Biosorption of hexavalent chromium from aqueous solution by pristine and CaCl2-modified erythromycin production residues

Abstract In this study, the adsorptive removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the pristine and salt-treated（CaCl2）erythromycin production residue (EPRs and SEPRs) were investigated. Batch experiments were carried out to determine the effect of contact time, sorbent dosage, pH, initial Cr concentration, and temperature on Cr(VI) sorption by EPRs and SEPRs. The highest adsorptive removal capacities were achieved at the pH equal to 1.0, and the maximum adsorption capacities for EPRs and SEPRs at optimized conditions were 21.74 and 35.24 mg g-1, respectively. Moreover, thermodynamic results indicated that Cr sorption by EPR/SERPs was feasible, spontaneous and endothermic under the given conditions. Langmuir model fitted well with the experimental data. The pseudo-second order could better describe the adsorptive removal kinetics and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. Furthermore, adsorption-coupled-reduction process was believed as the main mechanism of Cr(VI) removal by EPRs and SEPRs. Both adsorbents could be considered as promising low-cost biosorbent for the removal of Cr(VI) from aqueous systems.