Diffusion of H+, H2O and D2O in polymer/silicate gels

General features of H+, H2O and D2O diffusion in polymer/silicate gels applied in different industrial areas were analyzed. It was found that the cumulative mass transport curves consist of two sections: an unsteady-state and a steady-state one. The length of the transient period is strongly dependent on the silicate content of the gel and the concentration gradient of H+ ions. Using the length and the intersection point of these periods the effective diffusion coefficient, break-through time and the ion retention capacity of gel could be calculated. The obtained effective diffusion coefficients were very close to the values characteristic in aqueous solutions. The diffusion mass transport could be described by the modified Fick's I law, however, it was stated that on account of the high ion retention in all gels the one-dimensional random-walk equation may not be used for prediction of the mean diffusion distance (break-through time). Using the formation factor of gel (effective "porosity" and tortuosity) the effective diffusion coefficient can be predicted with good accuracy and vice versa, the gel structure can be determined by the absolute and the effective diffusion coefficients characteristic in bulk aqueous phase and gel, respectively. The laboratory experiments provided valuable new information and data to design and formulation of the industrial "gel" technologies in both the enhanced oil recovery and the environmental protection. (C) 2004 Elsevier B.V. All rights reserved.