New focus on technology
The big breakthrough for Cominco almost a century ago was discovering how to treat mixed ores of lead, silver and zinc, and recover each metal as a separate refined product. It is therefore not surprising that the company has supported metallurgical research over the succeeding decades.
Renewing their commitment to this area, Teck Cominco’s diverse research groups were brought together at the end of last year to form a technology division under vice-president Dr. John Thompson. This includes the Applied Research & Technology Group at Trail, B.C., and the Product Technology Centre in Mississauga, Ont.
The third group in the division is Cominco Engineering Services Ltd. (CESL), which since 1992 has been dedicated to developing its own hydrometallurgical process for copper and nickel sulphide concentrates as a replacement for the standard smelting process. CESL now consists of about 60 engineers, chemists and technicians (average age 31) under manager Dr. David Jones and operating superintendent Susan Stocker. In March CMJ toured the 5,600-m2 facility in Richmond, B.C., which handles testing at bench, pilot and demonstration plant scales. The demo plant can treat 3-10 tonnes of concentrate to make 1-2 tonnes of cathode copper per day.
The CESL process uses pressure oxidation, solvent extraction and electrowinning to produce LME-grade cathode metal from sulphide concentrates. The process consumes modest amounts of limestone and sulphuric acid; it requires electricity, which is used both to generate oxygen and to plate copper cathodes. About one tonne of oxygen is needed per tonne of copper produced.
The process is much ‘greener’ than smelting: there are no liquid effluents and the only byproducts are solid gypsum and a stable leach residue containing hematite and elemental sulphur. Therefore a plant could be located anywhere, including next to the mill, thus eliminating the shipping cost for concentrates. A CESL plant is expected to cost less to build than a smelter, with approximately the same operating costs.
Where the patented CESL process really shines, though, is in treating copper concentrate that is low grade (down to 18% Cu), bulk (such as mixed copper and nickel), or “dirty” (e.g., containing deleterious impurities such as fluoride, arsenic, uranium or bismuth). These concentrates are difficult or uneconomic to treat by smelting, but can be handled effectively with the CESL process.
Key to the process is the use of chloride ions as a catalyst during pressure oxidation. “We matched SX/EW (invented in the 1970s) with the Noranda process (c.1967) for making ankerite [also known as ‘basic copper sulphate’] in the autoclave, and then we engineered it using titanium vessels because of the chloride corrosion, and tinkered with the filtration and washing systems,” says Jones. “We try to match known technology to the job; we don’t invent it unless we need it, because there’s enough novelty in the front end [of the process].”
CESL has also developed hydrometallurgy for zinc, cobalt and molybdenum concentrates. Precious metals contained in the concentrates can be recovered. Full descriptions of the processes can be found at www.cesl.com.
Hydromet is not new and certainly not exclusive to CESL, but CESL is one of the foremost developers and has been continuously supported by Teck Cominco for the past 14 years. CESL has so far investigated over a hundred concentrates, with all but three being successful.
A major project using copper concentrate from the Highland Valley Copper mine, halted in 1998, has recently been restarted. “This is the tenth project that’s shown promise, and has gone as far as a prefeasibility level or higher,” says Jones. “Most of them have been successful at this level technically and financially, but have failed for corporate-political or [metal market] price reasons.”
However, the team is now helping Companhia Vale do Rio Doce build the first commercial CESL plant, to treat copper concentrate from CVRD’s Sossego mine in the Carajs region of Brazil. The US$58-million semi-industrial plant is designed to produce 10,000 tonnes/year of copper cathode over a two-year test period starting in the second quarter of 2007. CVRD is then intending to build a 235,000-tonnes/year plant for two new mines, Salobo and Alemo, which are particularly suited for hydrometallurgy.