Preparation And Adsorption Properties Of Hydroxyapatite With Different Calcium And Phosphorus Ratio

Hydroxyapatite has strong adsorption properties to heavy metal ions and becomes a new star in environmental material fields in recent years owing to its porosity, larger specific surface area and more calcium ions in the crystal structure.HA of calcium deficiency type, phosphorus deficiency type and normal type were prepared by sol-gel method. Calcium and phosphate ratio was 1.56, 1.78 and 1.67,respectively. HA powders were characterized by TG-DSC, XRD and SEM. The thermal stability of normal powders was better than calcium deficiency and phosphorus deficiency types. XRD analysis confirmed that powders were hydroxyapatite. The micro-morphology of three type powders was similar reticular- mesoporous structure.The adsorption properties of three different HA types to the cadmium ions in simulated wastewater were investigated. Effects of adsorption duration, p H value,temperature, initial concentration of cadmium ions and the dosage of HA on removal rate were analyzed. Effect of HA to cadmium ion adsorption capacity was analyzed as well.Adsorption of HA to cadmium ions reached equilibrium at about 1h under slow stirring condition. It was confirmed that the removal rate increased when p H value rose, while the removal rate declined when temperature increased. The removal rate declined when the concentration of cadmium ions increased under same volume. The removal rate increased when the dosage of HA increased. It was indicated that the adsorption capacity increased while the removal rate declined when the cadmium ions concentration increased under the same volume.The adsorption isotherm was researched with Langmuir and Freundlich equations. It was indicated that the calcium deficiency and phosphorus deficiency type powders were in the line with Freundlich isotherm while the normal type was in the line with Langmuir isotherm. Adsorption kinetics was investigated with the pseudo first-order kinetics, pseudosecond-order kinetics, the intraparticle diffusion model and Elovich model, respectively.The results showed that the pseudo second-order kinetics model can describe the adsorption process of HA well.