Adsorptive Removal Of Nitrate And Phosphate From Aqueous Solution Using Organo-modified Aluminum-Manganese Binary Oxide

Excessive nutrients discharing into waters may cause the eutrophication of water bodies,which has become a global environment problem.Eutrophication deteriorates the quality of the water environment,affects the development of the aquaculture,and seriously threatens the development of the social economy and the health of the people.Nitrate and phosphate are the two major nutrient anions that cause eutrophication of water bodies.Various water treatment technologies have been used to remove nitrates and phosphates from water.Among these technologies,adsorption is generally studied and designed due to these advantanges including high-efficient,convenience of use,simple of operation and low-cost.This study is based on previous research of the research group.The aluminum-manganese binary oxide?AMBO?was synthesized by oxidation reduction/co-precipitation method,and it has been modified by some organic solvents such as epichlorohydrin to prepare organo-modified aluminum-manganese binary oxide?OABO?.The removal efficiency and adsorption mechanism of nitrate and phosphate on OABO was investigated.The main results were as follows:?1?The surface structure and physicochemical characteristics of AMBO and OABO were analyzed by TGA,BET,XRD,TEM,SEM-EDS&Mpping,FTIR,XPS and Zeta potential methods.As compared with AMBO,the C and N elements appeared in OABO,and the Mn content was decaresed.The specific surface area of AMBO was53.01 m²/g.The specific surface area of OABO was 2.89m²/g,much lower than that of AMBO.This result was attributed to that the organic compunds loaded onto AMBO may block the surface micropores.The Zeta potential of OABO was increased relative to AMBO,which is beneficial to the adsorption of anions.?2?The adsorption kinetics of nitrate on OABO followed the pseudo-second-order kinetic model,it coulde be concluded that chemical adsorption be predominant during adsorprion process.The adsorption isotherm data of nitrate on OABO could be well described by the Langmuir model and the Sips model,which indicated a monolayer adsorption of nitrate on OABO.When the pH of the adsorption system was not maintained,the nitrate adsorption capacity of OABO remained relatively stable in a pH range of 3-10.When the pH of the adsorption system was maintained,the adsorption quantity decreases with the increase of pH.Co-existing anions can pose negative influence on the adsorption of nitrate nitrate on OABO(SO₄^2-?SiO₃^2--?CO₃^2-?F^-).Ca²⁺and Mg²⁺exhibited an inhibitory effect on nitrate adsorbed onto OABO,which was due to the competition for active sites between nitrate and chloride?added together with the cations?.?3?The kinetics data of phosphate adsorption on OABO were perfectly fitted by the Power model and the Elovich model,and the results demonstrated that the adsorption of phosphate was a complex process of multimolecular adsorption.The Sips model and the Freundlich model satisfactorily described the adsorption isotherm characteristics of phosphate on OABO.The results showed that there are many active sites on the surface of OABO for the adsorption of phosphate.The removal efficiency of OABO remained unchanged at pH=5-8.Co-existing anions displayed an adverse on phosphate adsorption following the order of F^-<NO₂^-<CO₃^2-<SiO₃^2-<SO₄^2-.Ca²⁺had a slight promotion effect on phosphate adsorption and Mg²⁺exhibited a minor inhibitory effect.?4?The results of simultaneous adsorption of nitrate and phosphate on OABO showed that there was no significant effect on the adsorption rate and adsorption effect between nitrate and phosphate,because OABO has different adsorption sites for nitrate and phosphate.?5?The adsorption mechanism of nitrate and phosphate on OABO were determined by using SEM-EDS&Mapping,FTIR,XPS and Zeta potentials,respectively.The results showed that the ion exchange with Cl^-is the main adsorption mechanism for nitrate removal.There are many active sites for the adsorption of phosphate,such as hydroxyl groups and sulfate ligands.The results showed that the main adsorption sites of nitrate and phosphate on the OABO were different,which had little effect on each other,and indicated that the simultaneous adsorption of nitrate and phosphate on OABO was achieved.?6?Regeneration studies showed that nitrate&phosphate adsorbed OABO was effectively regenerated by using 0.3 mol/L NaHCO₃ as an eluent.After five adsorption-desorption cycles,OABO still had a good adsorption capacity for nitrate and phosphate.