The present invention describes a procedure for the removal of sodium sulphate from a phosphate solution that has been used for absorption of SO₂ from flue gases, in which a precipitate forms when the absorption solution is regenerated by evaporation. In this procedure a part of the precipitate is separated from its solution and treated with water and SO₂ for transformation of disodium-hydrogen phosphate into monosodium dihydrogen phosphate in the aqueous solution. The sodium sulphate remains undissolved and is removed by filtration. The filtrate is then added back to the main process.