Removal of boron from aqueous solutions by batch adsorption on calcined alunite using experimental design

In the present paper, boron removal from aqueous solutions by batch adsorption was investigated and 23 full factorial design was applied. Calcined alunite was used as adsorbent. In the study, three parameters affected the performance and two levels of these parameters were investigated. The chosen parameters were temperature (25 and 45 °C, respectively), pH (3 and 10) and mass of adsorbent (0.5 g adsorbent per 25 mL solution and 1 g adsorbent per 25 mL solution). The significance of the effects was checked by analysis of variance (statistical software, MINITAB-Version 15). The model-function equation for boron adsorption on calcined alunite was obtained. The results showed that temperature, pH and mass of adsorbent affected boron removal by adsorption. Boron removal increased with increasing pH and adsorbent dosage, but decreased with increasing temperature. The optimum conditions were found as pH 10, adsorbent dosage = 1 g of calcined alunite per 25 mL solution and temperature = 25 °C by using factorial design. In addition, the effects of parameters such as calcination temperature, pH, temperature, adsorbent dosage and initial boron concentration on boron removal were investigated. The adsorption isotherm studies were also performed. Maximum adsorbent capacity (q0) was calculated as 3.39 mg/g. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were also determined.