| In recent years,water eutrophication caused by phosphate has become a serious environmental issue in the world.Eutrophicated water can lead to the decrease of water quality,decrease of biodiversity and even break-up of aquatic ecology.Additionally,excess algae in the water body can bring difficulties for water treatment.Therefore,effective method should be developed to remove phosphate from water.Adsorption is a simple,efficient,and low-cost method to remove phosphate from water at present.Hexagonal ferrite is a kind of iron oxyhydroxides in natural environment with high specific surface area and magnetic properties.Therefore,hexagonal ferrite is considered to be an ideal adsorbent for phosphate removal from water.The common synthetic method for hexagonal ferrite is based on H2O2oxidizating ferrous ion method.However,the effect of synthesic parameters,including H2O2supplying rate and p H value,on the morphology,particle size or specific surface area of hexagonal cellulite and its adsorption performance on phosphate have not been explored.Therefore,in this paper,the effect of H2O2supply rate and p H value on the properties of hexagonal cellulite and its adsorption performance on phosphate have been studied.Firstly,the influence of H2O2supply rate on the formation of the hexagonal ferrite was explored.The generated minerals were characterized by XRD,SEM,FTIR and etc.Adsorption kinetics studies were explored to optimize H2O2supply rate.Based on the optimized H2O2supply rate,the influence of initial p H on the formation of the hexagonal ferrite was studied.The two distinct minerals including schwertmannite and hexagonal ferrite obtained in the observed-mentioned study were further compared under various impact factors.The main results were obtained as follows:（1）The decrease of H2O2supply rate resulted in the changes of the mineral morphology and decrease its specific surface area and particle size.The minerals prepared at both of the first and the second H2O2supply rates were hexagonal ferrite,while the minerals formed at the third and fourth H2O2supply rates wereγ-Fe2O3.Adsorption kinetic studies suggested that hexagonal ferrite generated at the first H2O2supply rate had the best adsorption performance on phosphate with the maximum adsorption capacity of 61.38 mg/g.With the increase of H2O2supply rate,the amount of phosphate adsorption by minerals gradually decreased.Hexagonal ferrite generated at the first H2O2supply rate had a good adsorption performance in a wide p H range（p H=2-10）with the best adsorption capaticty at solution p H of 2 and 7.The inhibition effect of inorganic anions on phosphate removal by hexagonal ferrite adsorption followed order of Cl-<NO3-<HCO3-.（2）At the first H2O2supply rate,the initial p H on the formation of hexagonal ferrite was further studied.It was found that schwertmannite was the sole phase at p H ranging between 2.0 and 7.0,while under alkaline conditions（p H=8.5 and 10.5）hexagonal ferrite was sole phase.Hexagonite ferrite had a larger specific surface area（148.54 m2/g）,which was much larger than the specific surface area of schwermannite（35.70 m2/g）.The decrease of initial p H resulted in a decline of mineral yield.（3）Adsorption studies suggested that as adsorption equilibrium achieved,the adsorption capacity of phosphate by hexagonal ferrite（31.25 mg/L）was much higher than that by schwertmannite（15.27 mg/L）.Langmiur and Freundlich adsorption isotherm models indicated that the adsorption of phosphate by hexagonal ferrite was mainly multilayer adsorption,while the adsorption of phosphate by schwertmannite was through monolayer adsorption process.The adsorption kinetic studies suggested that the maximum adsorption capacity of hexagonite was 51.08 mg/L,which was higher than 37.67 mg/L achived by schwertmannite.The reason shoud be ascribed to the large specific surface area of hexagonal ferrite and the abundant hydroxyl functional groups on its surface.At all tested p H value,the adsorption capacity of phosphate by hexagonal ferrite was better than that by schwertmannite.Schwertmannite showed the best adsorption capacity only under acidic condition.Additionally,the adsorption capacity of phosphate by hexagonal ferrite was stronger than that of schwertmannite at all tested phosphate concentrations or under various anions condition. |
