Preparation Of Collagen-Immobilized Tannin Membranes And Their Adsorption Behaviours To Hg～(2+),Pb～(2+) And UO₂～(2+) In Water

Based on the mechanism of vegetable tannins–aldehyde combination tannage in leather-making, a kind of novel immobilized tannin membrane was prepared through cross-linking reaction of oxazolidine between condensed tannins and collagen fibers. The physical and chemical characters of the membrane were tested. It was found that when bayberry tannin was used, the destructure temperature of the membrane could reach 92℃ and the tensile strength could reach 18.73N/mm2. The transmembrane flow of water was 93.87 L/m2.h. The soaked water ratio of the membrane was 173%. When the membrane was soaked in water for 96 hours, no tannins were detected. As a result, the combination tannage could be utilized as a new method to make immobilized tannins.Using Hg2+ and Pb2+ as examples, the adsorption capacity of immobilized bayberry tannin membrane to heavy metal ions was investigated. The results showed that the phenols of tannins played a significant role on adsorption to the heavy metal ions. The pH value of the solution had a remarkable effect on the equilibrium adsorption capacity, and the optimal pH range for adsorption was between 5.0-7.0. Temperature also impacted the equilibrium adsorption capacity and higher temperature leaded to higher equilibrium adsorption capacity. When the adsorption temperature was 303K and the initial concentrations of Hg2+ and Pb2+ were 249.19mg/L and 311.75mg/L respectively, their equilibrium adsorption capacities were 75.21mg(Hg2+)/g and 41.94mg(Pb2+)/g. Under the given temperatures, the adsorption isotherm of Pb2+ on immobilized tannin membrane could be described by the Langmuir model. However, the isotherms of Hg2+ tended to be fitted well by the Frenudlich model at high temperatures. These data showed that the complexation mechanism between immobilized tannins membrane and heavy metal ions was different with various metal ions and temperatures. The adsorption kinetic data showed that the adsorption rate was fastest in the first one hour and the equilibrium was reached in 5h and 3h for Hg2+ and Pb2+ individually. The data of adsorption rate could be described by pseudo-second-order rate model. Continuous adsorption experiments indicated that fluid bulk of Hg2+ and Pb2+ were 120ml and 110ml before the breakthrough point when their initial concentrations were 102.02mg/L and 141.35mg/L and mono-layer membrane was used. However, the fluid bulk of Hg2+ and Pb2+ were 1100ml and 950ml respectively when tri-layer membrane was used. The membrane was easy to be regenerated by 0.1M HNO3 after continuous adsorption and the concentration of the fluid was highest when 35ml 0.1M HNO3 was used. At the same time, no considerable change of adsorption property was observed after adsorption and desorption cycles. These showed that the membrane was endued strong resistance to the regeneration of 0.1M HNO3.The adsorption of immobilized tanning membranes to uranium (UO22+) showed that the optimal pH range was between 5.0-8.0. The tannins contributed much to the adsorption of the heavy metal ions. The higher the temperature was, the stronger equilibrium adsorption capacity was. At 303K, when the initial concentration of UO22+ was 298.94mg/L, the equilibrium adsorption capacity of the immobilized bayberry tannin membrane was 61.14mg(UO22+)/g. The adsorption isotherm was fitted well by the Frenudlich model. The adsorption kinetic data showed that the equilibrium was reached in 4h and the data of adsorption ratio could be described by pseudo-second-order rate model. Continuous adsorption experiments indicated that fluid bulk was 200ml before the breakthrough point when the initial concentration was 259.72mg/L and mono-layer membrane was used. While under the same conditions, the fluid bulk was 1800ml when tri-layer membrane was used. The membrane was easy to be regenerated by 0.1M HNO3 and the desorption curves could be well overlapped with each other. It could be concluded that the immobilized tannin membrane had excellent adsorption ability to uranium.The second part of the paper focused on...