Study On The Adsorption Performance Of Organic Phosphonates/nano-hydroxyapatite Composites For Heavy Metal Ions

Hydroxyapatite（HAP）has been widely used in the removal of heavy metal ions from wastewater due to its unique structural characteristics and excellent ion exchange ability.In this paper,three kinds of organic phosphonates/nano-hydroxyapatite composites were prepared by using several common organic phosphonates as modification agents.The structures of the composites were characterized by XRD,FTIR,SEM and BET,and the adsorption properties of the composites for lead,cadmium,cobalt and zinc ions in water were studied.The main research contents are as follows:（1）The composites of amino-trimethylphosphonic acid（ATMP）and HAP（ATMP/HAP）were prepared by chemical precipitation method.The effects of the dosage of ATMP,solution p H,initial concentration of metal ions,reaction time,reaction temperature on the adsorption capacity of ATMP/HAP for Pb²⁺and Cd²⁺were investigated.The results show that when the amount of ATMP is 10%,10ATMP/HAP has the best adsorption capacity to Pb²⁺and Cd²⁺of1458.79 mg/g and 321.26 mg/g,respectively,while the adsorption capacity of unmodified HAP for two metal ions is 810.44 mg/g and 169.08 mg/g.The interaction between ATMP,HAP and heavy metal ions has been studied by using Multifwn wave function program from the theoretical perspective of quantum chemistry.The results show that ATMP,HAP and heavy metal ions can form ternary surface complex,which significantly improves the adsorption capacity of HAP to heavy metal ions.The adsorption mechanisms of 10ATMP/HAP for Lead ions include surface complexation,ion exchange and dissolution precipitation,while the adsorption mechanisms for cadmium ions are mainly surface complexation and ion exchange.（2）Ethylenediamine tetramethylene phosphonic acid（EDTMP）-HAP composites were prepared by chemical precipitation method,and the removal effect of Co²⁺and Zn²⁺by the composite was studied under different conditions.The results show that when the doping ratio of EDTMP is 20%,the adsorption capacity of 20EDTMP/HAP composite for Co²⁺and Zn²⁺is155.81 mg/g and 225.38 mg/g,respectively,which is 11.3 times and 10.5 times of that of HAP,respectively.The adsorption of Co²⁺and Zn²⁺by 20EDTMP/HAP reaches equilibrium at about300 min and 480 min,respectively.（3）In order to achieve the purpose of magnetic separation,the complex（HDTMP/HAP/Fe₃O₄）of hexamethylene diamine tetramethylene phosphonic acid（HDTMP）,ferric oxide and HAP was prepared by ultrasound-assisted hydrothermal method.The influence of solution p H,initial concentration of metal ions,reaction time and coexisting ions on the adsorption of Co²⁺by HDTMP/HAP/Fe₃O₄ was inspected.The results show that the optimal conditions for HDTMP/HAP/Fe₃O₄ to adsorb Co²⁺are as follows:initial concentration of Co²⁺is 250 mg/g,initial p H 5 and contact time 240 min,and the maximum adsorption capacity of HDTMP/HAP/Fe₃O₄ to Co²⁺is 142.98 mg/g.