Adsorption recovery of thorium(IV) by Myrica rubra tannin and larch tannin immobilized onto collagen fibres

Novel adsorbents which can concentrate Th(IV) in aqueous solution were prepared by immobilizingMyrica rubra tannin and larch tannin onto collagen fibre matrices. The adsorption capacities of the immobilized tannins to Th(IV) are related to temperature and pH value of the adsorption process. For example, when the initial concentration of Th(IV) was 116.0 mg·l^-1 and the immobilized tannin was 100 mg, the adsorption capacities of immobilized Myrica rubra tannin and larch tannin were 55.98 mg Th(IV)·g^-1 and 13.19 mg Th(IV)·g^-1, respectively at 303 K, and 73.67 mg Th(IV)·g^-1 and 18.19 mg Th(IV)·g^-1 at 323 K. It was also found that the higher adsorption capacity was obtained at higher pH value. The adsorption equilibrium data of the immobilized tannins for Th(IV) can be well fitted by the Langmuir model and the mechanism of the adsorption was found to be a chemical adsorption. In general, the adsorption capacity of immobilized Myrica rubra tannin to Th(IV) is significantly higher than that of immobilized larch tannin, probably due to the fact that the B ring of Myrica rubra tannin has a pyrogallol structure which has higher reaction activity with metal ions. The breakthrough point of the adsorption column of immobilized Myrica rubra tannin was at 33 bed volumes for the experimental system. The mass transfer coefficient of adsorption column determined by Adams-Bohart equation was 1.61·10^-4 l·mg^-1.min^-1. The adsorption column can be easily regenerated by 0.1 mol·l^-1 HNO₃ solution, showing outstanding ability of concentrating Th(IV). This revised version was published online in July 2006 with corrections to the Cover Date.