| Hydroxyapatite (HAp) can be used as an adsorbent for the adsorption of heavymetal ions because of its unique chemical composition and crystal structure. Theadsorption efficiency of HAp depends on its morphology, size, spatial structure andother features. Therefore, controlling the morphology of HAp to achieve highadsorption efficiency is of great significance. However, the HAp adsorbent has adrawback of inconvenience to separation. Iron oxide can not only be used as adsorbentfor heavy metal ions but also be separated from the solutions by the external magneticfield. HAp hollow microspheres and their magnetic composites with Fe3O4nanoparticles were prepared through using a hydrothermal method in this study. Theproducts have the advantages of uniform particle size, controllable morphology, largesurface area and strong adsorption ability. X-ray diffraction (XRD), scanning electronmicroscopy (SEM), transmission electron microscopy (TEM), fourier transforminfrared spectroscopy (FTIR) and surface area analyzer (BET) were employed tocharacterize the phase composition, morphology and surface area of the products.Kinetics and thermodynamics of the adsorption of Pb2+and Cd2+onto HAp/Fe3O4composites as well as the adsorption mechanism were also studied. The results aresummarized as follows. (1) HAp particles were prepared by a hydrothermal method through usingcalcium nitrate (Ca(NO3)2) as sources of calcium, diammonium phosphate((NH4)2HPO4) as sources of phosphorus and polyaspartic acid (PASP) as a chelatingagent. The effects of reaction temperature, time and pH on the morphology andcrystallinity of the products were studied. The results show that the crystallinity of theproducts increases with the increase of the pH value, reaction temperature and time.The products with spherical morphology can be prepared at the condition of acidic pH.Finally, HAp hollow microspheres with good sphericility, uniform size (about1.5μm),and high crystallinity were successfully prepared at temperature of180oC, pH value of5and time of24h. The specific surface area of HAp hollow microspheres was128.19m2/g.(2) Fe3O4nanoparticles with particle size of10-20nm were prepared by aco-precipitation method through using FeCl36H2O and FeCl24H2O as reactants andconcentrated ammonia as a precipitating agent. Then, HAp/Fe3O4composites weresuccessfully fabricated by a hydrothermal method through using the as-prepared Fe3O4nanoparticles as magnetic additives. The results show that the HAp/Fe3O4compositeshave a3D urchin-like hierarchical structure composed of many radically out-extending1D nanorods. Many Fe3O4nanoparticles dispersed among the building units. Moreover,the composites have good mangetic responsibility and dispersed ability in queoussolution. The BET specific surface area of the composites was113.48m2/g.(3) In this study, the as-prepared HAp/Fe3O4composites were used as adsorbentsto study the adsorption process of Pb2+and Cd2+. The effects of pH, initial metal ionconcentration and adsorption time on adsorption efficiency were investigated. Theresults show that the optimum adsorption pH value for Pb2+and Cd2+were3and7, respectively. The adsorption process for Pb2+and Cd2+was both in line withpseudo-secon-order kinetic equation. The adsorption isotherm types for Pb2+and Cd2+belong to the Langmuir-type adsorption isotherm. The maximum adsorption capacityof Pb2+and Cd2+were172.09mg/g and88.04mg/g, respectively. The removalmechanism of Pb2+ions by HAp/Fe3O4composites was the adsorption of Pb2+ions onthe composite surface and ion exchange reaction between Ca2+and Pb2+in aqueoussolution. |
PDF Full Text Request