Effect of particle size, pH, and residence time on mobility of copper and cobalt from copper slag

Abstract

Mining waste such as copper slag contains different types of potentially toxic metal elements. Transportation, crushing and subsequent storage of copper slag in undesignated areas can increase the potential of these elements being released to the environment, resulting in negative environmental impacts. This study investigated the leaching behavior of copper and cobalt from Nkana smelter copper slag dump under different conditions. The effect of particle size, pH of the leaching agent, and contact time on the release of copper and cobalt was investigated. The slag samples were granulated into six different grain sizes and subjected to different pH levels treated for 33 days. To assess the hazardous nature of a material within the natural environment, batch leaching techniques, as outlined in EN 12457–2:2002, were employed. The results showed that the pH 2.0 of the leaching agent had a more significant effect on the release of both copper and cobalt than residence time and particle size. The optimal particle sizes for copper and cobalt release were 0.075–0.150 and 0.150–0.250 mm, respectively. The optimal leaching time was 33 days for both metals. In order to prevent the mobility of copper and cobalt from Nkana slag dump into the aquatic environment, acidic pH levels and smaller particles <0.150 mm should be avoided.