The dynamics and adsorption of Cd (II) onto hydroxyapatite attapulgite composites from aqueous solution

To obtain cheap and environmentally friendly adsorbents, an attapulgite hydroxyapatite composite (HAA) was prepared via a co-precipitation method with attapulgite as the matrix. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used for material characterization. The isothermal, thermodynamics, factors experiments (pH, anions), kinetics, and competitive adsorption were studied. The formation of Ca (II) and rate equation were used to explain the mechanism of adsorption and mechanism of anionic action. The data showed that the adsorption was well described by the Langmuir model and quasi-second-order kinetics model. Thermodynamic parameters (Delta H (0) > 0, Delta S (0) > 0, Delta G (0) < -20 kJ/mol) suggested that the adsorption was an endothermic chemical adsorption process. Further analysis of the mechanism showed that ion exchange also contributed to the removal of Cd (II). Studies found that pH values < 5 caused partial dissolution of HAA and high temperature was conducive to rapid adsorption. The F- and SO4 (2-) promoted adsorption by the precipitate with Ca (II), and Cl- hindered adsorption by complexation with Cd (II). The adsorption capacity of HAA was 3(.)70, 1.99, 1.17, 0.98 mmol/g for Pb (II), Cu (II), Cd (II), and Zn (II), respectively, indicated that HAA may be promising for composite materials to remove heavy metals from water. [GRAPHICS] .