Study On Controllable Synthesis And Application Of Magnetic Hydroxyl Phosphate Composites

In recent years,the improper discharge of sewage has brought a severe test to the survival of mankind and the protection of the natural environment.Hydroxyapatite,as a kind of cheap,efficient and environmental friendly adsorption material,has become a research hotspot.It has ionic exchange characteristic which is conducive to the absorption of heavy metals in the water.However,its adsorption properties still need to be improved.The improvement of the preparation method and the doping of the materials are helpful to improve the comprehensive properties of the adsorbent.In this paper,strontium-doped carbonate hydroxyapatite and magnetic strontium hydroxyapatite composite material were prepared by hydrothermal method.The Pb²⁺ removal behavior and mechanism of these materials were investigated.The main results are shown as follows:1.Monodisperse nanosheets-assembled hydrangea-like strontium-doped carbonate hydroxyapatite?Sr-CHAp?was synthesized by a hydrothermal method.It had a large specific surface area as 43.54 m2·g-1.It showed a good performance in Pb²⁺ adsorption,and the saturated adsorption capacity was 985.1 mg·g-1 at optimal pH?pH=3.0?.It raised the possibility to obtain highly efficient Pb²⁺adsorbents in acidic solutions.The isotherm data accorded with the Langmuir model and the dynamic data conformed to the pseudo-second order kinetic model.The mechanism of Pb²⁺adsorption was ascribed to dissolution/precipitation process in acid solutions.The products were different according to the different pH value.The strong acidic solution was favorable for the formation of PbHPO4,while Pb10?PO4?6?OH?2 was the main product when pH was between 3.0-6.0.2.Using Fe₃O₄/SrCO₃ as a hard template,Fe₃O₄/SrHAp1 magnetic composite material was synthesized.It was composed of shuttle rods with prisms,and the specific surface area was 51.68m2·g-1.Fe₃O₄/SrHAp2 magnetic composite material was prepared by directly hydrothermal method,and it was composed of spherical Fe₃O₄ nanoparticles and strontium hydroxyapatite nanorods.The average particle diameter of Fe₃O₄ was about 150 nm.The average length of strontium hydroxyapatite nanorods was about 800 nm,and its average diameter was about 90 nm.3.The saturation magnetization of Fe₃O₄/SrHAp2?20.6 emu·g-1?was larger than Fe₃O₄/SrHAp1,so,as a kind of adsorbent,it was more favorable for the magnetic separation.The Pb²⁺ adsorption performance of Fe₃O₄/SrHAp2 magnetic composite material was better,and themaximum adsorption capacity was 291.1 mg·g-1.The Pb²⁺ adsorption process of Fe₃O₄/SrHAp2 reached equilibrium within 20 min.Pseudo-second order kinetic model could well fit the adsorption kinetics data,and Langmuir model could well fit the adsorption isotherm data.The mechanism of Pb²⁺ adsorption was mainly ascribed to absorbent's surface adsorption and ionic exchange of Pb²⁺ and Sr²⁺ in weakly acidic solutions,while it was dissolution/precipitation mechanism in strongly acidic solutions.The product was PbHPO4 when pH was 2.5,while Pb10?PO4?6?OH?2 was the main product when pH was 3.0.In this study,strontium-doped carbonate hydroxyapatite and magnetic strontium hydroxyapatite composite materials exhibited excellent performance in the removal of heavy metal Pb²⁺ from acidic aqueous solution.It has a good application prospect.The performance and mechanism research for it has a certain reference value in the field of heavy metals wastewater treatment.