COMMENTARY — Caring for the environment

The Prospectors and Developers Association of Canada recently recognized Hudson Bay Mining and Smelting for its environmental initiatives. The company mines and process metals — primarily copper, zinc, gold and silver — in northern Manitoba and Saskatchewan.

HudBay’s former zinc processing plant was constructed at the metallurgical complex in Flin Flon, Man., in the late 1920s. It extracted zinc from concentrate by roasting or burning the concentrate feed and leaching or dissolving the leftover materials into a solution from which zinc metal was electroplated.

The roasting produced “smoke” containing sulphur dioxide gas, which was released into the atmosphere. Roasting and leaching also released gases and vapors into the work environment.

Following extensive research, the company decided to replace this zinc plant with one using safe, modern technology. On Nov. 9, 1993, HudBay officially opened its new plant, which had been in full operation since August of the same year.

The plant employs a new 2-step process which eliminates the roasting stage. Zinc concentrate is ground to sufficient fineness to make it amenable to pressure-leaching. About 75% of the zinc is leached out of the concentrate in the first of three autoclaves. Most of the remaining metals are recovered through a second stage of autoclaving.

The second stage of leaching is what makes the plant the first of its kind in the world. The third autoclave is used for standby. The remaining solids are processed to recover precious metals and marketable elemental sulphur. The process generates no “pollutants” as such (though it does generate waste materials, such as sulphur, iron and gypsum residues which are stored in containment areas), and the change in energy source from fossil fuels to electricity conserves non-renewable energy resources and reduces the production of carbon dioxide (the “greenhouse” gas) . . .

During the past several years, the company has undertaken an extensive program of decommissioning former mining sites. So far, four sites have been completely decommissioned, including one in a provincial park, one on the boundary of a provincial park and one adjacent to a public highway and a popular recreational fishing area.

Seven sites are now in the process of being decommissioned. The company is planning to start work on four more in the near future. Of the mines on the sites, some were only recently closed, while others have been closed for many years.