Canadian smelters succeed in clearing the air

There is one clear winner in the effort to cut mining-related sulphur dioxide emissions — the air itself over much of Canada.

For example, between 1950 and 1972, sulphur dioxide emissions from the Sudbury, Ont., smelters alone totaled 2.2 million tonnes annually. From 1979 to 1985, it fell to 600,000 tonnes. And further reductions are on the way. This has led to noticeably fresher air in the Sudbury region, less acidic lakes and healthier forests. Fossil fuel-burning power plants and smelters all across Canada are making similar progress.

The federal and provincial governments have been working for two decades to curtail acid rain. The gains are costly, however. Regulations have, according to federal estimates, forced large sulphur dioxide producers to invest about $1.7 billion between 1987 and 1994 to reduce emissions. Inco alone has spent more than half a billion dollars on its sulphur containment projects during that time.

In the early 1970s, industries were coming under government pressure to cut airborne pollutants. Inco’s first major initiative, the 381-metre superstack built in 1972, replaced a large number of shorter stacks at its Copper Cliff nickel smelter. Local sulphur deposition has decreased by as much as 75% since then.

Today, each province sets a sulphur dioxide limit for individual smelters, power plants and others within its borders. Inco must live with a 265,000-tonne limit in Ontario, beginning in 1994. The company approached the problem as one of sulphur containment in the concentrator as well as in the smelter. Its efforts are impressive: immobilization of 90% of the ore-bound sulphur so that it can never generate acid rain.

Building on its Ontario success, Inco is implementing similar pyrrhotite-rejection processes and smelting changes at its Thompson, Man., nickel smelter.

Inco’s Sudbury Basin neighbor, Falconbridge, is also subject to a provincial emissions order — in its case, 100,000 tonnes. Falconbridge, too, has made significant changes to its nickel smelting process, lowering sulphur dioxide emissions by 43% between 1980 and 1991. In fact, in 1991 only 70,000 tonnes of sulphur dioxide escaped its plant. Further improvements are expected to maintain that level.

Falconbridge’s Kidd Creek division in Timmins, Ont., does not have a provincially regulated emissions limit. The copper smelter, which was commissioned in 1981, features modern, continuous smelting and a modern acid plant. From the outset, it has been a very clean operation.

In Manitoba, Hudson Bay Mining & Smelting has installed a new zinc pressure leaching system and altered its smelting practice in an effort to meet its 220,000-tonne limit by 1994. Together, these projects should cut emissions by 25%. Sulphur is captured during leaching as a sludge rather than being blown into the atmosphere, as is the case in high-temperature conventional smelting. The copper refinery will undergo updating, as well. Noranda Minerals operates two copper smelters in Quebec: Horne at Rouyn-Noranda and Gaspe at Murdochville. These plants have been assigned limits of 165,000 tonnes and 65,000 tonnes, respectively. Careful management cut sulphur dioxide emissions from the Gaspe smelter by 51% during the 1980s. At Horne, the drop has been even more dramatic — a 70% reduction achieved when Noranda installed an acid plant and improved various other aspects of its process.

All these improvements began in the 1970s when Ontario first began to take an interest in reducing the sulphur problem. The province set

“point-of-impingement” standards to reduce the amount of sulphurous compounds falling to the ground. But emission levels remained higher than desirable. In 1985, Ontario introduced control orders setting sulphur dioxide limits for the four major sources within its boundaries. The limits have been reduced since then and are still reviewed periodically.

“Our first priority now is the monitoring of progress and compliance with the orders,” said Walter Chan of the Ontario Ministry of Environment’s air resources branch.

By the end of the 1970s, Canada and the U.S. agreed to exchange information, co-ordinate research and develop an acid rain database. As more became known about the problem, it was realized a common solution must be sought. Both countries signed a memorandum of intent in 1980 and pledged to enforce air pollution legislation.

Canada established its own sulphur dioxide control program covering the seven eastern provinces in 1985. It called for reducing emissions 40% to 2.3 million tonnes by 1994 from more than 3.8 million tonnes in 1980. Individual agreements were signed with the provinces over the next three years. The provincial limit is referred to as a “bubble,” and it is the province’s responsibility to set levels for individual sources which, when totaled, do not exceed the bubble. The limit for Ontario in 1994, for example, is set at 885,000 tonnes.

With Canada’s previous commitment in mind, negotiators began in the late 1980s to write a definitive Canada-U.S. air quality agreement, binding on both countries. It was signed on March 13, 1991, by Prime Minister Brian Mulroney and President George Bush.

Canada, using the 1985 figures, is committed to maintaining a limit of 2.3 million tonnes per year from the eastern provinces. A permanent national cap of 3.2 million tonnes by the year 2000 was also set. The U.S. will cut sulphur dioxide emissions by a corresponding 40% from the 1980 level. The U.S. cap of 8.9 million tonnes is to be reached by 2010.

The air quality agreement also sets limits for concentrations of specific air-borne pollutants, either in parts per million or micrograms per cubic metre. Both countries have been relatively successful in meeting these targets.