Application of Mesopore-Activated Red Mud for Phosphorus Adsorption

Abstract

In this paper, the mesopore-activated red mud (M-ARM) was prepared by treating red mud (RM) with acid under an ultrasonic batch and through heat treatment at 750 C. The surface area and adsorption average pore width of M-ARM were calculated and obtained values of 13.408 m2 g-1 and 25.160 nm, respectively. Therefore, the maximum adsorption capacity of M-ARM for phosphorus was $200.85\pm 1.66\text{mg}{\text{g}}^{-1}$ at 318 K and $\text{pH}=5$ . At a low initial concentration (75 mg L-1), the phosphorus removal capacity by M-ARM material was up to $97.09\pm 0.15\%$ at 313 K. With the temperature scales varying from 298 to 313 K, the values of Gibbs free energy change ( $\Delta G°$ ) were negative and also vary from -37.47 to -36.68. The phosphorus adsorption process in an aqueous solution is spontaneous, and this adsorption process was exothermic with enthalpy change $∆{\text{H}}^{\text{o}}=-14.36$ . From the results of investigations and calculations of thermodynamic values, kinetics, and adsorption capacity of materials, we can confirm that the materials in this study had a low-cost and potential material for applications to treat phosphorus-contaminated water. In addition, the adsorption kinetics of this material for phosphorus were also studied and discussed.