Chitosan immobilized Chinese gallotannin: A potential adsorbent to enrich the rare metals Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ)

Abstract

In this study, a solid adsorbent based on Chinese gallotannin and chitosan was generated and applied to adsorb rare and scattered metals, including Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ), from simulated zinc plant leachates. Fourier-transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (SSNMR) were performed to characterize the grafting way of Chinese gallotannin on the chitosan matrix. It was clearly showed that Chinese gallotannin was immobilized on the chitosan by Schiff-base condensation and phenol-formaldehyde reaction at the molar ratio of glutaraldehyde to tannin of 2:1. And the amount of chitosan amino groups was ten times that of tannin, with an initial pH of 4. The adsorption experiments showed that an appropriate increase in pH was more beneficial to enhance the adsorption capacity of immobilized Chinese gallotannin (ICGT). At a temperature exceeding 30 °C, the immobilized tannin became less sensitive to temperature. Adsorption kinetics studies showed that the adsorption of the three scattered metals by ICGT followed a quasi-second-order kinetic equation, with chemisorption as the mechanism. The adsorption isotherm was well fitted by the Langmuir model, indicating uniform adsorption sites on the surface of ICGT. The adsorption capacities of Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ) in solution by the adsorption model of monolayer were 61.39 mg/g, 63.82 mg/g, and 59.92 mg/g, respectively. Mechanical property and stability tests showed that ICGT had good resistance to harsh adsorption conditions of scattered metal ions.