Adsorption Property of in Situ Immobilized Black Wattle Tannin to La3+, Pr3+ and Nd3+

A new kind of adsorbent was prepared from the bark of black wattle being rich of tannin; furthermore, the cross-linking reaction of formaldehyde was used to immobilize tannin in situ to get the adsorbent. The adsorption property of this new adsorbent to ions of light rare earth such as La3+, Pr3+ and Nd3+ (RE3+) in aqueous solution was investigated. Results show that the optimum pH value of this adsorbent to La3+ is about 5.0, while the optimum value of Pr3+ and Nd3+ is about 5.5. The equilibrium adsorption capacity will decline significantly when the pH value of reaction system is changed from the optimum pH value. Compared with the effect of pH value, the influence of the temperature on the equilibrium adsorption capacity is weaker, and at 303 K the equilibrium adsorption capacity of this adsorbent to RE3+ is optimal. At 303 K and the optimum pH value, when the initial concentration of RE3+ solution is 5.0 mmol.L-1 and the dosage of adsorbent is 0.10 g, the equilibrium adsorption capacity of this adsorbent to La3+, Pr3+ and Nd3+ are 217.26, 228.56 and 329.76 mg.g(-1), respectively. The adsorption isotherm can be described by the Freundlich equation. This adsorption kinetics data of this adsorbent to RE3+ is fitted with the pseudo-second-order rate model well and the equilibrium adsorption capacities calculated by the model are consistent with the experimental data with the warps in 7 %.