Study On Efficient And Mechanism Of Phosphate Removal By Zero-valent Iron And Silicified Zero-valent Iron

Phosphorus is an essential nutrient for the growth of animals and plants,and it is also recognized as a non-renewable resource.However,excessive phosphorus in water environment will cause eutrophication,which will lead to algae boom,oxygen depletion in water and fish and other aquatic animals death.The mechanism of phosphate removal by zero-valent iron（ZVI）had basically reached a consensus,including adsorption,chemical precipitation and co-precipitation,but the contribution among them was unclear.In practical applications,ZVI had some problem,such as easily agglomeration,easily surface oxidation and slowly electron transfer speed.Therefore,this study analyzed the magnetic solids and suspended solids in different reaction time,and deeply explored the adsorption and precipitation mechanism of phosphate removal by ZVI.At the same time,ZVI was ball-milled and modified with silica to prepare Si-ZVI^BM,and utilized SEM,EDS,FTIR,XRD,XPS and other methods to analyze materials and products.The specific conclusions are as follows:（1）The phosphate removal efficient and mechanism by ZVI was studied.Phosphate decreased from 100 mg·L^-1 to 9.53 mg·L^-1 in the rapid removal stage,and from 9.53 mg·L^-1 to 0.15 mg·L^-1 in the slow removal stage,and the final removal rate reached 99.85%.Through characterization of reaction products,it was found that the EDS results indicated that the spherical particles contained a large amount of adsorbed phosphate at the beginning of reaction.XPS results showed that the P-O-Fe bond might be formed,demonstrating that the phosphate in the suspended solid transitions from the adsorption state to the precipitation state.ATR-FTIR results cleared that phosphate was firstly adsorbed in the process of phosphate removal by zero-valent iron,and the adsorbed phosphate was slowly converted into phosphate mineral precipitation,proved to be FeH₂P₂O₇ by XRD detection after 3 days of reaction.（2）Preparing of siliconized zero-valent iron(Si-ZVI^BM)with different silicon content ratios.SEM-EDS,XRD,FTIR and other comprehensive characterization results confirmed that elemental silicon was successfully introduced into the zero-valent iron surface during the ball milling process.The optimal silicon molar ratio of the Si-ZVI^BM was 10%.（3）The effects of pH,dosage,initial phosphate concentration and coexisting anions on Si-ZVI^BM phosphate removal was studied,and a preliminary study was made on the Si-ZVI^BM phosphate removal mechanism.The experimental results show that the initial pH of the reaction system was an important factor in the removal of phosphate by Si-ZVI^BM.A lower pH can significantly increase the reactivity of zero-valent iron and accelerate the removal of phosphate.The optimal conditions for Si-ZVI^BMphosphate removal are the dosage of 2 g·L^-1,the initial phosphate concentration of 2g·L^-1,and pH=3.0.Anions in the water environment have a certain effect on the removal of phosphate by zero-valent iron.NO^3-and SO₄^2-had no significant effect on the removal efficiency of phosphate.CO₃^2-and SiO₃^2-inhibited phosphate removal,and the inhibitory effect of SiO₃^2-was the most obvious.The analytical experiment results showed that phosphate removal mechanism of Si-ZVI^BM was mainly chemical precipitation.