Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (06): 1209-1218.doi: 10.3866/PKU.WHXB201304031

• THEORETICAL AND COMPUTATIONAL CHEMISTRY • Previous Articles     Next Articles

Comparison of the Poisson-Boltzmann and Donnan Models for Calculating the Ion Equilibrium between Compacted Bentonite Porewater and External Solution

TIAN Wen-Yu, LIU Xiao-Yu, LI Chun, WANG Lu-Hua, ZHENG Zhong, LIU Chun-Li   

  1. Beijing National Laboratory for Molecular Sciences, Radiochemistry and Radiation Chemistry Key Laboratory for Fundamental Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2013-01-29 Revised:2013-04-03 Published:2013-05-17
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (11075006, 91026010) and Special Foundation for High-Level Waste Disposal, China (2007-840, 2012-851).

Abstract:

The ion equilibrium at the interface of solution within compacted bentonite, and the external solution is an important factor influencing the diffusion of ionic species in the compacted bentonite. The ion equilibrium can be calculated by the Donnan model using macroscopic compacted bentonite parameters. By constructing a single pore type structure model for compacted bentonite, where the montmorillonite TOT-layers are depicted as a parallel array of rectangles, the ion equilibrium can also be calculated by the Poisson-Boltzmann (PB) model with a scale-defining variable H. We demonstrated that the ion equilibrium coefficients calculated by the PB model are always larger than those calculated by the Donnan model, and the models are linked by the factor H. The mathematical transition from the PB model to the Donnan model occurs in the limiting case H→0. The application of the two models to diffusion problem is also discussed, and the PB model is shown to be more realistic and suitable for solving actual diffusion problems.

Key words: Bentonite, Porewater, Ion equilibrium, Donnan model, Poisson-Boltzmann model

MSC2000: 

  • O647