Radiolysis products of nitrate-acetate aqueous solutions and their influence on pH of the solutions

Article abstract of DOI:10.1007/s11137-006-0015-3

The influence of the components of nitrate-acetate aqueous solution and products of their radiolysis on pH of the solutions was experimentally studied in a wide dose range. The results can be used to estimate the speciation and migration conditions of radionuclides in a reservoir bed of underground disposed sites of liquid radioactive waste. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11137-006-0015-3

Radiochemistry, Vol. 47, No. 6, 2005, pp. 595 598. Translated from Radiokhimiya, Vol. 47, No. 6, 2005, pp. 547 549.
Original Russian Text Copyright 2005 by Egorov, Danilin, Zakharova, Darskaya, Zubkov.
Radiolysis Products of Nitrate Acetate Aqueous Solutions
and Their Influence on pH of the Solutions
G. F. Egorov*, D. I. Danilin*, E. V. Zakharova*,
E. N. Darskaya*, and A. A. Zubkov**
*
Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Moscow, Russia
*
* Siberian Chemical Plant, Seversk, Tomsk oblast, Russia
Received September 20, 2004
Abstract The influence of the components of nitrate acetate aqueous solution and products of their radioly-
sis on pH of the solutions was experimentally studied in a wide dose range. The results can be used to esti-
mate the speciation and migration conditions of radionuclides in a reservoir bed of underground disposed sites
of liquid radioactive waste.
Here were continue our previous study [1] on
radiochemical behavior of nitrate acetate solutions
used in deep disposal of nuclear waste [2]. In this
study we examined experimentally the behavior of the
radiolysis products of nitrate acetate solutions and
their influence of pH of aqueous solutions with the
aim to estimate the speciation and migration condi-
tions of radionuclides in a reservoir bed.
was determined by potentiometric titration, with
the determination error not exceeding 10%. The con-
centration of sodium nitrite was determined by the
calorimetric procedure described in [4]. The pH was
measured with an Ekotest-2000 pH meter.
RESULTS AND DISCUSSION
The potentiometric titration procedure used allowed
determination of the concentration of nitric acid and
the total concentration of acetic acid (HAc) and its
acidic radiolysis products. The dependences of the
The composition of the radiolysis products of
aqueous acetic acid solutions was studied insufficient-
ly [2, 3]. The data on radiolysis of aqueous nitrate
solutions were reviewed in the monograph [3]. How-
ever, the behavior of radiolysis products of acetates
in aqueous nitrate solutions exposed to prolonged ir-
radiation has not been studied quantitatively.
concentrations of HNO , acidic organic compounds
3
(
HAc + products), and NaNO in the solutions con-
2
taining 0.125 M HNO , 0.245 M HAc, and 1.2 M
3
NaNO and of pH of these solutions on the radiation
3
dose are presented in Table 1 and Fig. 1.
EXPERIMENTAL
Table 1. Concentration of components (M) and pH of
nitrate acetate solutions at different radiation doses
We studied aqueous solutions simulating the
macrocomposition of radioactive waste and containing
0
.125 M nitric acid, 0.24 M acetic acid, and 1.17 M
Dose,
MGy
HAc +
products
HNO3
NaNO2
pH
sodium nitrate. The pH of nonirradiated model
CH COOH NaNO , NaNO CH COOH NaNO , and
NaNO NaNO solutions was measured. The com-
position of the model solutions was similar to that of
irradiated solutions.
3
3
2
3
3
0
0.245
0.210
0.180
0.147
0.105
0.068
0.065
0.075
0.03
0.125
0.065
0.030
0.025
0
0
0
0
0
0
0
0.7
2
3
0
0
0
1
.21
.39
.6
0.95
1.75
2.35
2.70
3.15
The kinetic curves of decomposition of nitric and
acetic acids on exposure to -ray radiation of 60Co and
accumulation of their radiolysis products were studied
in a temperature-controlled glass cell at 23 C and
.0
1.6
2.0
2.4
2.8
0.017(0.027)* 2.8(4.5)*
0.024(0.038)* 3.0
0.034(0.051)* 3.75(5.5)*
0.060(0.100) 4.05(6.2)*
1
a dose rate of 1.2 Gy s .
3
.6
0.006
The content of nitric and acetic acids and of liquid
acidic radiolysis products of acetic acid in the samples
* Ten days after irradiation.
1
066-3622/05/4706-0595 2005 Pleiades Publishing, Inc.

596
EGOROV et al.
trite ions is due to their oxidation with hydrogen
peroxide.
The yield of HAc radiolysis was determined at low
radiation doses (up to 0.2 MGy) when the influence
of the acidic radiolysis products was minimal. The
yield is 1.2 and 0.8 0.9 molecule/100 eV in the pres-
ence and in the absence of HNO , respectively, which
3
agrees with our previous data [1]. The HAc consump-
tion and the total accumulation of its radiolysis prod-
ucts were calculated in the whole range of radiation
doses at a constant yield of HAc radiolysis. The
results are presented in Table 2 and Fig. 2.
Fig. 1. Concentration of (1) HAc + radiolysis products,
2) HNO , and (3) NaNO as a function of radiation dose.
(
3
2
The experimental dependences of the concentra-
tions of HAc and its acidic radiolysis products on the
radiation dose (Fig. 2, curve 1) can be accounted for
on the basis of our calculations. The maximum at
1
.5 3 MGy is due to accumulation of acidic radiolysis
products which are more stable to radiolysis than
HAc. The total radiation-chemical yield of decomposi-
tion of the acidic radiolysis products can be estimated
from the data of Table 2 and the portion of curve 1
(
3
Fig. 2) in the range of radiation dose from 2.4 to
.6 MGy where the HAc concentration is close to
Fig. 2. Concentration of (1) HAc + radiolysis products,
2) HAc, and (3) radiolysis products as a function of radia-
(
zero. The total radiation-chemical yield of decom-
position of acidic products (0.55 molecule/100 eV)
is lower by a factor of 1.5 than the yield of decom-
position of HAc (0.8 molecule/100 eV) in the absence
tion dose.
The initial radiation-chemical yield of HNO de-
3
composition (1.4 molecule/100 eV) was consistent
with our previous results [1]. Radiolysis of 0.125 M
HNO3 solution is complete at doses lower than
MGy. Nitrous acid was not detected up to complete
decomposition of HNO . Probably, in acid solution,
of HNO . The acidic products are accumulated in
3
a radiation-chemical yield of 0.34 molecule/100 eV
in the dose range 1 2.4 MGy in the absence of HNO3.
Since the increase in the product concentration is
proportional to the difference between the yield of
their formation and decomposition, the total yield
of the product formation should be equal to 0.34 +
0.55 = 0.89 molecule/100 eV, which is close to the
initial yield of HAc decomposition under these condi-
tions.
1
3
HNO is completely spent for oxidation of CH COOH
2
3
to form nitrogen dioxide. In the absence of HNO ,
3
NaNO is accumulated with the radiation-chemical
2
yield of 0.26 molecule/100 eV. The low yield of ni-
Table 2. Experimental and calculated concentrations (M)
of CH COOH and its radiolysis products in nitrate acetate
solutions at different radiation doses
3
The main final liquid products of radiolysis of
nitrate acetate solutions are glyoxylic acid (CHO
COOH), glycolic acid (CH OHCOOH), succinic acid
2
Dose,
MGy
HAc + products,
experiment
HAc,
Products,
(
CH COOH) , formaldehyde (CH O), and sodium
calculation calculation
2
2
2
nitrite [3, 4]. Formation of these compounds can be
tentatively described by the following general scheme:
0
0.245
0.210
0.180
0.147
0.105
0.068
0.065
0.075
0.03
0.245
0.210
0.177
0.141
0.096
0.035
0.020
0.003
0
0
0
0
0
0
1
1
2
2
2
3
.21
.39
.6
.0
.6
.0
.4
.8
.6
0.003
0.006
0.009
0.033
0.045
0.072
0.03
0.006
H O
H, OH, e , H O , H ;
(1)
2
aq
2
2
2
CH COOH + H(OH)
CH COOH + H (H O); (2)
3
2
2
2
CH COOH + O2
O CH COOH;
(3)
(4)
2
2
2
2
O CH COOH
CH (OH)COOH
2
2
2
0.006
0
+
CH(O)COOH + O2;
RADIOCHEMISTRY Vol. 47 No. 6 2005

RADIOLYSIS PRODUCTS OF NITRATE ACETATE AQUEOUS SOLUTIONS
597
2
CH COOH
(CH COOH) ;
(5)
2
2
2
2
NO3 + eaq
NO3 + H
NO + H O
NO2 +2OH ; (6)
3
2
HNO3
NO2 + OH ;
(7)
(8)
NO2 + NO2
N O ;
2 4
N O + H O
NO2 + NO3 + 2H+;
(9)
2
4
2
H O + NO2
NO3 + H O.
(10)
2
2
2
The products are formed mainly by reaction of
acetic acid with radical products of water radiolysis
Fig. 3. The pH of (1) the solutions right after irradiation,
(2) the model nonirradiated HAc + sodium nitrite solution,
and (3) the solution 15 days after the irradiation, as a func-
tion of the radiation dose.
[
reactions (1), (2)]. In the presence of HNO , HAc
additionally decomposes by the reaction with nitrogen
dioxide:
3
In the dose range from 1 to 2 MGy (in the absence
of HNO ), the pH is determined by the concentrations
CH COOH + NO
CH COOH + HNO . (11)
3
3
2
2
2
of HAc and NaNO ; the influence of acidic radiolysis
2
products of HAc on the pH in this dose range is
negligible.
In the presence of dissolved oxygen, acetate radi-
cals form the peroxy radicals [reaction (3)] which dis-
proportionate [reaction (4)] to form glycolic and gly-
oxylic acids. These reactions compete with recombi-
nation of acetate radicals (5) to form succinic acid.
The recombination yield increases with a decrease in
the oxygen content in the irradiated solution.
In the dose range from 2 to 4 MGy, the pH (on the
background of low HAc concentration) depends on
the concentration ratio of acidic radiolysis products
of HAc and NaNO . The acidic products decrease
2
pH to a greater extent than does HAc, and NaNO2
increases it. The minimum on the pH dose curve
(Fig. 3) appears at the concentration ratio of these
products formed at the radiation dose from 2 to
This reaction scheme is not complete and requires
an experimental study to estimate the kinetic param-
eters of accumulation and consumption of the radioly-
sis products.
3
MGy.
The pH of the irradiated solutions is determined by
a change in the concentrations of the initial compo-
nents and their radiolysis products. At the radiation
dose of up to 1 MGy, the pH of solutions is deter-
The pH of model HAc + NaNO + NaNO solu-
2
3
tions (Fig. 3, curve 2) is similar to that of the irra-
diated solutions of the similar composition (Fig. 3,
curve 1). The only exception is solutions irradiated to
doses of 2 3 MGy. In this case the pH is lower owing
to the maximal concentrations of acidic radiolysis
products of HAc.
mined mainly by the HNO concentration. It increases
3
from 0.7 to 2.7 as the HNO concentration decreases
3
from the initial value to 0. The pH of aqueous solu-
tions of acetic acid with the concentration equal to
that in the irradiated solutions is 2.7. When the radia-
tion dose is higher than 1 MGy, the pH depends on
the concentration ratio of HAc, its acidic radiolysis
The following postradiation effects are observed.
During storage of the irradiated solutions, their pH
increases (Fig. 3, curve 3) as well as the NaNO con-
2
products, and NaNO . Sodium nitrite increases the
centration in these solutions (Table 1). This is prob-
ably due to slow (at room temperature) chemical
reduction of nitrate ions with radiolysis products
of HAc.
2
pH of the solutions, and acidic radiolysis products
of HAc decrease the pH. Comparison of pH of the ir-
radiated solutions with that of model aqueous NaNO3
solutions containing the same amounts of HAc and
The quantitative relationships of the behavior of
the initial components and radiolysis products of
nitrate acetate solutions should be taken into account
in long-term prediction calculations of the state of
filtered acidic liquid radioactive waste in deep
disposal sites. To calculate the dose rate and residence
time of wastes in a bed, data on the average activity
NaNO (Fig. 3) confirms this conclusion.
2
The results presented in Fig. 3 and Table 1 allow
the following conclusions.
When HNO is present in an irradiated solution
0.5 1 MGy), the pH is determined by its concen-
3
(
tration.
RADIOCHEMISTRY Vol. 47 No. 6 2005

598
EGOROV et al.
of the waste are required. To calculate the radius of
their distribution in the bed, the total volume of
wastes disposed of within this time should be known.
2. Mikhal’chuk, B.V. and Osherovich, R.E., Zavod. Lab.,
1940, vol. 9, no. 8, pp. 836 838.
3. Josimovic, L. and Draganic, I., Int. J. Radiat. Phys.
Chem., 1973, vol. 5, pp. 505 512.
REFERENCES
4. Pikaev, A.K., Sovremennaya radiatsionnaya khimiya.
Radioliz gazov i zhidkostei (Modern Radiation Chemis-
try. Radiolysis of Gases and Liquids). Moscow:
Nauka, 1986, p. 245.
1
. Egorov, G.F., Danilin, D.I., Zakharova, E.V., et al.,
At. Energ., 2002, vol. 93, no. 1, pp. 54 58.
RADIOCHEMISTRY Vol. 47 No. 6 2005