Acid Rock Drainage Prediction from O’Kiep, an Arid Region of Namaqualand, South Africa, of Soils Using Humidity Cell Test
Erdogan, Innocentia Gugulethu (1,2,3); Fosso-Kankeu, Elvis (1); Ntwampe, Seteno K.O. (2); Waanders, Frans B. (1); Hoth, Nils (4)
1: Water Pollution Monitoring and Remediation Initiatives Research Group (WPMRIRG) in the CoE of C-based fuels School of Chemical and Minerals Engineering, North-West University, Potchefstroom, South Africa; 2: Bioresource Engineering Research Group (BioE
The O’Kiep area was once one of the major copper producers in the world during the 18th century. The major potential toxic elements measured using X-ray florescence were S > Cu > F > Mn > Cl > Zn > Cr > V > Pb > Ni > Co. The soil minerology comprise of quartz, albite, calcian, anorthite, sodian, microcline, phlogopite-1M, goethite and orthoclase measured using X-ray diffractometer. Humidity cell tests (HCTs) were used to predict the potential for acid rock drainage (ARD) and to estimate the mineral reaction rates of soil from O’Kiep. In this study the HCTs were carried out on 1kg composite soil samples at the laboratory scale for a period of five weeks. Analysis for various geochemical parameters were measured from an average leachate of 0.7kg. Monitoring of the leachate quality indicated that the soil sample started producing acid very early in the test, in the first week of experiementation. The sulphate production rate of soil was very high at 2682 mg/kg during the first weeks of the HCTs experiment. The standard HCTs can be influenced by several factors that have a significant impact on sulphide oxidation. Leachates produced remained at a near mild acidic average pH of 4 with changes in electrical conductivity (>199 mS/m), total dissolved solids (>2302 mg/kg), Cl (>21 mg/kg), SO4 (>1324 mg/kg), for the duration of the tests being observed. The leachates also lacked CaCO3 and F, with low concentration values of less than 5 and 2 mg/kg being observed, respectively. The results also showed that in the leachates from the soils, the metal concentrations increased while the pH decreased with time, indicating an increased oxidation rate. Furthermore, the results also demonstrated weathering and the production of ARD. The HCTs had indicated that the soils around the old mining town of O’Kiep, are susceptible to ARD generation and can release acid for elongated periods under conducive conditions.