From Waste to Resource: Critical Mineral Recovery and Environmental Impact Mitigation in Copper Smelting Slag

Copper and cobalt are critically important metals for the transition to renewable energy and various aspects of modern life. Their production from primary sources, ores, necessitates metallurgical separation from the unwanted host materials, resulting in the generation of a huge amount of waste. Copper smelting slag is one of these metallurgical wastes, with 39 million tonnes of slag generated and discarded globally each year. These massive amounts of slag occupy a considerable and growing land footprint, often close to residential areas, and present a hazard that potentially releases contaminants into the environment. On the other hand, they also represent a material that often contains a significant residual amount of valuable copper and cobalt. To better understand and address the challenge of reducing the adverse impacts of the waste, as well as the possible commercial opportunity the contained critical metals present, this study reviews global smelting slag production over the last 25 years, its composition, and technical reprocessing options. A summary of the chemical and mineralogical characterization of the copper slag from diverse research is thus provided, as well as a comprehensive overview of the processing strategies for metal recovery from copper slag, such as flotation, pyrometallurgy, and hydrometallurgy. The study demonstrates that a huge amount of smelting slag has been produced, with great variation and complexity, which represents a major potential resource for cobalt and copper metals. The chemical and mineralogical composition of smelting slag varies from location to location, depending on the properties of the feed concentrate, type of fluxes, furnace type, and cooling rates employed during and after the smelting processes. The overview of the production trends and reprocessing techniques shows that while some notable effective options exist or are emerging, further research is needed into the reprocessing of smelting slag waste in order to create economic value, improve energy efficiency in metal production, increase critical metal supply, and reduce negative environmental impacts.