Adsorptive recovery of Au~(3+) from aqueous solutions using bayberry tannin-immobilized mesoporous silica

摘要

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 Au~(3+) from aqueous solutions. It was found that bayberry tannin-immobilized mesoporous silica (BT-SiO_2) was able to effectively recover Au~(3+) from acidic solutions (pH 2.0). The equilibrium adsorption capacity of Au~(3+) on BT-SiO_2 was high up to 642.0 mg/g at 323 K. Due to its mesoporous structure, BT-SiO_2 exhibited an extremely fast adsorption rate to Au~(3+) as compared with other tannin gel adsorbent. The presence of other coexisting metal ions, such as Pb~(2+), Ni~(2+), Cu~(2+) and Zn~(2+), did not decrease the adsorption capacity of Au~(3+) on BT-SiO_2, and BT-SiO_2 had almost no adsorption capacity to these coexisting metal ions, which suggested the high adsorption selectivity of BT-SiO_2 to Au~(3+). Additionally, about 73% of adsorbed Au~(3+) can be desorbed using aqua regia, and the Au~(3+) solution was concentrated about 18.0 times as compared with the original solution. Consequently, the outstanding characteristics of BT-SiO_2 provide the possibility of effective recovery and concentration of Au~(3+) from diluted solutions.