عنوان مقاله [English]
In the present study, carboxylated chitosan nano-particals grafted by citric acid was synthesized and used to remove Cr(VI) from a synthetic solution and a real electroplating wastewater. Nano-particles are formed by reaction of the amino group of chitosan with carboxyl group of citric acid as crosslinking agent. Synthesized materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) and zeta meter techniques. The optimization of different adsorption parameters, such as pH of the solution in the range of 3 to 6, the initial metal ions concentration in the range of 10 to 110 mg/l, the adsorbent dose in the range of 0.5 to 3.5 g/l and at different contact time intervals, were investigated. The results indicated that the adsorption of Cr(VI) ions on the surface of the adsorbent decreased with increasing solution pH. Optimal values of pH of the solution, concentration of metal ion, adsorbent dosage and contact time were attained at 3, 70 mg/l and 3 g/l and 60 min, respectively. Under these conditions, efficiency of maximum removal was 94\% for Cr (VI) at concentration of 70 mg/l
in a synthetic solution and 82.27\% for electroplating wastewater. The adsorption data fairly fitted to Langmuir, Freundlich, and Sips isotherms. The adsorption isotherm was better explained by the Sips rather than by the Langmuir and Freundlich model. The kinetic data of adsorption reactions and the evaluation of adsorption equilibrium parameters just in some dosages were described by pseudo-first-order equations. To calculate thermodynamic parameters of Cr(VI) adsorption, experiments were performed at temperatures of 25, 35, $45^0C$ in a batch system. Thermodynamic parameters, such as $\Delta Go$, $\Delta Ho$ and $\Delta So$, were also evaluated.Regeneration of chitosan nano-particles was investigated and the results indicated that three cycles of adsorption-desorption for adsorbent re-use without significant loss of adsorption capacity is attainable.The results suggest that carboxylated chitosan nano-partical can be utilized as an adsorbent for an efficient removal of hexavalent chromium from aqueous solution and electroplating wastewater.