The Mechanisms On Shape Evolution Of Aluminum Substituted Hematite And Its Adsorption Characteristics Of Phosphate

Aluminum?Al?as the third abundant element in the Earth's crust,incorporated into the structure of hematite by means of isomorphous substitution and occupied the Fe³⁺ position.Compared with pure hematite,the lattice parameters,grain size,crystallization degree,growth orientation,morphology of Al-substituted hematite changed as a function of the amount of Al substitution within structure.These changes in mineralogical properties have in turn influenced the surface charge characteristics,adsorption capacity,thermodynamic stability,magnetic properties and dissolution properties of hematite.Therefore,it is theoretically meaningful to understand the growth process of Al substitution hematite nanoparticles.Here,we investigated the influence of Al substitution on the microstructure and morphology of hematite nanoparticles.Then,density functional theory?DFT?was employed to further discuss the effect of Al on structure of hematite.Finally,the adsorption characteristics of inorganic phosphorus onto hematite with various amount of Al substitution was explored.The main conclusions are as follows:1.Al induces the growth of hematite nanoparticles along a-b plane.With the increasing of aluminum substitution,the lattice parameters?a,b and V?decreased,the crystalline attenuated,the crystal size enlarged,the specific surface area increased,the structure water increased.The morphology of hematite nanoparticles changed from rhombic to plate-like shape.2.DFT results showed that due to the smaller ionic radius between Al³⁺ and Fe³⁺,metal octahedrons distorted,which results in hexagonal close packing O atoms remain at the same coordinate along c-axis,suggesting that the hexagonal oxygen layers remain flat even when the symmetry is not imposed in calculation.The specific surface energies of hematite were related to Al atomic structure on hematite surface.When hematite?001?and?100?interaction with Al,their surface energies were overturn obviously.In addition whether OH in structure or in surface of hematite,the above mention changes were aggravated.3.The adsorption behaviors of phosphorus onto hematite is shown as two stage: initial rapid adsorption,and subsequently slow adsorption.With the increase of the Al substitution with in structure,the initial adsorption rate of phosphorus increased,and the same trend was also observed for the slow adsorption rate.The slow adsorption rate is a small order of magnitude relative to rapid that.The Langmuir and Freundlich isothermal adsorption model can well describe phosphorus adsorption behavior onto Al substituted onto hematite.Compared with the Langmuir model,the Freundlich model can better simulate the phosphorus adsorption process on Al substituted onto hematite.