In situ immobilization of tannin of Larix gmelini and its adsorption to Au(Ⅲ)

Tannins in the bark of Larix gmelini were immobilized in situ by cross-linking reaction of formaldehyde. The adsorption behavior of this new adsorbent to Au(Ⅲ) in aqueous solution was investigated. It was found that the adsorption capacity of this adsorbent to Au(Ⅲ) was Au 1 821.9 mg/g at 303 K when the initial concentration of Au(Ⅲ) was 522.3 mg/L.The optimal pH for the adsorption of Au(Ⅲ) was 4.0, and that higher temperature led to higher adsorption capacity. The adsorption isotherm of Au(Ⅲ) on the immobilized tannin of L.gmelini could be described by the Langmuir equation. The data of adsorption rate could be well fitted by the pseudo-second-order rate model. The breakthrough point of adsorption column was at 117 bed volumes when the inlet concentration of Au(Ⅲ) was 239.2 mg/L, indicating that this adsorbent has outstanding ability of recovering Au(Ⅲ). Further studies indicated that the adsorption mechanism of immobilized tannin of L.gmelini to Au(Ⅲ) was mainly redox adsorption.