Concentration levels of some inorganic contaminants in streams and sediments in areas of pyrometallurgical and hydrometallurgical activities at the Obuasi gold mine, Ghana

Abstract

This study assessed the levels of selected inorganic contaminants in streams and stream sediments in the effluent areas relating to the pyrometallurgical and hydrometallurgical treatment of gold ores in the Obuasi gold mine, Ghana. Water and stream sediment samples were taken from specific locations during the consecutive rainy and dry seasons, and concentrations of phosphate (PO₄ ³⁻), nitrate (NO₃ ⁻), chloride (Cl⁻), sulphate (SO₄ ²⁻), sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), arsenic (As), copper (Cu), iron (Fe), zinc (Zn) and lead (Pb), were determined. Alkalinity, pH, temperature and specific electrical conductivity were also measured. In the water samples, the average pH range for both the seasons is 6.9–7.4, most anions and metals have relatively higher concentrations in the wet season than in the dry season at both the metallurgical sites. Trace metals concentrations were comparatively low (<0.01–5.00 mg/l), higher in the dry season at the pyrometallurgical sites. Irrespective of seasons, SO₄ ²⁻ (0.80–949.50 mg/l) and PO₄ ³⁻ (<0.01–6.30 mg/l) were pronounced at the pyrometallurgical sites, while NO₃ ⁻ (0.01–98.45 mg/l) and Cl⁻ (1.88-49.05 mg/l) were higher at the hydrometallurgical sites. In water samples, Ca²⁺ and SO₄ ²⁺ were the dominant cation and anion, respectively. In the stream sediments, except pH, NO₃ ⁻, Cl⁻, Na⁺ and Mg²⁺, all other parameter values were relatively higher at the hydrometallurgical areas. The average concentrations of Ca²⁺, Mg²⁺, As and Fe are remarkably high at both metallurgical sites (3,217–46,026 mg/kg). Overall, the level of parameters in the water samples are pronounced at pyrometallurgical sites, whereas the levels in sediments are higher at the hydrometallurgical sites.