Metallurgical Recovery of Copper from Smelting Slags

Metallurgical recovery of copper from smelting slags has emerged as a critical component in closing the loop on copper production and mitigating the environmental footprint of pyrometallurgical operations. Smelting slags, rich in iron silicates, copper oxides and sulphides, present both a challenge and an opportunity: their complex mineralogy demands an integrated suite of physical, chemical and biological treatments, yet they contain residual copper grades sufficient to justify secondary processing. Contemporary approaches encompass controlled cooling and modification of molten slag to promote coarsening of copper-rich matte, high-temperature reduction to extract pig iron alloy, low-temperature mechanical activation to enhance reactivity, hydrometallurgical leaching under acidic or ligand-driven conditions, and microbial leaching to mobilise recalcitrant phases. These strategies are underpinned by precise control of slag chemistry—binary basicity, additive dosage and temperature regimes—to tailor phase assemblages, reduce viscosity and optimise phase separation. Beyond metal recovery, treated slags may serve as cementitious raw materials or construction aggregates, exemplifying circular-economy principles. Advances in process kinetics, reactor design and reagent selection are rapidly transforming what was once industrial waste into a valuable secondary resource, with global significance for resource security and greenhouse-gas reduction.

Research from Nature Portfolio

Recent studies have demonstrated that selective reduction of magnetic iron in molten copper slag can markedly decrease viscosity and accelerate copper droplet coalescence. In one foundational investigation, waste cooking oil was employed as a reductant in a smelting-reduction process, converting Fe₃O₄ to fayalite and promoting copper phase detachment. Kinetic modelling revealed a first-order reaction mechanism, with mass transfer of iron oxide through the liquid boundary layer identified as the rate-limiting step. This work highlights the potential of low-cost, carbon-neutral reductants to improve copper recovery efficiency in flash-smelting operations.

Metallurgical Recovery of Copper from Smelting Slags publication trend

The graph below shows the total number of articles in metallurgical recovery of copper from smelting slags across all publications each year (not limited to Nature Index journals).

Technical terms

Smelting slag: A heterogeneous solid by-product formed during copper smelting, comprising oxides of iron, silicon, aluminium, calcium and residual copper minerals.
Fayalite: An iron silicate phase (Fe₂SiO₄) predominant in copper slags, influencing slag viscosity and the partitioning of copper-rich matte.
Hydrometallurgy: Extraction of metals from solid materials via aqueous chemistry, notably acid and ligand-driven leaching.
Mechanical activation: Physical pretreatment of solid particles by high-energy milling to increase surface area, defect density and chemical reactivity.
Bioleaching: Use of acidophilic microorganisms to oxidise and solubilise metal-bearing phases, facilitating subsequent metal recovery.

References

1. Effect of Cooling Rate and Slag Modification on the Copper Matte in Smelting Slag. Mining, Metallurgy & Exploration (2020).
2. Smelting reduction and kinetics analysis of magnetic iron in copper slag using waste cooking oil. Scientific Reports (2017).
3. Selective room-temperature leaching of copper from mechanically activated copper smelter slag. Journal of Materials Research and Technology (2021).
4. Processing of Waste Copper Converter Slag Using Organic Acids for Extraction of Copper, Nickel, and Cobalt. Minerals (2020).
5. A Study on Reduction of Copper Smelting Slag by Carbon for Recycling into Metal Values and Cement Raw Material. Sustainability (2020).