Synthesis And Performance Of Several Novel Phosphate Adsorbents

Eutrophication of lakes and reservoirs is one of the most serious problems in aquatic environment.Phosphorus has been recognized as the limiting factor for eutrophication and algae blooming,thus synthesis of new-type phosphate absorbents is a vital field in phosphorus control,which has drawn more and more attention.In this study,3 kinds of new-type phosphorus absorbents were manipulated,including hydrous iron oxide modified diatomite(HIOMD),magnetic nanoparticle with a magnetite core and a zirconia shell(magnetic zirconia)as well as a composite absorbent of zeolite/hydrous lanthanum oxide.The former two adsorbents were developed for the removal and recovery of phosphate from(waste)water,and the latter one was synthesized for the control of internal phosphorus load in lakes and reservoirs.HIOMD was prepared via loading hydrous iron oxide on diatomite surface.X-ray diffraction(XRD)and scanning electron microscope(SEM)were employed to characterize the structure of HIOMD,revealing that amorphous hydrous iron oxide was loaded on diatomite surface.Modification of diatomite by hydrous iron oxide significantly enhanced its specific surface area and phosphate adsorption capacity,while decreased its filtration velocity slightly at the same time.For instance,loading28%hydrous iron oxide caused increase in adsorption amount by 24.52 folds,while75%of the raw diatomite filtration velocity could still be maintained.Increasing of pH and higher ionic strength at alkaline condition could favor adsorption of phosphate by HIOMD.It could be inferred that the mechanism of phosphate adsorption by HIOMD was the formation of innersphere complex.The competing effect of common co-existing anions on phosphate adsorption by HIOMD was limited.In a 5 cycles adsorption and desorption experiment,HIOMD could keep an relatively high performance,absorbed phosphate could be stripped using 1M Na OH solution,obtaining a phosphate desorption solution with a high P concentration(174-208 mg/L).Fixed bed column adsorption experiments indicated that HIOMD could serve as a potential filtration medium for phosphorus capture.A magnetic nanoparticle absorbent-magnetic zirconia was prepared via a one step co-precipitation method.The material was characterized by means of X-ray diffraction(XRD),transmission electron microscopy(TEM),vibrating sample magnetometer(VSM)and specific surface area(BET).Results indicated that magnetic zirconia had a core-shell structure,in which magnetite is located in the core while amorphous zirconia is in the shell.When Fe/Zr molar ratio is 4/1,the saturated magnetization was 23.65 emu/g,and its phosphate adsorption maxima was 42.19mg/g,meeting the needs of both adsorption and magnetic separation.Adsorption kinetics experiment had shown that in a 50 mg/L phosphate solution,90%removal of phosphate by magnetic zirconia could be achieved within 20 min.Decreasing of pH and increasing ionic strength at alkaline condition promoted adsorption,common competitive anions in waste water did not have significant influence on the phosphate adsorption by magnetic zirconia.In a 5 cycle"adsorption-desorption and regeneration"experiment,magnetic zirconia could keep 85%of the original adsorption capacity.Following an"adsorption-desorption and regeneration"procedure,magnetic zirconia had shown a good phosphate removal performance,and the P concentration of desorption solution is 60-120 mg/L,which could benefit the recovery process.Base on the results of pH change experiment and phosphorus fractionation in P-saturated magnetic zirconia,it was suggested that the adsorption mechanism was the formation of innersphere complex.This mechanism was confirmed by Zeta potential analysis.Results of FTIR measurements and P/Zr ratio further illustrated that phosphate was coordinated with zirconia in the form of(Zr O)PO₂(OH).Zeolite/hydrated lanthanum oxide(ZHLO)was obtained by incorporating La Cl₃to zeolite synthesized from coal fly ash.In ZHLO,amorphous hydrous lanthanum oxide swathed the zeolite particles,with a specific surface area of 57.7 m²/g.ZHLO could remove phosphorus from lake water effectively.In a dosage experiment conducted in lake water collected from five Chinese lakes,phosphate concentrations could be reduced to below the detection limit(3?g/L)with a La/P molar ratio ranging from 2 to 4.Statistic analysis indicated that alkalinity was the main factor inhibiting its adsorption performance.The absorbed phosphorus could not be re-released when pH increased.Phosphorus release under high pH and anaerobic conditions could be effectively inhibited by adding ZHLO.In a 28-day incubation experiment,upon adding ZHLO,SRP and TP concentrations in overlying water could be reduced to 13.1%and 18.9%of the SRP and TP concentrations in control group.In a 212-day simulated tank experiment,the addition of ZHLO reduced the SRP and TP in the overlying water to26.77%and 42.95%of the concentration level in control mesocosm.The mechanism to control phosphorus release by ZHLO included:“interception”,enhancement of phosphorus fixation capacity of sediment,as well as stabilization of mobile phosphorus in sediment.