Study On Adsorption Capability Of China-hemp Fiber For Heavy Metalions

Nowadays, heavy metal ions pollution is a serious problem in China. Some heavy metal moved onto the food chain, which would lead the death of human beings.There are several methods for heavy metal ions removal, such as chemical precipitation ion-exchange and so on. However, adsorption is the most convenient and effective method. Especially, the biomass absorbents, as environment friendly and renewable resources, have great potential. China-hemp fibers consist of a large number of active chemical groups such as hydroxyl group, which is regarded as good natural adsorbent materials.In this study, citric acid and potassium permanganate modified China-hemp were used for heavy metal ions(Pb2+ and Cd2+) removal from aqueous solution to study the relative adsorption properties. The optimum adsorption conditions and adsorption mechanism were studied. Three theoretic adsorption models, Langmuir, Freundlich and Nernst isotherms, were used to simulate the thermodynamic performances of heavy metal ions on modified China-hemp. Pseudo first-order, second-order kinetic models, Elovich equation model and Particle diffusion control model were used to study the adsorption kinetics of heavy metal ions on modified China-hemp.The results show that by the modifications of citric acid and potassium permanganate on China-hemp fibers, a great deal of carboxyl groups and manganese groups are introduced into China-hemp fibers, and the adsorption capacity is significantly increased. The optimal adsorption condition to metal ions Pb2+ and Cd2+is 0.12 g/L and 0.08 g/L at pH 5.5 for 30 min, for citric acid modified China-hemp fibers, respectively, and 0.12 g/L and 0.08 g/L at pH 4.5 and 5.5 for 30 min for potassium permanganate modified China-hemp fibers, respectively. The batch equilibrium data fitted well to the Langmuir isotherms, that is, the process is mainlymonolayer adsorption and the force between the metal ions and the adsorbent is the ion bond. The adsorption kinetics of the heavy metal ions on modified China-hemp fibers was followed the pseudo second-order kinetic model, which supported the adsorption due to Van der waal' force and other intermolecular force apart from monolayer positioning adsorption due to coulomb force.