Adsorption kinetics of Eu(III) and Am(III) onto bentonite: analysis and application of the liquid membrane tidal diffusion model
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A new liquid membrane tidal diffusion model (LMTD) was applied based on three assumptions to analyze the kinetics of Eu(III) adsorption on Ca-bentonite and Am(III) adsorption on Na-bentonite. The changes in adsorption quantities as a function of contact time presented the phenomenon of tidal fluctuation according to the experiments. The tidal fluctuation showed a periodic change, and the change period was slightly affected by temperature. An adsorption event includes at least one fluctuation and each fluctuation can be divided into three steps: liquid membrane diffusion, surface diffusion and internal diffusion. Each step consists of one to three processes: physical adsorption, physical desorption and chemical adsorption. The pseudo-first-order or pseudo-second-order kinetic model did not fit the experimental curves well at t = 6 h. The first-order reaction and the second-order reaction were introduced to establish the LMTD and to explain the adsorption steps and processes. This new kinetic model is helpful to better explain the mechanism of adsorption reactions.
KeywordsLiquid membrane tidal diffusion Adsorption Kinetics Adsorption quantity
This work was financially supported by the National Natural Science Foundation of China (21561001) and the Natural Science Foundation of Jiangxi Province, China (20161BAB203100).
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