Removal of cadmium from aqueous solution using sonochemically modified clinoptilolite: Optimization and modeling

Abstract Clinoptilolite (CL) has been sonochemically modified by using NaCl solution and applying a 35 kHz ultrasound in 30 min and at 60 o C. The modified clinoptlolite (SNa–CL) has been characterized by X-ray diffraction (XRD), laser scattering, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and nitrogen adsorption/desorption isotherms. Results showed that the sonochemical modification process could reduce particle size, enhance effective cation exchange capacity from 0.10 to 1.58 meq/g, and enlarge the surface area of CL from 31.14 to 37.25 m2/g The cadmium removal efficiency of the modified CL was optimized using response surface methodology (RSM) with central composite design (CCD). Under the optimal condition with pH of 6.3, the contact time of 309 min, Cd initial concentration of 79.41 mg/L, and SNa–CL dosage of 7.02 g/L, the removal efficiency reached 99%. The adsorption kinetics was obeyed the second-order model and controlled by multiple steps. The adsorption isotherms were well fitted to the Langmuir model and the maximum adsorption capacity at different temperatures was more than 20 mg/L. The thermodynamic study showed that the adsorption of Cd onto SNa–CL was a spontaneous, endothermic, and physical–chemical process. The results in this work suggested that the sonochemical modification is a potential method for fabricating effective and low-cost adsorbents from natural resources.