Preparation And Dephosphorization Of Hydroxyapatite Modified By Lanthanum And Yttrium

Nowadays,eutrophication caused by excessive phosphorus content in water is a common environmental problem in all countries,and the situation in China is also very serious.The eutrophication in 25 large and medium-sized lakes in China is as high as 92%.Compared with biological method,crystallization method and membrane method,adsorption method has the advantages of wide source of materials,imple operation,high efficiency and fast,and is the most widely used wastewater phosphorus removal technology in the current method.The adsorption properties such as adsorption capacity and adsorption efficiency are the key factors affecting the adsorption effect.Hydroxyapatite has low adsorption capacity and unstable adsorption for phosphorus in wastewater because of its wide source and low price.The rare earth metals lanthanum and yttrium have high adsorption capacity,high adsorption efficiency and good phosphorus affinity,but the price is high.Based on the advantages and disadvantages of hydroxyapatite,lanthanum and yttrium,two new adsorption dephosphorizers modified by lanthanum and yttrium were prepared for the purpose of phosphorus removal by wastewater adsorption.The research content and results are as follows:Lanthanium-modified hydroxyapatite（La-HAP）composite was prepared by simple ultrasound-assisted chemical precipitation method,and the prepara-tion process of La-HAP and the adsorption specificity of P^-hydroxyapatite were studied.The experimental results show that the factors influencing the phosphorus adsorption effect include not only the preparation factors,such as the molar mass ratio of lanthanum-calcium,roasting temperature,etc.but also the amount of materials added,the initial concentration of P in the solution,pH value and common SO₄^2-,Cl^-,F^-and CO₃^2-.Under 25℃,the isothermal adsorption model to explain the process of adsorption,using the Langmuir model is better than the Freundlich model,La-HAP saturated adsorption capacity of 42.92 mg P g^-1;Under 30℃,the Pesudo-second-order kinetics model fitting degree is higher,the theory of the adsorption capacity of 22.59 mg g^-1,prove its reaction belongs to the physical and chemical adsorption process.In order to further improve the adsorption and phosphorus removal capacity of hydroxyapatite,yttrium modified hydroxyapatite（Y-HAP）com-posite was prepared by modifying the hydroxyapatite with yttrium,which has better phosphorophilic effect.XRD and other characterization methods were used to analyze its morphology and structure,and the specificity of Y-HAP adsorption on P^-was investigated.The experiment showed that the factors influencing the phosphorus adsorption effect were not only the preparation factors,such as the molar mass ratio of material Y/Ca,roasting temperature,etc.,but also the amount of material,the initial P^-concentration in the solution,pH value,common coexisting ions,such as SO₄^2-,Cl^-,F^-and CO₃^2-,as well as ionic strength.Under 25℃and 30℃and 35℃isothermal adsorption experiments,respectively,the maximum adsorption capacity(q_max)43.42 mg P g^-11 and 45.72 mg P g^-1,54.21 mg P g^-11 of the adsorption process and lanthanum modified hydroxyapatite is consistent,also belong to the Langmuir model.The adsorption of Y-HAP on P^-was in accordance with the Pesudo-second-order kinetic process,and the theoretical adsorption capacity was 17.52mg g^-1.In this paper,ultrasonic assisted chemical precipitation method was used to prepare two kinds of rare earth metal modified hydroxyapatite adsorption and phosphorus removal materials,La-HAP and Y-HAP.Therefore,La-HAP and Y-HAP have wide application in treating phosphorus-containing wastewater.