Abstract: The removal efficiency of sulfate from reverse osmosis concentrated water by ettringite method is studied, and the effects of pH value, calcium sulfate ratio n(Ca/S), aluminum sulfate ratio n(Al/S), initial sulfate concentration and other factors on the reaction are explored. The results show that for reverse osmosis concentrated water with a mass concentration of sulfate of 1 015 mg/L, the removal rate of sulfate can be increased to over 80% through the ettringite method. The optimal process parameters are as follows:pH=12.0, n(Ca/S)=4,n(Al/S)=0.7. The ranking of the impact of the three factors on the experiment is as follows:pH>n(Al/S)>n(Ca/S),with pH being the key factor and playing a dominant role in the treatment effect, followed by aluminum content. This method has significant differences in treatment efficiency for wastewater with different initial sulfate concentration. Within the range of initial sulfate mass concentration of 1 090~1 550 mg/L, as the initial mass concentration of sulfate increases, the removal rate of sulfate gradually increases.The disadvantage of this method is that the mass concentration of residual calcium is relatively high, and subsequently residual calcium can be converted to calcium carbonate by adding sodium carbonate to achieve its resource utilization.

Key words: ettringite(AFt), sulfate, orthogonal test, NaAlO₂