Leaching of uranium ores in the process of sodium sulphate electrolysis
When uranium is extracted from concentrates with high silicon content, acid leaching is usually used. The disadvantage of this method is the high consumption, high cost and corrosion activity of the reagents. Moreover, for the oxidation of tetravalent uranium to highly soluble hexavalent uranium, it...
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| Zitieren: | Leaching of uranium ores in the process of sodium sulphate electrolysis / V.G. Nefedov, Yu.E. Sknar, O.A. Kharytonova // Problems of atomic science and technology. — 2019. — № 5. — С. 113-117. — Бібліогр.: 2 назв. — англ. |
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irk-123456789-1952282023-12-03T17:37:38Z Leaching of uranium ores in the process of sodium sulphate electrolysis Nefedov, V.G. Sknar, Yu.E. Kharytonova, O.A. Thermal and fast reactor materials When uranium is extracted from concentrates with high silicon content, acid leaching is usually used. The disadvantage of this method is the high consumption, high cost and corrosion activity of the reagents. Moreover, for the oxidation of tetravalent uranium to highly soluble hexavalent uranium, it is necessary to process it with oxidizing agents, for example, oxygen. The work shows the possibility of development and chemical concentration of uranium ores using electrolysis of sodium sulfate. During electrolysis the pH in the anode chambers ranges from 2.2…2.5 to 0.5…0.7 in the near-electrode layer of the electrolyte, which corresponds to the pH range during leaching in agitators. Oxygen released at the anode is able to oxidize uranium to hexavalent one. Під час вилучення урану з концентратів з високим вмістом оксиду кремнію зазвичай застосовується кислотне вилуговування. Недоліками такого способу є велика витрата, висока вартість і корозійна активність реагентів. При цьому для окислення чотирьохвалентного урану до добре розчинного шестивалентного необхідна операція його обробки окислювачами, наприклад, киснем. У роботі показана можливість розтину і хімічного концентрування уранових руд за допомогою електролізу сульфату натрію. рН в анодних камерах при електролізі коливається від 2,2…2,5 до 0,5…0,7 в приелектродному шарі електроліту, що відповідає діапазону рН при вилуговуванні в агітаторах. Кисень, що виділяється на аноді, здатний окислювати уран до шестивалентного. При извлечении урана из концентратов с высоким содержанием оксида кремния обычно применяется кислотное выщелачивание. Недостатками такого способа являются большой расход, высокая стоимость и коррозионная активность реагентов. При этом для окисления четырехвалентного урана до хорошо растворимого шестивалентного необходима операция его обработки окислителями, например, кислородом. В работе показана возможность вскрытия и химического концентрирования урановых руд с помощью электролиза сульфата натрия. рН в анодных камерах при электролизе колеблется от 2,2…2,5 до 0,5…0,7 в приэлектродном слое электролита, что соответствует диапазону рН при выщелачивании в агитаторах. Выделяющийся на аноде кислород способен окислять уран до шестивалентного. 2019 Article Leaching of uranium ores in the process of sodium sulphate electrolysis / V.G. Nefedov, Yu.E. Sknar, O.A. Kharytonova // Problems of atomic science and technology. — 2019. — № 5. — С. 113-117. — Бібліогр.: 2 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/195228 621.357.1:661.883.1; 541.135 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Thermal and fast reactor materials Thermal and fast reactor materials Nefedov, V.G. Sknar, Yu.E. Kharytonova, O.A. Leaching of uranium ores in the process of sodium sulphate electrolysis Вопросы атомной науки и техники |
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When uranium is extracted from concentrates with high silicon content, acid leaching is usually used. The disadvantage of this method is the high consumption, high cost and corrosion activity of the reagents. Moreover, for the oxidation of tetravalent uranium to highly soluble hexavalent uranium, it is necessary to process it with oxidizing agents, for example, oxygen. The work shows the possibility of development and chemical concentration of uranium ores using electrolysis of sodium sulfate. During electrolysis the pH in the anode chambers ranges from 2.2…2.5 to 0.5…0.7 in the near-electrode layer of the electrolyte, which corresponds to the pH range during leaching in agitators. Oxygen released at the anode is able to oxidize uranium to hexavalent one. |
| format |
Article |
| author |
Nefedov, V.G. Sknar, Yu.E. Kharytonova, O.A. |
| author_facet |
Nefedov, V.G. Sknar, Yu.E. Kharytonova, O.A. |
| author_sort |
Nefedov, V.G. |
| title |
Leaching of uranium ores in the process of sodium sulphate electrolysis |
| title_short |
Leaching of uranium ores in the process of sodium sulphate electrolysis |
| title_full |
Leaching of uranium ores in the process of sodium sulphate electrolysis |
| title_fullStr |
Leaching of uranium ores in the process of sodium sulphate electrolysis |
| title_full_unstemmed |
Leaching of uranium ores in the process of sodium sulphate electrolysis |
| title_sort |
leaching of uranium ores in the process of sodium sulphate electrolysis |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2019 |
| topic_facet |
Thermal and fast reactor materials |
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http://dspace.nbuv.gov.ua/handle/123456789/195228 |
| citation_txt |
Leaching of uranium ores in the process of sodium sulphate electrolysis / V.G. Nefedov, Yu.E. Sknar, O.A. Kharytonova // Problems of atomic science and technology. — 2019. — № 5. — С. 113-117. — Бібліогр.: 2 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-16T23:05:57Z |
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2025-07-16T23:05:57Z |
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1837846663500136448 |
| fulltext |
ISSN 1562-6016. PASТ. 2019. №5(123), p. 113-117.
UDC 621.357.1:661.883.1; 541.135
LEACHING OF URANIUM ORES IN THE PROCESS OF SODIUM
SULPHATE ELECTROLYSIS
V.G. Nefedov
1
, Yu.E. Sknar
1
, O.A. Kharytonova
2
1
State Higher Educational Institution Dneprovsky State University of Chemical Technology,
Dnipro, Ukraine
E-mail: vnefedov@i.ua, tel. +38-050-732-45-65;
2
Dneprovsky State Technical University, Kamenskoe, Ukraine,
E-mail: eah@ukr.net
When uranium is extracted from concentrates with high silicon content, acid leaching is usually used. The
disadvantage of this method is the high consumption, high cost and corrosion activity of the reagents. Moreover, for
the oxidation of tetravalent uranium to highly soluble hexavalent uranium, it is necessary to process it with oxidizing
agents, for example, oxygen. The work shows the possibility of development and chemical concentration of uranium
ores using electrolysis of sodium sulfate. During electrolysis the pH in the anode chambers ranges from 2.2…2.5 to
0.5…0.7 in the near-electrode layer of the electrolyte, which corresponds to the pH range during leaching in
agitators. Oxygen released at the anode is able to oxidize uranium to hexavalent one.
INTRODUCTION
Uranium in nature is mainly found in granites,
pegmatites and hydrothermal deposits. Uranium in its
compounds can be trivalent, tetravalent, quinquevalent,
and hexavalent. The compounds of tetravalent and
hexavalent uranium with oxygen: UO2, UO3, U3O8,
UO4∙2H2O are of the greatest importance, as well as the
uranyl anion UO2
2+
. There are also minerals that are the
salts of oxygen acids.
Uranium feedstock passes through several
successive stages of processing: dressing, chemical
concentration and extraction treatment.
At the first stage of uranium ore dressing, the
radiometric method, which allows waste rock separation
that does not have radioactive emission, is used, as well
as gravity and flotation methods.
The second stage of dressing is the concentration
carried out by the hydrometallurgical method, at the
first stage of which calcination can be carried out for
sulfide ores. The leaching process is carried out in
agitators with mechanical agitation, or in autoclaves at
elevated pressure. Sorption leaching of uranium is
possible in capacities with air mixing. Most of the
minerals containing uranium dissolve in mineral acids
and hot solutions of alkali metal carbonates. The final
products of uranium plants are “yellow cake”
concentrate with uranium content of 55…60%, and
uranium protoxide-oxide with uranium content of more
than 84%.
In nuclear purity fuel, the content of impurities
should be no more than 10
-3
…10
-6
%. This is due to the
fact that the impurities of Fe, Si, P, V, Al, Mn, B, rare-
earth metals and other substances found in uranium ores
are distinguished by a large effective cross section for
thermal neutron capture. Their presence in nuclear fuel
reduces its efficiency. Sorption, precipitation, and
extraction methods are used for cleaning of these
impurities during the finishing treatment of uranium
concentrates.
Uranium compounds are extracted from ores at the
stages of leaching and sorption concentration. The
tendency of uranium compounds to complex formation
with oxygen-containing molecules ensures the
selectivity of its extraction during sorption. There are a
lot of minerals containing uranium and the technology
of leaching with acidic or alkaline carbonate solutions is
selected for each of them. When uranium is extracted
from high calcium concentrates, carbonate leaching
should be used. The ores of the Zheltue Vodu deposit, in
which uranium is contained in granites, are
characterized by a high content of silicon and iron. It is
advisable to carry out their processing by acid leaching
[1].
Concentrated sulfuric and nitric acids interact with
uranium slowly, diluted sulfuric acid with oxidizing
agents dissolves uranium quickly. The leaching of
hexavalent uranium takes place according to the
reaction:
3 2 4 2 4 2 .UO H SO UO SO H O (1)
Since tetravalent uranium practically does not
dissolve in acids, its leaching is carried out with
oxidizing agents, nitric acid, sodium nitrate or
pyrolusite. It is also possible to use oxygen at an
overpressure of up to 7…14 atm. In this case, the
reaction happens with the formation of the hexavalent
compound of uranium, which is readily soluble in water
and the consumption of sulfuric acid decreases:
2 2 2 4 2 4 2
1
.
2
UO O H SO UO SO H O (2)
It is impossible to obtain anhydrous sulfate by
reactions (1) and (2), the product of these reactions is a
cationic aquacomplex 2
622 OHUO or neutral
aquacomplexes 4422 SOOHUO ,
n
SOOHUO 4322
,
2 2 42
,UO H O SO
n
SOOHUO 422
.
For acid leaching, crushed ore to 60% – 200 mesh
(0.074 mm) is used. It is processed in a cascade of
agitators for approximately 48…60 h at an initial pH of
0.5…0.7 and a final pH of 1.8…2.5.
The disadvantages of acid leaching include the high
consumption of reagents per unit of extracted uranium.
Therefore, the main parameter for choosing reagents is
their cost, the duration of the processing, and the degree
mailto:eah@ukr.net
of uranium extraction. Most often, the industry uses
sulfuric acid which is the most affordable, but still
expensive and aggressive at low concentrations.
To reduce the cost of the leaching process, it is
proposed to obtain sulfuric acid directly in reactors
using sulfide ores by the reactions:
2 2 2 4 2 43.5 ,FeS O H O FeSO H SO (3)
( 4 2 2 4 2 4 23
0.5 ,FeSO O H SO Fe SO H O (4)
2 2 4 4 2 43
2 ,UO Fe SO FeSO UO SO
(5)
2 4 2 2 43 3
6 2 3 .Fe SO H O Fe OH H SO (6)
Electrolysis of cheaper sodium sulfate in
electrolyzers with separated electrode spaces is the other
option for producing sulfuric acid directly in the reactor
and, accordingly, reducing leaching costs, which
account for up to 40% of the production cost. In this
case, the reaction of yielding oxygen and acidification
of the solution takes place at the anode,
2 2 4 2 2 42 0.5H O Na SO e O H SO (7)
and at the cathode – hydrogen yielding and alkalization
of the medium
2 2 4 22 2 2 .H O Na SO e H NaOH (8)
Sodium sulfate does not decompose during electrolysis,
but SO4
2
-ions in the anode space provide the formation
of sulfuric acid.
The advantages of the method include the low cost
of raw materials and electricity, low corrosivity, and the
constant generation of Н
+
-ions in the electrolysis
process. The disadvantages are the relatively low
concentration of acid in the anode chamber, which is
related with the migration and diffusion transfer of Н
+
-
and ОН
–
-ions from the cathode chamber towards each
other and their mutual neutralization. To reduce the
diffusion and migration transfer of Н
+
- and ОН
–
-ions, it
is advisable to use solutions with the highest possible
concentration of indifferent carrier ions, in this case
sodium ions and sulfate ions. As acid and alkali
accumulate in the electrode chambers, the transport
numbers of Н
+
- and ОН
–
-ions increase, which limits the
value of the achieved pH value. In addition, the pH
value varies with time depending on the magnitude of
the electrolyte volume in the electrode chambers and the
current strength.
The aim of this work is to assess the possibility of
using sodium sulfate electrolysis to produce sulfuric
acid and leaching of uranium-containing ores.
1. EXPERIMENTAL TECHNIQUE
During the experiments, we studied the change in
pH in the anode space of the electrolyzer and acidity in
the anode layer of the electrolyte.
Sodium sulfate was electrolyzed in electrolysis cells
with separation of electrode spaces by ion-exchange
membranes. The electrodes used were stainless steel
cathodes and titanium dioxide manganese anodes
(TDMA). The change in acidity was monitored by pH
meter. Sodium sulfate with concentration of 15, 30, 50,
70, and 150 g/l was used as a solution in the anode
space, and the same solutions were used in the cathode,
or a solution of sodium hydroxide with a concentration
of 20 g/l. The current load varied from 0.5 to 3 A. The
volume of electrolyte in the electrode chambers was
0.5 l.
A variation of the sampling method was used for
assessment of the pH of the anode layer. The main point
was the following: a pre-weighed platinum working
electrode with an area of 1.5 cm
2
was suspended on the
beam of a torsion balance. The electrode was connected to
a potentiostatic power supply circuit and was removed
from the solution under current. The current density on the
electrode varied from 100 to 10.000 A/m
2
. After extraction
from the solution, the electrode was weighed with a
wetting liquid film. The difference in the weight of the dry
and wetted electrodes was used to determine the mass of
the solution on the electrode, after that its thickness was
calculated. The solution from the electrode surface was
washed off with a fixed amount of distilled water (one
milliliter), and the content of Н
+
-ions was determined by
titration in it. Methyl red was used as an indicator (pH of
the color transition 4.5…5.5). The titrant was a 0.01 mol/l
NaOH solution. In the measurements, it was believed that
the density of the solution extracted on the surface of the
electrode is equal to the density in the volume of the
electrolyte. The concentration of these ions in the liquid
film and on the electrode surface was calculated by the
number of Н
+
- or ОН
-
-ions and the volume of the
electrolyte.
2. EXPERIMENTAL RESULTS
AND DISCUSSION
2.1. CALCULATION OF THE SULFURIC ACID
CONCENTRATION DURING
THE ELECTROLYSIS OF Na2SO4
The following assumptions were made to calculate
surface ion concentrations and pH in sodium sulfate
solutions.
The distribution of the Н+-ions concentration in the
near-electrode layer of the electrolyte is uneven. It is
maximal on the electrode surface and is equal to the
concentration in the volume outside the diffusion layer.
To determine the concentration at the electrode surface,
it was assumed that the concentration in the diffusion
layer varies linearly. It was also assumed that the
thickness of the diffusion layer is commensurate with
the film thickness on the electrode surface. In this case,
the total number of ions per unit electrode surface is
0
0
,
dif
S
T S
dif
N N
N N d
(9)
where δdif is the thickness of the diffusion layer; NS, N0
is the number of ions at the electrode surface and in the
depth of the solution
The solution of this equation with respect to the number
of ions at the electrode surface gives
22
0
dif
T
dif
S NNN
(10)
or
02
.
T dif
S
dif
N N
N
(11)
Passing to the concentrations, we obtain
02
,
dif dif
S
dif
C C
C
(12)
where СS is the concentration of acid on the surface of
the electrode; C is the concentration in the near-
electrode layer; C0 = 10
-4
…10
-7
is the concentration in
the electrolyte volume.
2.2. ESTIMATES OF PH CHANGES
IN THE ANODE CHAMBER
The pH during electrolysis was measured discretely,
with a frequency of 1…2 min. To go over to the
conditions of industrial electrolysis with an arbitrary
volume of electrolyte, a change in pH was constructed
depending on the amount of transmitted electricity per
unit volume of electrolyte. The dynamics of pH changes
in a solution with a concentration of 15 g/l and at
current loads from 0.5 to 3 A is shown in Fig. 1. It
follows from the figure that, despite the different rate of
change in pH in the first minutes of electrolysis at
different current loads, reaching a stationary pH occurs
when 1 A·h passes the amount of electricity per liter of
solution in the anode chamber. The pH in this case is
about 1.94…2.30, which corresponds to the final pH
values during leaching with sulfuric acid.
Fig. 1. The dependence of pH changes in the anode
chamber of the electrolyzer on the specific amount of
electricity. A solution of Na2SO4 concentration of 15 g/l.
Current load, A: 1 – 0.5; 2 – 1; 3 – 2; 4 – 3
At the same time, it should be noted that acid during
electrolysis is constantly generated throughout the
leaching period, in contrast to the leaching in the
cascade of agitators. The advantages of this method
include the lower aggressiveness of the solutions used
and the constant generation of oxygen necessary for the
oxidation of tetravalent uranium. In addition, in the
near-electrode layer, the concentration of dissolved gas
exceeds the saturation concentration by about an order
of magnitude. This is due to the need for supersaturation
during the formation of a gas bubble nucleus [2].
In addition to the above experiments, the effect of
the concentration of sodium sulfate solution on the
stationary pH value was estimated (Fig. 2).
From the figure it follows that with an increase in
the concentration of the solution, the rate of pH change
decreases, but the effect of the concentration of sodium
sulfate on the concentration of acid (of the pH solution)
is negligible. Therefore, the choice of the working
concentration of sodium sulfate will be determined by
the conditions of electrolysis and ore leaching.
Fig. 2. The pH changing of sodium sulfate solution in
the anode chamber of the electrolyzer, depending on the
amount of electricity per unit volume of electrolyte.
Concentration, g/l: 1 – 15; 2 – 50; 3 – 70
So, with increasing concentration, the electrical
conductivity of solutions increases and the cost of
electricity for electrolysis decreases.
In addition, with solution concentration increasing,
the solubility of oxygen in it decreases. We can assume
and this was confirmed by the experiment that the
concentration of sodium sulfate in industrial electrolysis
will vary from 15 to 150 g/l (approximately, from 0.1 to
1 mol/l).
The decrease in pH in the anode chamber of the
electrolyzer occurs due to the transfer of Н
+
-ions from
the electrode surface to the volume of the electrolyte. In
this case, it is of interest to determine the pH in the
near-electrode layer and on the surface of the electrodes.
2.3. THE DEPENDENCE OF THE PH CHANGE
AT THE ANODE SURFACE
ON THE CURRENT DENSITY
The experiments showed that the thickness of the
wetting film on the electrode surface, calculated by the
weight gain, in different experiments, varied within
0.1…0.2 mm. This is really close to the thickness of the
diffusion layer, which was stated earlier. During
electrolysis, the acid concentration in this layer
increases with increasing current density and depends
on the concentration of the initial solution. The density
dependences of the acid concentration at the anode
surface calculated according to (1) for the upper and
lower possible concentrations of sodium sulfate are
shown in Fig. 3.
Fig. 3. Dependence of acid concentration on the anode
surface on current density.
The concentration of sodium sulfate, g/l: 1 – 15; 2 – 150
It follows from the figure that the surface
concentration of Н
+
-ions increases in proportion to the
logarithm of the current density and at a current density
of, for example, 1000 A/m
2
and a concentration of
150 g/l, reaches 0.2…0.3 mol/l. This approximately
corresponds to a pH of 0.…0.7, which is comparable
with the initial pH of the medium during leaching in
agitators.
To use the advantages of electrolysis during the
leaching of silicate uranium ores, it is advisable to use
wire or mesh anodes uniformly distributed in the
volume of the apparatus. This will ensure the contact of
the particles of the suspension solid phase with the
electrode surface, where the acid concentration is high.
The following ratios can be initial data for preliminary
calculations.
For the internal volume of VA anolyte and hourly
acid productivity, the current load is:
,A
SP
V
I
Q
(13)
where VA is the volume of electrolyte in liters,
QSP ~ 1 (A∙h)/l is the specific amount of electricity
necessary to obtain a constant concentration of acid in
the anode chamber. The area of the electrodes will
be, m
2
:
,
I
S
i
(14)
where i is the selected current density, A/m
2
.
For example.
For electrolysis, we choose a rectangular
electrolyzer. The anode chamber is located in the center,
and the cathode cells are located on two sides. This
allows you to assemble a filter-press structure with the
serial connection of any number of unit cells “cathode-
anode-cathode-anode-cathode ...” (Fig. 4). To reduce
thevoltage drop in the electrolyte, it is advisable to make
the thickness of the anode chamber small, for example,
100 mm. Consider an electrolyzer with dimensions of
1000×1000×100 mm and an electrolyte volume of 100 l.
In this case the current load on one anode chamber will
be (2) 100 A. When using a current density of
1000 A/m
2
,
the area of the anode (3) will be 0.1 m
2.
If we use the metal oxide electrodes based on a
titanium wire, with a diameter of, for example,
d = 1 mm as anode material, then its
length will be equal to
30 m.
S
l
d
In the electrolyzer with a width of 1 m, this will
make it possible to make an anode consisting of 5 wires
in a row and 6 rows located at different heights.
Fig. 4. Schematic diagram of the electrolyzer for the
electrolysis of sodium sulfate solution:
1 – case; 2 – ion exchange membrane;
3 – mesh or wire anodes
Based on the results obtained, the following
conclusions can be drawn.
FINDINGS
1. The electrolysis of sodium sulfate solution allows
you to get acid in the anode chamber in the pH range
from 0.5…0.7 to 2…2.5, which corresponds to the pH
range of the medium during leaching of uranium-
containing ores in the agitators.
2. The high concentration of dissolved oxygen in the
electrode layer eliminates the use of pyrolusite for the
oxidation of U
4+
in U
6+
.
3. The proposed design of the electrolyzer for the
electrolysis of sodium sulfate allows you to provide the
optimal range of pH and the concentration of dissolved
oxygen for the leaching of uranium ores.
4. The selected parameters of sodium sulfate
electrolysis provide the transition degree of uranium of
the ore from the solid phase into the solution at the level
of 90%.
REFERENCES
1. V.V. Shatalov, I.P. Smirnov, A.A. Matveev,
K.M. Smirnov. Leaching of uranium and complex ores.
// Non-ferrous metals. 2003, N 4, p. 27-34
2. V.G. Nefedov. The evolution of the gas phase
during the electrolysis of water in the fields of mass and
electric forces. Dnepropetrovsk: UGHTU, 2008, p. 292.
Article received 14.01.2019
ВСКРЫТИЕ УРАНОВЫХ РУД В ПРОЦЕССЕ ЭЛЕКТРОЛИЗА СУЛЬФАТА НАТРИЯ
В.Г. Нефедов, Ю.Е. Скнар, Е.А. Харитонова
При извлечении урана из концентратов с высоким содержанием оксида кремния обычно применяется
кислотное выщелачивание. Недостатками такого способа являются большой расход, высокая стоимость и
коррозионная активность реагентов. При этом для окисления четырехвалентного урана до хорошо
растворимого шестивалентного необходима операция его обработки окислителями, например, кислородом.
В работе показана возможность вскрытия и химического концентрирования урановых руд с помощью
электролиза сульфата натрия. рН в анодных камерах при электролизе колеблется от 2,2…2,5 до 0,5…0,7 в
приэлектродном слое электролита, что соответствует диапазону рН при выщелачивании в агитаторах.
Выделяющийся на аноде кислород способен окислять уран до шестивалентного.
РОЗКРИТТЯ УРАНОВИХ РУД У ПРОЦЕСІ ЕЛЕКТРОЛІЗУ СУЛЬФАТУ НАТРІЮ
В.Г. Нефьодов, Ю.Є. Скнар, О.А. Харитонова
Під час вилучення урану з концентратів з високим вмістом оксиду кремнію зазвичай застосовується
кислотне вилуговування. Недоліками такого способу є велика витрата, висока вартість і корозійна
активність реагентів. При цьому для окислення чотирьохвалентного урану до добре розчинного
шестивалентного необхідна операція його обробки окислювачами, наприклад, киснем. У роботі показана
можливість розтину і хімічного концентрування уранових руд за допомогою електролізу сульфату натрію.
рН в анодних камерах при електролізі коливається від 2,2…2,5 до 0,5…0,7 в приелектродному шарі
електроліту, що відповідає діапазону рН при вилуговуванні в агітаторах. Кисень, що виділяється на аноді,
здатний окислювати уран до шестивалентного.
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