Preparation Of Zinc-containing Hydroxyapatite And Its Adsorption Capacity For Heavy Metals In Water

Hydroxyapatite[hydroxyapatite（HAP）]isanimportantphosphoruscontaining mineral in nature,and its molecular formula is Ca₁₀（PO₄）₆（OH）₂.Isomorphic substitution can occur at the Ca²⁺position of the hydroxyapatite,[PO4]tetrahedral position and channel position[OH].Certain divalent cations(such as Mg²⁺,Sr²⁺,Mn²⁺,Fe²⁺,Pb²⁺,Zn²⁺,Cd²⁺,etc.)can be substituted with Ca²⁺ions.This displacement reaction characteristic makes hydroxyapatite have excellent adsorption ability.In this experiment,the environmentally friendly divalent cation Zn²⁺was selected as the doping ion,and it was introduced into the hydroxyapatite structure according to a different molar ratio to Ca²⁺for doping modification.Zinc-calcium hydroxyapatite solid solution series(ZnHAPs,（Zn+Mg）/P=Zn²⁺/Ca²⁺with different ratios were prepared by the mixed precipitation method1.67,nZn²⁺/nCa²⁺=0¹0),the adsorbent ZnHAP-0.2 with relatively good adsorption performance was selected through static adsorption test,used for the adsorption research of heavy metal wastewater containing lead,copper,cadmium and chromium,and the initial heavy metal solution was explored The influence factors such as ph value,initial concentration of solution,dosage of adsorbent,reaction temperature and time on the adsorption effect,and the kinetic model and isotherm model were used to explore its adsorption mechanism.It is an environment-friendly apatite adsorbent And provide theoretical basis for the application of heavy metal removal in water.The experimental results are as follows:1)Characterization and analysis of the prepared ZnHAP-0.2,the results of scanning electron microscopy showed that ZnHAP-0.2 is composed of fine particles,the crystal is a short rod-like structure,the surface is not smooth,and the grains are agglomerated.The energy spectrum results show that all the elements in the hydroxyapatite are present in the energy spectrum results,and the zinc element is also present,indicating that zinc has entered the hydroxyapatite lattice as a dopant.2)ZnHAP-0.2 has a good adsorption effect on Cd²⁺in wastewater.With the increase of Cd²⁺concentration in the solution,the adsorption amount of ZnHAP-0.2to Cd²⁺shows a trend of first increasing and then decreasing,and the removal rate is also continuously decreasing;When the ph value of the solution is 1⁸,the optimal adsorption ph value is 6;the removal rate of Cd²⁺in the solution increases with the increase of the adsorption amount,the initial amount of the optimal adsorbent is 0.05g/50mL,Langmuir isotherm adsorption The model and quasi-second-order kinetic model can well describe the process of this adsorption reaction.3)ZnHAP-0.2 has a good adsorption effect on Pb²⁺in wastewater.As the concentration of Pb²⁺in the solution increases,the adsorption amount of ZnHAP-0.2to Pb²⁺shows a trend of increasing first and then approaching saturation,and the removal rate is also constant.Decrease;when the ph value of the solution is 1⁸,the optimal adsorption ph value is 6;the removal rate of Pb²⁺in the solution increases with the increase of the adsorption dose,the optimal initial amount of adsorbent is0.03g/50mL;Langmuir The isothermal adsorption model and the quasi-second-order kinetic model can describe the process of the adsorption reaction well.4)ZnHAP-0.2 has a good adsorption effect on Cr⁶⁺in wastewater.With the increa-se of Cr⁶⁺concentration in the solution,the adsorption amount of ZnHAP-0.2 to Cr⁶⁺shows a trend of first increasing and then decreasing,and the removal rate is also continuously decreasing;The optimal adsorption ph value is 6,so the adsorption capacity of ZnHAP-0.2 is good under neutral or weakly acidic conditions;the removal rate of Cr⁶⁺in the solution increases with the increase of the adsorption dose,and the optimal initial amount of adsorbent is 0.25g/50mL;Langmuir isotherm adsorption model and quasi-second-order kinetic model can well describe the process of this adsorption reaction.5)ZnHAP-0.2 has a good adsorption effect on Cu²⁺in wastewater.As the concentration of Cu²⁺in the solution increases,the amount of ZnHAP-0.2 adsorbing Cu²⁺shows a trend of first increasing and then decreasing,and the removal rate is also continuously decreasing;The optimal adsorption ph value is 6,and the adsorption capacity of ZnHAP-0.2 is better under neutral or weakly alkaline conditions;the removal rate of Cu²⁺in the solution increases with the increase of the adsorption amount,and the optimal initial amount of adsorbent 0.04g/50mL;Langmuir isotherm adsorption model and quasi-second-order kinetic model can well describe the process of this adsorption reaction.