The Research On Adsorption Of Congo Red, Light Green And Acid Chrome Blue K From Aqueous Solution By Chitosan Coated Zeolite

Zeolite has a relatively large surface area, and good adsorption properties, which has been widely used in water treatment, but it has a low capacity on the adsorption of anionic dyes. Chitosan is a renewable and abundant natural macromolecule compound, which is nontoxic, biocompatible and biodegradarable, and it has been widely used in environmental engineering, life sciences and other fields, but it is expensive. To improve the adsorption properties of zeolite and the utilization of chitosan, the research designed an adsorbent, chitosan coated zeolite (CCZ), which was prepared by coating chitosan onto the surface of zeolite, for removal of congo red (CR), light green (LG) and acid chrome blue K (AK) from synthetic solutions.In the batch adsorption, the effect of various experimental conditions, such as contact time, adsorbents dose, pH values, coexisting ions, initial concentration of the adsorbate and temperature were carried out. The experimental results showed that the appropriate initial pH for the three dyes adsorption on CCZ was 4. During the pH value 4～10, the adsorption quantity of CCZ binding CR was approximately constant. Adsorbate concentration and temperature had varying degrees on the adsorption rates. The adsorption quantities of dyes increased with the increase of the adsorbate concentration, and all the isothermal data followed the Langmuir model. The maximum adsorption capacity (qm) of CR, LG and AK from Langmuir model was 10.0,40.7 and 29.8 mg·g-1, respectively. Compared with zeolite, adsorption quantities of CCZ for three dyes were all improved. The kinetics process of adsorption consisted of two phases:an initial rapid phase and a slower second phase. The Elocich model showed good correlation for the adsorption of CR and AK on CCZ, while for LG adsorption, it was the pseudo-second-order model fitted best. Electrostatic attraction may be the main mechanism of the three dyes adsorption. The activation energy (Ea) of CCZ binding CR, LG and AK was determined as 66.0, 37.3 and 57.4 kJ·mol-1, respectively. The negative values of AG indicated that the adsorption processes were spontaneous. In the binary system, CR and LG were simultaneously adsorbed, and there was competitive adsorption between them. In addition, the used CCZ, which was used to remove CR and AK, could be regenerated by NaOH solution (0.01 mol·L-1) and the regeneration rate could reach 98.7% and 40.9%, respectively. But the LG-loaded CCZ was regenerated by microwave irradiation with 320 W for 10 min, and the regeneration rate was 98.7%.