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The transformation of copper slag

The safe disposal of copper slag-- the process of converting copper sulphide ores into refined copper, through crushing, flotation, smelting and conversion— has been a universal problem among copper manufacturers for centuries.

That challenge may not lost much longer. A study released on January 19, 2024, in the “Transactions of Nonferrous Metals Society of China”  presents a novel method for the recovery of copper, lead, and zinc from copper smelting slag using a novel sulfurization-reduction approach. Titled “Synergistic recovery of copper, lead and zinc via sulfurization–reduction method from copper smelting slag,” it represents a significant stride in metallurgical waste management, with potential impacts on both industry practices and environmental sustainability. (1)

After all, this slag contains valuable metals like copper (0.5%–6%), lead (0.2%–0.6%), and zinc (1%–5.5%), which if not recovered, results in resource waste and environmental hazards from leaked toxic ions. Nearly 20 million tonnes of primary copper is produced worldwide every year, generating 45million tonnes of slag. Thus, every ton of refined copper manufactured generates around 2.2 to 3 tons of slag. (2). Moreover, the copper slag occupied vast tracts of land, which could be used for more productive activities such as farming and other industrial ventures.

While the recent study opens new avenues for the recycling of copper slags, earlier attempts at reducing its adverse environmental impact has shown impressive results. The slag is an effective replacement for sand for cement manufacturers, a great boon for India, which suffers from an increasing scarcity of river sand and natural aggregates for cement manufacturing.

Moreover, in states like Kerala, Maharashtra and Gujarat, where sand mining in rivers is banned, it offers a great alternative material for cement industries. Use of copper slag or ferro slag reduces cement cost as it is either free or priced very cheap. Second, it helps cement manufacturers meet their emission targets because it is highly stable and is non-toxic in nature.

“Copper slag have also been used as abrasives --polishing and cleaning-- of metallic structures and in the building industry, for manufacturing concrete material with fine particles, as basic construction materials. More recently, it has been used as a filler in glass–epoxy composites, a fine advanced material, which is used in many industries like electrical insulators in induction systems, static electrical insulators in power installations, construction of electric furnaces, induction furnaces and arc furnaces, high-voltage switchgear etc,” argues *Aruna Sharma economist, former Secretary in the Ministry of Steel and Electronics and Information Technology.*

Thus, both recovery of materials from copper slag and recyclability presents an attractive solution for reducing waste and greenhouse gas emissions, as well as promoting the concept of circular economy through effective waste utilisation. Moreover, as a secondary source of valuable metals, copper slag retains its intrinsic value for use in different industries.