Enhanced adsorptive removal of phosphate from aqueous solution by activated sand/metal layered double hydroxides

In the present study, Mg-Fe and Ni-Fe layered double hydroxides have been examined to enhance the uptake capacity of activated sand as low-cost adsorbents for adsorption of phosphate. The physical and chemical properties of adsorbents were investigated by X-ray diffractometer (XRD), X-ray fluorescence (XRF) spectrum, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis. The best efficiency of both adsorbents was obtained at the optimum condition of initial phosphate concentration: 1000 mg/L, adsorbent dose: 1 g, pH: 7-7.5, and a temperature of 298 K. The equilibrium isotherm studies show that the best result was attained in the Langmuir model for phosphate; therefore, homogeneous adsorption is dominated, which was also emphasised by three-parameter-isotherm models. The maximum adsorption capacity for functionalised sand with Mg-Fe and Ni-Fe layered double hydroxides were obtained 69.47 and 66.64 mg/g, respectively. The kinetic data fit well with the pseudo-second-order kinetics and demonstrate that the porous diffusion effectiveness is over film diffusion. Thermodynamic parameters evoke the feasibility of the adsorption process as well as the positive influence of temperature on adsorption.