Effective removal of basic dye onto sustainable chitosan beads: Batch and fixed-bed column adsorption, beads stability and mechanism

This study aims to develop sustainable low-cost chitosan-based beads by a simple dropping method, with instantaneous formation by reticulation with tripolyphosphate anion. The beads were characterized and applied to basic blue 7 (BB7) uptake. The adsorption process was optimized through variation of several parameters in batch experiments such as bead loading, pH, dye concentration and temperature. At a BB7 concentration of 400 mg/L and 60 min, the best BB7 adsorption capacity (1410 mg/g) and partition coefficient (8.22 mg/g/mu M) were achieved by chitosan beads, which were quite superior to others described in the literature. The obtained data best fitted to mixedand pseudo-first order kinetic models and to Redlich-Peterson isothermal model. A fixed-bed column experiment was conducted and the adsorption capacity and partition coefficient at 100% breakthrough were 12.06 mg/g and 0.06 mg/g/mu M. The bead storage study indicated that its adsorption capacity was not affected for a two-week period and reached 325 mg/g. Also, the presence of basic brown 4 (BB4) dye did not harm basic blue 7 in the simultaneous adsorption process and a removal capacity of 232 and 259 mg/g was reached for BB4 and BB7 dye, respectively. The presence of NaCl reduced the percentage of BB7 removal from 91% to 73%. The removal mechanism based on XPS, FTIR and BET analyses suggests that hydrogen bonds are the main adsorption mechanism followed by cation-exchange. This study gave rise to encouraging results and chitosan/tripolyphosphate beads proved to be potential adsorbents for industrial effluent treatments.