Preparation of EDTA modified chitooligosaccharide/sodium alginate/Ca2+ physical double network hydrogel by using of high-salinity oilfield produced water for adsorption of Zn2+, Ni2+ and Mn2+

A novel EDTA functionalized chitooligosaccharide/sodium alginate/Ca2+ physical double network hydrogel (ECSDNH) was prepared by using of high-salinity oilfield produced water. The formation and structure of ECSDNH were characterized by FT-IR and SEM. Various factors, including EDTA functionalized chitooligosaccharide content, pH of solution, initial concentration of heavy metal ions, temperature and contact time, were thoroughly investigated to explore their effect on adsorption capacity of ECSDNH. The obtained results showed that ECSDNH had higher adsorption capacity for Zn2+, Ni2+ and Mn2+. The maximum adsorption capacities of Zn2+, Ni2+ and Mn2+ were 160.19 mg/g, 72.67 mg/g and 52.43 mg/g at 298 K, respectively. The pseudo-second-order kinetic model and Langmuir isotherm model fit the experimental data fairly well. The thermodynamic parameters of the adsorption, ΔH°, ΔS°, and ΔG°, were also calculated. In addition, the ECSDNH still had higher removal efficiency for three metal ions after three adsorption-regeneration cycles, indicating its potential application for removing heavy metal ions from wastewater.