Adsorption of methylene blue onto clay/carbon composite: kinetics and isotherms study

Waste treatment for pollution control is a hot topic being studied and has received growing attention. In this study, spent bleaching earth (SBE), a waste material from the oil refineries, was pyrolyzed in a N-2 atmosphere to produce an environmentally sustainable clay/carbon composite (SBE@C (500 degrees C)). SBE@C (500 degrees C) was tested for its ability to remove methylene blue (MB) from water. The Langmuir model best explained the adsorption isotherms, with maximum adsorption capacity of 29.54 mg/g (MB solution (10-60 mg/L)). The pseudo-second-order kinetic model effectively described the adsorption kinetics data. Thermodynamic parameters indicated spontaneous and endothermic processes. The impact of coexisting cations on MB adsorption by SBE@C (500 degrees C) decreased in the following order: Fe3+ > Al3+ > Mg2+ > K+ > Na+. The ionic strength results indicated that increasing the concentration of Na+ ions led to a decrease in adsorption capacity. MB removal was greatest at pH level of 8. The adsorption mechanisms involved pi-pi interactions, electrostatic interactions, and changes in physicochemical properties. After 3 cycles, SBE@C (500 degrees C) may be recycled up to 11 times before completely losing its adsorption capacity. Overall, SBE@C (500 degrees C) shows promise for removing MB from wastewater, while mitigating secondary pollution from SBE.