An international team of scientists from GEOHI RAS, UrFU, Lomonosov Moscow State University and Tongji University (Shanghai, China) presented a breakthrough resource-saving technology for producing aluminum polyoxychloride from fly ash from coal-fired power plants. The developed method solves two acute environmental problems: the disposal of millions of tons of hazardous waste and the production of a sought-after chemical reagent for water treatment.
The technology is based on preliminary mechanical activation of the ash and subsequent firing with ammonium sulfate. Optimization of the parameters (activation for 60 minutes, firing at 450 °C for 30 minutes) made it possible to achieve a high degree of aluminum extraction — 78.6%. Then, calcium is removed from the treated substance. Scientists have proposed adding calcium hydroxide to the acidic leaching of the burnt product, as a result of which more than 95% of calcium is deposited as anhydrous anhydrite. The high-purity alum obtained from the purified solution is used to synthesize a nanopowder of amorphous aluminum hydroxide with a high specific surface area, which dissolves in hydrochloric acid to form aluminum polyoxychloride.
"Our approach combines a deep fundamental study of the mechanism of opening ash with ammonium sulfate with applied engineering. We have not only increased the extraction of aluminum, but also found an effective solution to the calcium problem, which opens the way to scaling the technology," said the project manager, a leading researcher at the Laboratory of Sorption Methods of GEOHR RAS, Candidate of Technical Sciences Dmitry Valeev.
The results showed that about 0.58 tons of powdered aluminum polyoxychloride with an aluminum oxide content of 30% can be obtained from one ton of ash.
According to the researchers, the developed scheme offers a practical way for large-scale ash disposal in a closed-loop economy, contributing to both the environment and resource security.
The study was carried out with the financial support of the Russian Ministry of Education and Science.
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