Application of Response Surface Methodology for Optimization of Cadmium Ion Removal from an Aqueous Solution by Eggshell Powder

The removal of cadmium(Cd) from synthetic solutions by batch adsorption process was performed using eggshell powder, which is mainly composed of calcite(CaCO3). In order to optimize the adsorption process, a re-sponse surface methodology(RSM) based on Central Composite Design(CCD) was applied. Developed model for Cd remo- val yields(R, %) response was statistically validated by variance analysis(ANOVA) which showed a high de-termination coefficient value(R2=0.9889). According to Minitab software, the optimal conditions were found at tem-perature of 44 °C, eggshell adsorbent dose of 2.98 g, initial Cd concentration of 36.74 mg/L and initial pH of 7. Un-der these conditions, the Cd removal yield was 98.76%. The deviation value of 1.24% confirms the validity of the model for the adsorption process optimization. The adsorption isotherm has been described by a Freundlich model. In addition, the predominant sorption mechanisms are the chemisorptions or precipitation(non-reversible) and ion ex-change(reversible).