A Review of Nchanga Tailings Dam Operations and Seasonal Assessment of Its Effluent Quality

Abstract

The Nchanga tailings dam, a reservoir of mine waste from Konkola Copper Mines (KCM) operations in Zambia, discharges its effluent into the local Muntimpa stream. The Muntimpa stream, a possible source of drinking and domestic water for the local population, flows into Mwambashi stream which subsequently discharges into Kafue river. The Kafue river is a significant support of economic development in Zambia and is a source of 40% of drinking water for the cities with about 50% of the population living in the catchment. This study looks at an overview of the operations of Nchanga tailings dam and assesses the levels of pH, TSS, TDS, Cu, Mn, Co and SO4 in the effluent discharged in rainy and dry seasons. It also provides possible methods that could be used to lower pollutant levels to below recommended Zambia Environmental Management Agency (ZEMA) limits. To determine the pollutant concentrations, sixty (60) samples were collected from the tailings dam spillway in rainy season (April) and dry season (October) of 2015 and analysed on a daily basis. The results indicated that the average pH, TSS and Cu levels in the samples from both wet and dry seasons were within the permissible range of 6.0-9.0, below 100 mg/l and 1.0 mg/l respectively. The TDS average figure (2658±331 mg/l) recorded in April was less than the allowable limit while significantly higher value (4783±86.6 mg/l) was obtained in October. The concentrations of Mn and Co were significantly high and above ZEMA limits with mean values of 79±22.1 mg/l and 11±5.9 mg/l for rainy season and 189±19.2 mg/l and 19±1.3 mg/l for dry season respectively. The SO4 content was observed to be high in both seasons with average figures of 2071±240 mg/l in April and 3628±261 mg/l in October. It was observed that the levels of all the parameters analysed (with exception of Cu) showed seasonal variations attributed to evaporative effects. To minimise contaminants levels in the effluent, it is recommended that the discharged effluent should be restricted in dry season until the levels of dissolved pollutants are sufficiently low in wet season. Recycling of water from the decantation pond of the tailings impoundment back to the main plant is an effective alternative that would eliminate pollution of water bodies. Other methods that could be employed involve the use of chemical and biological treatment technologies.