Epichlorohydrin-crosslinked chitosan beads as an efficient and highly acid-resistant adsorbent for hexavalent chromium removal

Epichlorohydrin crosslinked chitosan (E-CS) bead, an acid resistant and efficient adsorbent was successfully prepared for Cr(VI) removal. From morphological observation, the surface of E-CS bead was more porous than CS one. FTIR band corresponding to C-N-C asymmetric stretching (∼1420 cm- 1 ) was clearly observed after crosslinking process. After adsorption, crystalline characteristics of Cr-adsorbed E-CS clearly reduced, compared with those of CS and E-CS beads. E-CS bead exhibited rapid adsorption with high resistance under strong acidic condition. The maximum removal efficiency of E-CS bead was up to 97 % which was higher than that of the CS bead. Adsorption behavior of E-CS followed the pseudo-second-order kinetics and fitted well with Langmuir isotherm. The maximum adsorption ability of E-CS based on Langmuir calculation was 13.7 mg/g and reached adsorption equilibrium at 2 h. The prepared adsorbent could be regenerated at least five cycles with maintaining the removal efficiency higher than 95 %. The electrostatic attraction between protonated amine groups and negatively charged Cr(VI) ions (HCrO 4 − and Cr2O 7 2 − ions) and physical adsorption at porous surfaces were proposed as main adsorption mechanisms. Thermodynamic data showed that the adsorption process was proven more favorable at low temperatures and endothermic. The crosslinking of chitosan using epichlorohydrin as a simple and efficient method for preparation of highly acidic-stable CS bead without additional requirement of further modification has a high potential application for practical Cr(VI) removal process.