Slag use at cement plant raises more air concerns

The Holcim Trident cement plant near Three Forks, Montana in the US is drawing more criticism for its use of industrial waste, this time slag imported from a Canadian lead and zinc operation. The Montana Environmental Information Center says firing metals-laden waste from a British Columbia smelter raises even more concern about hazardous air pollution than does Holcim’s use of slag from an old smelter at East Helena.

Holcim says buying slag, to get iron for cement production is cheaper and more environmentally responsible than using mined iron. Smokestack tests show slag from the Teck Cominco Ltd. smelter at Trail, British Columbia, burns "even cleaner" than slag from the defunct Asarco Inc. lead smelter in East Helena, said Nicole Prokop, alternative materials manager for Holcim.

Hedges cited a consultant’s report, prepared for the Montana Department of Environmental Quality, that found the Teck Cominco slag has some heavy metals at levels three to five times higher than Asarco’s waste. But what is in the slag is different from what puffs out of the smokestack, Prokop said. "Even if there are higher metals in the raw material, it gets incorporated into our (cement) product," she said, adding some of the metals in the Teck Cominco slag are higher than in Asarco’s, and others are lower.

The state agency recently received the analyses of the Canadian and East Helena slag content. Now DEQ is awaiting a toxicologist’s report to help assess how Holcim’s use of slag could affect human health and safety. Following up on use of the Asarco slag, the agency learned this spring that Holcim had used the Canadian slag, as well, Opper said. "At the very least, DEQ should be putting the brakes on," Hedges said.

Prokop said Holcim began getting the material from Canada a couple of years ago and used about 1000t of it in 2004. None has been used this year, she said. The Asarco slag better met Holcim’s recent needs, she said, but the Canadian slag is on hand at the cement plant and "it’s there to be consumed." She said Holcim also uses mill scale, that is brought from Washington.

Because DEQ has been focusing attention on the slag issue, agency review of another endeavor proposed by Holcim is on hold. The company wants to burn old tyres as a source of kiln fuel, raising still more air-quality concerns for MEIC and others.