METHOD FOR DEFLUORINATION AND ISOLATION OF ANHYDROUS SODIUM SULPHATE FROM WORKING GAS CLEANING SOLUTIONS OF ALUMINUM ELECTROLYSERS Russian patent published in 2021 - IPC C01D5/00 

FIELD: defluorination.

SUBSTANCE: invention relates to method of defluorination and separation of anhydrous sodium sulfate from circulating solutions of wet gas cleaning of aluminum electrolyzers. Method includes causticizing the soda-sulphate circulating gas purification solution, which is carried out with milk of lime prepared on the initial soda-sulphate solution, dosing active CaO in the form of milk of lime into the soda-sulphate solution in an amount of 110-120% of active CaO from the stoichiometrically necessary for the causticization reaction of sodium bicarbonate and soda, and binding fluorine from sodium fluoride to fluorite. Resulting purified sulphate-caustic solution is alkalinized with a circulating mother liquor sulphate-caustic solution and evaporated to a caustic alkali content of Na₂O_ky = 90-100 g/l, while anhydrous sodium sulfate precipitate is isolated from one stripped off sulfate-caustic solution, and one stripped off sulfate-caustic solution is returned for gas cleaning. Precipitated of calcite CaCO₃ and fluorite CaF₂ separated from the sodosulfate circulating solution is washed and filtered, thus obtaining a washed precipitate of calcite CaCO₃ and fluorite CaF₂ and an alkaline filtrate, which is returned to the wet gas cleaning of off-gases from the electrolysis process.

EFFECT: reduces the amount of waste from electrolysis production due to the processing of waste gas cleaning solutions for high-quality sodium sulfate and calcite sediment CaCO₃ and fluorite CaF₂.

1 cl, 1 tbl, 1 dwg