The Study On Phosphorus Removal And Mechanism Of Y-Type Molecular Sieve Loaded Rare Earth Elements Adsorbent

Phosphate(PO4)plays an important role in eutrophication of water bodies.In this study,novel adsorbents were prepared by loading rare earth elements on Y-type molecular sieve owing to selective adsorption properties for PO4 of rare earth elements.The adsorption behavior and mechanism for PO4 removal by the adsorbents in water bodies were investigated,respectively.The results were as follows:(1)The adsorbent(CHMS)was developed by loading Ce on Y-type molecular sieves(MS-Y)and phosphate removal using CHMS was studied.Results showed that the change of pH value(4-11)had no significant effect on the adsorption behavior of CHMS.When the immersion time was 120 min and concurrently the solution pH was 5,the adsorption capacity reached the equilibrium and the maximum adsorption capacity was 1.17 mg/g.The adsorption process followed the pseudo-second-order kinetic model and Freundlich isotherm model.Among the coexisting ions,only SiO32-restrained the adsorption for PO4 by CHMS.The proposed mechanisms were explicated by various analytical techniques,such as XPS and NMR analysis,and found that ligand exchange reaction between hydroxide and phosphate determined the adsorption.Finally,CHMS showed the excellent regeneration(at least 5 times recycling)ability with 1 mol/L NaOH and the removal rate could still exceed 86.94%.(2)The adsorbent was developed by loading La,Ce,La and Ce,respectively,on MS-Y and phosphate removal by adsorbents was studied.Results indicated that the better adsorption ability of La as compared with that of Ce.The effect of calcination temperature on the adsorption was studied and results showed that when the best calcination temperature was determined to be 100 ?,the highest adsorption capacity was achieved when La alone was loaded on MS-Y,which was abbreviated as LHMS.When pH reached 7,the adsorption process by LHMS followed the pseudo-second-order kinetic model and Freundlich where the maximum adsorption capacity was 12.22 mg/g,as well as Termkin isotherm model,indicative of the existence of chemisorption and strong intermolecular interactions(i.e.ligand exchange).The potential mechanism for the adsorption process by LHMS was explained based on XRD,XPS and NMR analysis.Furthermore,the formation of LaPO4 was considered to be the primary pathway for selective adsorption by the immobilized La(OH)3.Among the coexisting ions,only SiO32-restrained the adsorption for PO4 by LHMS.LHMS could also efficiently remove PO4 from real wastewater.The results of regeneration tests illustrated that the re-adsorption capacity reached approximately 70%after three cycles.(3)The magnetic adsorbent was developed through the methods that Fe3O4 was doped on the best adsorbent above(LHMS)in order to solve the problem of solid-liquid separation.Results indicated that LHMS@3Fe,i.e.,La:Fe=1:3,exhibited the best phosphate removal performance among the adsorbents(LHMS@XFe)at pH=7.The adsorption capacity of LHMS@3Fe decreased with the increase of pH.Significant effects of coexisting anions(e.g.CO32-and SiO32-)were observed.The proposed mechanisms for the adsorption process by LHMS@3Fe were revealed based on FTIR and XPS analysis,which was beneficial for practical application in future.