Abstract: In the process of soda production，usually the ion concentration of sulfate in the raw material brine is too high and needs to be removed. In this work，the steamed ammonia wastewater（the main component is CaCl₂） was used to remove SO₄^2- from brine，meanwhile producing CaSO₄ by-product.On the premise of guaranteeing the removal efficiency of SO₄^2-，polyacry- lamide was added to the reaction system as a flocculating agent to improve the sedimentation rate of calcium sulfate effectively in the process.The effects of the type，relative molecular mass，dosage of polyacrylamide，temperature，pH，and stirring time on sedimentation were investigated，and the sedimentation effects of several common flocculants were also compared.Results showed that the optimal experimental conditions were as follows：the temperature was 50~60 ℃，pH was at 4~8，stirring time was 30 min，and the relative molecular mass and dosage of anionic polyacrylamide were 1.2×107 and 20 mg/L，respectively.It can greatly reduce the sedimentation time of calcium sulfate particles and improve the production efficiency.

Key words: sulfate radical, removal, polyacrylamide, calcium sulfate, sedimentation