Enhanced copper adsorption by DTPA-chitosan/alginate composite beads: Mechanism and application in simulated electroplating wastewater

A novel composite adsorbent of Ca-DTCS/ALG bead was prepared by immobilization of DTPA-modified chitosan micro-gels (DTCS) into the alginate matrix. The copper sorption properties of Ca-DTCS/ALG beads were tested and compared with the other two adsorbents of DTCS powder and plain alginate (ALG) beads. In addition, the mechanisms of copper sorption on the adsorbents were investigated by FTIR and XPS analysis. Similar to DTCS powder, Ca-DTCS/ALG beads exhibited high copper removal efficiency in strongly acidic solutions, whereas calcium, sodium and aluminum salts had little effect on its copper adsorption capacities. The maximum adsorption capacities of Ca-DTCS/ALG and DTCS were 107.5 and 106.0 mg g−1 at pH 3.0, respectively, which were close to the values predicted by the Sips model. However, the maximum adsorption capacity of ALG beads predicted by the Sips model was much higher than its experimental one (101.1 mg g−1). The copper adsorption equilibrium by DTCS powder was achieved within 1 min, nevertheless, ALG and Ca-DTCS/ALG gel beads reached the adsorption equilibrium within 500 min and 1440 min, respectively. Moreover, Ca-DTCS/ALG gel beads showed good reusability, but DTCS powder was not easily reused due to its notable swelling property. Furthermore, the efficiency of copper recovery by Ca-DTCS/ALG beads in the simulated electroplating wastewater at the copper concentration of 1-5 mg L−1 was much higher than that of DTCS and ALG beads. These results reveal that immobilization of DTCS into the alginate matrix greatly improves the adsorption and separation performance of the adsorbent.