Removal of phosphates using eggshells and calcined eggshells in high phosphate solutions

Abstract

This study was conducted to evaluate the phosphate sorption properties of eggshell (ES) and calcined ESs (C-ESs) in a high-concentration phosphate solution. The C-ESs yield decreased rapidly at 900 degrees C, indicating that the CaCO3 constituting the ES was converted to CaO by the high calcination temperature. The optimum calcination temperature for phosphate removal using C-ES was 900 degrees C. The actual sorption amount of phosphate by ES and C-ES900 was in agreement with the Langmuir isothermal sorption equation, and the maximum sorption capacities derived from this equation were 178.6 and 270.3 mg/g, respectively. The sorption rate of phosphate by ES and C-ES900 was divided into two stages: an initial fast sorption stage, followed by a slow sorption stage. The sorption of phosphate by ES was dominantly influenced by the initial pH and salt concentration, whereas C-ES900 exhibited a constant sorption capacity regardless of environmental changes. The SEM-EDS and XRD results demonstrated that phosphate was successfully adsorbed on the ES and C-SE900 surfaces. In this study, it was found that the sorption of phosphate by ES occurred via ion exchange and precipitation reactions and that the sorption of phosphate by C-ES900 was dominantly affected by precipitation. Above all, C-ES can be applied as an effective adsorbent for removing high concentrations of phosphate under a wide range of environmental conditions.