The Influence Of Lattice Aluminum On Transformation Of Goethite And Its Adsorption Of Phosphate

Goethite is one of the most important components of soil and sediment,which is highly active and bioactive.The presence of aluminum in soil will affect the mineralogical characteristics and the thermal transformation rule of goethite and further affect the surface physicochemical properties of its transition products.Hence,in this study,Al-substituted goethite was synthesized,and heat treatment products were obtained under air atmosphere and reducing atmosphere,respectively.Characterization by XRD,FESEM,TEM,Zeta Potential,BET,infrared spectroscopy,Raman and XPS indicated that substitution of lattice aluminum in goethitenot only change the crystal morphology,affect crystal surface reactivity,restrain the nucleation and growth of goethite,but also greatly improves the crystal surface area.On the other hand,the substitution of aluminumhindered the transformation of goethite into zero valent iron and generated a lot of porous zero valent iron containing Al substituted iron oxide under reductive atmosphere.Batch experiments showed that pseudo-second-order kinetic model and Langmuir model could describe the reaction processbetter,and the adsorption capacity of phosphate was directly proportional to the amount of aluminum substitution.Weak acid condition would improve the adsorption of phosphate onto Al-substituted goethite and its heat treatment products,and inner surface complexation dominanted the reaction process.The thermodynamic parameters suggested that the adsorption of phosphate on Al-substituted goethite and its heat treatment products was spontaneous and endothermic.The effect order ofcoexisting anions and HA in phosphate adsorption onto Al-substituted goethite was Cl^-?NO₃^-<HCO₃^-<SO₄^2-<CO₃^2-<HA,Cl^-/CO₃^2-<NO₃^-<SO₄^2-<HCO₃^-<HA for the heat treatment products under air atmosphere,SO₄^2-<NO₃^-<HCO₃^-<CO₃^2-/Cl^-<HA for the heat treatment products under reducing atmosphere.The results demonstrated that the presence of HA significantly inhibited the reaction.The results of IR and XPS analysis showed thatthe oxygen-containing functional groups played an important role in the reaction process,which provided enough adsorption sites for phosphate adsorption.Phosphate was mainly adsorbed on the surface of Al-substituted goethite in the form of bidentate complex,while with the form of bidentate complex and three-dimensional precipitation on the products obtained under air atmosphere.The reaction mechanism of phosphate adsorption was not only adsorptive,but also chemical precipitation or coprecipitation onto the products obtained under reducing atmosphere.