Collagen-Fiber-Immobilized Tannins and Their Adsorption of Au(III)

Novel adsorbents that have an excellent adsorption capacity for Au(III) were prepared by immobilization of bayberry tannins and larch tannins onto collagen fiber matrixes. When the initial concentration of Au(III) was 478 mg/L and the amount of adsorbent was 20.0 mg, the adsorption capacities at equilibrium of immobilized bayberry tannins and larch tannins were 877 and 784 mgAu(III)/g respectively at 303 K. As the temperature was increased, the adsorption capacities were further increased. At a temperature of 323 K, the adsorption capacities at equilibrium of the immobilized tannins were as high as 1.50 × 103 and 1.36 × 103 mgAu(III)/g, respectively. The adsorption equilibrium data for Au(III) on the immobilized tannins can be well fitted by the Langmuir model, and the mechanism of the adsorption was found to be chemical adsorption. Furthermore, the adsorption isotherms of Au(III) in buffer solutions with different pH values could also be described by the Langmuir model, and the adsorption capacities increased at lower pH values. The kinetics of the adsorption can be well described by a pseudo-second-order rate model, and the adsorption capacities calculated by the pseudo-second-order rate model were close to the values actually measured at higher temperatures. It was found that the breakthrough point of the adsorption column was at 223 bed volumes for the experimental system, indicating that the immobilized tannins have an outstanding ability to concentrate Au(III). The mass-transfer coefficient of Au(III) adsorption in the adsorption column determined by the Adams−Bohart equation was 3.34 × 10-5 L/(mg·min).