A Noval Cation–Anion Absorbent of Tannin-Dialdehyde Carboxymethyl Cellulose for Removal of Cr(VI) and Ni(II) from Aqueous Solutions with High Adsorption Capacity.

A novel cation–anion adsorbent based on dialdehyde carboxymethyl cellulose (DCMC) and tannin (TA) was produced. The obtained absorbents were characterized by the scanning electron microscopy, energy dispersive spectrometer, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The influences of absorbent dosage, pH values, initial concentration and temperature on Cr(VI) adsorption and Ni(II) adsorption were discussed. Adsorption results were evaluated by four kinetic models and four adsorption isotherms fitting. The adsorption capacities of Cr(VI) and Ni(II) on TA/DCMC were 281.94 mg/g and 43.68 mg/g, respectively. The adsorption kinetics of Cr(VI) and Ni(II) on TA/DCMC were both consistent with the pseudo-second-order kinetics model. Besides, the adsorption data of Cr(VI) fitted into the Langmuir model and the adsorption results of Ni(II) fitted into the Freundlich model. Thermodynamic analysis demonstrated the adsorption was endothermic, spontaneous, and entropy increased process. The restrained adsorption followed the order Cl⁻ > NO⁻₃ > H₂PO⁻₄ > HCO⁻₃ for Cr(VI) adsorption and Pb(II) > Ca(II) > Cu(II) > Zn(II) for Ni(II). After 4 recycles, the Cr(VI) and Ni(II) adsorption capacities were 52.89% and 68.95% of the absorbent in first use, respectively. The absorbent shows great potential in water treatment field. [ABSTRACT FROM AUTHOR]