A New Insight into the Nature of the Leached Layers Formed on Basaltic Glasses in Relation to the Choice of Constraints for Long Term Modelling

Abstract

Experimental basaltic glass dissolution in fresh water is compared with analyses made on subglacial hyaloclastites from Iceland. The dissolution is initially selective and remains selective if the solution is renewed, whereas it becomes apparently congruent in non-renewed conditions. The congruent dissolution is ascribed to a pH increase (up to 7.0–7.5) which is hampered in the former conditions. The palagonite hydrated layer on the Icelandic basaltic glasses is made up of amorphous to crystallized clay-like materials. The chemical composition of palagonite is close to that of the intergranular clayey material, thus, it is inferred that in most cases no significant chemical gradient exists in the solution between the reaction zone, namely the glass/palagonite interface, and the intergranular solution. We conclude that the dissolution of basaltic glass under subglacial conditions is controlled by thermodynamics and that kinetic constraints, such as the diffusion of species through the altered layers, do not play a major role.

Accelerated Leach Testing of Glass (ALTGLASS): II. Mineralization of hydrogels by leachate strong bases

“…During laboratory experiments with volcanic glass in pure water, halloysite and smectite were observed as well as alteration layers rich in ferrihydrite which later developed into cryptocrystalline silicates. Experiments in closed systems identified imogolite and α‐,β‐FeOOH . These phases are all poorly crystalline and as such are known as mineraloids.…”

The dissolution rates of natural glasses as a function of their composition at pH 4 and 10.6, and temperatures from 25 to 74°C

“…Ewing and Haaker, 1979;Byers et al, 1985;Lutze et al, 1985). To model the long-term behaviour and stability of this radioactive waste confinement host studies have concentrated on laboratory corroded basaltic and synthetic borosilicate glasses and naturally altered basaltic glasses (Furnes, 1975(Furnes, , 1978Seyfried Jr. and Bischoff, 1979;Allen, 1982;Malow et al, 1984;Crovisier et al, 1983Crovisier et al, , 1985Crovisier et al, , 1987Crovisier et al, , 1989aCrovisier et al, , 1989bGrambow, 1985;Grambow et al, 1985;Berger et al, 1987Berger et al, , 1988Berger et al, , 1994Gislason and Eugster, 1987a;Eggleton et al, 1987;Guy and Schott, 1989;Murukami et al, 1989;Jercinovic et al, 1990aJercinovic et al, , 1990bAdvocat et al, 1990Advocat et al, , 1991Advocat et al, , 1998Nesbitt and Wilson, 1992;Ghiara et al, 1993;Gislason et al, 1993;Morgenstein and Shettel, 1994;Daux et al, 1994Daux et al, , 1997Leturcq et al, 1999;Abraitis et al, 2000;Techer et al, 2001). Most of the natural glass dissolution studies were performed in either high ionic strength/seawater solutions or at high temperatures, and many were carried out in closed system batch reactors.…”

Modelling the alteration gel composition of simplified borosilicate glasses by precipitation of an ideal solid solution in equilibrium with the leachant

“…Once the network hydrolysis rate becomes faster than the alkali/boron diffusion rate, the dissolution becomes congruent (second step). At the third step, secondary alteration products (the amorphous gel and mineral phases) form and the glass dissolution becomes incongruent again [2,3,8,9,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. As the reaction proceeds, the glass matrix dissolution rate decreases, due to the accumulation of dissolved glass constituents in the solution.…”