Removal of Cr(VI) from aqueous solution using amine-impregnated crab shells in the batch process

Abstract

To increase adsorption capacity of Cr(VI) ions in aqueous solution, crab shells was chemically modified by means of copolymerization method using tri-ethyl amine and epichlorohydrine. Functional groups of chemically modified adsorbents were analyzed by Fourier Transform Infrared (FT-IR) and surface condition was confirmed by the SEM (scanning electron microscopy) and EDX (energy dispersive X-ray). It was found that the amino, amide and hydroxyl groups play an important role in adsorption of Cr(VI) ions. The adsorption capacity for Cr(VI) ions of the amine-impregnated crab shells was about 36.865 mg/g-dry mass and higher than that of virgin adsorbents (16.564 mg/g-dry mass) at initial solution pH 2.0. Langmuir and Freundlich models were used to fit the equilibrium data and the Langmuir isotherm model well fit the data. The maximum adsorption capacity (qm) for Cr(VI) ions was calculated as the 41.412 mg/g-dry mass. Also, the pseudo-second-order kinetic model well fit the experimental data better than that of the pseudo-first-order. In addition, the adsorption capacity of Cr(VI) decreased as the temperature rose, indicating the exothermic nature of the adsorption process. Furthermore, adsorption capacity of Cr(VI) for reused amine-impregnated crab shells can be still maintained at 33.653 mg/g level until the 2nd cycle. It was concluded that the adsorption process using amine-impregnated crab shells could be applied to the removal system of Cr(VI) ions from aqueous solution and it could sufficiently replace the commercial ion-exchange resins.