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Tractor with CHAC

Industrial waste is fertile ground

Finding a new use for a by-product of aluminium production

Last updated: 6 December 2024

 

In Canada’s Quebec region, a by-product of aluminium production is helping local farmers correct soil acidity and provide the nutrients their crops need.

The product, CHAC (chaux hydratée aqua-catalysée or aqua-catalysed hydrated lime) offers local farmers a lower-cost local soil treatment, while also finding use for a waste material.

Making the most of waste

It鈥檚 one example of the work our scientists and engineers are doing to create new products from the waste created when producing minerals and metals.

Anodes are essential to making aluminium, but their production generates a waste gas, sulphur dioxide, that can be harmful to people鈥檚 health and the environment.

To prevent the sulphur dioxide being released into the air, special reactors called scrubbers capture and 鈥渃lean鈥 potentially harmful emissions, like gas and dust.

Normally the scrubbing process involves adding a reactant to the gas to create a solid, which is then carefully treated and stored as landfill. Instead, our scientists developed a process to combine lime with the sulphur dioxide, causing a chemical reaction that creates CHAC 鈥 a product that can serve as a safe and effective soil treatment.

Around 17,000 tonnes of CHAC is recycled every year for use in construction and industrial applications. While we have more work to do to remove all waste from our operations, products like CHAC are helping us reduce our impact.

鈥淕iving a second or third life to a material is the way we need to work for the future,鈥 Fran莽ois, Manager, By-Product Valorisation says.

鈥淚f we don't move forward in this way, and if we don't change our way of doing things, we will exhaust our resources.鈥

Tractor distributing CHAC

Ingredients essential for plant growth

CHAC is a mixture of a sulphur compound called gypsum (calcium sulphate) and hydrated lime (calcium hydroxide) – both important ingredients for plant and soil health.

"Calcium is important for the structure of plants' membranes and cell walls," Julie Élize, a RioExpert and R&D Soil Scientist at our Arvida Research and Development Centre, says.

"And sulphur is needed for the synthesis of sulphur amino acids that make up proteins. Both are essential for plant growth.

"The lime in CHAC helps correct soil acidity, which helps farmers optimise their crop yields."

Before it could be used, CHAC was rigorously tested across different soil types and on 15 different crops for performance and safety. It also complies with the standard from the Bureau de normalisation du Québec.

"In the past, cash crop producers in the Saguenay-Lac-St-Jean region of Canada may have been reluctant to lime their soils, as the materials available on the market have often had to come from outside the region, making them very expensive," Julie Élize says.

"Our industrial-scale trials allowed farmers to validate whether they could use our product, at the right dose, with their equipment to offer an alternative local, lower-cost, quality product.”

We recently entered a 5-year partnership with to moisten 5,000 tons of CHAC per year from the Arvida Plant at their Éco-Luzerne plant in Hébertville-Station. They’ll then sell it to farmers, who can use it as a soil treatment in their fields – a locally grown and sourced option.

In November 2024, our CHAC project received the Eureka! 2024 recognition from . The project was for its innovation, potential for reproducibility and contribution to environmental protection.

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