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Material Science and Applied Chemistry
ISSN 1407-7353 print / 2255-8713 online
2013 / 27_________________________________________________________________________________________________
Separation of Cobalt(II) and Nickel(II) by Liquid
Membranes during Electrodialysis
Tatiana Sadyrbaeva, Riga Technical University
Abstract. The article focuses on the process of separation of
Co(II) and Ni(II) ions extracted from 3−4 M hydrochloric acid
solutions by supported liquid membranes, containing tri-noctylamine or trialkylbenzylammonium chloride in 1,2dichloroethane, during galvanostatic electrodialysis. It is
determined how the current density, composition of the liquid
membrane and aqueous solutions affect the rate and selectivity of
the cobalt(II) transport. An effective separation of cobalt(II)
from nickel(II) is achieved. Maximum separation factors of 147
(equimolar mixture), 330 (nickel(II) in excess) and more than 400
(cobalt(II) in excess) are obtained under optimum conditions.
Keywords: liquid membrane, electrodialysis, separation of
cobalt and nickel, tri-n-octylamine, trialkylbenzylammonium
chloride.
I. INTRODUCTION
Cobalt and nickel are widely used in different branches of
industry. Cobalt and nickel have similar physicochemical
properties; therefore, separation of the metals is of great
practical value. Anion-exchange extraction by tertiary amines
and quaternary ammonium salts can be used for Co(II) and
Ni(II) separation in HCl solutions, where nickel(II) exists as
cationic aquacomplexes, whereas cobalt(II) partially forms
anionic chlorocomplexes [1]. A liquid membrane is a layer of
an organic solvent separating two aqueous solutions. Liquid
membranes offer a lot of advantages over solvent extraction,
such as combination of extraction and stripping processes into
a single stage, more effective separation of elements with
similar properties and small amounts of extractants [2].
Separation of cobalt(II) from nickel(II) using supported [3, 4],
emulsion [5, 6] and polymer [7] liquid membranes containing
tertiary amines is reported in the literature.
Application of a direct electric field significantly intensifies
transport of metal ions through the liquid membranes and
facilitates the stripping of metals from organic solutions of
tertiary amine salts [8]. The electric field gradient is a driving
force of the membrane extraction process during
electrodialysis. It has been demonstrated by the author
previously that tri-n–octylamine based liquid membranes
ensure an effective platinum(IV) separation of iron(III) [9] and
nickel [10] extracted from HCl solutions, as well as
separation of palladium(II) from macroadmixtures of
copper(II), nickel(II) and iron(III) during electrodialysis [11].
The aims of the present article are to study the membrane
extraction of cobalt(II) from binary hydrochloric mixtures
with nickel(II) by supported liquid membranes, containing trin-octylamine (TOA) or trialkylbenzylammonium chloride
(TABAC) in 1,2-dichloroethane, during galvanostatic
electrodialysis and to find out optimal conditions for metal
separation.
II. METHODS AND MATERIALS
A. Instrumentation
The experiments were carried out in a five-compartment
Teflon electrodialysis cell in the system:
(−) Pt H2SO4
CoCl2
NiCl2
Liquid
membrane
HCl
H2SO4 Pt (+)
The liquid membrane (thickness of 0.5 or 0.8 cm, volume of
4 or 5.5 cm3, surface area of 7.1 cm2) was separated from the
aqueous solutions by two vertical cellophane films. The
cathodic solution (volume of 17 cm3) was separated from the
feed solution (volume of 13 cm3) by the solid anion exchange
membrane MA-40. The anodic solution was separated from
the strip solution by the solid cation exchange membrane MK40. The cellophane films and the solid membranes were
soaked in water for more than 24 h before use. The solutions
were not agitated. The direct electric current was supplied to
the plane platinum electrodes (surface area of 7.1 cm2).
Potentiostat П-5827М was used as a current source. Voltage
was measured by a digital voltmeter. The concentrations of
cobalt(II) and nickel(II) in the aqueous solutions were
determined by spectrophotometry [12], using KSCN and
dimethylglyoxime, respectively. UV-Vis spectrophotometer
СФ-46 was used for the analysis of metal ions.
B. Reagents and Materials
The solutions of tri-n-octylamine (pure grade) or
trialkylbenzylammonium chloride (alkyl C7−C9, technical
grade, purity of 87.8 %) in 1,2-dichloroethane were used as
the liquid membranes. They contained usually 0.1 M TOA or
0.01 M TABAC. The feed solution was prepared by dissolving
of CoCl2·6H2O and NiCl2·6H2O in hydrochloric acid solution.
It contained, as a rule, 0.01 M CoСl2 and 0.01 M NiCl2 in 3−4
M HCl. Reagents of pro-analysis grade were used without
further purification.
III. RESULTS AND DISCUSSION
Cobalt(II) ions were extracted by TOA and TABAC due to
the interfacial anion-exchange mechanism:
R3N(o) + H+(aq) + Cl−(aq) ↔ R3NH+Cl−(о)
(1)
CoСl42−(aq) + 2R3NH+Cl−(о) ↔ (R3NH)2CoСl4(о) + 2Cl−(aq) (2)
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Material Science and Applied Chemistry
________________________________________________________________________________________________2013 / 27
CoСl42−(aq) + 2R4NCl(о) ↔ (R4N)2CoСl4(о) + 2Cl−(aq)
(3)
where subscripts aq and o – aqueous and organic species.
The amine first reacted with hydrochloric acid to form the
amine salt (1). Co(II) anions were transferred by diffusion to
the interface feed solution / liquid membrane and interacted
with the carrier forming the complex. The extracted complex
could partially dissociate in a polar organic solvent. The
transported compound was transferred through the liquid
membrane layer and dissociated at the interface liquid
membrane / strip solution. The carrier’s molecules returned
back according to their concentration gradient. Chloride ions
permeated across the membrane in the same direction as
cobalt(II) anions.
Without electric field application, the transport of cobalt(II)
through the liquid membranes was not observed in practice. It
was found out that the application of an electric field allowed
transfering cobalt(II) through the TABAC-based liquid
membranes selectively over nickel(II) into the strip solution of
0.1 M HCl. Table 1 illustrates the influence of current density
and hydrochloric acid concentration in the feed solution on the
rate and selectivity of cobalt(II) transport. The extraction
degree of cobalt(II) into the strip solution comprises 14%, and
the extraction of nickel(II) is, as a rule, about 0.1%. The
increase in the current density from 4.2 to 9.9 mA/cm2 led to
an increase in the CoСl42− anion transport rate (Table 1). The
increase in hydrochloric acid concentration in the feed
solution from 3 to 6 M resulted in a rise of the cobalt(II) flux
due to the increase in CoСl42− content in the feed solution. The
maximum cobalt flux was obtained at I = 8.5 mA/cm2 in the
system, containing 6 M HCl. However, the electrodialysis was
accompanied by formation of emulsion in the feed solution in
case of 6 M HCl in the aqueous phase. The decrease in
hydrochloric acid concentration from 3 to 1 M sharply
decreased the cobalt(II) flux (Table 1) as cationic
aquacomplexes of cobalt(II) predominated in 1 M HCl
solution. When cobalt(II) was extracted from the equimolar
mixture, the maximum separation factor of 145 was obtained
at the current density of 9.9 mA/cm2.
Fig. 1. Change in voltage during electrodialysis for various current densities
and CHCl in the feed solution (СТАBАC = 0.01 M; lm = 0.8 сm)
I (mА/сm2): ● – 4.2; ▲, □, ◊, – 8.5; ○ – 9.9.
СHCl (М): ▲ – 0.1; ●, ○, □ – 3.0; ◊ – 6.0.
During cobalt(II) transport through TABAC-based liquid
membranes from 3-6 M HCl solutions the voltage usually
decreased gradually, and the duration of electrodialysis at high
current densities (I > 4.2 mA/cm2) was limited by electrical
breakdown – an abrupt voltage decrease in the membrane
system (Fig. 1). The main reason of electrical breakdown was
the water accumulation in the liquid membrane due to the
transfer of ions in the hydration–solvation sheath as well as
due to electroosmosis [13]. An emulsion was formed in the
bulk of organic liquid membrane during electrodialysis. The
voltage increased in case of 0.1 M HCl in the feed solution,
which was related to the lack of anions at the interface feed
solution / liquid membrane as a result of the extraction of
CoСl42− and chloride ions into the liquid membrane.
TABLE II
EFFECT OF CURRENT DENSITY ON THE EXTRACTION DEGREE E, STRIPPING
DEGREE S, FLUX J AND SEPARATION FACTOR β
(CTOA = 0.1 M; strip solution – 0.5 M HCl; lm = 0.5 cm)
I, mA/cm2
t, min
ECo
SCo
%
SNi
JCo·106,
mol/(m2s)
βCo/Ni
2.8
227
34
16
0.33
2.2
48
3.5
265
27
16
0.31
1.8
52
4.2
182
20
14
0.34
2.3
41
6.4
154
25
14
0.3
2.8
47
TABLE I
EFFECT OF CURRENT DENSITY AND HCl CONCENTRATION IN THE FEED
SOLUTION ON THE STRIPPING DEGREES S, FLUX J AND SEPARATION FACTOR β
(CTABAC = 0.01 M; strip solution – 0.1 M HCl; lm = 0.8 cm)
I, mA/cm2
t, min
CHCl, M
4.2
235
3.0
SCo
SNi
%
5
6.4
114
3.0
9
8.5
133
3.0
9.9
127
3.0
11.3
111
3.5
210
5.0
8.5
8.5
0.17
JCo·106,
mol/(m2s)
βCo/Ni
0.6
29
8.5
106
19
14
0.3
4.1
47
9.9
106
25
17
0.36
4.9
47
0.19
2.4
47
11
0.1
2.6
110
13
0.09
3.2
145
3.0
11
0.09
3.2
122
6.0
14
0.11
2.0
127
170
6.0
14
0.35
2.6
40
110
6.0
12
0.12
3.2
100
180
1.0
0.5
0.04
0.09
13
Liquid membranes containing 0.1 M TOA solutions had
higher viscosity and were more stable if compared to 0.01 M
TABAC solutions; therefore, thickness of the organic layer
could be less in case of TOA-based liquid membranes. When
cobalt(II) was extracted from 4 М HCl solutions by the liquid
membranes containing TOA, the cobalt(II) flux and the
stripping degree were higher if compared to the extraction
from 3 М HCl solutions by TABAC-based liquid membranes
(Table II). This may be due to the increase of CoСl42− content
in the feed solution. The maximum extraction degree of
57
Material Science and Applied Chemistry
2013 / 27_________________________________________________________________________________________________
cobalt(II) into the liquid membrane of 34% and the maximum
stripping degree of 17 % were obtained for a system
containing TOA. Complete removal of Co(II) from the feed
solution
could not be achieved under the experimental
conditions as cationic complexes of cobalt(II) predominated in
the 4 M HCl solution. The stripping degree of nickel(II) from
the organic phase containing TOA was somewhat higher if
compared to TABAC-based membrane system (about 0.3%).
solution. The current was transferred across the liquid
membranes mainly by Cl anions from the feed HCl solution.
TABLE III
EFFECT OF AQUEOUS SOLUTIONS AND LIQUID MEMBRANE COMPOSITION
UPON THE MEMBRANE EXTRACTION AND SEPARATION OF METALS
(I = 8.5 mA/cm2; t = 90 min; CHCl = 4.0 M; lm = 0.5 cm)
CCo
-3
0.01
The voltage-time dependencies for the system with TOA
are presented in Fig. 2. Initial voltage is significantly higher if
compared to the liquid membrane system containing TABAC.
During electrodialysis the voltage gradually decreased or
electrical breakdown was observed in the system containing
0.1 M TOA. The initial voltage decrease was related to the rise
of the total concentration of ions in the liquid membrane due
to the extraction of CoСl42− and chloride ions by carrier
accompanied by the formation of ion pairs. The electrical
breakdowns of the liquid membrane were observed at high
current density due to the water accumulation in the organic
phase (Fig. 2, curve ○).
The effects of cobalt(II) and nickel(II) concentrations in the
feed solution on the rate and selectivity of cobalt(II) transport
through the TOA-based liquid membranes are illustrated in
Table III. The increase in cobalt(II) content in the feed
solution from 5·10-3 to 0.1 M with the nickel(II) concentration
being constant led to a sharp rise of the Co(II) flux and to an
increase in the transport selectivity, whereas the Co(II)
stripping degree was about 12% and practically did not vary
within 1.5 hours of electrodialysis. The increase in the
cobalt(II) concentration from 0.01 to 0.1 M led to a decrease
in the nickel(II) stripping degree and to a sharp rise of the
separation factor. The maximum separation factor βCo/Ni > 400
was achieved for a system containing 0.1 M CoCl2. The
increase in cobalt(II) content in the feed solution led to a rise
of the current efficiency; however, the maximum current
efficiency did not exceed 10% for a system with 0.1 M CoCl2
58
CTOA
M
5·10
Fig.2. Change in voltage during electrodialysis for various current densities
(СТOА = 0.1 M; lm = 0.5 сm)
I (mА/сm2): ● – 2.8; ▲ – 3.5; ◊ – 4,2; □ – 6.4; ○ – 8,5.
CNi
strip
solution
(0.5 M)
SCo
SNi
JCo·106,
mol/(m2s)
βCo/Ni
%
0.01
0.1
HCl
11
0.2
1.9
48
0.01
0.1
HCl
13
0.3
4.3
45
0.05
0.01
0.1
HCl
12
0.05
20
240
0.1
0.01
0.1
HCl
12
< 0.03
40
> 400
0.01
5·10-3
0.1
HCl
11
0.6
3.9
18
0.01
0.05
0.1
HCl
11
0.06
3.7
190
0.01
0.1
0.1
HCl
10
0.03
3.5
330
0.01
0.01
0.2
HCl
12
0.2
4.0
56
0.01
0.01
0.3
HCl
10
0.2
3.5
45
0.01
0.01
0.1
H2SO4
16
0.3
5.3
58
0.01
0.01
0.1
HclO4
11
0.2
3.6
48
0.01
0.01
0.1
HNO3
11
0.2
3.6
50
The increase in nickel(II) concentration in the feed
solution from 5·10-3 to 0.1 M with the cobalt(II) concentration
being constant, led to insignificant reduction in the Co(II) flux
into the strip solution and cobalt(II) stripping degree, while
the nickel(II) stripping degree reduced from 0.6 to 0.03%,
separation factor increased, and a maximum separation factor
of 330 was obtained for a system containing 0.1 M NiCl2.
The influence of TOA concentration in the liquid membrane
on the rate and selectivity of the cobalt(II) transport is
presented in Table III. The increase in the carrier’s
concentration from 0.1 to 0.3 M did not exert significant
influence on the Co2+ extraction rate in the organic phase and
separation factor; however, led to some reduction in
cobalt(II) transfer rate through the liquid membrane and
cobalt(II) stripping degree. Negative effect of TOA excess on
cobalt(II) ion transfer might be connected with an increase in
the viscosity of the organic phase. The optimal composition of
the liquid membrane was 0.1 M TOA in 1.2-dichloroethane.
The electrical conductivity of the membrane system was
determined usually by the composition of the liquid
membrane. The increase in TOA concentration in the organic
phase led to a decrease in the Ohmic resistance of the liquid
membrane and to a decrease in the voltage of galvanostatic
electrodialysis (Fig. 3).
In contrast to traditional membrane extraction, the nature of
mineral acid in the strip solution did not exert a considerable
influence on the electrodialytic transport of metals. The
transfer of Co(II) proceeded with an approximately equal rate
into 0.5 M solutions of sulphuric, nitric, hydrochloric and
perchloric acids (Table III). The cobalt(II) flux decreases in
the case of nitric acid in the strip solution due to the electrical
breakdown during 1.5 hours of electrodialysis (Fig. 3, curve
●). When perchloric acid was used as a strip solution, timedependent voltage reached its maximum (Fig. 3, curve ▲).
Material Science and Applied Chemistry
________________________________________________________________________________________________2013 / 27
The Ohmic resistance and composition of the liquid cobalt(II) transport rate. Increase in the initial concentration of
membrane changed considerably in the course of Co(II) or Ni(II) in the feed solution led to an increase in the
electrodialysis. The amine reacted with perchloric acid to form separation selectivity. The maximum separation factors βCo/Ni
tri-n-octylammonium perchlorate R3NHClO4. Solutions of of 147 (equimolar mixture), 330 (excess of Ni(II)) and more
R3NHClO4 in 1,2-dichloroethane had higher electrical than 400 (excess of Co(II)) were achieved under optimal
conductivity than the organic solutions of tri-n- conditions.
octylammonium chloride. The decrease in the concentration
of perchlorate ions in the organic phase due to their backREFERENCES
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174 s.
decrease, which followed the rise, was determined by
A., Eyupoglu, V., Tutkun, O. Selective separation of cobalt
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and nickel by flat sheet supported liquid membrane using Alamine 300 as
by water accumulation in the organic phase.
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Fig. 3. Change in voltage during electrodialysis for various CTOA in the liquid
membrane and various strip solutions (I = 8.5 mА/сm2; lm = 0.5 сm)
СTOA (М): ○, ●, ▲ – 0.1; ◊ – 0.2; □ – 0.3.
Strip solution (C = 0.5 M): ○, ◊, □ − HCl; ● – HNO3; ▲− HclO4.
IV. CONCLUSION
The liquid membranes containing tri-n-octylamine or
trialkylbenzylammonium chloride
in 1,2-dichloroethane
ensured the tansport of cobalt(II) anionic complexes into
diluted solutions of HCl, HClO4, H2SO4 and HNO3
accompanied by an effective separation from nickel(II) when
extracted from binary hydrochloric mixtures during
galvanostatic electrodialysis. The cobalt(II) transport rate
increased along with an increase in the current density,
cobalt(II) initial concentration and HCl concentration in the
feed solution. Change in nickel(II) concentration in the feed
solution, TOA concentration in the organic phase and
composition of the strip solution insignificantly affected the
[4] Suruku, A., Eyupoglu, V., Tutkun, O. Selective separation of cobalt
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N 3. p. 1155-1156.
[5] Kumbasar, R.A. Extraction and concentration of cobalt from acidic
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[6] Fang, J., Li, M., Xu, Zh. Separation of cobalt from a nickelhydrometallurgical effluent using an emulsion liquid membrane. Separ.
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[7] Pospieh, B., Walkowiak, W. Separation of copper(II), cobalt(II) and
nickel(II) from chloride solutions by polymer inclusion membranes.
Separ. Purif. Technol. 2007. vol. 57. N 3. p. 461-465.
[8] Purin, B.А. Ekstrakcionnо-elektrohimicheskij metod poluchenija osobo
chistih metallov i ih sojedinenij. Izvestija АN Latv. SSR. Ser. Him., 1971,
N 5, str. 31-36.
[9] Sadyrbaeva,Т.Z. Razdelenije platini (IV) i zeleza (III) zidkimi
membranami v uslovijah elektrodializa: Zhurnal prikladnoj himiji, 2003,
t. 76, N 1, str. 78-81.
[10] Sadyrbaeva, T.Zh. Membrane extraction of platinum(IV) by tri-noctylamine in the presence of nickel(II). Scientific Journal of Riga
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[11] Sadyrbaeva, T.Zh., Purin, B.А. Elektrodializnij perenos i razdelenije
pallādija i neblagorodnih metallov v sistemah s zhidkimi membranami.
Latvijas ķīmijas žurnāls, 1993, N 3, p. 301-308.
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[13] Golubev, V.N., Purin, B.А. Issledovanie elektricheskogo proboja
zhidkostnih membran pri perenose cherez nih nekotorih anionov.
Dokladi AN SSSR, 1977, t. 232, N 6, str. 1340-1342.
Tatiana Sadyrbaeva graduated from the Latvian State University, the Faculty
of Chemistry (1984). She obtained a Doctoral Degree in Chemical
Engineering from the Institute of Inorganic Chemistry of the Latvian
Academy of Sciences in 1993. She is a Leading Researcher at the Laboratory
of Electrochemistry of the Institute of Inorganic Chemistry, RTU.
Current and previous research interests include electrodialysis through liquid
membranes, electrodeposition, separation of metals, liquid extraction.
E-mail: [email protected].
Tatjana Sadirbajeva. Kobalta (II) atdalīšana no niķeļa (II) ar šķidrām membrānām elektrodialīzes apstākļos
Izpētīts kobalta (II) ekstrakcijas process no sālsskābiem šķīdumiem, kas satur 0,01 M CoCl2 un 0,01 M NiCl2, ar šķidrām membrānām uz tri-noktilamīna un trialkilbenzilamonija hlorīda bāzes galvanostatiskās elektrodialīzes apstākļos. Noteikts, ka šķidrās membrānas īsteno kobalta
(II) jonu pārnesi atšķaidītos sālsskābes, sērskābes, perhlorskābes un slāpekļskābes šķīdumos un nodrošina efektīvu kobalta (II) atdalīšanu no
niķeļa (II) vienā procesa stadijā. Noteikts, ka, paaugstinot strāvas blīvumu (0 – 9,9 mA/cm2) un palielinot membrānekstrakcijas procesa
ilgumu (50 – 230 min), pieaug kobalta (II) izdalīšanas pakāpe uztvērējšķīdumā. Parādīts, ka kobalta (II) koncentrācijas palielināšana izejas
šķīdumā no 5·10-3 līdz 0,1 M CoCl2 palielina kobalta (II) jonu plūsmu caur šķidro membrānu, kas praktiski neietekmē kobalta (II) jonu
reekstrakcijas pakāpi un negatīvi ietekmē niķeļa( II) reekstrakcijas pakāpi. Noteikts, ka, palielinot sālsskābes koncentrāciju izejas šķīdumā no
1,0 līdz 6,0 M, pieaug kobalta (II) pārneses ātrums caur šķidro membrānu. Konstatēts, ka sistēmā, kas satur 6,0 M HCl izejas šķīdumā,
iespējama organisko katjonu izdalīšana no organiskās fāzes ūdens šķīdumā. Noteikts optimāls izejas šķīduma skābums: 3,0 – 4,0 M HCl.
Noteikts, ka niķeļa (II) satura palielināšana izejas šķīdumā no 5·10−3 līdz 0,1 M, tri-n-oktilamīna daudzuma izmaiņa organiskajā fāzē no 0,1
59
Material Science and Applied Chemistry
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līdz 0,3 M, sālsskābes koncentrācijas izmaiņas uztvērējšķīdumā no 0,5 līdz 5,0 M un skābes raksturs uztvērējšķīdumā maz ietekmē kobalta (II)
transmembrānās pārneses ātrumu un izdalīšanas selektivitāti. Konstatēts, ka izpētītajās sistēmās var notikt šķidrās membrānas elektriskās
caursites – krasa sprieguma samazināšana elektrodialīzes beigu periodā atkarībā no strāvas blīvuma un procesa ilguma. Noteikts, ka, kobalta
(II) vai niķeļa (II) koncentrācijas palielināšana izejas šķīdumā dod metālu sadalīšanas koeficienta pieaugumu. Optimālajos apstākļos iegūti
metālu sadalīšanas koeficienti βCo/Ni = 147 (0,01 M CoCl2 un 0,01 M NiCl2), βCo/Ni = 330 (0,01 M CoCl2 un 0,1 M NiCl2), βCo/Ni > 400 (0,1
M CoCl2 un 0,01 M NiCl2).
Татьяна Садырбаева. Разделение кобальта(II) и никеля(II) жидкими мембранами в процессе электродиализа.
Разделение кобальта(II) и никеля(II) с помощью анионообменных экстрагентов основано на различной устойчивости анионных
хлоридных комплексов этих металлов в растворах соляной кислоты. Процесс электродиализного разделения ионов Co(II) и Ni(II)
изучали с помощью пятикамерной ячейки с объемной жидкой мембраной толщиной 0,5-0,8 см, заключенной между вертикальными
целлофановыми пленками. Исследован процесс мембранной экстракции ионов кобальта(II) из бинарных солянокислых смесей,
содержащих, как правило, 0.01 M CoCl2 и 0.01 M NiCl2 в 3 – 4 M HCl растворами три-н-октиламина и хлорида
триалкилбензиламмония в 1,2-дихлорэтане в условиях гальваностатического электродиализа. Было установлено, что при наложении
электрического поля происходит перенос ионов Со(II) из исходного раствора. НСl через жидкие мембраны, в растворы разбавленной
соляной кислоты, и осуществляется эффективное отделение кобальта(II) от никеля(II). Установлено, что скорость трансмембранного
переноса ионов Co(II) повышается при увеличении плотности тока электродиализа в интервале 0 – 9.9 мА/см2, концентрации
ионов кобальта(II) (5·10-3 – 0.1 M) в исходном растворе и концентрации соляной кислоты (1.0 – 6.0 M) в исходном растворе.
Определена оптимальная кислотность исходного раствора: 3 – 4 M HCl. Установлено, что в изученных системах могут происходить
электрические пробои – резкое падение напряжения вследствие накопления воды в оранической фазе. Показано, что изменение
содержания никеля(II) в исходном растворе (5·10-3 – 0.1 M) и содержания три-н-октиламина в органической фазе (0.1 – 0.3 M), а
также природа кислоты в принимающем растворе (HCl, HClO4, H2SO4, HNO3) незначительно влияют на скорость мембранной
экстракции кобальта(II). Показано, что селективность разделения кобальта(II) и никеля(II) возрастает при повышении концентрации
одного из металлов в исходной смеси. Полученные в оптимальных условиях коэффициенты разделения металлов βCo/Ni составляют
147 при извлечении из эквимолярной смеси, достигают 330 в условиях десятикратного избытка никеля(II) и превышают 400 при
десятикратном избытке кобальта(II) в исходном растворе.
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