Characterization of copper slag for beneficiation of iron and copper

Abstract

Before disposal of any metallurgical waste to the environment, it is the responsibility of mining institutes to adhere to the permissible metal content limits. Base metals, especially iron and copper, have adverse effects of reducing the soil pH and excessive concentrations of these in the disposed waste may result in soil pollution and toxicity, with adverse effects on plant growth and animal health. Copper slag is a metallurgical waste that is disposed by way of stockpiling at designated dump sites within a mining site. The observed depletion of high-grade iron ores in Botswana and the environmental hazards associated with disposal of untreated metallurgical waste, presents an opportunity for research on secondary sources of iron and copper. Our characterization results show that this BCL copper slag is a good secondary source of base metals, especially iron and copper. These results reveal that the elemental proportion of iron was around 35.4%. Literature states that an iron grade that is considered viable for economic beneficiation should be at least 25% and this slag has an iron content above this limit, hence poses a serious environmental threat upon disposal. This article presents an investigation into the mineralogy of the copper slag at a plant situated in Selebi Phikwe, a town in the northern part of Botswana. Quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) quantified that no cobalt – sulphide was detected and strongly indicated that the cobalt within the sample occurs in solid solution in either the fayalite phase or glass phase. Spot analysis from electron probe micro – analyzer (EPMS) images indicated an unusually high content of copper compared to any other metal. We elucidate that, this was due to the inefficient processing techniques employed during operational years of the mine. The relative compositions of Co, Fe, Ni and Cu were 0.14%, 35.4%, 0.28% and 0.29% respectively. This analysis justifies our interest in considering this copper slag as a secondary source of iron for beneficiation purposes.