Metsä Fibre is actively looking for new uses for the green liquor dregs that results from pulp production.
The research is driven by the company’s sustainability goal of making 100 per cent use of its production side streams by 2030.
One potential use for green liquor dregs is in making geopolymers, materials produced from industrial side streams that can replace concrete. The dregs act as the alkali activators required in the process.
One of Metsä Fibre’s research programmes is being carried in collaboration with the University of Oulu. Their joint MIMEPRO project, currently underway, explores the utilisation and commercialisation of industrial side streams as well as geopolymers. The project was launched in 2020.
The work is ongoing, but promising results have already been obtained with green liquor dregs.
“We used them to replace varying amounts of the commercial activator in the geopolymer formula,” says Professor Mirja Illikainen, from the University of Oulu, who heads the research.
“We found it was possible to replace 40 per cent of the original activator with dregs.”
Metsä Fibre and the University of Oulu are also collaborating on a project in which green liquor dregs are used to produce artificial stone. Illikainen explains that this is a simpler task than replacing concrete. The dregs are used as a binder and activator in this production process, too.
“In granulation, green liquor dregs and other side streams are made into small granules that can be used as material for artificial stone.”
The granules can be used as stone for earthworks or as a replacement for gravel in concrete.
Outi Poukka, Development Manager at Metsä Fibre, says that as part of the research collaboration, the production of artificial stone material was piloted in summer 2021 with JTP-Industria, a company in Ostrobothnia, Finland. A larger volume of geopolymer granules was produced during the pilot project.
“The project is still underway, but we found that granulation is feasible on a larger scale.”
This means that the formula, which was originally developed in a laboratory environment, also works for industrial production and that artificial stone material is a potential use for green liquor dregs. More development work will be required before the product is ready.
Metsä Fibre is conducting active research and development on many fronts and will continue to collaborate with various partners in the coming years.
“The Fibre and Particle Engineering research unit at the University of Oulu is extremely good and has a great deal of competence in geopolymers. We have found a good partner for our projects,” says Poukka.
Interest in the circular economy drives development
Professor Illikainen from the University of Oulu explains that the development of geopolymers is driven by interest in the circular economy and the effort to save natural resources. It is also significant that geopolymer emissions of carbon dioxide are up to 80 per cent less than from concrete, imposing a smaller load on the environment.
Simple products made of geopolymers, such as garden stones, are already on the market, and development is ongoing.
However, recycled materials are still novel from the perspective of legislation. As Illikainen points out, standardisation and clearer regulation are required for the materials to become more common in construction.
Poukka adds that the use of recycled materials still calls for more planning than the use of virgin materials. Nevertheless, she is confident that geopolymers will gain in popularity. Illikainen agrees:
“I see no obstacle to these products being launched in the next few years. As for geopolymers, we are on the verge of commercialisation, if not there yet.”
What are geopolymers?
- Geopolymers are materials that can be used to replace materials like concrete. They are also a practical example of the circular economy.
- Mineral side streams from metal processing, the mining industry and the energy industry can be used as binding agents for geopolymers. Millions of tonnes of such side streams are generated in Finland annually.
- Green liquor dregs can be used as an alkali activator to strengthen the binding agent. They are less expensive than commercial alkali activators and have lower carbon dioxide emissions.