The Study On Removing Phosphorus In Water By Fe/Zr-modified Reed Biochar

Phosphate(P)removal is significant for the prevention of eutrophication in natural water.In this project,reed biochar was modified by surface-loaded metal ions to enhance the adsorption capacity.The results showed that zirconium modification and zirconium-iron hybrid modification significantly improved the phosphorus removal performance of reed biochar.(1)The optimum mass ratio of biochar and Zr was 1:1 in zirconia modified reed biochar.The effects of dosage,initial pH and ionic strength on PO43-removal in aqueous solution were studied by intermittent adsorption experiments.The results showed that after modification,the surface of the biochar became rough and the pores were loaded with a lot of particles.Acidic water was more conducive to adsorption,the optimal pH was 4.The adsorption capacity was not affected by HCO3-,SO42-and Cl-.And the phosphorus release of biochar would not be affected by the pH and temperature in the environment.The Adsorption isotherm fitting was more consistent with Freundlich model.The experimental data fitting was more in line with the pseudo second order equation.After 5 hours,the adsorption rate tended to be stable,and the adsorption capacity of the phosphate solution was 6.196mg/g.The FTIR analysis showed that the mechanism of the adsorption process was mainly the exchange of ligands.The XRD analysis showed that the surface of the biochar formed a new material,possibly a mixture of ZrO2 and Zr3O.In the selection of desorbent,it was found that NaOH was more suitable as a desorbent for zirconium modified carbon.The desorption rate of Zr-BC reached more than 90%with 0.1 mol/L NaOH,and the removal rate of phosphate from Zr-BC after 2 times of regeneration reached more than 80%.(2)The phosphate adsorption property of biochar reached optimum level when it was mixed with the solution of zirconium oxychloride and ferric chloride.It has been demonstrated that using ratio of zirconium to iron of 1:1 and total concentration of zirconium to 0.03mol/L to modify biochar was the optimum condition.The pH of the solution had a relatively large effect on the phosphate adsorption property of biochar.The adsorption capacity decreased as the solution pH increased.When the initial concentration of phosphorus was 10mg/L and the dose of ZrFeCl3-BC was 0.8g/L,removal efficiency of ZrFeCl3-BC for phosphate was more than 90%,and the residual phosphorus concentration was below 1 mg/L.The anions in the solution also had a definite effect on the uptake of phosphate with the order of influence being HCO3->NO3->SO42->Cl->F-.The adsorption isotherms were well fitted to Freundlich model,and increasing temperature was favorable for adsorption.Moreover,The kinetic experimental data of the adsorption fitted to the pseudo-second-order kinetic equation.XRD analysis showed that the zirconium-iron oxide and hydroxide crystals were supported on the ZrFeCl3-BC surface in an amorphous form.FTIR analysis showed that-OH participated in the adsorption process,and the adsorption process was mainly the exchange of ligands in the inner layer.It was found that NaOH was more suitable as a desorbent for ZrFeCl3-BC and the removal rate of phosphate reached more than 80%after 5 times of regeneration,which was better than regeneration performance of Zr-BC.