Performance Of Zirconium Loaded Adsorbent Materials For Phosphate Control In Eutrophicated Water Bodies

Control of phosphorus level is one of the main management measures for eutrophicated water bodies.In this study,zirconium loaded diatomite and zirconium loaded zeolite were developed by using the cost-effective and easily available diatomite and coal fly ash as raw material,respectively.After characterization,the two materials were investigated for their effectiveness for phosphate removal from water and their performances to control phosphorus in overlying waters and sediments of eutrophicated water bodies.Study on zirconium loaded diatomite showed that:1)mass fraction of zirconia in zirconium loaded diatomite was 12.39%,which was identified to be amorphous via XRD measurements.SEM images showed that porous floccules covered the surface of diatomite after modification and the specific surface area of the zirconium loaded diatomite was 75.22 m²/g,which was larger than that of raw diatomite?14.00 m²/g?.XPS spectra indicated that zirconia and diatomite were bonded together through chemical linkage,rather than physical deposition.2)The adsorption isotherm of phosphate by zirconium loaded diatomite was fitted better to the Langmuir model with a calculated maximum adsorption capacity reaching 10.56 mg/g.The adsorption amount of zirconium oxide component in the material was estimated to be 81.67 mg/g ZrO₂,which was higher than that of pure zirconium oxides reported in previous literatures.3)The adsorption amount of phosphate by zirconium loaded diatomite decreased with the increase of pH.The adsorption was shown to be a ligand exchange process,which was supported by the XPS spectrum of Zr3d region before and after adsorption.4)Chloride ion,sulfate ion and nitrate ion did not inhibit the adsorption of phosphate on the material,whereas coexistence of bicarbonate ions competed with phosphate ions to a certain extent.When treating eutrophicated Taihu lake water containing phosphate concentration of 2 mg/L,the phosphate concentration level could meet the?rank of Surface Water Environment Quality Standard of China by adopting the dosage of zirconium loaded diatomite?1.25 g/L.Study on zirconium loaded diatomite showed that:1)zirconium loaded zeolite has a specific surface area of 193.1 m²/g,nearly 7 times higher than zeolite and 176 times higher than coal fly ash.The number and position of XRD peaks were the same as those of zeolite,which confirmed that the hydrous zirconium oxide in the material was amorphous.2)According to the Langmuir model,the maximum phosphate adsorption capacity of zirconium loaded zeolite was 22.62 mg/g.In addition,zirconium loaded zeolite had the capacity of adsorbing NH₄⁺and Mn²⁺ions which had the releasing potential from sediment under anaerobic condition.3)When the pH ranged from 5 to 10,the adsorption amount of phosphate decreased with the upward pH,but completely reversible dissolution of phosphate did not occur when raising pH.4)The 28-day sediment incubation experiments showed that capping sediment with zirconium loaded zeolite resulted in a more efficient,rapid and sustained decrease in P concentration when compared with the traditional alum treatment method.Furthermore,zirconium loaded zeolite increased the sediment stability,resulting in the lowest turbidity,total phosphorus and soluble reactive phosphorus concentrations in overlying water following artificially induced resuspension of sediment.5)Phosphorus fractionation of sediment showed that the dominant P form transferred from HCl-extractable P to residual P,and the most release-sensitive P?labile P and reductant reactive P?was significantly decreased after zirconium loaded zeolite application,proving that zirconium modified zeolite had both adsorption and stabilization effect on phosphorus.In this paper,adsorption mechanism,influencing factors and practical application for adsorbing and controlling phosphorus in eutrophicated water bodies by zirconium loaded diatomite and zirconium loaded zeolite were investigated.Combining with the backgroud that diatomite was widely used as filter material and zeolite synthesized from fly ash could be used as in situ capping agent,this study provided effective basis for the practical application of the two materials in eutrophicated water bodies.