U for all the samples collected ranged from 0,96 to 1,14. The resultant values in this study indicated that 238U activity concentration is significant throughout the spring, summer, and autumn seasons. Some values exceeded 500 Bq/kg, which is the National Nuclear Regulator's limit for exclusion of operations. Some low values observed during the December 2020 period could be due to the rainfall during that time.