Hydrometallurgy has long been used in mineral processing, leaching metal ions into solution that can be then refined into high-purity metals. Early successes were mainly achieved with oxide mineralisation and secondary sulphide minerals. Hydrometallurgical treatment of primary sulphide minerals has traditionally required an initial pyrometallurgical step to reduce sulphides to oxides using a roaster or kiln. The conventional route from sulphide concentrate to refined metal involved smelting the entire concentrate and releasing the oxidised sulphur as SO2 gas in the process.
A fully hydrometallurgical approach for treating sulphide concentrates could deliver significant benefits. Refining can be performed on a relatively small-scale as part of on-site processing, enabling a mine to achieve vertical integration at a single location from extraction to final metal production. Moreover, producing metal without smelting or roasting eliminates the generation of SO2 gas, offering a cleaner and potentially more sustainable processing route.
Over the past forty years, numerous hydrometallurgical processes have been developed, though few have reached commercial implementation. Commercial-scale success has been achieved with pressure oxidation, used for processing refractory gold ores. This technology has also been applied to base metal concentrate refining, with notable operations at Mt Gordon (Australia, now closed), Sepon (Laos), Kansanshi (Zambia), and Freeport’s Bagdad and Morenci mines (USA). Glencore have deployed several plants utilising the Albion Process™, while reagents- or catalyst-based systems such as the Jetti and Ceibo processes have found use in low-grade, heap leaching applications.
Two pioneering sulphide leach processes have been developed to pilot scale in southern Spain. First Quantum’s Cobre Las Cruces (CLC) operation initially processed the secondary mineralisation cap on a polymetallic deposit through leaching. When this cap was exhausted, the mine transitioned to primary sulphide ore. To maintain on-site refining through copper cathodes, CLC developed the in-house Silver-Catalyzed Atmospheric Leach (SICAL) process, which was successfully piloted on a bulk copper-lead-zinc concentrate from a conventional crush-mill-flotation circuit. The mine is currently on care and maintenance pending permitting and capital approval. Meanwhile, at the Atalaya mine, Lain Technologies’ E-LIX™ process has been advanced to industrial scale to treat polymetallic ores, reportedly capable of producing 10,000 tonnes per annum of copper cathode and currently undergoing commissioning.
Several halide-based leach technologies have also been piloted but not yet commercialised. These include Cominco’s CESL process (which employs fine grinding); the Kell process (which uses an autoclave); and the Halion Loop™ (commonly referred to simply as the “Loop process”), capable of extracting copper, silver and other co-metals without high pressure or noxious gas emissions.
