The State of Canada's Environment — 1996 Chapter 11 — Human Activities Minerals, Metals, and Mining Environmental impacts of mining Smelting and refining Sulphur dioxide

Sulphur dioxide

The largest emission source of sulphur dioxide in Canada is smelting of metal concentrates, which contributed 50% of total eastern Canadian sulphur dioxide in 1994. Power generation and other sources contributed 20% and 30%, respectively (Environment Canada 1996a).

There are 10 Canadian primary base metal smelters, producing nickel, copper, lead, and zinc. Their metallurgical processes result in the production of large amounts of sulphur dioxide during the smelting process. Most of these smelters have implemented sulphur dioxide controls that reduce the amount of sulphur dioxide that enters the atmosphere (MacLatchy 1994). Figure 11.31 shows that quantities of sulphur dioxide released from eastern smelters and refineries have been substantially reduced since 1980, as a result of the Eastern Canada Acid Rain Control Program.

Figure 11.31 Sulphur dioxide emissions and base metal production from eastern Canadian base metal smelters, 1980–1994

Reductions have been achieved by a combination of installing new equipment to capture sulphur dioxide for the manufacture of sulphuric acid, upgrading existing equipment for sulphur dioxide recovery, and metallurgical changes to the milling and smelting processes (E. Gardiner, Mining Association of Canada, personal communication). New smelting technologies and processes have resulted in major reductions in sulphur dioxide releases. Figure 11.32 shows the generally decreasing trend in emissions of sulphur dioxide per kilotonne of metal produced at selected smelters in eastern Canada.

Figure 11.32 Sulphur dioxide emissions per kilotonne of metal production at selected smelters in eastern Canada, 1980, 1987, 1992, and 1994ª

The industry is addressing environmental and social concerns related to mining. In 1987, the governments of Canada and Quebec and Noranda Inc. cooperated financially to create a project at Noranda's Horne division to reduce the 1980 emission level of sulphur dioxide by 50% by 1990. This project cost in the order of $83.2 million and permitted a reduction of sulphur dioxide emissions from 550 kt in 1980, or 1 507 t/day, to 156 kt in 1995, or 427 t/day. Additional investments are predicted to reduce sulphur dioxide emissions to around 40 kt/year to meet the new Quebec standards that will be in place by 2002 (G. Houle, Direction des politiques du secteur industriel, Ministère de l'Environnement et de la Faune du Québec, personal communication).

Another notable example of industry response was the $600 million modernization of Inco's Copper Cliff smelter near Sudbury, Ontario, over a five-year period from 1988 to 1993. This modernization involved the rejection of iron sulphide in the milling process. State-of-the-art smelting furnaces using oxygen instead of air and new sulphuric acid and liquid sulphur dioxide plants have resulted in a major reduction in sulphur dioxide releases. The operation's sulphur containment has increased from 70% to 90%, and Inco is marketing the recovered sulphur dioxide as sulphuric acid. The investment in improved technology has benefited the environment and also substantially reduced the company's annual energy costs.

Also in Sudbury, Falconbridge Ltd. has reduced its sulphur dioxide emissions to the point where it can operate its smelter at 100% capacity, yet remain below the provincial sulphur dioxide limits. In 1993, Hudson Bay Mining and Smelting at Flin Flon, Manitoba, began operation of its oxygen pressure leach zinc plant. This technology reduced sulphur dioxide emissions from the zinc plant by recovering sulphur as a solid waste. In Trail, British Columbia, Cominco Ltd. is proceeding with a new lead smelter and slag plant that will reduce lead emissions by some 70–80% (McLellan 1995).

Internationally, the federal government, with provincial support, is active with the United Nations Economic Commission for Europe (UN–ECE) on atmospheric issues. In June 1994, Canada signed the Second UN–ECE Sulphur Dioxide Protocol, which commits Canada to cap sulphur dioxide emissions and to work towards critical loads (the level of acidic deposition that causes insignificant environmental harm). Canada is participating in UN–ECE negotiations on a second nitrogen oxide protocol and will take part in negotiations on potential protocols for persistent organic pollutants and for heavy metals.

Bilaterally, the Canada–United States Air Quality Agreement, signed in 1991, committed Canada to cap national sulphur dioxide emissions at 3.2 million tonnes annually (from 4.6 million tonnes) by the year 2000 and to cap eastern Canadian sulphur dioxide emissions at 2.3 million tonnes annually between 1994 and 2000. By 1994, industry had exceeded the target, reducing emissions to 1.7 million tonnes. The United States also committed to reducing sulphur dioxide emissions by 40% from 1980 levels. Despite these successes, acid rain will continue to be an issue in the next century. As a result, Canada is considering further sulphur dioxide emission reductions (Government of Canada 1996).

The economic impact of controlling airborne pollutants in the metals industry has been generally positive. The introduction of technologies that reduce sulphur dioxide emissions has generally improved productivity and reduced operating costs, while controlling airborne pollutants.