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One of the methods of alkali metal recovery is causticisation. Sodium or potassium carbonate is mixed with lime hydrate to liberate the lye. In addition to the lye solution, calcium carbonate is formed, which is filtered and deposited as a waste in a landfill. The calcium carbonate thus formed is amorphous and has a flaky structure. This is the cause of a large surface and, consequently, of a high reactivity when reacted with acid gases. Modern combustion plants are equipped with technology to fill emission limits for acidic gases and persistent organic compounds, but the input materials used are based on natural raw materials having a crystal structure and must be crushed into fine particles before use. The use of waste limestone with a different surface structure can be of great potential. The aim of the project is to propose new technologies for the elimination of acid gases and emissions of persistent organic matter, which will be based, together with the addition of activated carbon, to the use of the aforesaid waste calcium carbonate.