A revolutionary hydrometallic process developed by Cominco Engineering Services Ltd. (CESL) for processing copper concentrate is on the cusp of being commercialized by Cia. Vale do Rio Doce (CVRD), which is poised to start up the first commercial-scale plant using the technology before the end of this year.
CVRD's $100-million Usinas Hidro Carajas plant in the Carajas region of Brazil will soon begin refining copper concentrate from its Sossego Mine, with production forecast to reach 10,000 tonnes of copper cathode per year. CESL, a Vancouver, British Columbia, subsidiary of Teck Cominco Metals Ltd., is providing process design, engineering input and startup support, said David Jones, chief metallurgist for Teck Cominco Technology.
CVRD also has plans for a much larger plant with a capacity of between 200,000 and 250,000 tonnes of copper cathode per year that will use the CESL approach to process concentrates from two new mines Salobo and Alemao.
The CESL process is said to offer a myriad of advantages, ranging from an enhanced environmental profile to the ability to treat classes of concentrates not suitable for traditional smelter refining.
One of the process' biggest benefits, Jones said, is its elimination of the sulfuric acid by-product, which results in lower production costs and reduced environmental risk. Smelting copper produces about 3 tonnes of sulfuric acid for every 1 tonne of copper produced, he explained, and a large smelter can store only a few days of by-product acid on site. It must be disposed of regularly and there must be a nearby, ready market for the acid.
"As a result, smelter economies are tied to the market for sulfuric acid," Jones said. "The hydromet process allows the de-linking of sulfuric acid disposal from copper production."
Besides lowering any potential environmental risk, the hydromet process also allows for significant freight cost savings. Since a smelter must be located to provide convenient disposal of the acid, it generally is far from the mine supplying concentrates, which translates to significant freight costs to transport the concentrates to the smelter plus the cost of moving the acid for disposal. With the CESL process, the copper refinery can be located close to whatever mine is supplying the concentrates, eliminating the freight costs to ship concentrates as well as those incurred to move acid for disposal.
Versatility is another key asset of CESL hydromet, which is capable of refining concentrates that might not be suitable for smelting using more conventional technologies. "Hydromet could lead to processing material which might not have been smelted," Jones said. "There have always been quite a lot of low-grade concentrates which may not have been economical to treat." The process can handle concentrates with a copper content as low as 20 percent, Jones said, whereas smelters prefer levels closer to 40 percent.
The hydromet process also is well-suited for processing bulk concentrates that contain more than one metal. While copper is frequently found in company with nickel, zinc or even gold, smelters are designed to recover one metal at a time. Indeed, Jones said that in some cases a penalty is assessed for contained nickel or zinc in copper smelting.
"Typically, bulk concentrates have held limited market appeal to smelters because smelters are designed to recover one metal or another, not both," Jones said. "The hydromet process unlocks the possibility of processing previously unprocessable bulk concentrates. Metals can be recovered simultaneously, which is a huge advantage." CESL is now in the process of piloting a nickel-recovery circuit for its hydromet process, he added.
The CESL hydromet process also opens the possibility of refining so-called "dirty concentrates"—material that contains deleterious impurities, including mercury and arsenic, the two most commonly found impurities. Smelters can't process dirty concentrates, Jones said. "Some mines which were never developed due to impurities are now developable, because the impurities are transparent to the hydromet process; they pose no trouble."
Developing the CESL hydromet process has been no small task for Teck, which to date has spent more than $100 million on research and development and is now plowing another $20 million annually into the project.
There are currently 140 employees working on the project, and Teck has had more than 1,000 students involved in the effort over the past 12 years, during which the company has been testing concentrates from all over the world to fine-tune the process. "We have pretty exhaustive test data," Jones said. To run the tests, CESL has been using both a pilot plant with a capacity to treat about 150 kilograms of copper concentrate daily and a larger demonstration plant that can treat up to 5 tonnes of concentrates per day.
While the CESL hydromet refining process holds significant promise, the program is just now reaching commercial potential and is not likely to affect copper markets for some time. "It won't change the supply-demand balance," Jones said. "This is a long-term project."