Heavy metals and radionuclide status and characterisation of pre-mined soils in Serule, North East Botswana

Abstract

Characterisation of soils and establishment of heavy metal and radionuclide concentrations prior to mining disturbance provides an essential benchmark for post-mining reclamation. Land disturbance from uranium mining could result in metal contamination of surface soils with subsequent negative impacts on soil quality and human and ecosystem health. This soil characterization study was conducted because there is no background data of soil trace metals and radionuclide for this region. These benchmark data are essential for post-mining monitoring and possible future remediation. The planned conventional open pit mine will produce 15,000 and 50,000 tonnes (ore and waste rock) per day. The envisaged overburden and waste dumps are likely to enhance potential for heavy metal contamination of soils. To establish the baseline data and pre-mining site environmental conditions, (1) the physico-chemical properties of soils and (2) potential heavy metal and radionuclide pollutants in identified different sites were determined. The sampling sites were selected based on the variation in soil classes in the study area. The physico-chemical properties were measured using the standard methods while heavy metals were analysed using a Finnigan MAT Element 2 high resolution Inductively Coupled Plasma Mass Spectrometer. The following heavy metals and radionuclides were determined: Th, U, Sr, Ba, Be, Cd, Pb, V, Cr, Ni, Cu, Zn and Co. Most soils are predominately sandy clay (>17.2 %) suggesting their suitability for agricultural use. The results also indicate that most heavy metals were at or below expected ranges for non-contaminated soils and there was no evidence of any geochemical anomalies.