Sulfate Removal from Water Using Activated Red Mud: Kinetic, Isotherm and Thermodynamic Studies

In this study, absorption of sulfates on activated aluminum industry waste (red mud) has been investigated in a batch system by OFAT method. The properties of the absorbents were analyzed using scanning electron microscope (SEM), BET surface area, X-ray diffraction (XRD), XRF. The process of sulfate absorption was done in a volume of 200 mL and a mixer speed of 150 rpm. The optimum adsorption conditions were derived for in an equilibrium time of 90 minutes, the initial concentration of 100 ppm, pH=4, the temperature of 65 ◦C and 1.5 g/L dose of the absorbent. The efficiency of sulfate removal was 73.1 percent at the optimum conditions. Thermodynamic analysis of absorption showed that the absorption process at all analyzed temperatures had occurred spontaneously. Sulfate adsorption kinetics on composite surfaces followed a pseudo second order equation and absorption isotherm had a high conformity with Langmuir, Dobinin-Radoshkovich and Temkin isotherms respectively and the maximum absorption capacity of it according to Langmuir isotherm is 13.07 mg of sulfate per gram of the absorbent.