Environmental Assessment of Acid Mine Drainage Pollution on Surface Water Bodies around Ngwenya Mine, Swaziland

Abstract

Twenty-three water samples and three "yellow boy" samples were obtained from different water bodies located at the foot of the Ngwenya Mountain on top of which the old Ngwenya Iron Ore Mine is located. The samples were analysed for pH, electrical conductivity (EC), redox potential (ORP) and temperature (T). The dominant Fe species was determined using a UV-VIS spectrophotometer. Selected anions namely: halogens (F − , Br − , Cl −), the nutrients (2 NO − , 3 NO − , 4 PO 3−) and the best indicator for AMD pollution (4 SO 2−) were analysed using Ion Chromatography (IC) while the selected heavy metals, namely: Cr, Mn, Fe, Ni, Co, Cu, Zn, Pb and Cd were analysed using Flame Atomic Absorption Spectrometry (FAAS). The physico-chemical parameters ranges obtained were pH (6.32-8.63), EC (11.00-585.33 µS/cm), ORP (−93.67-79.33 mV) and T (7.60˚C-18.57˚C). The levels of the Fe species (ppm) in the water samples were Fe 2+ (0.56-3.17) and Fe 3+ (0.00-0.73). Measured mean anion ranges in ppm were F-(0.00-0.15), Cl − (1.5-11.19), 3 NO − (0-13.25) and 4 SO 2− (0.05-22.29). The mean ranges for the heavy metals in the water samples in mg/l were Cr (0.00-2.46), Mn (0.00-0.30), Fe (0.00-0.34), Ni (0.00-0.34), Co (0.00-0.29), Cu (0.00-0.07), and Cd ((0.01-0.11) whilst Zn and Pb were not detectible. The average pH in all the sites was within the acceptable range (6.5-8.5) according to WHO standards except for two sites. Fe 2+ was the dominant Fe species in the water samples. The water was free from anion pollution because all measured anion levels were below the guideline by WHO. The relative percentages of sites polluted by the respective heavy metals were: Cd (83%), Cr (71%), Ni (46%), Co (42%), Mn (17%), Fe (4%) while no site was polluted by Cu, Zn and Pb. The State needs to set up sound remediation strategies to save the populations around the Ngwenya Mine from the heavy metal pollution they are exposed to by using water polluted by the mining activities.

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