SUPER CONDUCTORS

Denison Mines of Toronto has found itself in a happy situation thanks to some new technology. An efficient extraction method called solvent extraction and a revolution in solid-state physics could boost demand for yttrium over the next 10-15 years. Last year the company got back into the yttrium business by commissioning a new $10-million plant in Elliot Lake, Ont. Five months later, physicists in Zurich, Switzerland, reported the discovery of a ceramic compound that superconducts* at temperatures as high as -245C. This major discovery was followed quickly in February by the discovery of another compound, which superconducts at the even balmier temperature of -183C. Yttrium is one of the three elements that make up this particular ceramic compound. The other two are barium and copper oxide.

What makes the discovery of this latest new superconductor significant is the fact that it can be cooled with liquid nitrogen instead of higher- priced liquid helium. This development could bring superconductors into the market over the next 5-10 years. The first applications will likely be in computers. Although advances in the field are advancing rapidly, work is still in the early stages. Other larger- scale applications of superconductors, which realistically would take 10-15 years to become commonplace, include: the manufacture of electricity transmission lines, electric motors, generators, magnets and electrical storage devices. While it is still too early to tell whether or not yttrium will be the element of choice in the commercial use of superconductors, its potential has producers of yttrium concentrate, like Denison, very excited.

The highly computerized plant at Elliot Lake, which cost slightly more than $10 million, has been recovering yttrium at a rate slightly below its design capacity of 150 tonnes a year. Recoveries were supposed to be 85%. But with some bugs yet to be ironed out, that level has yet to be reached. The plant has been running for about nine months.

Yttrium occurs naturally in Denison’s uranium ore and is being recovered as a by-product from the barren solution that comes from the company’s ion exchange plant. (Yttrium producers in China, Malaysia and Australia also produce the rare earth as a by-product of other mining activities. There are no primary producers.) This solution, which is produced at a rate of 400 cu m per hour, would normally go to the tailings pond. In the 1970s Denison recovered yttrium from this waste stream using an old centrifugal method. But a technological breakthrough in the way yttrium is used with europium to produce a more brilliant picture in color television picture tubes increased the efficiency of this application. However, owing to the change in application, demand for the rare earth dropped significantly. The market subsequently went soft and production at Elliot Lake, using a centrifuge, became uneconomic.

In 1985 Denison, Molycorp Inc. of Colorado (through its parent company’s Canadian subsidiary, Unocal Canada), Shin-Etsu Chemical and Mitsui & Co. (both of Japan) struck a deal to finance construction of a new plant, using updated solvent extraction technology. The four companies developed the chemical processes and Denison agreed to operate the plant.

The version of the solvent extraction process, developed by the consortium, works by mixing the ion exchange barren water with kerosene. By adding certain chemicals, which the company prefers not to specify, and allowing the mixture to settle into two phases, the kerosene floats to the top and the water drops to the bottom. By adjusting the acidity of the water, it is possib le to have the yttrium pass from the water into the kerosene or vice versa. The solution is treated in three stages to concentrate the yttrium and remove undesirable contaminants such as uranium and thorium. The kerosene is recirculated, some uranium goes back to the uranium plant and the waste water is pumped to the tailings area. Yttrium, in its oxide form (Y2O3) is precipitated from the resulting water solution by raising the ph. It is then filtered using drum filters, dried and packed into drums. The final product grades about 40%-50% yttrium.

Half of the concentrate is sold to Molycorp in the U.S. while the other half goes to the Japanese consortium members. They refine the material to 99.99% pure yttrium and sell it to end users. Molycorp, for example, sells its high purity yttrium for $32.50(US) per lb. Once the capital costs of the Elliot Lake plant have been recovered by the U.S. and Japanese partners, Denison will begin participating in the profits generated from sales. Denison is the operator of the plant, which employs 12 people. * A superconductor is a material that conducts electricity, with little or no energy losses, thanks to a very low electrical resistance.