Analysis of the Performance and Mechanism of Phosphorus Removal in Water by Steel Slag

Abstract

In view of the significant differences in phosphorus removal processes by different steel slags, electric furnace slag was taken as the research object to discuss the effects of environmental factors, including the adsorption time and adsorption temperature, on phosphorus removal and to verify the phosphorus removal performances of steel slag for phosphate, pyrophosphate, and actual water bodies. With the help of spectral techniques including scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), X-ray fluorescence spectroscopy(XRF), and an X-ray diffractometer(XRD), the phosphorus removal mechanisms of steel slag were explored. Moreover, the phosphorus removal abilities of different absorptive media of steel slag, ceramsite, and zeolite were compared, and the safety performances of phosphorus removal by steel slag were evaluated. The results showed that the adsorption time significantly affected the phosphorus removal efficiency of steel slag. The phosphorus removal efficiencies of phosphate solutions with a concentration range of 1-20 mg·L-1 using steel slag could reach over 97% when the adsorption time was 30 min. The effect of temperature on phosphorus removal by steel slag was not significant. The pyrophosphate adsorption capacity of steel slag was weaker than that of orthophosphate, and the removal rate of pyrophosphate with an initial concentration of 3 mg·L-1 was 82.45%. Spectral analysis showed that the mechanisms of phosphorus removal by steel slag were chemical adsorption assisted by physical adsorption, and calcium-phosphorus was the main precipitate component. CaHPO4·2H2O was the main precipitate. Steel slag exhibited excellent phosphorus removal properties for removing phosphorus in the biological pond effluent and wetland system, achieving total phosphorus removal rates of 98.36% and 93.33%, respectively. In comparison, the phosphate removal performance of steel slag was better than that of ceramsite and zeolite, and the removal efficiencies of PO43- were 96%, 40%, and 10%, respectively. The contents of heavy metals in the leaching solution of steel slag met the requirements of the Class I standard of surface water; thus, the steel slag was safe and reliable.