ISSN 1070-4272. Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 5, pp. 715!721. + Pleiades Publishing, Inc., 2006.
Original Russian Text + N.G. Rachkova, I.I. Shuktomova, A.I. Taskaev, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 5, pp. 725!731.
AND ION-EXCHANGE PROCESSES
Sorption of Uranium, Radium, and Thorium from Saline
Solutions on Hydrolyzed Wood Lignin
N. G. Rachkova, I. I. Shuktomova, and A. I. Taskaev
Institute of Biology, Komi Scientific Center, Ural Division, Russian Academy of Sciences, Syktyvkar,
Komi Republic, Russia
Received July 22, 2005; in final form, January 2006
Abstract-Sorption of U, Ra, and Th from multicomponent aqueous salt solutions on hydrolyzed wood lignin
is studied. The mechanism of radionuclide sorption from saline solutions is suggested on the basis of the
results of sequential extraction.
Making decision on a sorbent for deactivation of
natural waters is a difficult task. Such a sorbent
should meet a series of requirements; the major
among them is its ability to tightly fix radionuclides.
Because of a great diversity of radionuclide speciation
in natural waters, it appears advisable to use polyfunc-
tional sorbents, e.g., hydrolyzed wood lignin. We
demonstrated previously [1, 2] that it tightly absorbs
Th, U, and Ra from aqueous solutions of various
acidities. In this case, Ra and Th are effectively
sorbed at pH 339, and U, at pH 639. Our results
showed that the sorption of radionuclides on lignin
may proceed by several mechanisms including surface
absorption of colloids and pseudocolloids, ion ex-
change, complexation with ionic species of radionu-
clides, and formation of strong sorption complexes
with organic-bound species. An IR study of the
U-loaded sorbent showed for the first time that the
interaction of the carboxy and phenolic groups of lig-
nin with uranium occurs as ion exchange between the
hydrogen ion and uranyl and its hydrolyzed species,
and also by the coordination mechanism with the for-
mation of oxonium complexes.
In this study we examined the capacity of hy-
drolyzed wood lignin to sorb radionuclides from
multicomponent aqueous salt solutions.
Working solutions were prepared by adding potas-
sium, calcium, and ammonium nitrates, ammonium
dihydrogen phosphate, and magnesium and ammoni-
um sulfates to a solution of dioxouranium nitrate
]. The elements were taken in amounts
typical of soil solutions in loam podzolic soils .
The salinity of the resulting solution amounted to
3.3 mg-equiv l
(Table 1). The radionuclidic com-
position corresponded to the natural mixture of iso-
topes . The initial concentrations of the radionu-
clides were as follows: Th 1.0 and 10.0 mg l
, U 1.0
and 10 mg l
, and Ra 1.19 and 11.90 ng l
, which is
higher by 133 orders of magnitude than the maximal
permissible concentrations of
in potable water . The initial (before sorption) pH
of the liquid phase was 6. The sorption experiments
were carried out in the static mode at room tempera-
ture. Each experiment was replicated three times.
In all the experiments, the sorption time was 24 h.
The particle size of hydrolyzed lignin was 0.253
0.5 mm. The Komarov’s lignin fraction in the sorbent
was 82 wt % at the ash content of 6%. Prior to use,
weighed portions of hydrolyzed lignin were kept in
distilled water for 1 day, to increase its specific sur-
face area. After the sorption, the phases were sepa-
rated by filtration. The degree of recovery and distri-
bution coefficient were estimated from the metal
concentration loss in the liquid phase. The concentra-
tions of Th, U, and Ra were determined by the pho-
tometric, luminescence, and emanation methods,
respectively . The tightness of fixation of the
radionuclides on the sorbent was studied by sequential
extraction with distilled water and 1 M solutions of
and HCl. The residual radionuclides in
the sorbent phase constitute the so-called tightly fixed
fraction. The statistical data treatment was carried out
by the standard methods .