Preparation And Properties Of ZnAl And ZnAlZr Hydrotalcite Phosphate Adsorbents

The main purpose of this thesis is to prepare ZnAl hydrotalcite adsorbent by co-precipitation method to improve the content of phosphorus in high concentration phosphorus wastewater by hydrotaclite adsorption.The orthogonal experimental design method and single factor experiment are used to optimize the preparation process of ZnAl hydrotalcite（Zn/Al metal molar ratio,p H value of mixed solution,the aging time and synthesis temperature）,and the best process parameters for preparing ZnAl hydrotalcite are filtered.The adsorption capacity of the prepared ZnAl hydrotalcite is109.02 mg/g.In order to improve the adsorption performance of ZnAl hydrotalcite,doping Zr⁴⁺modifies ZnAl hydrotalcite,recorded as ZnAlZr hydrotalcite.When the metal molar ratio of Zn/Al/Zr is 6:0.7:0.3,the prepared hydrotalcite has the highest adsorption capacity of 116.38 mg/g,which records as ZnAlZr-0.3 hydrotalcite.Analysis of the structure of the adsorbent by XRD,SEM and BET,ZnAlZr-0.3 hydrotalcite has better adsorption performance than ZnAl hydrotalcite.Calcination method modifies hydrotalcite and calcinating ZnAl hydrotalcite and ZnAlZr-0.3 hydrotalcite at different temperatures.The highest adsorption capacity of ZnAl hydrotalcite and ZnAlZr-0.3 hydrotalcite at 300℃and 500℃,respectively,is141.17 mg/g,which is higher than that of uncalcined hydrotalcite.The effects of influencing factors（initial phosphorus concentration,initial p H value,adsorbent dosage,adsorption time,adsorption temperature,coexisting anions）on the adsorption of phosphorus removal in ZnAl hydrotalcite and ZnAlZr-0.3 hydrotalcite adsorption experiments are investigated.The results show that the optimal adsorption effect can be obtained by the adsorption experiment at the initial phosphorus concentration of 200 mg/L,the initial p H value of 6,the adsorbent dosage of 1 g/L,the adsorption time of 4 h and the adsorption temperature of 40℃.The pseudo second-order kinetic equation and the Freundlich adsorption isotherm can well control the adsorption process.The solution contains CO₃^2-,which promotes the adsorption of phosphorus.As the concentration of CO₃^2-increases,the adsorption effect of hydrotalcite increases.Seleting the comfortable desorbent studies the regenerability of ZnAlZr-0.3 hydrotalcite,and result shows that regenerated hydrotalcite has poor adsorption performance.Regeneration rate is less than 10%.Based on the characterization analysis of ZnAl hydrotalcite and ZnAlZr-0.3hydrotalcite before and after adsorption of phosphorus,it is speculated that the adsorption mechanism of ZnAl hydrotalcite and ZnAlZr-0.3 hydrotalcite is surface electrostatic attraction,ion exchange and formation of hopeite（Zn₃（PO₄）₂·4H₂O）through surface precipitation.