Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 6, pp. 862−866.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © G.S. Akuzhaeva, Yu.Yu. Gavronskaya, V.N. Pak, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 6, pp. 870−874.
AND INDUSTRIAL INORGANIC CHEMISTRY
Dimensional and Concentration Dependences of Diffusion
of Aqueous Alkaline-Earth Metal Nitrate Solutions
in Porous-Glass Membranes
G. S. Akuzhaeva, Yu. Yu. Gavronskaya, and V. N. Pak
Herzen Russian State Pedagogical University, St. Petersburg, Russia
Received January 23, 2012
Abstract—Diffusion coefﬁ cients characterizing penetration of aqueous solutions of magnesium, calcium, strontium,
and barium nitrates across porous-glass membranes with predominant pore radii of 4.5–70 nm were determined.
A decrease in the pore radii of the membranes is accompanied in all cases by an exponential fall of the diffusion
mobility. A reversal of the diffusion mobility series was observed for membranes with pore radii of 4.5 and 70 nm
on the background of the general tendency toward a concentration-related rise in the diffusion coefﬁ cients.
The decrease in the mobility of solution components
in membranes, observed as the radius of transport
channels becomes lower, seems to be apparent.
However, the nature and, moreover, the analytical form
of this dependence can only be found by performing
experiments on a number of membranes of the same
chemical nature with variable and rather precisely settable
parameters. The fact that this opportunity is provided
in the case of a porous glass (PG) creates exclusive
conditions for studies and practical application of the
dimensional speciﬁ c features of membrane separation
and concentration processes. The development of studies
in this area is mostly restricted by the unavailability of
a set of PGs as a commercial product. At the same time,
both general principles and particular speciﬁ c features
of the related preparative procedures can be considered
sufﬁ ciently developed [1–5], which served as a basis for
fabrication of mechanically strong GS membranes with
reliably controlled structure of their inner space. The use
of these membranes in a series of studies [6–9] made
it possible to reliably conﬁ rm the known concept [10,
11] that the transport of electrolyte solutions across thin-
porous hydrophilic membranes is largely controlled by
speciﬁ c properties of structured near-wall layers. For
example, it has been shown [6–9] that there is a stable
“dimensional” dependence of the diffusion coefﬁ cients
of aqueous solutions of a number of inorganic salts on
the pore radius of PG membranes
D = D
corresponds to a free solution (r
→ ∞), and
characterizes the effective thickness of the
near-wall structured layer with a hindred diffusion.
The substantial decrease in the numerical values of K
and the corresponding rise in the diffusion mobility may
be due to the speciﬁ c destructive effect of electrolytes,
which causes a decrease in the thickness of near-wall
layers with increasing concentration of aqueous salt
solutions [6–8, 10, 11].
In this communication, we report generalized results
of a study of the diffusion transport of alkaline-earth
metal nitrates in PG membranes. The porous structure
parameters of the membranes and the experimental
conditions of mass-transfer measurements have been
described in detail previously . The dependences
shown in Fig.1a demonstrate speciﬁ c features of
diffusion for the example of calcium nitrate solutions,
typical of all the systems studied. The diffusion