Adsorption of phosphate ions from aqueous solution by modified bentonite with magnesium hydroxide Mg(OH)2

Abstract This study investigated phosphate ions removal from aqueous solutions by using modified bentonite with magnesium hydroxide in batch system. Raw bentonite (RB) and Mg-modified bentonite (MB) were characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR). Adsorption experiments were conducted on the adsorption of phosphate onto RB and MB in batch experiments. Phosphate ion removal by MB was pH dependent, and the optimum adsorption was observed at pH 7. The adsorption process was relatively fast and equilibrium conditions were established within 120 min at 45 °C. The results were analyzed according to the Langmuir and Freundlich isotherm equations. The adsorption data is well interpreted by the Langmuir isotherm. Phosphate solution at a concentration of 25 mg/L was adsorbed by MB, and the final adsorption efficiency was > 54%. The results showed that phosphate adsorption density of MB was high with the maximum adsorption density of 14.33 mg/m2, which suggested that MB was an excellent adsorbent for effective phosphate removal from water. Thermodynamically negative ΔG°, positive ΔH°, and positive ΔS° demonstrated the high affinity, and endothermic adsorption process between MB and phosphate from aqueous solutions.