ISSN 1070-4272. Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 3, pp. 367!371. + Pleiades Publishing, Inc., 2006.
Original Russian Text + D.E. Chirkst, O.V. Cheremisina, M.V. Ivanov, A.A. Chistyakov, I.T. Zhadovskii, 2006, published in Zhurnal Prikladnoi Khimii,
2006, Vol. 79, No. 3, pp. 374 !377.
AND ION-EXCHANGE PROCESSES
Isotherm of Strontium and Sodium Cation Exchange
on Iron!Manganese Nodules
D. E. Chirkst, O. V. Cheremisina, M. V. Ivanov, A. A. Chistyakov, and I. T. Zhadovskii
St. Petersburg State Mining Institute, St. Petersburg, Russia
Received February 17, 2005
Abstract-The isotherm of ion exchange of Sr
ions on iron!manganese nodules was obtained.
It was suggested to describe the ion exchange by an equation analogous to the Langmuir isotherm equation.
The limiting sorption and apparent ion exchange constant were calculated. The effective radius of sorbed
strontium ions was determined.
Iron3manganese nodules (IMNs) as natural cation
exchangers show promise for the recovery of stronti-
um-90 from radioactively contaminated water and
also from reactor conduits.
Radiation pollution of territories near nuclear
plants is mainly caused by emergency emissions of
cesium-l37 and strontium-90. Strontium is largely
sorbed by the mineral component of soils , and
its migratory activity is noticeably higher compared to
cesium. A process for treatment of soils contaminated
Sr  by flushing the soil with solutions of
salts of multicharged cations was developed previous-
ly on the pilot scale. The study of the ion exchange on
IMNs will make it possible to develop a procedure
for the removal of strontium-90 from wash waters and
also from underground waters.
In this study we examined the isotherm of the ex-
change of sodium and strontium ions on the IMN sur-
face. As natural IMN samples contain various ex-
changing cations, iron3manganese nodules were con-
verted to the sodium form.
According to the simplest Helmholtz model, the
spatial separation of charges near a surface can be
considered as an electrical double layer representing
two parallel plates of a charged capacitor separated by
a layer of a dispersing medium . One capacitor
plate is formed by potential-determining ions fixed on
the solid surface and the other, by counterions con-
tained in a liquid. Because of short range of action of
adsorption forces, we can distinguish two main parts
of an electrical double layer: a dense part (Stern3
Helmholtz layer) and a more distant diffuse part
(Gouy3Chapman layer). According to the Stern3
Graham scheme, the dense part of an electrical double
layer consists of internal and external parts. The inter-
nal part is formed by partially of completely dehy-
drated ions specifically adsorbed on the surface in
question. The external part consists of hydrated ions,
sodium ions in our case, which can exchange with
strontium ions according to the Gedroits lyotropic
[5, 6]. The tendency of the
cations to adsorption in this series increases in parallel
with the ionic potential, which is equal to the ratio
of the charge and radius of the hydrated ion.
It is known that
Cs is fixed in soils much more
strongly than does
Sr, despite smaller ion charge .
As compared to strontium, cesium has a smaller Stokes
radius of the hydrated ion. The higher ionic potential
of cesium in aqueous solutions compared to strontium
is indicated by the fact that the equivalent conductance
of cesium ions, equal to 7.72 0 10
298 K and infinite dilution, is higher than that of
strontium ions, 5.94 0 10
to higher ionic potential in aqueous solution, cesium
ions are bonded more strongly than strontium ions to
negatively charged structural fragments on the surface
An air-dry IMN sample with granules of size 0.103
0.25 mm was treated with a 5% NaOH solution for
5 days with intermittent stirring. The alkali solution
was replaced daily by a fresh solution. The complete-
ness of converting IMN into the sodium form was
monitored by reaching the constant activity of Na