Solid waste incineration produces millions of tons of fly ash that ends up in landfills. But it often contains a large number of valuable metals such as zinc. A new method from scientists at the Chalmers University of Technology will help in extracting them.
During waste incineration, flue gases are purified, and fine particles are separated, resulting in fly ash formation. It contains toxic substances, dioxins and, therefore, usually classified as hazardous waste and disposed of in landfills. But it also contains valuable metals such as zinc, which are lost during disposal.
But a new method at the Chalmers University of Technology, tested and refined over several years of research, involves treating this waste with acid to separate zinc from fly ash. The zinc can then be extracted, washed, and processed into raw materials.
“In our pilot study, we found that 70% of the zinc present in fly ash can be recycled. Zinc is recovered not as a pure metal, but as a zinc-rich product that is useful in the metallurgical industry, ”explains Karin Karlfeldt Fedier, associate professor at Chalmers University of Technology and researcher at recycling and disposal company Renova AB.
By further improving the method, the researchers were able to reduce the toxicity of the waste significantly.
“After extracting the metals, we burn the residual ash again to break down the dioxins. 90% of this ash is then converted into bottom ash, which, for example, can be used as a building material, ”explains Karin Karlfeldt Fedier.
“Fly ash zinc recovery technology can have several beneficial effects, such as reducing the need for primary zinc extraction, lower ash toxicity and a significant reduction in landfill volumes,” concludes Sven Andersson, Adjunct Professor at the Chalmers University of Technology and Research Manager and developments by Babcock & Wilcox Vølund AB, a flue gas cleaning company.