Improvement of anionic-dye removal efficiency of clinoptilolite by cobalt-impregnation

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Clinoptilolite that is an abundant natural-zeolite was modified by cobalt-impregnation for the sorptive removal of anionic-anthraquinone dye Lanaset-Green-B from its neutral solutions. Co-content loaded on the Na-form of the clinoptilolite from its nitrate solution was determined as 2, 15, 30 and 37% (w/w) by atomic-absorption and inductively coupled-plasma-mass-spectrometry. All of the sorbents dried at 105°C have quite high probability for the Lanaset-Green-B but heat treatment at 500°C decreased their removal efficiency. The sorbent containing 15% cobalt can remove 0.202 mmol/g Lanaset-Green-B, which is more than 10 times higher that of natural-clinoptilolite. Sorption results were explained by considering their porosity, surface area, morphology, crystal-structure, functional-groups and electro-kinetic properties determined from nitrogen adsorption-desorption, scanning-electron-microscopy, X-ray-diffraction, Fourier-transform-infrared-spectroscopy and zeta-potential measurements, respectively. The pseudo-second-order rate-constants and diffusion-coefficients regularly decrease in 43.830–0.865 g mmol/s and 5 × 10−14 − 0.25 × 10−14 m2/g range with the cobalt-loading, respectively. Parameters obtained from the Freundlich, Dubinin-Radushkevich and Langmuir equations revealed that dye is sorbed mainly on the positively charged Co-surface-complex, hydrogen-bonding interactions and ion-exchange between Lanaset-Green-B and nitrate ions. Sorption capacities of cationic-dye Methylene-Blue on the Co-loaded sorbents both in dried and calcined form are lower than that of the natural-clinoptilolite.