Diffusion of chromium ions in polymer/silicate gels

Diffusion transport of Cr(III) and Cr(VI) ions in polymer/silicate gels was studied. The effective diffusion coefficient, break-through time and ion retention capacity were determined as a function of the geometry and the composition of gel. It was found that the effective diffusion coefficients were very close to the value characteristic in aqueous solutions and they are proportional to the radii of hydrated ions. The high retention of Cr(III) ions in gels was attributed to in situ chemical reactions, mechanical entrapment and sorption. The diffusion mass transport of chromium ions could be described by Fick's first law. It was found that the diffusion coefficient decreases, while the break-through time and ion retention increase with the solid content of gel. The relative effect of polymer is greater by an order of magnitude than that of the silicate content. The influence of gel components can be interpreted by a diffusion model elaborated originally for porous systems. It was also shown that the polymer concentration is mostly effective in increasing the tortuosity, while in the case of silicate content both the porosity and the tortuosity must be considered. The laboratory experiments provided valuable information and data to design efficient profile correction and containment technologies in enhanced oil recovery and environmental protection. (C) 1998 Elsevier Science B.V. All rights reserved.