Resource utilization of water treatment residual sludge (WTRS): effective defluoridation from aqueous solution

For resource utilization, water treatment residual sludge (WTRS) and its cerium-modified product (Ce-WTRS) were used as adsorbents to remove F− from aqueous solution. The adsorbent materials were characterized by energy dispersive X-ray, scanning electron microscope, X-ray diffraction, Fourier transform infrared, and specific surface area test techniques. Different experimental conditions such as pH, initial F− concentration, contract time, and temperature were investigated. The appropriate adsorption capacity was achieved in the pH range of 3–9. Adsorption kinetics, isotherm, and thermodynamic studies were used to illustrate the nature of F− onto adsorbents materials. Good fitting of pseudo-second-order kinetics model indicated the chemisorption nature. Further analyses of intra-particle diffusion model were carried out to determine the rate controlling step. It was found that the Langmuir and Temkin isotherm models fitted the experimental data better. The maximum adsorption capacity (qm) determin...