Removal of Methylene Blue from Aqueous Solutions by Sewage Sludge Based Granular Activated Carbon: Adsorption Equilibrium, Kinetics, and Thermodynamics

Sewage sludge based granular activated carbon (SSGAC) was prepared using calcium sulfate as binder. The porous structure and surface chemical properties of SSGAC were characterized by N2 adsorption isotherm, FTIR, PZC, and Boehm titration. The results showed that the SSGAC was a typical mesoporous adsorbent of which the percentages of mesoporous surface area and volume are 72.81 % and 88.89 %, and the acid groups were dominant on its surface. The adsorption mechanism of MB adsorption onto SSGAC was also investigated by different adsorption models. The results showed that the maximum MB adsorption amount could be 131.8 mg g–1, and the MB adsorption onto SSGAC was a heterogeneous, spontaneous, and endothermic process while physisorption was dominant. The MB adsorption process was well described by the pseudosecond-order kinetic mode, and the MB diffusion in micropores was the potential rate-controlling step.