Study on an effective industrial waste-based adsorbent for the adsorptive removal of phosphorus from wastewater: equilibrium and kinetics studies

In this work, an effective adsorbent for removing phosphate from aqueous solution was developed from modifying industrial waste — lithium silica fume (LSF). The characterization of LSF before and after modification was investigated using an N2 adsorption–desorption technique (Brunauer–Emmett–Teller, BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Studies were conducted to investigate the effect of adsorbent dose, initial solution pH, contact time, phosphate concentration, and temperature on phosphate removal using this novel adsorbent. The specific surface area for modified LSF (LLSF) is 24.4024 m²/g, improved 69.8% compared with unmodified LSF. XRD result suggests that the lanthanum phosphate complex was formed on the surface of LLSF. The maximum phosphate adsorption capacity was 24.096 mg P/g for LLSF, and phosphate removal was favored in the pH range of 3–8. The kinetic data fitted pseudo-second-order kinetic equation, intra-particle diffusion was not the only rate controlling step. The adsorption isotherm results illustrated that the Langmuir model provided the best fit for the equilibrium data. The change in free energy (△G⁰), enthalpy (△H⁰) and entropy (△S⁰) revealed that the adsorption of phosphate on LLSF was spontaneous and endothermic. It was concluded that by modifying with lanthanum, LSF can be turned to be a highly efficient adsorbent in phosphate removal.