Is it possible to reduce arsenic emissions from the Horne smelter to “acceptable levels”, as demanded by health authorities, without having to close up shop altogether? It’s all about cost, say metallurgy specialists.
The stakes are high: the foundry located in Rouyn-Noranda produces 200,000 tonnes of copper anodes each year – a metal essential to the energy transition – whose value varies between 2 and 3 billion. The ore used comes from all over the world.
However, its polluting emissions give lung cancer to the local population. The foundry, which belongs to the multinational Glencore, currently benefits from a special permit allowing it to emit 30 times more arsenic into the air than the Quebec standard, which is 3 ng/m3.
A first option to reduce arsenic emissions would be to simply accept “cleaner” copper ore. However, the scarcity of good quality deposits on Earth has meant that, over the past 20 years, copper ore has become increasingly rich in arsenic.
Also, for smelters, it is more profitable to process these “complex” ores, rich in arsenic, because they can impose additional costs for their services, explains Jean-François Boulanger, a professor in extractive metallurgy of critical and strategic elements. at the University of Quebec in Abitibi-Témiscamingue.
“How far will Glencore go to process cleaner concentrates and make less profit? It’s hard to say,” says Mr. Boulanger. Only a handful of facilities worldwide, including the Horne smelter, process arsenic-rich ore, according to a 2019 McKinsey analysis.
Modernization in progress
The Horne smelter can also reduce its arsenic emissions by capturing the gases and dust emitted by its activities, or by preventing their dissemination from the vats. Essentially, it is on this strategy that Glencore is currently betting.
In a copper smelter, ore is heated to very high temperatures in a series of reactors to separate copper, iron and sulphur. Arsenic is an impurity in the ore. The extreme heat of the reactors causes it to volatilize. As it cools, arsenic vapors can condense and create toxic dust.
Some Horne Foundry reactors operate continuously. Their emanations can therefore be channeled and sucked up without interruption. Other reactors must periodically be loaded and unloaded with molten metal. These manipulations generate “fugitive” emissions which, according to Glencore, are considerable at the Abitibi plant.
The company presented in 2020 an update of its action plan to reduce emissions from the Horne smelter. Several measures are detailed there, including the VELOX/PHENIX project to modernize metallurgical vessels (high temperature reactors), requiring investments of 170 million.
This project, which is already underway, consists of replacing certain old metallurgical vessels, for which gas capture was difficult, with modern vessels, in cast iron, with a higher level of sealing. This new equipment also reduces handling, which reduces fugitive emissions. In all, this project would reduce arsenic emissions by 10 to 15%.
Other projects concern the capture of fumes floating in the plant. This is to filter the air that passes through the roof vents of the building. Glencore expects short-term reductions of 8-20% of arsenic emissions through these means. Other measures aim to reduce the exposure of the population to contaminants by acting outside the walls of the foundry.
“It’s certain that their plan will help,” said Philippe Ouzilleau, a professor of metallurgy at McGill University. The question, really, is how much it will reduce arsenic emissions. Will they reach 60 or 20 ng/m3? Unfortunately, it’s impossible to say at this time. »
“A long way to go”
To go beyond the current – rather “classic” – strategy, the owners of the Rouyn-Noranda foundry could consider more sophisticated metallurgical processes, based for example on activated carbon. Some approaches developed by the iron industry could be transferable to the copper industry, believes Mr. Ouzilleau.
“It’s all about cost: how much are you willing to pay to reduce arsenic? ” he asks. Investments will thus depend on the target set by the government for arsenic emissions. If the existing methods do not make it possible to reach it, other technologies can always come in reinforcement.
The VELOX/PHENIX project constitutes a “good effort”, also says Jean-François Boulanger. “But let’s say that there is a long way to go between what some are asking for – the Quebec standard of 3 ng/m3 — and the potential of this one solution. He believes a range of avenues, including new ones, will need to be considered to get there.
Mr. Boulanger has just applied for funding for a research project that could help reduce arsenic emissions from the Horne smelter.
This is a chemical pre-treatment of the copper concentrate, before it enters the smelter, during which critical elements, such as tellurium and antimony, would be recovered. The process would also make it possible to extract arsenic. “We can give a push to remove some of the arsenic,” says the professor.
The Horne foundry is one of three industrial partners in this research project. An American factory has already used this process in the past, but no foundry currently integrates it. In the best of scenarios, an industrial deployment in Rouyn-Noranda would take place within ten years.