Adsorption of Cr(VI) from aqueous solutions using chitosan-coated fly ash composite as biosorbent

The structure characteristics of chitosan/fly ash composite and equilibrium adsorption of Cr(VI) from aqueous solutions on this novel biosorbent were investigated. Adsorption experiments were carried out as a function of contact time, types of adsorbent, ratio, pH, temperature and coexisting ions. It was found that the adsorption of Cr(VI) reached equilibrium within 50 min. Adsorption capacity of Cr(VI) on composite adsorbent was higher than that on chitosan and fly ash, respectively. Composite adsorbent had the highest adsorption efficiency when the ratio was 30 wt%. The composite adsorbent was particularly effective for the Cr(VI) removal at pH 5.0 with the mechanism of electrostatic adsorption coupled reduction. Evaluation of adsorption process from 288 K to 328 K identified its exothermic nature. The maximum adsorption capacity of Cr(VI) was 33.27 mg/g at 288 K. Equilibrium data of Cr(VI) onto this composite adsorbent was well described by Langmuir isotherm model which indicated a physical adsorption process. Recovery studies showed that an effective desorption can be achieved by adding NaOH at pH 10.0, while it decreased as the adsorption–desorption cycles.