Reduction-roasting and ferric chloride leaching of copper converter slag for extracting copper, nickel and cobalt values

Abstract

In a previous investigation the optimum conditions for recovering copper, nickel and cobalt from converter slag through ferric chloride leaching have been described. The study of various parameters revealed that nickel and cobalt recovery could not be improved beyond 24 to 26% respectively from converter slag, though more than 90% of the copper could be extracted. Further attempts were made to bring the metal values completely into solution through reduction-roasting followed by ferric chloride leaching of the slag. The present work comprises a study of various experimental conditions such as concentration of ferric chloride, duration of leaching, duration of reduction-roasting, temperature and nature of reducing agent, to arrive at the optimal recovery of the metal. Under identical experimental conditions a decrease in copper recovery, but an increase in nickel and cobalt recovery has been observed above a roasting temperature of 750°C. The decrease in copper recovery has been attributed to copper ferrite formation which has been confirmed both by leaching experiments with synthetic mixtures and by X-ray diffraction studies with both slag samples and synthetic mixtures. Recovery of nickel has also shown little decline when solid reductants were used above 850°C whereas cobalt recovery remains nearly the same even above 850°C. Under optimum conditions 80% copper, 95% nickel and 80% cobalt could be recovered by reducing the slag at 850°C with 10 wt % furnace oil, followed by leaching with ferric chloride.