| Because of its unique crystal structure and micropores formed by natural pore structure,nano-hydroxyapatite (HA) possesses excellent properties involving adsorption, ion-exchange,thermostability. In recent years, it has appealed much researches as a kind of new environmentalmineral materials and has been extensively applied in the removal of heavy metals in wastewater.Surfactants as templates act as a function of structure oriented in the prepare of materials,which have significant influence on pore shape, pore size and morphology. In this research, thevariety and the concentration of templates, the reaction temperature were proposed to regulatethe morphology, the pore shape and pore size of HA, and meanwhile to improve the porevolume and the specific surface area. The morphologies and microstructures of the obtained HAwere analysed by thermogravimetric/different thermal analysis (TG/DTA), x-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM),N2adsorption-desorption measurement (BET), etc. The results showed that using a cationsurfactant of cetyl trimethyl ammonium bromide (CTAB) as templates, the morphology ofobtained powders was much connected with pH value of reaction solution. When pH value wasbetween9and11, the morphology of synthesized HA was rod-like, and its surface area was24.78m2/g. However, when pH value was raised to13, the morphology changed to sphere andobtained powders were pure-phase, which surface area increased to28.73m2/g. Lamellar HAwas obtained using a anion surfactant of lauryl sodium sulfate (SDS) as templates, and itssurface area of HA obtained by adding1g,2g,5g SDS was39m2/g,39.6m2/g,54.87m2/g,respectively. The results indicated that the surface area of HA synthesized by SDS as templatewas larger.In this study, the wastewater was simulated by copper nitrate solution. The copperadsorption properties of these different types of HA were researched. The adsorption resultsshowed that these two types of HA with different morphologies both had a good adsorption property. The adsorption capacity of HA increased with the increase of initial concentration ofheavy metal ion, but the removal efficiency reflected a contrary result. These two types of HAboth had rapid adsorption rates, which the adsorption equilibrium could be achieved within15min. The removal efficiency decreased with the rising of adsorption temperature. As the pHvalue of copper solution increased, the adsorption capacity increasing, too. The comparison ofadsorption property of copper ion between rod-like and lamellar HA was studied under thesame conditions. The adsorption capacity of lamellar HA was better than that of rod-like HA,which was attribute to larger surface area of lamellar HA, indicating that the surface area wasone of the most important factors affecting the adsorption capacity.The Freundlich and Langmuirequation were used to fit the adsorption isotherm types ofHA. The results showed that the rod-like HA was belong to the Freundlich-type adsorptionisotherm and lamellar HA was belong to the Langmuir-type adsorption isotherm, indicating thetwo different types of HA had strong adsorption capacity, and Cu2+was easy to be adsorbed.The adsorption results were fitted by pseudo-first-order kinetic equation, pseudo-second-order kinetic equation, Elovich model and interparticle diffusion model. The resultsshowed that the process of rod-like hydroxyapatite and lamellar hydroxyapatite adsorption ofcopper ions both followed pseudo-second-order kinetic equation. The adsorption processincluded two steps, separately for rapid surface adsorption and interparticle diffusion. Theresults of adsorption mechanism indicating that surface adsorption and ion exchange played animportant part in the removal of Cu2+by HA. |
PDF Full Text Request