Development of ceramic honeycomb monolith from natural zeolite tested as adsorbent to remove methylene blue in aqueous media

This work presents a ceramic monolith with a honeycomb structure obtained from a natural zeolite (clinoptilolite), bentonite, and alumina. The monolith obtained by extrusion had a cell density of 57 CPSI (cells per square inch), an open frontal area of 52% w/w, and a wall thickness of 0.9 mm. The raw materials and the natural zeolite ceramic monolith (NZCM) were characterized by X-ray diffraction, N₂ adsorption-desorption at 77 K, CO₂ adsorption at 273 K, mercury intrusion-extrusion, axial compression tests, resistance to leaching at acidic and basic pH, and point of zero charge. The NZCM presented an S_BET = 31 m²∙g^-1, a modal micropore size of 0.44 nm, a porosity of 39%, the compressive stress = 14 MPa, and a pH_PZC = 7.5. The NZCM was used as an inexpensive and easy-to-handle adsorbent to remove methylene blue (MB) dye in batch studies of kinetics and adsorption isotherms. From modeling of adsorption kinetic data, the predominant phenomenon in this system was physisorption. The modeling of adsorption isotherm data shows that the material has homogeneous active sites. The adsorption occurs by monolayer formation, finding a maximum capacity removal rate of 27 mg MB per gram of NZCM. Compared to other structured materials, a high capacity for removing MB with the ceramic monolith was obtained along with good mechanical properties and resistance in acidic and alkaline environments.