EDITORIAL PAGE — The SX-EW alternative

For conventional producers of copper, especially those at the high end of the cost curve, SX-EW is a dirty word. Their antipathy toward the process is well founded because, on average, it is much cheaper than the older, conventional means of producing copper cathode.

SX-EW — an acronym for solvent extraction-electrowinning — got its start at the Bluebird mine in Arizona in 1968. Over the next 10 years, another seven projects that incorporated the technology were brought on-stream. And since the late 1970s, SX-EW has won still more converts as another 26 projects entered production. Currently, 31 such projects are at the feasibility or development stage and another six are under construction, according to William Pincus, an executive vice-president of Pincock Allen & Holt, who reviewed the history of SX-EW in Metal Bulletin Monthly’s May “Copper Supplement.”

In 1980, the process accounted for 230,000 tonnes, or 2% of total copper output from market-economy countries. Today, it accounts for 10% of copper metal production. By the turn of the century, Pincus predicts, SX-EW could represent 15% of world production.

SX-EW’s impressive gains have everything to do with its affordability, with direct operating costs estimated to be US37 cents per lb. To get a handle on the cost advantage inherent in that number, consider that the average operating cost for copper produced conventionally (i.e., through concentration, smelting and refining) is US60 cents per lb. There is no question that this technology is at the low end of the cost curve for copper producers — and there’s no question the technology has forced high-end operators either into severe cost-cutting measures or out of the market entirely.

The process, which is relatively simple, involves three stages: acid leaching of ores in old dumps or (in the case of heap leaching low-grade gold ores) new ore heaps; solvent extraction of copper from leach solutions; and electrowinning to produce copper cathodes.

But not every copper orebody can benefit from the technology. Ore mineralogy is key. Copper oxide minerals (excluding cuprite) and the sulphide minerals chalcocite and covellite are amenable to SX-EW. While oxides generally produce better recovery rates, sulphide recoveries can be enhanced by bacteria that promote oxidation.

In Canada, the technology is rare, mostly because copper orebodies here are of the wrong mineralogical type. The Gibraltar mine in British Columbia is the sole operation, relying on SX-EW for at least part of its production (5,500 tons per year). The Williams Creek project in the Yukon (a joint venture between Western Copper Holdings and Thermal Exploration) could become the country’s second SX-EW operation, if the deposit is developed. However, Pincus’s study notes that Canadian companies are taking advantage of the technique with regard to offshore orebodies. For example, in various stages of development or feasibility are three Chilean projects that will incorporate SX-EW as part, or all, of the production process — Quebrada Blanca (owned jointly by Teck, Cominco, ENAMI and SMP); Collahuasi (Falconbridge, Shell and Minorco); and Zaldivar (Placer Dome and Outokumpu). In Mexico, junior Exall Resources has pegged its Santo Tomas property as an SX-EW operation (if a feasibility study now under way grants the project a green light).

There is no doubt that, with its low cost, the SX-EW process will continue to be the preferred processing method wherever mineralogy makes it possible.