Fissure adsorption experiments

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

Fissure Adsorption Experiments. To perform fissure sorption experiments, one end of each fissure was connected via small bore tubing to a microliter pipetter as is shown in Figure 2. Rock-equilibrated water, described below, was injected into each fissure and the fissure walls were allowed to equilibrate with the solution for a period of two days before the adsorption experiments were performed. 

Adsorption experiments were performed by removing rock-equilibrated water from the fissures and injecting stock solution which was made by dissolving tracer amounts of americium-241 in rock equilibrated water. The stock solution was allowed to equilibrate within the fissures for different periods of time and was then removed from each fissure. The stock solution was assayed before injection and after removal from the fissures so that the change in americium concentration was determined for a different time in each fissure. Ten adsorption experiments were performed in this manner and the results are presented in table I. Figure 3 is a graphical representation of the initial part of the adsorption curve. 

Figure 2. Apparatus used in static fissure adsorption experiments...

Fissure Desorption Experiments. Desorption experiments were performed with two fissures by injecting rock equilibrated water into the fissures immediately after removing the americium-bearing solution from the fissures in adsorption experiments. After injection, the rock-equilibrated water was allowed to react within the fissures for a period of time before removal. The rock-equilibrated water was assayed after removal from the two fissures and the amount of nuclide desorbed as a function of contact time was determined. Between five and seven desorption experiments were performed for each of six time periods between ten seconds and sixty minutes for each of the two fissures. The results of the desorption experiments are presented in table 2 as the percent of 3 (at equilibrium) that desorbed from the fissures in a period of time. 

Table I. Am Adsorption by Gray Hornblende Schist Fissure Experiments (static)...

Model Predictions. The rate for desorption of americium from the fissure surfaces into solution was assumed to equal the rate for the adsorption of americium from solution by the fissure surfaces. The sorption rate and the equilibrium fractionation of americium that were determined in the static experiments were used to determine input parameters to the ARDISC model. The ARDISC model predictions for the distributions of americium on the fissure surfaces in both sets of experiments are presented in Figures 5 through 10 along with the autoradiographs and the experimental histograms representing the various distributions of americium on the fissure surfaces. 

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