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Abstract: This study describes a new approach for the preparation of tannin-immobilized adsorbent by using mesoporous silica bead as the supporting matrix. Bayberry tannin-immobilized mesoporous silica bead (BT–SiO2) was characterized by powder X-ray diffraction to verify the crystallinity, field-emission scanning electron microscopy to observe the surface morphology, and surface area and porosity analyzer to measure the mesoporous porous structure. Subsequently, the adsorption experiments to Cr(III) were applied to evaluate the adsorption performances of BT–SiO2. It was found that the adsorption of Cr(III) onto BT–SiO2 was pH-dependent, and the maximum adsorption capacity was obtained in the pH range of 5.0–5.5. The adsorption capacity was 1.30mmolg−1 at 303K and pH 5.5 when the initial concentration of Cr(III) was 2.0mmolL−1. Based on proton nuclear magnetic resonance (HNMR) analyses, the adsorption mechanism of Cr(III) on BT–SiO2 was proved to be a chelating interaction. The adsorption kinetic data can be well described using pseudo-first-order model and the equilibrium data can be well fitted by the Langmuir isothermal model. Importantly, no bayberry tannin was leached out during the adsorption process and BT–SiO2 can simultaneously remove coexisting metal ions from aqueous solutions. In conclusion, this study provides a new strategy for the preparation of tannin-immobilized adsorbents that are highly effective in removal of heavy metals from aqueous solutions. [Copyright &y& Elsevier]

Abstract: Tannin is well known to be an inexpensive and ubiquitous natural biomass, which has high chelating affinity towards many metal ions. In this study, bayberry tannin (BT) was immobilized on mesoporous silica matrix to prepare a novel adsorbent, which was subsequently used for the adsorptive recovery of Au3+ from aqueous solutions. It was found that bayberry tannin-immobilized mesoporous silica (BT-SiO2) was able to effectively recover Au3+ from acidic solutions (pH 2.0). The equilibrium adsorption capacity of Au3+ on BT-SiO2 was high up to 642.0mg/g at 323K. Due to its mesoporous structure, BT-SiO2 exhibited an extremely fast adsorption rate to Au3+ as compared with other tannin gel adsorbent. The presence of other coexisting metal ions, such as Pb2+, Ni2+, Cu2+ and Zn2+, did not decrease the adsorption capacity of Au3+ on BT-SiO2, and BT-SiO2 had almost no adsorption capacity to these coexisting metal ions, which suggested the high adsorption selectivity of BT-SiO2 to Au3+. Additionally, about 73% of adsorbed Au3+ can be desorbed using aqua regia, and the Au3+ solution was concentrated about 18.0 times as compared with the original solution. Consequently, the outstanding characteristics of BT-SiO2 provide the possibility of effective recovery and concentration of Au3+ from diluted solutions. [Copyright &y& Elsevier]

Abstract: Collagen–tannin resin (CTR), as a novel adsorbent, was prepared via reaction of collagen with black wattle tannin and aldehyde, and its adsorption properties to UO2 2+ were investigated in detail, including pH effect, adsorption kinetics, adsorption equilibrium and column adsorption kinetics. The adsorption of UO2 2+ on CTR was pH-dependent, and the optimal pH range was 5.0–6.0. CTR exhibited excellent adsorption capacity to UO2 2+. For instance, the adsorption capacity obtained at 303K and pH 6.0 was as high as 0.91mmol UO2 2+/g when the initial concentration of UO2 2+ was 1.0mmol/L. In kinetics studies, the adsorption equilibrium can be reached within 300min, and the experimental data were well fitted by the pseudo-second-order rate model, and the equilibrium adsorption capacities calculated by the model were almost the same as those determined by experiments. The adsorption isotherms could be well described by the Freundlich equation with the correlation coefficients (R 2) higher than 0.99, the adsorption behaviors of UO2 2+ on CTR column were investigated as well. Present study suggested that the CTR can be used for the adsorptive recovery of UO2 2+ from aqueous solutions. [Copyright &y& Elsevier]