Purification of crude In(OH)3 using the functionalized ionic liquid betainium bis(trifluoromethylsulfonyl)imide

Article abstract of DOI:10.1039/c7gc02958f

The recovery of indium from a crude indium(iii) hydroxide using the ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf₂N], was investigated. Leaching and solvent extraction were combined in one step using the thermomorphic properties of the [Hbet][Tf₂N]-H₂O system. During leaching (80 °C) a homogeneous phase was formed. Upon lowering the temperature below the lower critical solution temperature (UCST), the dissolved metals distributed themselves between the two phases. The optimal leaching/extraction conditions were determined to be a leaching time of 3 hours at 80 °C in a 1:1 wt/wt [Hbet][Tf₂N]-H₂O mixture. Large separation factors (>100) between In(iii) and Al(iii), Ca(ii), Cd(ii), Ni(ii) and Zn(ii) were obtained implying an easy separation. Fe(iii), As(v) and Pb(ii) are co-extracted. The separation factor between indium and iron was improved to >1000 by addition of ascorbic acid to reduce Fe(iii) to Fe(ii). The stripping was done very efficiently by HCl solution. The ionic liquid was regenerated during the stripping step. By combining a prehydrolysis and hydrolysis step, indium(iii) hydroxide with a purity >99% was obtained.

Full text of DOI:10.1039/c7gc02958f

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DOI: 10.1039/C7GC02958F
Journal Name
ARTICLE
Purification of crude In(OH)
3
using the functionalized ionic liquid
betainium bis(trifluoromethylsulfonyl)imide
a,b
b
b
c
*a
Clio Deferm , Jan Luyten , Harald Oosterhof , Jan Fransaer and Koen Binnemans
0Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
The recovery of indium from a crude indium(III) hydroxide using the ionic liquid betainium bis(trifluoromethylsulfonyl)imide,
[Hbet][Tf N], was investigated. Leaching and solvent extraction were combined in one step using the thermomorphic
properties of the [Hbet][Tf N]–H O system. During leaching (80 °C) a homogeneous phase was formed. Upon lowering the
2
2
2
temperature below the lower critical solution temperature (UCST), the dissolved metals distributed themselves between
the two phases. The optimal leaching/extraction conditions were determined to be a leaching time of 3 hours at 80 °C in a
1:1 wt/wt [Hbet][Tf
2
N]–H O mixture. Large separation factors (>100) between In(III) and Al(III), Ca(II), Cd(II), Ni(II) and Zn(II)
2
were obtained implying an easy separation. Fe(III), As(V) and Pb(II) are co-extracted. The separation factor between indium
and iron was improved to >1000 by addition of ascorbic acid to reduce Fe(III) to Fe(II). The stripping was done very efficiently
by HCl solution. The ionic liquid was regenerated during the stripping step. By combining a prehydrolysis and hydrolysis step,
indium(III) hydroxide with a purity > 99% was obtained.
makes use of pyrometallurgical and/or hydrometallurgical
processes. It involves unit operations such as leaching, solvent
extraction, cementation/precipitation, electrowinning and
Introduction
Indium finds applications in many electronic devices e.g.
photovoltaic cells, flat television screens, laptops and mobile
phones, as metal, alloy or indium tin oxide (ITO). The demand
refining. Crude indium(III) hydroxide (In(OH)
3
)
is an
intermediate that is often created during the processing of
3,4,6-9
indium sources.
Hydrometallurgical processes are very suitable for
extracting indium from crude In(OH) . Typically, strong acids or
of indium is expected to grow by more than 5% per year until
1
2
020. China dominates the indium supply from primary mining
3
(>58% of the global production in 2013), and the worldwide
bases are used to generate aqueous leachates by selective
dissolution of the metals present in concentrates. The insoluble
compounds can be readily separated from the leachate. Further
purification is generally carried out by solvent extraction or ion
exchange. Pure metals or metallic compounds can be produced
once the metal salts have been prepared in a pure form by, for
example, precipitation, cementation or electrowinning.
1,2
recycling rate is still very low (<1%). Indium is a scarce
element with an abundance of only 0.1 ppm in the Earth’s
3-5
crust. It is most commonly found in association with zinc ores
such as sphalerite, although it also occurs in lead, copper, iron
3-5
and tin ores. The typical indium content of zinc deposits
ranges from 10 to 20 ppm.1,3,5 Thus, indium is a by-product of
mining and refining operations of other metals. Indium is
accumulated in low concentrations in residues formed during
the processing of these ores. Possible primary sources of indium
are by-products of refining, flue dusts, slags and metallic
Advances in extractive metallurgy are mainly driven by
environmental considerations, optimal metal recovery and
9
reduction of in-process inventory. Processes frequently involve
multiple precipitation and dissolution steps with large volumes
of waste water. Multiple processing steps lead to product losses
3
,4
intermediates. The recovery of indium from primary sources
is often complex and difficult, and many of the flow sheets are
9
in reject streams and high processing costs. Among the
5
proprietary to each producer. Extractive metallurgy has been
developed to recover indium from primary and secondary
residues. Secondary indium sources comprise mostly e-waste
and impure indium (<99%). The recovery of indium from
primary and secondary sources through extractive metallurgy
approaches to overcome the disadvantages of the existing
metal manufacturing technologies, ionic liquids can be
alternative solvents in hydrometallurgy. Ionic liquids are
1
,5
1
0,11
solvents that consist entirely of ions.
Ionic liquids can be
used either for replacing the aqueous phase in leaching
processes or for replacing the molecular solvents in the organic
1
2-19
phase of solvent extraction processes.
It is even possible to
a
KU Leuven, Department of Chemistry, Celestijnenlaan 200F, bus 2404, B-3001
Heverlee, Belgium. E-mail: Koen.Binnemans@kuleuven.be;
Umicore, Group Research & Development, Competence Area Recycling
carry out solvent extraction with two mutually immiscible ionic
liquid phases. The term “ionometallurgy” has been coined by
b
20
and Extraction Technologies, Watertorenstraat 33, B-2250 Olen, Belgium
c
Abbott to describe processes in extractive metallurgy that make
KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, bus
2
450, B-3001 Heverlee, Belgium.
21
use of an ionic liquid phase instead of an aqueous phase. More
†Electronic Supplementary Information (ESI): Figures with additional leaching and
general, leaching with an ionic liquid can be considered a
distribution results available.
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Journal Name
solvometallurgical process.22 Solvometallurgy makes use of
processes involving nonaqueous solvents for the extraction of
metals from ores, industrial process residues, production scrap,
and urban waste.
To achieve selectivity and high metal loading upon leaching
3
crude In(OH) , an alternative treatment is proposed that uses a
3
Table 1 Metal composition of crude In(OH) determined by ICP-OES.
View Article Online
DOI: 10.1039/C7GC02958F
Element
wt%
Element
wt%
Element
wt%
Al
As
Bi
1.4
0.54
0.0018
0.20
0.18
1.6
Ga
Ge
In
0.0046
0.0095
58
Se
Sn
Te
Zn
0.0027
0.0028
0.0015
5.0
reusable ionic liquid leaching agent, the carboxyl-functionalized
ionic liquid betainium bis(trifluoromethylsulfonyl)imide
Ca
Cd
Fe
Ni
0.027
0.26
Pb
Sb
(
[Hbet][Tf
dissolve different metal oxides,
lamp phosphor waste and rare-earth permanent magnets,
2
N], Fig. 1). [Hbet][Tf
2
2
N] has been used to selectively
0.035
3,24
to recycle rare earths from
2
5,26
to a resistivity of >18.2 MΩ cm with a Milli-Q® Academic
ultrapure water system. The crude In(OH) was obtained from
2
7
and to recover rare earths from bauxite residue (red mud) . In
this paper, [Hbet][Tf N] was studied to purify crude In(OH) by
selective leaching. Crude In(OH) was leached by water-
saturated [Hbet][Tf N] and by taking the thermomorphic
behavior of [Hbet][Tf N] into account. [Hbet][Tf N]–H
3
2
3
the Umicore Group Research & Development and its
composition is shown in D2O (99.9 atom% D) were purchased
3
2
from Sigma-Aldrich (Diegem, Belgium). Mg(NO3)2
was obtained from Merck (Overijse, Belgium) and 1,4-dioxane
99.9 wt%) from Acros Organics (Geel, Belgium). l(+)-Ascorbic
6H2O (>99%)
2
2
2
O
mixtures display thermomorphic behavior with an upper critical
solution temperature (UCST) of 55 °C for a 1:1 wt/wt
(
2
3,26,28-30
acid (technical grade) and NaOH pellets (>99%) were purchased
from VWR (Leuven, Belgium). Hydrochloric acid solutions were
prepared from concentrated HCl (37%, Acros Organics, Geel,
Belgium) and water. All chemicals were used as received,
without further purification. Water was always of ultrapure
quality, deionized
system.
The mixture forms one homogeneous phase
above the UCST and two phases below that temperature. The
metals might selectively distribute themselves between both
phases, which can lead to the separation of metals upon cooling
down the leachate below the critical temperature, and hence to
2
phase separation. Metals dissolved in [Hbet][Tf N] can be
Table 1. The crude In(OH)
C overnight before use.
3
was dried in a vacuum oven at 100
stripped with an acidic solution while the ionic liquid is
simultaneously regenerated. This leaching strategy has been
studied previously for the selective dissolution of rare-earth
°
Instrumentation and analysis methods
2
5,26,27
elements.
Our process combines leaching and solvent
A Heraeus Labofuge 200 centrifuge was used to separate the
undissolved flue dust particles from the ionic liquid after the
leaching experiments. Metal concentrations were determined
using inductively coupled plasma optical emission spectrometer
extraction in a single step and can thus be considered as a form
of process intensification. Contamination of the water phase by
dissolved ionic liquid [Hbet][Tf
by using a salting-out agent.
2
N] is avoided during the process,
(ICP-OES; Agilent, type E730) with an axial plasma configuration.
For analysis of the aqueous phase by ICP-OES, a calibration
curve was prepared with multi-element solutions over a
O
O
O
N-
−
1
concentration range of 0–10 mg L with a quality control of
N+
S
S
-
1
2
mg L and scandium as an internal standard. The calibration
OH
F3C
CF3
solutions and the samples were diluted in 10 vol% HCl. The
spectra were measured with a power of 1.4 kW, an argon flow
O
O
Fig. 1 Structure of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide,
Hbet][Tf N].
of 15 L min− and an auxiliary argon flow of 1.5 L min . For the
1
−1
[
2
organic phase, the sample was first digested with a mixture of
H
2
SO
4
and HNO
3 2 4
in a quartz beaker on a heating plate. H SO
Experimental
Chemicals
and HNO
3
were evaporated (at 400 °C) and the residue was
dissolved in 10 vol% HCl before measurement. The calibration
and measuring procedure have been performed in the same
way for the organic phase as described for the aqueous phase.
pH and potential measurements of the aqueous phase after
leaching were performed with an Protos 3400 (X) pH/ORP/T
meter (Knick) and a InPro 3250i/SG/120 (Mettler-Toledo)
electrode. A Mettler-Toledo DL38 volumetric Karl Fischer
titrator (Hydranal® AG reagent) in combination with the oven
sample changer Stromboli was used with to determine the
water content of the ionic liquid.
MgCl
99%) were obtained from Alfa Aesar (Karlsruhe Germany).
Lithium bis(trifluoromethylsulfonyl)imide (LiTf N) (>99%) and
O (99.9 atom% D) were purchased from Sigma-Aldrich
Diegem, Belgium). Mg(NO 6H O (>99%) was obtained from
Merck (Overijse, Belgium) and 1,4-dioxane (99.9 wt%) from
Acros Organics (Geel, Belgium). (+)-Ascorbic acid (technical
grade) and NaOH pellets (>99%) were purchased from VWR
Leuven, Belgium). Hydrochloric acid solutions were prepared
2
anhydrous (99%) and betaine hydrochloride (HbetCl)
(
2
®
D
2
®
(
3
)
2

2
L
(
Synthesis of [Hbet][Tf
2
N]
from concentrated HCl (37%, Acros Organics, Geel, Belgium)
and water. All chemicals were used as received, without further
purification. Water was always of ultrapure quality, deionized
The ionic liquid [Hbet][Tf
one-step literature method based on the reaction between
2N] was synthesized according to a
2
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[
Hbet]Cl and LiTf
2
N.25 Chloride impurities were removed by
test in the
m
IL and maq are the mass of the ionic liquid and aqVuieewoAursticplehOansliene,
respectively.
DOI: 10.1039/C7GC02958F
several washing steps with ice water until the AgNO
3
water phase after the washing step was negative. The level of
chloride impurities in the ionic liquid phase after washing was
below 1 ppm (Bench top total reflection X-ray fluorescence
spectrometer; Bruker S2 Picofox). The water-saturated ionic
liquid obtained after washing was used as such (water content:
The separation efficiency between two metals can be
described by the separation factor αM1,M2, which is defined as
the ratio of the respective distribution ratios of two extractable
solutes measured under the same conditions:
1
3.25±0.04 wt% H
2
O).
ꢂꢃꢄ
훼푀ꢁ,푀2 = ꢂ
(3)
ꢃꢅ
Leaching
Small glass vials (20 mL) were filled with 10 g of [Hbet][Tf
and 700 mg sample of the crude In(OH) , resulting in a
solid/liquid ratio of 70 mg g . Water-saturated [Hbet][Tf N] (13
wt%) or a [Hbet][Tf N]–H O mixture (1:1 or 1:0.5 wt/wt) was
where DM1 and DM2 are the distribution ratios of metal M
M , respectively. By definition, the value of the separation
2
factor is always greater than unity.
1
and
2
N]
3
−
1
2
1
Quantitative H NMR
2
2
The concentration of ionic liquid in the aqueous phase was
used depending on the experiment. For the reduction of iron(III)
to iron(II), a fixed amount of ascorbic acid was added to the
aqueous phase to achieve a concentration of 0.010 M. This
concentration was chosen based on the assumption that an iron
leaching percentage of 100 % was obtained and all iron is
present in the form of iron(III). A magnetic stirring bar was then
added to each of the vials after which were closed using a plastic
screw cap. The leaching experiments were carried out on a
heating plate with an integrated magnetic stirrer and a
temperature sensor. A copper block was placed on top as the
vial container. The vials were placed in the copper block at the
appropriate temperature and stirred at 500 rpm for a certain
period of time. The content of the vials was then filtered
through an MF-Millipore mixed cellulose membrane, pore size
1
determined using quantitative H NMR using 1,4-dioxane as an
internal standard. A sample of the water phase was taken (100
mg) and a known amount of 1,4-dioxane–D O solution was
2
added so that the concentration of 1,4-dioxane internal
standard would be comparable to the concentration of ionic
1
liquid in the sample. The H NMR spectrum of 1,4-dioxane
shows one resonance at δ = 3.7, corresponding to 8 equivalent
protons, that does not overlap with the resonances of water or
[
Hbet][Tf
2
N]. The relative concentration versus 1,4-dioxane and
N] were calculated by
the absolute concentration of [Hbet][Tf
2
integration of the peaks by the Topspin software. Liquid-state
1
H NMR spectra were recorded on a Bruker Ascend™ 400 MHz
spectrometer, operating at 400 MHz.
0
.45 µm, by means of a vacuum filtration to separate the
Scrubbing
undissolved crude In(OH) from the ionic liquid before cooling
3
Co-extracted metal ions are removed after extraction from
the organic phase by a scrubbing agent, leaving the metal ions
of interest in the loaded organic phase. First, leaching
experiments were performed in which 700 mg sample of the
took place. After leaching and filtration, the vials were cooling
down in air to ambient temperature. Separation of the phases
was assisted by centrifugation for 15 min at 3500 rpm. The
metal contents dissolved in the ionic liquid and aqueous phase
were determined using ICP-OES.
crude In(OH)
3
was leached with a 1:1 wt/wt [Hbet][Tf
2 2
N]–H O
mixture (10 g [Hbet][Tf
2
N]). The loaded ionic liquid phase
The percentage leaching (%
L) is defined as the amount of
obtained after leaching/extraction was contacted with an
aqueous phase containing different stripping agents: Milli-Q
water, HCl (1, 1.5 and 2 M), H SO (0.75 and 1 M) and MgSO
2 4 4
metal leached to the ionic liquid or ionic liquid–water mixture
over the initial amount of metal present in the crude In(OH) :
3
mIL[M]IL+maq[M]aq
(0.1 and 1 M) in a 1:1 wt/wt ratio. The scrubbing experiments
were carried out in small glass vials (20 mL) on a heating plate
with an integrated magnetic stirrer and a temperature sensor.
%
퐿 =
× 1ꢀꢀ%
(1)
푚0
where [M]IL (ppm) is the metal concentration in the ionic liquid A copper block was placed on top as the vial container. A
after leaching/extraction, [M]aq (ppm) is the metal magnetic stirring bar was added to each of the vials and they
concentration in the aqueous phase after leaching/extraction were closed using a plastic screw cap. The vials were placed in
0 3
and m is the initial metal mass present in the crude In(OH) . mIL
and maq are the mass of the ionic liquid and aqueous phase,
respectively.
the copper block at the appropriate temperature and stirred at
00 rpm for 1 h. After scrubbing, separation of the phases was
assisted by centrifugation for 15 min at 3500 rpm. The metal
content dissolved in the ionic liquid and aqueous phase was
determined using ICP-OES.
5
The distribution ratio D
M
of a metal is defined as:
The percentage scrubbing (%S) in the scrubbed phase can be
defined as the amount of metal scrubbed from the ionic liquid
phase to the total amount of metal in the ionic liquid phase
before scrubbing:
mIL[M]IL
maq[M]aq
퐷 =
M
(2)
where [M]IL (ppm) is the metal concentration in the ionic liquid
after leaching/extraction and [M]aq (ppm) is the metal
concentration in the aqueous phase after leaching/extraction.
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Journal Name
Vaq([M]IL,0−[M]IL
VIL[M]IL,0
)
Ca
View Article Online
%
S =
× 1ꢀꢀ
(4)
DOI: 10.1039/C7GC02958F
100
As
Cd
Ga
Ge
Ni
Pb
Al
Fe
In
Zn
where [M]IL,0 is the metal concentration in the organic phase
after extraction or before scrubbing.
80
Stripping
60
40
Stripping of the loaded ionic liquid phase to selectively
recover the indium ions after scrubbing was performed in the
same way as the scrubbing experiments. The stripping
efficiency was expressed using the scrubbing percentage %S (eq
20
4
).
0
0.5
1.0
1.5
Results and discussion
Reaction time (h)
Leaching of crude In(OH)
The protonated carboxyl-functionalized ionic liquid
betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf N] can
dissolve large quantities of metal oxides due to the carboxylic
acid group (pK = 1.83) located on the cation of the ionic
This difference in solubility can be exploited to 40°C, 60 °C and 80 °C) for increasing periods of time (30 min, 1
selectively recover indium from the crude In(OH)
. The h, 3 h). The percentages leaching for the various elements from
selectivity and kinetics of the dissolution process are affected dissolution of crude In(OH) in water-saturated [Hbet][Tf N] as
3 2
in [Hbet][Tf N]
Fig. 3 Leaching (%) of different metals from crude In(OH)
3
2
in water-saturated [Hbet][Tf N]
as a function of reaction time at 80 °C. The concentrations of Sb, Se, Sn and Te were
below the detection limit (<1 ppm) so these elements have been excluded from the
graph.
2
a
2
3,31
liquid.
3
3
2
by the water content in the ionic liquid. Water accelerates the a function of temperature and reaction time are shown in Fig.
dissolution of metal oxides because it lowers the viscosity, S1†. Overall, the percentages leaching of the elements are
facilitates the exchange of protons from the betaine groups and increasing with increasing temperature. Fig. 2 displays the
2
3,25,26,28,31
enhances the solvation of ions in the ionic liquid.
Therefore, all the leaching tests were executed with a water- temperature and reaction time. The percentages leaching of
saturated ionic liquid (13 wt%).
indium are increasing with time and temperature, reaching a
percentages leaching for indium specifically as a function of
First, the effect of temperature and reaction time were maximum of 94% after 3 h at 80 °C (Fig. 2). 80 °C is the optimal
tested on the solubility of indium in the water-saturated ionic indium leaching temperature since leaching results close to the
liquid. Crude In(OH)
3
particles were added to the ionic liquid (70 maximum percentage leaching are already obtained after 30
−
1
mg g ) and stirred (500 rpm) at various temperatures (20 °C,
min. However, no selectivity for indium was observed at this
temperature (Fig. 3). All impurities, except for Pb and Ge, have
percentages leaching above 50% at 80 °C.
1
00
0
1
3
.5 h
h
h
94
89
94
91
Thermomorphic leaching/extraction in a [Hbet][Tf N]–H O system
2
2
9
1
An alternative leaching system is proposed to improve the
selectivity based on the same ionic liquid, but with an excess of
water (>13 wt%) so that it forms a biphasic system at room
temperature. This system combines leaching with metal
extraction (separation) in one convenient step thanks to the
thermomorphic properties of this ionic liquid-water system. The
combined leaching/extraction process started by leaching the
3
80
60
40
20
0
7
4
64
5
2
5
3
crude In(OH) particles in a 1:0.5 or 1:1 wt/wt mixture of
9
.9
.7
.7
2 2
[Hbet][Tf N]–H O at 60 or 80 °C (above the cloud point
5
2
temperature) so that it formed one homogeneous phase.
Afterwards, the solution was filtered at 60 or 80 °C and cooled
again to room temperature so the mixture could phase
separate. Besides varying the mass composition of the mixture
and the temperature, the experiments were also executed for
increasing periods of time (30 min, 1 h, 3 h). The total
percentage leaching was determined by combining the
measured metal content in the water phase and in the ionic
liquid phase.
20
40
60
80
T (°C)
3 2
Fig. 2 Leaching of indium (%) from crude In(OH) in water-saturated [Hbet][Tf N] as a
function of temperature and reaction time.
After cooling the filtered solution to room temperature, a
gel-like precipitate appeared at the interphase under the
4
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Journal Name
ARTICLE
following conditions: 1:0.5 wt/wt mixture of [Hbet][Tf
at 60 °C and 80 °C and 1:1 wt/wt mixture of [Hbet][Tf
2
N]–H
N]–H
2
O
O
View Article Online
1
00
DOI: 10.1039/C7GC02958
80 °C
F
F
e
2
2
As
Cd
Ni
at 60 °C after a 3h leaching (Fig. S2†). This precipitate was
probably formed in the upper aqueous phase upon cooling. The
pH of the aqueous phase was always between 1 and 1.5,
excluding hydrolysis of the present metals. The composition of
the precipitate on a piece of glass fiber filter was analyzed using
SEM-EDS (Fig. S3†) and XRD (Fig. S4†). Two types of particles
were observed on the SEM pictures: dark and bright. The dark
particles consisted of Fe, As, In, Si, S and O. This can imply the
Pb
Al
Ca
In
1
0
Zn
1
0
.1
formation of iron(III) arsenate (FeAsO
4
) or indium(III) arsenate
32,33
4
(InAsO ).
The presence of sulfur cannot be explained by the
formation of sulfides since the potential of the aqueous phase
was always between 450 and 500 mV. According to Pourbaix,
sulfides are present in solution below 223 mV at a pH of 1.34
0.01
0.5
1
3
Reaction time (h)
Crude In(OH)
SiO
Crude In(OH)
3
contains 0.25 wt% of sulfur. The presence of silica
) can explain the gel-like appearance of the precipitate.35 Fig. 5 Distribution ratio of the various elements in a biphasic 1:1 wt/wt [Hbet][Tf
N]–
O system as a function of reaction time. A high distribution ratio corresponds to a
greater affinity for the ionic liquid phase. The concentrations of Bi, Ga, Ge, Sb, Se, Sn
(
2
2
H
2
3
contains 0.17 wt% of silicon. It is also possible
that the silica is attributed to the glass fiber filter. Another
explanation for the gel-like appearance of the precipitate is the
possibility that the metals form a metal complex with the
and Te content were below the detection limit (<1 ppm) so these elements have been
excluded from the graph.
betainium ligands that exhibit polymeric structures. Ag(I), Table 2 Separation factors (α) between indium and various elements for a biphasic 1:1
2 2
wt/wt [Hbet][Tf N]–H O system at 80 °C as a function of reaction time.
Mn(II), Cu(II), Cd(II) and rare-earth complexes with betainium
ligands that exhibit polymeric structures have already been
1
:1 wt/wt [Hbet][Tf
1 h
2 2
N]–H O
2
3,31,36
reported in the literature.
When the filtered solution was
Element pair
0
.5 h
3 h
cooled, phase separation occurred, consequently decreasing
the water content of the ionic liquid phase, water that was
previously preventing the indium from coordinating with the
betainium ligands. The bright particles observed with SEM
consisted of Pb, S and O, possibly indicating the presence of
In/Al
In/As
In/Ca
In/Cd
Fe/In
In/Ni
In/Pb
In/Zn
(4.1 ± 0.7)*102
21 ± 8
(2.0 ± 0.8)*102
(2.0 ± 0.5)*102
1.2 ± 0.3a
(5.2 ± 1)*102
13 ± 3
(2.1 ± 1)*102
(2.5 ± 0.2)*102
1.4 ± 0.2a
(2.8 ± 0.6)*102
(5.8 ± 2)*102
8.6 ± 1
(1.6 ± 0.3)*102
(2.1 ± 0.1)*102
1.4 ± 4*10-2a
(2.4 ± 0.3)*102
22 ± 4
PbSO
presence of PbSO
phase, Fe((AsO
identify with XRD.
The percentages leaching of crude In(OH)
mixture of [Hbet][Tf N]–H O at 60 or 80 °C as a function of the
reaction time for the various elements are shown in Fig. S5† and with temperature and reaction time. The leaching process itself
4
. The precipitate was further analyzed with XRD. The
was confirmed alongside with an amorphous
0.5(OH)0.5 and compounds unable to
(2.8 ± 1)*102
4
26 ± 12
(3.9 ± 1.5)*102
25 ± 8
(4.0 ± 1.2)*102
4 4
)0.5(SO )
(3.9 ± 0.4)*102
a
These values represent the Fe/In ratio. According to IUPAC, by convention the ratio of
in a 1:1 wt/wt the respective distribution ratios has to be chosen so that α> 1.46
3
2
2
Table S1†. The percentages leaching of the elements increase
shows very poor selectivity towards indium. Fig. 4 displays the
percentages leaching for indium as a function of temperature
and reaction time. The percentages leaching increase with
increasing reaction time and temperature. In general, a
temperature of 80 °C and a reaction time of 3 h seems to be the
optimal condition for dissolution of indium. A percentage
leaching for indium of 100% was obtained under these
2
1
00
9
9
7
0
1
3
.5 h
h
h
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
8
68
conditions. The solubility of [Hbet][Tf N] in the aqueous phase
-
1
was 2.56 g L at 25 °C.
4
7
3
Next, the metal distribution over the two phases was
studied by determining the distribution of the elements
between the ionic liquid and the water phase. The leaching
temperature of the process was set to 80 °C, because the
leaching is sufficiently fast at this temperature in this water-
saturated system. At 80 °C the thermomorphic ionic liquid-
water system is also certainly homogeneous and the viscosity is
also sufficiently low (0.87 ± 0.02 mPa s) and almost equal to
1
60
80
T (°C)
2
6,37
pure water (0.89 mPa s at 25 °C).
Moreover, from previous
Fig. 4 Leaching indium (%) from dissolution of crude In(OH)
3
in a 1:1 wt/wt mixture of
results showed that 80 °C is the optimal leaching temperature
for indium. Fig. 5 shows that the distribution ratios for the
[
Hbet][Tf N]–H O as a function of temperature and reaction time. The result at 60 °C
2
2
after leaching 3 h is not shown because a precipitate was formed that contains indium.
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ARTICLE
Journal Name
various elements are comparable across the reaction times. The implying an easy separation between indium aVniedw Airroticnle.OTnlhinee
low distribution ratios of aluminum, calcium, cadmium, nickel separation factors of arsenic and lead aDlOsoI: 1i0n.c10re39a/sCe7dGCs0li2g9h5t8lyF
and zinc in combination with high separation factors (α ≥ 100) which is only beneficial to the separation of these elements
between these elements and indium(III), imply an easy from indium, but they are still insufficient to completely
separation (Fig. 5, Table 2, Table S2†). Separating indium eliminate co-extraction. The solubility of the ionic liquid in the
-1
completely from arsenic and lead is more difficult due to the aqueous phase is 2.63 g L at 25 °C.
lower separation factors between these elements and indium.
The effect of inorganic salts in the aqueous phase on the
Especially iron is very difficult to separate from indium. The distribution of the metals was also tested. According to its
−
separation factors between iron and indium are close to 1.
position in the Hofmeister series, Tf
2
N is one of the most
To improve the separation between indium and iron, hydrophobic anions. Therefore, anion displacement from the
38
2
iron(III) was reduced to iron(II). Ascorbic acid (vitamin C) was ionic liquid is very unlikely to occur when using [Hbet][Tf N].
chosen as the reducing agent since it performs well in the Fe(III) A high salt concentration can therefore be used in the water
reduction in aqueous solution and it has been used before in phase without exchanging anions. The addition of inorganic
extraction systems with [Hbet][Tf
2
N]. Moreover, ascorbic acid is salts has a twofold advantage. First, the water-soluble salt
anions can form complexes with the metal ions and therefore
HO
OH
O
change their affinity of the metal ions for the aqueous phase.
O
Secondly, salt anions and cations can influence the solubility of
2
Fe3+ + O
2 Fe2+ + O
+ 2 H+
OH
26,45
the ionic liquid in the aqueous phase.
The salting-out effect
O
OH
O
for cations follows the order NH4+ < K < Na < Li < Ca < Mg ,
+
+
+
2+
2+
−
OH
OH
whereas the salting-out effect of anions follows the order ClO
4
< I− < NO
−
< Cl− < SO
2−
. Furthermore, a higher salt
Fig. 6 Fe(III) to Fe(II) reduction by ascorbic acid with formation of dehydroascorbic acid.
3
4
concentration increases the salting-in or salting-out effect of a
salt, respectively. Therefore, it was interesting to investigate
to what an extent salts could influence the betaine content in
the aqueous phase, thereby influencing the distribution of the
different metal ions. The above experiments concerning the
combined leaching/extraction process were repeated with the
Table 3 Percentages leaching (%L) and distribution ratios (D) of the elements and the
corresponding separation factors (α) between indium and various elements for a
26
biphasic 1:1 wt/wt [Hbet][Tf
2 2 2
N]–H O and 1:1 wt/wt [Hbet][Tf N]– 0.01M ascorbic acid
system at 80 °C and a reaction time of 3 h.
1
2
:1 wt/wt [Hbet][Tf N]–0.01 M
2 2
1: 1 wt/wt [Hbet][Tf N]–H O
ascorbic acid
addition of 1 M of MgCl to the aqueous phase. Only one kind
Element
2
of cation was tested since they have a minor influence on the
distribution of the metal ions but greatly influence the solubility
of the ionic liquid in the aqueous phase. The magnesium(II)
cation was chosen to insure the largest salting-out effect.
The percentages leaching of indium from crude In(OH) in a
3
2 2
1:0.5 or 1:1 wt/wt mixture of [Hbet][Tf N]–1 M MgCl at 60 or
80 °C as a function of reaction time for the various elements are
shown in Fig. S6† and Fig. S7†. An average percentage leaching
of 96% and 93% was obtained for indium, when the leaching
took place in the 1:0.5 wt/wt mixture and in the 1:1 wt/wt
%
L
D
α
%L
D
α
Al
As
Ca
Cd
Fe
In
81
68
0.049
3.3
5.8*102
80
79
0.029
1.7
1.2*103
8.6
1.6*102
2.1*102
24
2.1*102
3.8*102
9.1*102
1.0
100
92
0.18
0.13
39
100
82
0.19
0.12
0.052
39
94
1.4
80
99
28
1.0
2.4*102
100
87
Ni
Pb
Zn
100
87
0.12
1.3
0.079
1.4
5.3*102
22
3.9*102
87
28
9.2*102
59
0.073
54
0.058
2 2
mixture of [Hbet][Tf N]–1 M MgCl , respectively. Small
differences were also observed between the percentage
leaching of the impurities when comparing the 1:0.5 wt/wt with
cheap, non-toxic and from biological origin.38-43 Addition of a
stoichiometric amount of ascorbic acid reduces Fe(III) in an
aqueous solution to Fe(II) (Fig. 6).
the 1:1 wt/wt mixture. Adding 1 M MgCl
Hbet][Tf N]–H O system has a positive effect on the kinetics.
Similar percentages leaching as for a 3 h leaching in the 1:1
wt/wt [Hbet][Tf N]–H O system, were obtained in the 1:1 wt/wt
Hbet][Tf N]–1 M MgCl system after leaching for only 30 min.
Next, the metal separation capability of the [Hbet][Tf N]–1
M MgCl mixture was examined by determining the distribution
of the elements between the ionic liquid and the 1 M MgCl
2
to the 1:1 wt/wt
[
2
2
A 0.01 M ascorbic acid solution in water is mixed together
with the saturated [Hbet][Tf
2
N] in a 1:1 wt/wt mixture at 80 °C
2
2
−
1
containing crude In(OH) particles (70 mg g ). From previous
3
[
2
2
tests, it was established that these are the optimal indium
leaching conditions. The percentage leaching and distribution
factors for the elements and the corresponding separation
factors between indium and the elements are compared in
2
2
2
aqueous phase. It has to be noted that no homogeneous phase
was formed below 100 °C due to the salting-out effect, therefor
Table 3 for the 1:1 wt/wt [Hbet][Tf
2 2
N]–H O and 1:1 wt/wt
[
Hbet][Tf N]–0.01 M ascorbic acid system. As expected, the
2
it
cannot
be
considered
as
a
thermomorphic
biggest difference in results is seen for iron. The distribution
ratio of iron is reduced by almost three orders of magnitude and
consequently the separation factor between indium and iron
increased by almost three order of magnitude. The affinity of
iron(II) for the ionic liquid phase is far less than of iron(III),
leaching/extraction system at temperatures lower than 100 °C.
Small differences were observed for the distribution ratios and
separation factors of the various elements when varying the
temperature or reaction time (Fig. 7, Fig. 8, Table 4 and 5).
However, increasing the ionic liquid : aqueous phase ratio has a
6
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Journal Name
ARTICLE
positive effect on the distribution ratio (Fig. 7, Fig. 8). The higher
distribution ratios are probably a consequence of the fact at
Ca
View Article Online
8
0 °C
1
: 1
1 : 1
1
: 1
DOI: 10.1039/C7GC02958F
As
Cd
1
00
10
1
1
: 0.5
Ga
1
: 0.5
1 : 0.5
Ni
Pb
Al
Fe
In
Zn
1
: 1
1 : 1
Ca
As
Cd
Ga
Ni
6
0 °C
1
: 1
100
1
: 0.5
1 : 0.5
1
: 0.5
Pb
Al
10
Fe
In
Zn
0.1
1
0.01
0.1
0.5
1
3
Reaction time (h)
0.01
0.5
1
3
Fig. 8 Distribution ratio of the various elements in a biphasic 1:0.5 or 1:1 wt/wt
Hbet][Tf N]–1 M MgCl system as a function of reaction time at 80 °C. A high
Reaction time (h)
[
2
2
distribution ratio corresponds to a greater affinity for the ionic liquid phase. The
concentrations of Bi, Ge, Sb, Se, Sn and Te were below the detection limit (<1 ppm)
so these elements have been excluded from the graph.
Fig. 7 Distribution ratio of the various elements in a biphasic 1:0.5 or 1:1 wt/wt
Hbet][Tf N]–1 M MgCl system as a function of reaction time at 60 °C. A high distribution
ratio corresponds to a greater affinity for the ionic liquid phase. The concentrations of
Bi, Ge, Sb, Se, Sn and Te were below the detection limit (<1 ppm) so these elements have
been excluded from the graph.
[
2
2
Table 5 Separation factors (α) between indium and various elements for biphasic 1:0.5
or 1:1 wt/wt [Hbet][Tf N]–H O system at 80 °C as a function of reaction time.
2 2
Table 4 Separation factors (α) between indium and various elements for biphasic 1:0.5
1
:0.5 wt/wt [Hbet][Tf
2
N]–H
2
O
2 2
1:1 wt/wt [Hbet][Tf N]–H O
or 1:1 wt/wt [Hbet][Tf
2
N]–H
2
O system at 60 °C as a function of reaction time.
Element
pair
0.5 h
1 h
3 h
0.5 h
1 h
3 h
1
:0.5 wt/wt [Hbet][Tf
2
N]–1 M
1:1 wt/wt [Hbet][Tf
2
N]– 1 M
In/Al
In/As
In/Ca
In/Cd
In/Fe
In/Ga
In/Ni
In/Pb
In/Zn
7.3
2.7
8.4
42
11a
1.2
4.5
5.7
7.9
7.1
3.5
8.6
42
8.8a
1.2
4.4
5.9
7.8
6.9
3.1
7.6
43
9.0a
1.1
4.4
5.9
8.1
5.9
2.6
8.1
58
23a
1.2
4.0
7.1
9.5
6.7
4.7
9.9
59
17a
1.2
4.2
7.3
9.9
6.1
4.4
2.9
60
23a
1.2
4.0
7.5
9.7
Element
pair
MgCl
2
MgCl
2
0
.5 h
1 h
3 h
0.5 h
1 h
3 h
In/Al
In/As
In/Ca
In/Cd
Fe/In
In/Ga
In/Ni
In/Pb
In/Zn
7.0
2.4
10
7.3
3.6
7.6
7.3
2.1
8.3
6.1
2.5
6.5
4.2
6.4
3.8
5.8
11.0
10.0
42
47
42
10a
61
61
61
28a
10a
8.7a
22a
32a
1.2
4.5
5.5
7.9
1.2
4.7
5.9
8.2
1.2
4.5
5.5
7.9
1.1
3.9
6.8
9.3
1.1
4.0
8.4
9.9
1.2
4.2
7.7
9.5
aAccording to IUPAC, by convention the ratio of the respective distribution ratios has to
be chosen so that α> 1.46
more water was present when the leaching was performed in
aAccording to IUPAC, by convention the ratio of the respective distribution ratios has to
be chosen so that α > 1.46
the 1:1 wt/wt mixture of [Hbet][Tf
the 1:0.5 wt/wt mixture (Fig. S6† and S7†). When comparing the
2
Hbet][Tf N]–1 M MgCl system with the [Hbet][Tf N]–H O
2 2
N]–1 M MgCl instead of in
[
2
2
2
system, it was observed that the distribution ratios of some
elements have decreased and for other increased (Fig. 5, Fig. 7,
Fig. 8). Adding MgCl to the aqueous phase increases the affinity
2
of aluminum, calcium, iron, gallium, nickel and zinc for the ionic
liquid phase. The affinity of indium, arsenic, cadmium and lead
2
for the ionic liquid phase decreases upon addition of MgCl .
These changes in distribution ratios have a direct effect on the
separation factors. As the difference in distribution ratios
between indium and the impurities decreases, so does the
separation factor, making it more difficult to separate indium
(Table 4, Table 5). No formation of a precipitate was observed
at the interphase under all the studied conditions. Although the
water content of the ionic liquid phase decreased due to the
salting-out effect, no precipitate was formed due to a lower
indium loading of the ionic liquid phase.
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ARTICLE
Adding a salt to the aqueous phase is necessary to decrease
Journal Name
Table 6). Table 7 shows the percentages scrubbing (%S) of
View Article Online
DOI: 10.1039/C7GC02958F
the loss of ionic liquid to the aqueous phase. Adding 1 M of the elements with HCl or H
MgCl to the [Hbet][Tf N]–H O system has a negative effect on concentration. The percentages
its separation capabilities. By decreasing the concentration of
2 4
SO as a function of the acid
2
2
2
this magnesium salt, precipitation can still be avoided without Table 6 The metal concentration in the organic phase after extraction or before
scrubbing [M]IL,0 and the percentages scrubbing (%S) of the elements with Milli-
Q water as a function of the temperature. Scrubbing of the IL phase after 3 h
leaching in a biphasic 1:1 wt/wt [Hbet][Tf N]–H O system.
2 2
losing significant amounts of indium to the aqueous phase. Also,
changing the anion of the magnesium salt can change the
distribution of indium across both phases. A 1 M Mg(NO )
3 2
solution was added to the aqueous phase, replacing the
chloride salt. Under all conditions studied, a precipitate was
formed at the interphase after cooling, probably due to the low
water content of the ionic liquid phase as a consequence of the
salting-out effect in combination with a high indium loading.
%
S
[
(
M]IL,0
ppm)
Element
25 °C
80 °C
Al
As
Cd
Fe
In
30±7
37
23
92
0
58
23
92
0
2
2.0*10 ±7
11±2
3
1.1*10 ±0
Metal scrubbing/stripping and recovery of ionic liquid
(42±2)*103
9.9
53
95
6.5
59
95
Pb
Zn
84±6
Scrubbing of the co-extracted metal ions and stripping of the
2
1.1*10 ±0
indium was investigated after loading the [Hbet][Tf
with metal ions by leaching crude In(OH) in the 1:1 wt/wt
Hbet][Tf N]–H O system and 1:1 wt/wt [Hbet][Tf N]–0.01 M
ascorbic acid system for 3 h. The 1:1 wt/wt [Hbet][Tf N]–1 M
MgCl system was not investigated due to the small separation
2
N] phase
The concentration of Ca and Ni were below the detection limit (<20 ppm for Ca
and <1 ppm for Ni) in the loaded ionic liquid phase so these elements have been
excluded from the table.
3
[
2
2
2
2
2
2 4
Table 7 Percentages stripping/scrubbing (%S) of the elements with HCl or H SO as a
factors obtained between indium and the impurities. First, function of the acid concentration. Scrubbing of the IL phase obtained after 3 h leaching
scrubbing/stripping experiments were executed on the loaded in a biphasic 1:1 wt/wt [Hbet][Tf
2 2
N]–H O system.
ionic liquid phase obtained after leaching in the 1:1 wt/wt
%
S
[
2 2
Hbet][Tf N]–H O for 3 h. The scrubbing of the metal ions and
Element
the stripping of indium from the ionic liquid phase was tested
by contacting the loaded ionic liquid phase obtained after
leaching/extraction with different stripping agents: Milli-Q
1.5 N HCl
2 N HCl
1.5 N H
2
SO
4
2 4
2 N H SO
Al
As
Cd
Fe
In
85
95
92
58
96
92
98
64
98
92
97
99
97
98
94
99
93
98
92
99
99
94
99
93
99
98
99
99
2 4 4
water, HCl (1.5 and 2 M), H SO (0.75 and 1 M) and MgSO (0.1
and 1 M) in a 1:1 wt/wt ratio. By contacting the ionic liquid
phase with an acidic solution, the extraction equilibrium is
shifted and (part of) the extracted complexes are decomposed
and transferred to the aqueous phase. First, the effect of
temperature was studied.
Pb
Zn
Table 6 shows the percentage scrubbing of the elements
with Milli-Q water as a function of the temperature. Little scrubbing/stripping agent. Scrubbing of the IL phase after 3 h leaching in a
difference in percentages scrubbing of the elements is observed
with varying temperature. Next, the effect of acid concentration
2 4
on the scrubbing percentages was tested using HCl and H SO
Table 8 Solubility of the ionic liquid in the aqueous phase dependent on the
biphasic 1:1 wt/wt [Hbet][Tf
2 2
N]–H O system.
-
1
Srubbing/stripping agent
Solubility of the Ionic liquid at 25 °C (g L )
2.1
2
H O
as scrubbing agents. From previous tests it was concluded that
co-extraction of Pb was unavoidable. Scrubbing the ionic liquid
1
.5 N HCl
N HCl
.5 N H SO
2 N H SO
4.4
4.4
4.5
4.9
2
phase with H
2
SO
4
can lead to the formation of PbSO
4
, which has
) than PbCl
can be
1
2
4
-1
a lower solubility in H
in HCl (g L range in 2 M HCl). The precipitated PbSO
2
SO
4
(mg L range in 1 M H
2
SO
4
2
2
4
-
1
47
4
easily separated from the solution by filtration. Table 6 stripping of indium increased with increasing acid
andTable 7 show the indium percentages stripping as a function concentration. Indium is almost completely stripped at an acid
of the HCl and H
.9% of the indium was stripped from the ionic liquid phase with elements are also almost fully stripped. Upon scrubbing with
Milli-Q water at 25 °C. Thus, acid-free scrubbing already H SO , a white PbSO precipitate was formed, leaving only 4
2 4
SO acid concentration. It was noticed that concentration of 2 N. When indium is fully stripped, the other
9
2
4
4
accounts for a substantial indium loss. Although high ppm of lead in the aqueous phase. The scrubbing/stripping with
percentages scrubbing were obtained for aluminum, cadmium, an acid leads to higher losses of the ionic liquid to the aqueous
nickel and zinc, low concentrations (1-110 ppm) of these phase than scrubbing/stripping with water (Table 8).
elements are present in the ionic liquid phase (
Since the Pb(II) ions can be removed via formation of PbSO4,
Table 6). Among the co-extracted elements, arsenic and lead the addition of MgSO to the stripping reagent can be sufficient
4
were only partly scrubbed, whereas iron is not scrubbed at all ( to shift the equilibrium of lead to the aqueous phase without
the presence of acids. Stripping experiments were performed
using 0.1 M and 1 M MgSO solutions. Unfortunately, the ionic
4
8
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Journal Name
liquid had a gel-like appearance after stripping. The high water-
ARTICLE
Table 11. A pH of 3 is clearly too high when VpieewrfAortricmleiOnnglinae
content in this ionic liquid phase impeded proper phase prehydrolysis step on the aqueous pDhOaIs: e10.1o0b39ta/Cin7eGdC02a9f5te8Fr
separation and analysis.
2 4
stripping with 2 N H SO , since over 40% of indium is removed.
Similar scrubbing/stripping experiments were also executed A Pourbaix diagram considers pure, single metal, aqueous
on the loaded ionic liquid phase obtained after leaching in the solutions at standard conditions and does not take into account
1
:1 wt/wt [Hbet][Tf
ionic liquid phase was contacted with different stripping agents: behavior of systems can deviate from the one predicted by the
Milli-Q water, 2 M HCl and 1 M H SO in a 1:1 wt/wt ratio. The Pourbaix diagram as seen for the aqueous phase obtained after
percentages stripping as a function of the acid concentration stripping with 2 N H SO . Lowering the pH is an evident choice
are presented in Table 9. As seen in the 1:1 wt/wt [Hbet][Tf N]– to decrease the amount of indium precipitated, but this in turn
O system, scrubbing with water led to a substantial loss of also lowers the prehydrolysis yield of the impurities. Contrary
indium (11%) considering that only elements present in low to the prehydrolysis of the aqueous phase obtained after
concentrations in the ionic liquid phase are scrubbed. Again, an stripping with 2 N H SO , none or a small amount of indium was
acid concentration of 2 N was sufficient to ensure an almost precipitated when prehydrolysis was performed on the
quantitative stripping of indium. Upon scrubbing with H SO , a aqueous phase obtained after stripping with 2 N HCl. If the
white PbSO precipitate was formed, leaving only 3 ppm of lead leaching/extraction prior to stripping and prehydrolysis was
in the aqueous phase. The solubility of the ionic liquid in the executed under reducing conditions (1:1 wt/wt [Hbet][Tf N]–
0.01 M ascorbic acid system), less arsenic is precipitated during
2
N]–0.01 M ascorbic acid system. The loaded non-ideal behavior of aqueous solutions, so in reality the
2
4
2
4
2
H
2
2
4
2
4
4
2
aqueous phase is shown in Table 10. Slightly higher values
Table 9 The metal concentration in the organic phase after extraction or before
scrubbing [M]IL,0 and the percentages stripping/scrubbing (%S) of the elements
Table 11 Metal concentration in the aqueous phase after prehydrolysis to pH 3
([M]Aq,ph) and the hydrolysis yield. Aqueous phase obtained after
scrubbing/stripping the loaded ionic liquid phase with an acid concentration of 2
N. Loaded ionic liquid phase obtained after 3 h leaching in a biphasic 1:1 wt/wt
with H
2
O, 2 N HCl or 2 N H
2
SO
4
. Scrubbing of the IL phase after 3 h leaching in a
biphasic 1:1 wt/wt [Hbet][Tf
2
N]–0.01 M ascorbic acid system.
%
S
[Hbet][Tf N]–H O or 1:1 wt/wt [Hbet][Tf2N]–0.01 M ascorbic acid system.
[
(
M]IL,0
ppm)
2
2
Element
H
2
O
2 N HCl
2 N H
2
SO
4
1:1 wt/wt [Hbet][Tf
2 N HCl
2
N]–H
2
O system
Al
As
Cd
Fe
In
23±5
92
44
95
98
97
99
2 N H SO
2 4
Element
2
1.8*10 ±0
9.6±3.5
37±15
-
1
[M]Aq,ph (mg L-1)
[
M]Aq,ph (mg L )
Yield (%)
Yield (%)
>94
62
>95
97
>94
91
98
99
99
Al
As
Cd
Fe
In
26
29
0
18
130
7
9.7
7.9
23
63
45
0
80
0
(43±0.7)*103
11
99
8
Pb
Zn
88±1
71
99
61
93
6.9
20
7.7
250
17000
4
86±48
98
98
28000
41
The concentration of Ca and Ni were below the detection limit (<20 ppm for Ca
and <1 ppm for Ni) in the loaded ionic liquid phase so these elements have been
excluded from the table. The concentrations of these elements in the ionic liquid
phase were below the detection limit (<1ppm).
Pb
Zn
74
18
22
1:1 wt/wt [Hbet][Tf N]–0.01 M ascorbic acid system
2
Element
2 N HCl
2 4
2 N H SO
Table 10 Solubility of the ionic liquid in the aqueous phase dependent on the
scrubbing/stripping agent. Scrubbing of the IL phase after 3 h leaching in a biphasic 1:1
-
1
[M]Aq,ph (mg L-1)
[M]Aq,ph (mg L )
Yield (%)
Yield (%)
wt/wt [Hbet][Tf
2
N]–0.01 M ascorbic acid system.
Al
As
Cd
Fe
In
23
100
9.7
0
32
0
29
150
11
0
0
-
1
Srubbing/stripping agent
Solubility of the Ionic liquid at 25 °C (g L )
2.4
0
2
H O
32
96
0
41
94
42
10
0
2
N HCl
5.9
6.0
33000
44
18000
3
2
N H SO
2
4
Pb
Zn
0
85
10
120
were obtained in comparison with the 1:1 wt/wt [Hbet][Tf
O system.
Since the stripping of indium with an acid is not selective in
2
N]–
The concentration of Ni was below the detection limit (<1 ppm) in the aqueous
phase after stripping so this element has been excluded from the table.
H
2
neither of the two systems, the pH of the aqueous phase after
stripping was increased up to the point where indium hydrolysis
prehydrolysis. The amount of iron extracted to the ionic liquid
phase under reducing conditions was much lower than without
the addition of ascorbic acid. Since almost everything got
stripped, the iron concentration in the aqueous phase after
stripping was consequently also lower and less iron was present
3
4
starts, pH 3 according to Pourbaix, for the given indium
concentration. It should also be possible to remove some
iron(III) as iron(III) hydroxide. Furthermore, arsenic is also prone
to sorption on iron(III) hydroxides or can be precipitated as
4
to precipitate arsenic as FeAsO or for the sorption of arsenic
48,49
FeAsO
4
.
The composition of the aqueous phase after
onto iron. The arsenic yield may be lower, but no indium is lost
when prehydrolysis was executed on the aqueous phase
obtained after stripping the ionic liquid phase, originating from
prehydrolysis to pH 3 and the hydrolysis yield is shown in
precipitated during
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Journal Name
a leaching/extraction under reducing conditions, with 2 N HCl.
Therefore, leaching/extraction under reducing conditions,
stripping with 2 N HCl and prehydrolysis to a pH of 3 were
preferred. The amount of indium precipitated during
prehydrolysis on the aqueous phase obtained after stripping the
ionic liquid phase, originating from a leaching/extraction under
non-reducing conditions, with 2 N HCl can be reduced by fine-
tuning the prehydrolysis pH.
1:1 wt/wt [Hbet][Tf
N HCl
2
N]–H
2
O system
DOI: 10.1039/C7GC02958F
View Article Online
2
2 4
2 N H SO
Element
Produced In(OH)
wt%
3
Produced In(OH)
3
Crude In(OH)
3
wt%
wt%
Al
As
0.024
0.065
0.045
0.31
1.4
0.54
Bi
0.0007
0.0022
0.0037
0.13
0.0007
0.0094
0.013
1.4
0.0018
0.20
Ca
Cd
Fe
After the prehydrolysis step to pH 3, the solution was
filtered and the pH was increased further to fully precipitate the
0.18
1.6
34
indium as indium(III) hydroxide. According to Pourbaix, at a pH
of 4.6 the indium concentration in solution should be equal to
the detection limit of the ICP-OES, 1 ppm. However, 77 and 79
ppm of indium still resided in the aqueous solution after
hydrolysis when stripping was performed using 2 N HCl and 2 N
Ga
Ge
In
0.0016
0.0001
61
0.0023
0.0002
61
0.0046
0.0095
58
Ni
0.0002
0.028
0.0017
0.0052
0.0046
0.0006
0.0006
<0.0001
0.13
0.027
0.26
Pb
Sb
H
2
SO
4
, respectively, after extraction under non-reducing
0.0026
0.0002
<0.0001
<0.0001
0.058
0.035
0.0027
0.0028
0.0015
5.0
Se
conditions. 130 and 1600 ppm of indium still resided in the
aqueous solution after hydrolysis when stripping was
performed using 2 N HCl and 2 N H SO , respectively, after
2 4
Sn
Te
Zn
extraction under reducing conditions. Fine-tuning the
hydrolysis pH can decrease the amount of indium still present
in the aqueous phase after hydrolysis, but care must be taken
not to increase the coprecipitation of impurities. The
composition of the indium(III) hydroxide produced is compared
with that of crude indium(III) hydroxide in Table 12. The
indium(III) hydroxide produced from an aqueous solution which
has its origin in stripping the ionic liquid phase with 2 N HCl, has
a higher purity than the one produced from an aqueous solution
which has its origin in stripping the ionic liquid phase with 2 N
Purity
99.48%
96.94%
86.23%
1:1 wt/wt [Hbet][Tf N]–0.01 M ascorbic acid
2
system
2
N HCl
2 4
2 N H SO
Element
Produced In(OH)
wt%
3
Produced In(OH)
3
Crude In(OH)
3
wt%
wt%
Al
As
0.030
0.19
0.057
0.24
1.4
0.54
Bi
0.0013
0.0030
0.0046
0.056
0.0009
0.0019
0.010
0.0018
0.20
2 4
H SO . A higher concentration of impurities was precipitated
Ca
Cd
Fe
during prehydrolysis and less impurities were coprecipitated
during hydrolysis. Also, the purity of the indium(III) hydroxide
produced from an aqueous solution which has its origin in
stripping the ionic liquid phase with 2 N HCl was very similar,
independent if leaching/extraction was performed under
reducing or non-reducing conditions. But as stated before, less
indium is lost during prehydrolysis of an aqueous solution
obtained after stripping the ionic liquid phase with 2 N HCl,
when the ionic liquid phase was obtained after extraction under
reducing conditions.
The ideal system comprises of a leaching/extraction of crude
3
In(OH) using a 1:1 wt/wt [Hbet][Tf2N]–0.01 M ascorbic acid
system, followed by a stripping of the loaded ionic liquid phase
with a 2 N HCl solution. A prehydrolysis step to a pH of 3 was
performed on the aqueous phase obtained after stripping and
ending with a hydrolysis step to a pH of 4.6 on the solution
0.18
0.071
1.6
Ga
Ge
In
0.0019
<0.0001
57
0.0019
<0.0001
51
0.0046
0.0095
58
Ni
0.0004
0.016
0.0004
0.0042
0.0010
0.0001
0.0015
0.0004
0.088
0.027
0.26
Pb
Sb
0.0011
0.0004
0.0004
0.0001
0.065
0.035
0.0027
0.0028
0.0015
5.0
Se
Sn
Te
Zn
Purity
99.36%
99.07 %
86.23%
obtained after prehydrolysis. The purity of the crude In(OH)
3
was improved from 86.2% to 99.4%. A flowsheet of the
proposed process is shown in Fig. 9.
3
Table 12 Metal composition of the produced and crude In(OH) determined by
ICP-OES in combination with the purity on metal basis.
1
0 | J. Name., 2012, 00, 1-3
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Acknowledgements
View Article Online
DOI: 10.1039/C7GC02958F
This research was supported by the Flemish Institute for the
Promotion of Innovation by Science and Technology (IWT
Vlaanderen) via a Baekeland PhD fellowship to Clio Deferm (IWT
1
30305) and by the Umicore Group Research & Development.
ICP-OES analyses were executed in the analytical laboratory of
Umicore Group Research & Development.
Conflicts of interest
There are no conflicts of interest to declare.
Fig. 9 Overview of the proposed purifying process for crude In(OH)
selective dissolution and revalorization of indium with the protonated functionalized
ionic liquid [Hbet][Tf N].
3
, based on the Notes and references
1
Ad-Hoc Working Group on Defining Critical Raw Materials,
Report on Critical Raw Materials for the EU, European
Commission, DG Enterprise & Industry, 2014.
Working Group on the Global Metal Flows to the International
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S.F. Sibley, G. Sonnemann, M. Buchert and C. Hagelüken,
Recycling Rates of Metals - A Status Report, UNEP
International Resource Panel, 2011.
2
2
Conclusions
The combined use of ionic liquid leaching and extraction
described in this work provides a sustainable and efficient
alternative for the recovery of indium from crude In(OH)
the ionic liquid [Hbet][Tf N]. Leaching and solvent extraction
were combined in one step by taking advantage of the
thermomorphic properties of the [Hbet][Tf N]–H O system. The
3
using
3
4
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mixture is homogeneous during leaching at 80 °C (temperature
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-
1
stripping/scrubbing ranged between 2.1 and 6.0 g L . This
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Green Chemistry
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DOI: 10.1039/C7GC02958F
Table of Contents Graphic
Crude In(OH)
3
Purified In(OH)
3
0
.01 M
Zn Ni Fe
Ascorbic acid Cd Ca Al
[
Hbet][Tf N]
2
Pb
In As
A process was developed to purify crude In(OH)
3
using a combined leaching/extraction system based
N].
on the thermomorphic and acidic properties of the ionic liquid [Hbet][Tf
2