metals
Article
Recovery of Vanadium from H2SO4-HF Acidic
Leaching Solution of Black Shale by Solvent
Extraction and Precipitation
Xingbin Li, Chang Wei *, Zhigan Deng, Cunxiong Li, Gang Fan, Minting Li and Hui Huang
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming
650093, China; [email protected] (X.L.); [email protected] (Z.D.); [email protected] (C.L.);
[email protected] (G.F.); [email protected] (M.L.); [email protected] (H.H.)
* Correspondence: [email protected]; Tel.: +86-871-6518-8819
Academic Editor: Corby G. Anderson
Received: 21 January 2016; Accepted: 3 March 2016; Published: 14 March 2016
Abstract: The recovery of vanadium from sulfuric and hydrofluoric mixed acid solutions generated by
the direct leaching of black shale was investigated using solvent extraction and precipitation methods.
The process consisted of reduction, solvent extraction, and stripping, followed by precipitation
and calcination to yield vanadium pentoxide. The influence of various operating parameters on
the extraction and recovery of vanadium was studied. Vanadium (IV) was selectively extracted
using a mixture of 10% (v/v) di(2-ethylhexyl)phosphoric acid and 5% (v/v) tri-n-butylphosphate
in sulfonated kerosene. Using six extraction and five stripping stages, the extraction efficiency for
vanadium was 96.7% and the stripping efficiency was 99.7%. V2 O5 with a purity of 99.52% was
obtained by oxidation of the loaded strip solution and precipitation of ammonium polyvanadate
at pH 1.8 to 2.2, followed by calcination of the dried precipitate at 550 ˝ C for 2 h. It was concluded
that the combination of solvent extraction and precipitation is an efficient method for the recovery of
vanadium from a multi-element leach solution generated from black shale.
Keywords: solvent extraction; vanadium precipitation; black shale; vanadium
1. Introduction
Black shale (also called stone coal) is an important vanadium resource in China, where it is found
extensively in the southern provinces and autonomous regions of the country. The gross reserves
of vanadium in black shale in Hunan, Hubei, Guangxi, Jiangxi, Zhejiang, Anhui, Guizhou, Henan,
and Shanxi provinces are 18 million tons in terms of V2 O5 , which accounts for more than 87% of
the domestic reserves of vanadium [1]. The vanadium grade in black shale generally ranges from
0.13% to 1.2%, while grades higher than a cut-off of 0.5% account for about 40% of the total vanadium
reserves [2]. Besides vanadium, some 60 different metallic and nonmetallic elements have been
identified in these sources, including molybdenum, nickel, uranium, copper, selenium, gallium, and
precious metals [3–5]. Black shale is therefore regarded as a complicated low-grade multi-element
ore. Because of its relatively high vanadium grade and abundant deposits, studies of the recovery of
vanadium from black shale have received considerable attention.
Vanadium exists as the (II), (III), (IV), and (V) species in nature [6]. A previous study showed
that vanadium in black shale is found mainly as vanadium (III), then as vanadium (IV) and vanadium
(V) [7]. Vanadium (III), which usually exists in the crystal lattices of aluminosilicate clay minerals,
comprises more than 90% of the total vanadium content because black shale originates from reducing
environments [8–10]. The principle of recovering vanadium from black shale is first to decompose the
crystal lattice of the aluminosilicate clay minerals and oxidize insoluble vanadium (III) to acid-soluble
Metals 2016, 6, 63; doi:10.3390/met6030063
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Metals 2016, 6, 63
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vanadium (IV) and/or water-soluble vanadium (V) compounds, then to dissolve these species by
acid, water, or alkaline leaching. Finally, pure vanadium products are produced from the leach
solution by separation and purification, using methods including solvent extraction, ion exchange,
and precipitation [11,12]. The traditional technique for the extraction of vanadium from black shale
was by roasting with sodium salts and water leaching [13–15]. Using this technique, the roasting
efficiency is about 45%–55%, the total vanadium recovery is less than 45%, and the released exhaust
gas containing Cl2 , HCl, and SO2 pollutes the environment. These serious disadvantages have limited
further development of this technology and the sodium salt roasting process has been prohibited by
the local government since 2006. A recently developed technique that does not involve roasting is
direct acid leaching [16–22]. Investigations have found that vanadium in aluminosilicate and mica
clay minerals can be leached by sulfuric acid with the addition of HF, NaF, or CaF2 to the leaching
processing [23–25]. The resultant hydrofluoric acid decomposes the vanadium-bearing aluminosilicate
clay minerals, allowing the exposed vanadium (III) to be oxidized to vanadium (IV) by Fe (III) and
converted to soluble VOSO4 in the leach solution. The extent of vanadium leaching can exceed
85%, which is much higher than that of traditional roasting processes. Furthermore, this process
completely avoids the discharge of roasting exhaust gas and lowers energy consumption. However,
the various impurities elements in black shale, for instance, Ni, Al, Fe, Mg, Mn, Si, and P, leach into
the solution with vanadium in the acid-leaching process. Selective extraction of vanadium is key to
the recovery of pure vanadium products from the multi-element leach solutions of vanadium-bearing
black shale [26,27].
Solvent extraction offers an attractive alternative for the extraction and recovery of pure metals
from multi-element leach solutions [28–30]. Although the extraction of vanadium from various
acidic solutions has been reported, there has been no systematic study of the recovery of vanadium
from multi-element H2 SO4 -HF leach solutions from black shale by combined solvent extraction and
precipitation, which is important for the practical application of this technology [31–33]. The aim of the
present work was to extract and recover vanadium from such solutions using solvent extraction and
precipitation. The effects of the aqueous-phase pH, extractant concentration, and organic-to-aqueous
phase ratio (O/A) on the extraction of vanadium, and the effects of pH, temperature, and vanadium
concentration on the precipitation of vanadium, are reported. This study provides data to develop a
flow sheet for the recovery of a high purity vanadium product from the solutions generated by the
direct leaching of black shale.
2. Experimental
2.1. Materials and Reagents
In our previous tests, a direct acid leaching process using sulfuric acid and hydrofluoric acid
solutions was proposed to recover vanadium from black shale and a high leaching ratio of 86% was
obtained. In the present study, the starting solution was generated by the same conditions as our
previous studies, using a liquid/solid ratio of 4 mL/g, a sulfuric acid concentration of 87.5 g/L, a
hydrofluoric acid concentration of 15 g/L, a sodium hypochlorite concentration of 1 g/L, a temperature
of 95 ˝ C, and a reaction time of 6 h [24]. The composition of the leach solution generated from black
shale from Hunan Province, China, is listed in Table 1.
D2EHPA (di(2-ethylhexyl)phosphoric acid) and TBP (tri-n-butylphosphate), supplied by Shanghai
Rare-Earth Chemical Co., Ltd., Shanghai, China, were used without further purification. Commercial
kerosene was contacted with 98% concentrated sulfuric acid to produce sulfonated kerosene for use as
the diluent. All other reagents and chemicals were of analytical reagent grade.
Metals 2016, 6, 63
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Table 1. Composition of the liquor generated from the leaching of black shale in the H2 SO4 -HF mixture.
Component
Concentration (g/L)
V2 O 5 *
Fe(II)
Fe(III)
Al
As
Zn
Cu
Mg
Si
SO4 2´
P
F´
6.75
8.10
5.30
9.20
0.10
1.01
0.43
1.20
0.50
78.50
0.32
15.0
* Vanadium concentrations are all represented as V2 O5 in this paper.
2.2. Experimental Procedure
2.2.1. Solvent Extraction
The metal equilibrium distributions between the organic and the aqueous phase were obtained
by contacting a given volume ratio of the two liquids in a 250 mL mechanically agitated extractor.
After the extraction, the two phases were separated in a separating funnel. The batch simulation
counter-current experiments were performed in a box-style mixer-settler unit which contained six
mixer-settler stages, while it was just used in the former five stages in the stripping. Each stage
consisted of square-box type mixing and settling compartments. The active mixer volume was 0.5 L
and the settler volume was 2.0 L. The agitation speed was 800 rpm. The vanadium (VO2+ and total
vanadium concentrations) in the aqueous solutions was determined by the ferrous ammonium sulfate
titration using 2-(phenylamino) benzoic acid as an indicator [34]. The Fe (II) concentration was
determined by potassium dichromate titration using sodium diphenylamine sulfonate as an indicator.
Fluoride ion selective electrode (Crison 9655, HACH, Loveland, CO, USA) was used to measure
fluoride concentration and the phosphorus concentration was measured by the ammonium molybdate
spectrometric method using UV-vis spectrophotometer (UV-vis, UV-2550, Shimadzu, Kyoto, Japan).
The compositions of other elements in the aqueous phases were analyzed by inductively coupled,
plasma atomic emission spectroscopy (ICP-AES) using an OPTIMA 5300DV (Perkin-Elmer, Waltham,
MA, USA). Metal concentrations in the organic solutions were calculated by mass balance. The analysis
method used for the vanadium pentoxide product is in accordance with the relevant industry standard
of YB/T5304-2011 in China [35].
The solution pH was adjusted using 3 mol/L H2 SO4 or 20% ammonia water, and the pH was
measured using a digital pH meter (INESA instrucment, Shanghai, China). All extraction and stripping
experiments were carried out at 25 ˘ 1 ˝ C.
2.2.2. Oxidation and Precipitation
The oxidation and precipitation processes were conducted at atmospheric pressure in a 1000 mL
stirred glass reactor that was placed in a temperature-controlled water bath. Hydrogen peroxide
was used to oxidize vanadium (IV) to vanadium (V). Aqueous ammonia was used to control the
pH and precipitate ammonium polyvanadate. The solid ammonium polyvanadate derived from
the precipitation process was separated by vacuum filtration (0.7 atm) and washed twice with
distilled water.
Metals 2016, 6, 63
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2.2.3. Calcination
The ammonium polyvanadate was dried at 60 ˝ C in a constant-temperature laboratory oven.
The V2 O5 product was obtained by calcining the dried ammonium polyvanadate in a muffle furnace
at a determined temperature and time.
3. Results and Discussion
3.1. Ferric Ion Reduction
Because the extraction order of D2EHPA is Fe3+ > VO2+ > VO2 + > Fe2+ [36], this means that Fe3+
in solution is more strongly extracted by D2EHPA than VO2+ . The presence of Fe3+ not only reduces
the maximum loading of vanadium on the extractant, but also compromises the purity of the final
vanadium product. To selectively extract vanadium and avoid the co-extraction of Fe3+ , it is necessary
to reduce Fe (III) to Fe (II) before the extraction of vanadium. Sodium sulfite was employed as the
reductant. The reaction can be expressed as:
2Fe3` ` SO23´ ` H2 O Ñ 2Fe2` ` SO24´ ` 2H`
(1)
VO2 + in the leach solution is also reduced to VO2+ in the reduction process:
2´
`
2`
2VO`
` SO24´ ` H2 O
2 ` SO3 ` 2H Ñ 2VO
(2)
To determine the amount of reductant necessary for Fe (III) reduction, different masses of Na2 SO3
were added into 300 mL of leach solution for 2 h at 30 ˝ C at different nR /nFe(III) coefficients, where
nR /nFe(III) is the molar ratio of Na2 SO3 to Fe3+ . The reduction results are shown in Table 2. With a
nR /nFe(III) coefficient of 0.8, more than 99.5% of the Fe (III) present was reduced to Fe (II). The further
addition of Na2 SO3 gave no further reduction of Fe (III). In subsequent experiments, the leach solution
was reduced by Na2 SO3 using a nR /nFe(III) coefficient of 0.8. The reduced leach solution was used as
the feed solution for the solvent extraction test work.
Table 2. Effect of Na2 SO3 /Fe (III) molar ratio on Fe (III) and V (V) reduction efficiency.
nR /nFe(III)
0.2
0.4
0.6
0.8
1.0
Percent of Fe (III) reduction, %
Percent of V (V) reduction, %
67.2
96.5
80.8
99.2
94.1
99.8
99.8
100
99.9
100
3.2. Solvent Extraction and Stripping of Vanadium (IV)
3.2.1. Effect of pH and Extractant Concentration
The effect of equilibrium pH in the range of pH 1.5 to 3.0 on the extraction of vanadium, carried
out using different concentrations of D2EHPA with 5% (v/v) TBP in sulfonated kerosene, is shown in
Figure 1.
The results show that vanadium extraction efficiency initially increases with increasing pH because
this is a cation exchange process. The maximum extraction was achieved at an equilibrium pH of 2.5 for
the various D2EHPA concentrations employed. Vanadium extraction reached 85.6% at an equilibrium
pH of 2.5 using 10% (v/v) D2EHPA and 5% (v/v) TBP in a single-stage extraction. Furthermore,
when the aqueous pH exceeded 2.5, the solution became turbid and there was a formation of a
third phase during the solvent extraction process. An X-ray diffraction (XRD) of the dried third phase
(Figure 2) indicates that the major phases precipitating were (NH4 )2 Fe(SO4 )2 ¨ 6H2 O, CaPO3 (OH)2 ¨ H2 O
or CaSO4 ¨ 2H2 O, and NaFe9 (PO4 )6 (OH)10 ¨ 5H2 O. The optimum aqueous pH for vanadium extraction
should therefore be determined by considering both the vanadium extraction efficiency and the need
Metals 2016, 6, 63
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to avoid third phase formation. An equilibrium pH of 2.5 was considered optimal and chosen for
Metals 2016, 6, 63
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subsequent
extraction experiments.
Metals 2016, 6, 63
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100
100
90
Vanadium
extraction,
Vanadium
extraction,
% %
90
80
80
70
70
60
60
50
50
40
5% (v/v) D2EHPA+5% (v/v) TBP
8% (v/v) D2EHPA+5% (v/v) TBP
5% (v/v)
10%
(v/v)D2EHPA+5%
D2EHPA+5%(v/v)
(v/v)TBP
TBP
8% (v/v)
15%
(v/v)D2EHPA+5%
D2EHPA+5%(v/v)
(v/v)TBP
TBP
10%
(v/v)
D2EHPA+5%
(v/v)
TBP
20% (v/v) D2EHPA+5% (v/v) TBP
15% (v/v) D2EHPA+5% (v/v) TBP
20% (v/v) D2EHPA+5% (v/v) TBP
40
30
30
20
20
10
10
0
0
1.4
1.6
1.8
2.0
1.4
1.6
1.8
pH
2.0Equilibrium
2.2
2.4
2.2
2.4
2.6
2.8
3.0
3.2
2.6
2.8
3.0
3.2
Equilibrium pH
Figure
Figure 1.
1. Effect
Effectof
ofequilibrium
equilibriumpH
pHon
onvanadium
vanadiumextraction.
extraction.(O/A
(O/A phase
phaseratio
ratio==1/1,
1/1, agitation
agitation speed
speed
˝
800
rpm,
time
25
C).vanadium extraction. (O/A phase ratio = 1/1, agitation speed
800
rpm,
extraction
time 10
10 min,
min,pH
25 on
°C).
Figure
1.extraction
Effect of equilibrium
800 rpm, extraction time 10 min, 25 °C).
3500
3500
3000
3000
2500
1
1- (NH4)2Fe(SO4)2•6H2O
1
•H O or CaSO42•2H2O
2-CaPO
1- (NH43)(OH)
Fe(SO
2 4)22•6H2O
2
) (OH) •5H2O •2H O
3-NaFe
(OH)
2-CaPO9(PO
4 6 •H O10or CaSO
Intensily
Intensily
3
2000
1500
1500
1000
1000
500
32
32
500
0
0
2
2
42
2
3-NaFe9(PO4)6(OH)10•5H2O
2500
2000
10
1
1
2
1
1
2
2
1 2
1
1
3 32111
1 2
1
1 2 2
3 3 11 2
1 2 2
2
20
30
40
50
60
70
2-Theta(°)
40
50
60
70
2-Theta(°)
Figure 2. XRD pattern of dried third phase produced during extraction process.
Figure 2.
2. XRD
XRD pattern
pattern of
of dried
dried third
third phase
phase produced
produced during
during extraction
extraction process.
process.
Figure
10
20
30
From the results of Figure 1, it also can be observed that the extraction of vanadium increased
of Figure
1, it alsoin
can
be observed
that the extraction
vanadium
increased
fromFrom
65.1%the
to results
85.6% with
the increase
D2EHPA
concentration
from 5% of
(v/v)
to 10% (v/v),
and
From the results of Figure 1, it also can be observed that the extraction of vanadium increased
from 65.1%
to 85.6%
with the
increase
in D2EHPA
concentration
to 10% extraction
(v/v), and
upon
the further
increase
in the
D2EHPA
concentration
to 20% from
(v/v),5%
the(v/v)
vanadium
from 65.1% to 85.6% with the increase in D2EHPA concentration from 5% (v/v) to 10% (v/v), and
upon theslowly.
furtherBased
increase
in the
D2EHPA concentration
to 20%
(v/v), the
increase
on the
experimental
results, 10% (v/v)
D2EHPA
wasvanadium
sufficient extraction
to extract
upon the further increase in the D2EHPA concentration to 20% (v/v), the vanadium extraction increase
increase slowly.
Based
the experimental results, 10% (v/v) D2EHPA was sufficient to extract
vanadium
from the
leachonsolution.
slowly. Based on the experimental results, 10% (v/v) D2EHPA was sufficient to extract vanadium from
vanadium from the leach solution.
the leach solution.
3.2.2. Effect of Fluoride Ion Concentration
3.2.2. Effect
Effect of
of Fluoride
Fluoride Ion
Ion Concentration
3.2.2.
The effect
of fluoride Concentration
ion concentration on the extraction of vanadium (IV) was studied. The
The
effect
of
fluoride
ion concentration
concentration
ondifferent
the extraction
extraction
of vanadium
vanadium
(IV) was
was
studied.
The
fluoride
ion
concentration
varied
in step with
concentrations
of sodium
fluoride
fromThe
15
The effect of fluoride ion
on
the
of
(IV)
studied.
fluoride
ion
concentration
varied
in
step
with
different
concentrations
of
sodium
fluoride
from
15
g/L
to
35
g/L,
the
results
of
which
are
shown
in
Figure
3.
It
was
observed
that
the
change
in
fluoride
fluoride ion concentration varied in step with different concentrations of sodium fluoride from 15 g/L
g/L35to
35 g/L,
results
of
which
are shown
in Figure
It was
observed
the change
in
fluoride
ion
concentration
in of
thewhich
investigated
range
had
almost
no
effect
on that
the that
vanadium
(IV)
extraction,
to
g/L,
the the
results
are shown
in Figure
3. It3.
was
observed
the change
in fluoride
ion
ion
concentration
in
the
investigated
range
had
almost
no
effect
on
the
vanadium
(IV)
extraction,
and
the
extraction
of
fluoride
ion
is
very
low,
which
indicates
that
the
fluoride
ion
does
not
concentration in the investigated range had almost no effect on the vanadium (IV) extraction, and the
and
the
extraction
of
fluoride
ion
is
very
low,
which
indicates
that
the
fluoride
ion
does
not
participateofinfluoride
the extracted
complexes.
extraction
ion is very
low, which indicates that the fluoride ion does not participate in the
participate
in the extracted complexes.
extracted
complexes.
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2016, 6,
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13
66 of
Metals 2016, 6, 63
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100
100
90
90
80
Extraction, %
Extraction, %
80
70
70
Vanadium
Vanadium
Fluoride
ion
Fluoride ion
60 60
50 50
4
3
2
1
0
4
3
2
1
0
15
20
15
25
30
35
20
25
30
Fluoride ion concentration, g/L
35
Fluoride ion concentration, g/L
Figure 3. Effect of fluoride ion concentration on the extraction of vanadium (IV) with D2EHPA and
Figure 3.
Effect of
of fluoride
ion concentration
on the
the extraction of
of vanadium
vanadium (IV)
(IV) with D2EHPA
D2EHPA and
Figure
3. (D2EHPA
Effect
fluoride
ion
concentration
on
TBP
= 10%(v/v),
TBP
= 5% (v/v), O/A
phaseextraction
ratio = 1/1, agitation
speed 800 with
rpm, extraction and
TBP
(D2EHPA
=
10%
(v/v),
TBP
=
5%
(v/v),
O/A
phase
ratio
=
1/1,
agitation
speed
800
rpm,
extraction
TBP (D2EHPA
10%(v/v),
TBP = 5% (v/v), O/A phase ratio = 1/1, agitation speed 800 rpm, extraction
time 10 min,=˝25
°C)
time
10
min,
25
C).
time 10 min, 25 °C)
3.2.3. McCabe-Thiele Plot for Vanadium (IV) Extraction
3.2.3. McCabe-Thiele
McCabe-Thiele Plot
Plot for
for Vanadium
Vanadium (IV)
3.2.3.
(IV) Extraction
Extraction
To determine the theoretical number of stages required for the maximum extraction of
To
determine
theoretical
number
of stages
required
for the
maximum
extraction
ofdrawn
vanadium
vanadium
at a the
chosen
phase ratio
and D2EHPA
concentration,
an extraction
isotherm
was
To
determine
the
theoretical
number
of stages
required
for the maximum
extraction
of
from
the
results
obtained
by
contacting
the
leach
solution
with
organic
phase
(10%
(v/v)
D2EHPA
at
a
chosen
phase
ratio
and
D2EHPA
concentration,
an
extraction
isotherm
was
drawn
from
the
vanadium at a chosen phase ratio and D2EHPA concentration, an extraction isotherm was drawn
and
5% (v/v)by
TBP
in sulfonated
kerosene
at different
O/A phase
ratios
(O/A
= 1/8, 1/5, 1/2, and
1/1, 2/1,
results
obtained
contacting
the leach
solution
with
organic
phase
(10%
(v/v)
5% (v/v)
from
the
results obtained
by contacting
the leach
solution
with
organic
phaseD2EHPA
(10% (v/v) D2EHPA
5/1).
The
McCabe-Thiele
plot
(Figure
4)
shows
that
quantitative
extraction
of
vanadium
can
be
TBP 5%
in sulfonated
kerosene
at different
O/A
phase ratios
1/8, 1/5,
1/1,
2/1,
and
(v/v) TBP in
sulfonated
kerosene
at different
O/A(O/A
phase=ratios
(O/A1/2,
= 1/8,
1/5,
1/2,5/1).
1/1, The
2/1,
theoretically achieved in five stages of counter-current extraction at an O/A phase ratio of 1.0.
McCabe-Thiele
plot
(Figure
4)
shows
that
quantitative
extraction
of
vanadium
can
be
theoretically
5/1). Because
The McCabe-Thiele
plot (Figure
4) number
shows that
quantitative
extraction
can be
the pH will decrease
as the
of extraction
stages
increases of
in vanadium
a continuous
achieved in five
stages in
of counter-current
extraction at anextraction
O/A phase
ratio
of 1.0.
Because
the
pH
theoretically
achieved
five
stages
of
counter-current
at
an
O/A
phase
ratio
of 1.0.
counter-current extraction process, which influences the extraction efficiency, one more stage was
will decrease
thewill
number
of extraction
stages
increases
in a extraction
continuous
counter-current
extraction
Because
theAas
pH
decrease
number
of extraction
stages was
increases
continuous
added.
batch
simulation
of as
six the
stages
of counter-current
carried in
outa and
the
process,
which
influences
the
extraction
efficiency,
one
more
stage
was
added.
A
batch
simulation
of
raffinates were
analyzedprocess,
for vanadium
other metals
concentration
(Table one
3). The
raffinate
counter-current
extraction
which and
influences
the extraction
efficiency,
more
stage was
six stages
counter-current
was carried
out and
the raffinates
were
contained
222simulation
mg/L V2O5, extraction
which
96.7%
extraction
efficiency.
The
initial
andfor
final
pH the
added.
A ofbatch
of sixcorresponds
stages
of to
counter-current
extraction
wasanalyzed
carried
outvanadium
and
and
other
metals
concentration
(Table
3).
The
raffinate
contained
222
mg/L
V
O
,
which
corresponds
of
the
solutions
are
2.5
and
1.52,
respectively.
The
loaded
organic,
containing
6.45
g/L
V
2
O
5
,
was
then
2
5
raffinates were analyzed for vanadium and other metals concentration (Table 3). The raffinate
usedextraction
to
carry
outefficiency.
stripping
studies.
to 96.7%
The initial and final pH of the solutions are 2.5 and 1.52, respectively.
contained
222
mg/L
V
2O5, which corresponds to 96.7% extraction efficiency. The initial and final pH
The
loaded
organic,
containing
g/L V2 O5The
, was
then used
to carry
out stripping
of
the
solutions
are 2.5
and 1.52,6.45
respectively.
loaded
organic,
containing
6.45 g/Lstudies.
V2O5, was then
Table 3. Chemical analysis of the raffinate.
used to carry out stripping studies.
raffinate.
Component Table 3.V2Chemical
O5
Feanalysis
Alof the As
Zn
Concentration (g/L)
0.222
13.0
9.0
0.93
0.93
Table 3. Chemical analysis of the raffinate.
Component
V2 O5
Fe
Al
As
Zn
Component
Concentration
(g/L)
V2O513.0
8
0.222
Concentration (g/L)
0.222
O/A=5 O/A=8
Fe 9.0 Al
0.93As
O/A=2
13.0
9.0
0.93
6
[V2O5]org, g/L
[V2O5]org, g/L
0.93
Cu
0.41
0.41
Mg
1.15
1.15
O/A=2
4
A/O=2
6
2
n
tio
era
Op
O/A=1
A/O=5
0A/O=2
0
1
2
A/O=5
1:1
A=
O:
e
lin
1:1
A=
O:
e
lin4
5
4
2
Zn
0.93
O/A=5 O/A=8
O/A=1
8
Cu
Mg
0.41
1.15
Cu
Mg
3
ion
rat[V2O5]aq, g/L
e
Op
6
7
8
Figure 4. Extraction isotherm for vanadium (D2EHPA = 10% (v/v), TBP = 5% (v/v), equilibrium pH = 2.5, 25 °C).
0
3.2.4. Stripping of Vanadium0 (IV) 1
2
3
4
5
6
7
8
[V2O5]aq, g/L
Figure
4. Extraction
isotherm
for vanadium
(D2EHPA
= 10% (v/v),
TBP(v/v),
= 5% (v/v),
= 2.5, 25 °C).
Figure
4. Extraction
isotherm
for vanadium
(D2EHPA
= 10%
TBP equilibrium
= 5% (v/v),pH
equilibrium
˝
pH = 2.5, 25 C).
3.2.4. Stripping of Vanadium (IV)
Metals 2016, 6, 63
7 of 13
Metals 2016, 6, 63
7 of 13
3.2.4. Stripping of Vanadium (IV)
The loaded organic was scrubbed using 0.15 mol/L sulfuric acid solution at an O/A phase ratio
The loaded organic was scrubbed using 0.15 mol/L sulfuric acid solution at an O/A phase ratio
of 2.0 to remove the entrainment impurities. The scrubbed loaded organic phase was stripped with
of 2.0 to remove the entrainment impurities. The scrubbed loaded organic phase was stripped with
sulfuric acid. Different concentrations of sulfuric acid were contacted with the loaded organic phase
sulfuric acid. Different concentrations of sulfuric acid were contacted with the loaded organic phase at
at various O/A phase ratios. The results (Figure 5) show that the vanadium stripping increases from
various O/A phase ratios. The results (Figure 5) show that the vanadium stripping increases from
40.6% to 97.9% as the sulfuric acid concentration increased from 0.5 to 2.5 mol/L at an O/A phase
40.6% to 97.9% as the sulfuric acid concentration increased from 0.5 to 2.5 mol/L at an O/A phase
ratio of 2/1. Additionally, the residual sulfuric acid in the spent strip solution also increased with the
ratio of 2/1. Additionally, the residual sulfuric acid in the spent strip solution also increased with the
increasing acid concentration. As the initial concentration of H2SO4 increased from 0.5 to 2.5 mol/L,
increasing acid concentration. As the initial concentration of H2 SO4 increased from 0.5 to 2.5 mol/L,
the residual H2SO4 in the strip solution increased from 0.26 to 2.1 mol/L. Greater residual sulfuric
the residual H2 SO4 in the strip solution increased from 0.26 to 2.1 mol/L. Greater residual sulfuric
acid in the strip solution means that more aqueous ammonia will be consumed during the
acid in the strip solution means that more aqueous ammonia will be consumed during the subsequent
subsequent vanadium precipitation process. The optimum amount of H2SO4 was determined by
vanadium precipitation process. The optimum amount of H2 SO4 was determined by considering both
considering both the vanadium stripping efficiency and the residual sulfuric acid concentration in
the vanadium stripping efficiency and the residual sulfuric acid concentration in the strip solution.
the strip solution. For the present study, 1.5 mol/L H2SO4 was chosen as optimum.
For the present study, 1.5 mol/L H2 SO4 was chosen as optimum.
100
90
O/A ratio=1/1
O/A ratio=2/1
O/A ratio=5/1
O/A ratio=8/1
O/A ratio=10/1
Stripping percentage, %
80
70
60
50
40
30
20
10
0
0.5
1.0
1.5
2.0
2.5
3.0
Concentration of H2SO4, mol/L
Figure
Figure 5.5. Effect
Effect of
of H
H22SO
SO44 concentration
concentration and
and organic-to-aqueous
organic-to-aqueous (O/A)
(O/A) phase ratio on
on vanadium
vanadium
˝ C).
stripping
stripping (agitation
(agitation speed
speed 1000
1000 rpm,
rpm, stripping
strippingtime
time10
10min,
min,25
25 °C).
3.2.5.
3.2.5. Stripping
Stripping Isotherm
Isotherm for
for Vanadium
Vanadium(IV)
(IV)
The
The stripping
stripping isotherm
isotherm for
for vanadium
vanadium was
was constructed
constructed to
to determine
determine the
the number
number of
of stages
stages
required
stripping at
at aachosen
chosenphase
phaseratio.
ratio.The
The
loaded
organic
phase
1.5 mol/L
SO4
required for
for stripping
loaded
organic
phase
andand
1.5 mol/L
H2SOH4 2were
were
contacted
at different
10:1
1:2, while
keeping
the total
volume
constant.
contacted
at different
O/A O/A
phasephase
ratiosratios
from from
10:1 to
1:2,towhile
keeping
the total
volume
constant.
The
McCabe-Thiele
plotplot
(Figure
6) illustrates
that
greater
than
be
The
McCabe-Thiele
(Figure
6) illustrates
that
greater
than99%
99%ofofthe
theloaded
loaded vanadium
vanadium can
can be
theoreticallystripped
strippedusing
usingfour
fourcounter-current
counter-current
stages
at an
O/A
flow
ratio
8. Considering
theoretically
stages
at an
O/A
flow
ratio
of 8.ofConsidering
thatthat
the
the sulfuric
acid concentration
will decrease
as the number
of stripping
stages which
increases,
which
sulfuric
acid concentration
will decrease
as the number
of stripping
stages increases,
influences
influences
the
strippingone
efficiency,
onewas
more
stageAwas
A batch
simulation
five stages of
the
stripping
efficiency,
more stage
added.
batchadded.
simulation
of five
stages ofof
counter-current
counter-current
stripping
was
out of
at 8anusing
O/A 1.5
ratio
of 8 using
mol/L
H
2
SO
4
.
The stripped
stripping
was carried
out at
ancarried
O/A ratio
mol/L
H2 SO1.5
.
The
stripped
organic
phase
4
organic phase
contained
20 mg/L
V2O5, that
which
indicates
that greater
than
99.7% vanadium
contained
only 20
mg/L V2only
O5 , which
indicates
greater
than 99.7%
vanadium
stripping
efficiency
stripping
efficiency was achieved.
was
achieved.
Metals 2016, 6, 63
Metals 2016, 6, 63
8 of 13
8 of 13
60
O/A=10
50
O/A=8
[V2O5]aq, g/L
40
30
O/A=5
n
tio
era
Op
20
8:1
:A=
O
e
lin
O/A=2
10
O/A=1
O/A=1/2
0
0
1
2
3
4
5
6
7
[V2O5]org, g/L
Figure
Figure6.6.McCabe-Thiele
McCabe-Thieleplot
plotfor
forvanadium
vanadiumstripping
stripping(V(V
2O
inloaded
loadedorganic
organicphase
phase==6.45
6.45g/L,
g/L,strip
strip
2O
5 5in
˝
solution
H22SO
SO44, ,25
25°C).
C).
solution== 1.5
1.5 mol/L
mol/L H
3.3.Oxidation
Oxidationand
andPrecipitation
Precipitation
3.3.
3.3.1.
3.3.1.Oxidation
Oxidation
2+)
The
The vanadium
vanadium (VO
(VO2+
) in
in the
the strip
strip solution
solution should
should be
be oxidized
oxidized to
toVO
VO22++ before
before precipitation.
precipitation.
KMnO
,
NaClO
,
H
O
,
and
H
SO
are
common
oxidants
that
can
be
used.
Among
these,
KMnO44, NaClO33, H22O22, and H22SO55 are common oxidants that can be used. Among these,HH
2O
was
2O
2 2was
chosen
chosenfor
forits
itsstrong
strongoxidizing
oxidizingability,
ability,low
lowcost,
cost,and
andeasy
easyoperation:
operation:
2+
`+ +H O
2VO
+H
H22OO2 2“=2VO
2VO
2VO2` `
2 H2 O2
2 `
(3).
(3)
2O2 at six times the stoichiometric
Inthe
thepresent
presentstudy,
study,oxidation
oxidationwas
wascarried
carriedout
outby
byadding
addingHHO
In
2 2 at six times the stoichiometric
amountat
at50
50˝°C
for 11h.
h. The
The color
color of
of the
the strip
strip solution
solution changed
changed from
fromblue
blueto
toyellow
yellowat
atthe
theend
endof
ofthe
the
amount
C for
reaction.
Sample
testing
showed
that
the
vanadium
(IV)
concentration
in
the
oxidized
solution
was
reaction. Sample testing showed that the vanadium (IV) concentration in the oxidized solution was
below0.1
0.1g/L,
g/L, which
which meant
meant that
that almost
almost all
all of
of the
the vanadium
vanadium (IV)
(IV) was
was oxidized
oxidized to
to vanadium
vanadium(V).
(V).The
The
below
vanadium(V)
(V)solution
solutionwas
wasused
usedas
asthe
thefeed
feedfor
forthe
theprecipitation
precipitationexperiments.
experiments.
vanadium
3.3.2.Precipitation
Precipitation
3.3.2.
After the
the oxidation
oxidation of
of the
the strip
strip solution,
solution, vanadium
vanadium can
can be
be precipitated
precipitated from
from the
the vanadium
vanadium
After
(V)-containing
solution
by
adding
an
ammonium
salt,
such
as
(NH
4
)
2
SO
4
,
(NH
4
)
2
CO
3
,
or
NH44Cl.
Cl.
(V)-containing solution by adding an ammonium salt, such as (NH4 )2 SO4 , (NH4 )2 CO3 , or NH
Becauseaqueous
aqueousammonia
ammonia
was
added
to feed
the feed
solution
to neutralize
the residual
acidpresent
in the
Because
was
added
to the
solution
to neutralize
the residual
acid in the
present
study,
a
large
amount
of
(NH
4
)
2
SO
4
was
produced
during
the
neutralization
reaction
and
study, a large amount of (NH4 )2 SO4 was produced during the neutralization reaction and additional
additional
ammonium
salt
was
not
required.
ammonium salt was not required.
The effect
effect of
of temperature
temperature on
on vanadium
vanadium precipitation
precipitation was
was studied
studied in
in the
the range
range of
of 25
25 to
to 95
95 ˝°C.
The
C.
The
results
shown
in
Figure
7
indicate
that
precipitation
efficiency
increases
with
increasing
reaction
The results shown in Figure 7 indicate that precipitation efficiency increases with increasing reaction
˝ Ccaused
temperature. Increasing
Increasing the
the solution
extent
of
temperature.
solution temperature
temperaturefrom
from60
60to
to90
90°C
causedananincrease
increaseininthe
the
extent
vanadium
precipitation;
little effect.
effect. According
According to
to
of
vanadium
precipitation;however,
however,a afurther
furtherincrease
increasein
in temperature
temperature had
had little
˝
these
data,
vanadium
precipitation
should
be
carried
out
between
90
and
95
°C.
these data, vanadium precipitation should be carried out between 90 and 95 C.
Metals 2016, 6, 63
Metals 2016, 6, 63
Metals 2016, 6, 63
Vanadium
precipitationratio,%
ratio,%
Vanadium
precipitation
9 of 13
9 of 13
9 of 13
100
100
95
95
90
90
85
85
80
80
75
75
70
70
65
65
60
60
55
55
50
50
20
20
30
30
40
40
50
50
60
60
70
70
80
80
Temperature, oC
Temperature, oC
90
90
100
100
Figure 7. Effect of temperature on vanadium precipitation (V2O5 concentration 52 g/L, equilibrium
Figure7.7.Effect
Effectofoftemperature
temperatureon
onvanadium
vanadiumprecipitation
precipitation(V(V
2O5concentration
52g/L,
g/L, equilibrium
equilibrium
Figure
2O
5 concentration52
pH of 1.8–2.2, reaction time of 2 h).
pH
of
1.8–2.2,
reaction
time
of
2
h).
pH of 1.8–2.2, reaction time of 2 h).
Vanadiumprecipitation
precipitationratio,%
ratio,%
Vanadium
The effect of pH on vanadium precipitation was studied under conditions of 90 °C for a reaction
The effect of pH on vanadium precipitation was studied under conditions of 90˝°C for a reaction
pH onare
vanadium
precipitation
wasresult
studied
under conditions
of 90 C forreaction
a reaction
time The
of 2 effect
h. Theofresults
shown in
Figure 8. This
suggests
that the precipitation
is
time of 2 h. The results are shown in Figure 8. This result suggests that the precipitation reaction is
time
of
2
h.
The
results
are
shown
in
Figure
8.
This
result
suggests
that
the
precipitation
reaction
is
promoted in the pH range of 1.8–2.2.
promoted in the pH range of 1.8–2.2.
promoted in the pH range of 1.8–2.2.
100
100
95
95
90
90
85
85
80
80
75
75
70
70
65
65
60
60
55
55
50
500
0
1
1
2
2
3
3
4
4
Equilibrium pH
Equilibrium pH
5
5
6
6
7
7
Figure 8. Effect of equilibrium pH on vanadium precipitation (V2O5 concentration 52 g/L, reaction
Figure8.8.Effect
Effectofofequilibrium
equilibriumpH
pHon
onvanadium
vanadiumprecipitation
precipitation(V(V
2O
concentration52
52g/L,
g/L, reaction
reaction
Figure
2O
5 5concentration
time of 2 h, 90 °C).
timeof
of22h,
h,90
90˝°C).
time
C).
3.4. Calcination
3.4. Calcination
Calcination
3.4.
The dried ammonium polyvanadate was calcined at 550 °C˝ for 2 h in a muffle furnace under an
The dried
dried ammonium
ammonium polyvanadate
inin
a muffle
furnace
under
an
The
polyvanadate was
wascalcined
calcinedatat550
550°CCfor
for2 2h h
a muffle
furnace
under
oxidizing atmosphere; the XRD analysis for this (Figure 9) fitted the vanadium pentoxide pattern
oxidizing
atmosphere;
thethe
XRD
vanadium pentoxide
pentoxide pattern
pattern
an
oxidizing
atmosphere;
XRDanalysis
analysisfor
forthis
this(Figure
(Figure9)
9) fitted
fitted the
the vanadium
well. The composition of the vanadium pentoxide product is shown in Table 4 and compared with
well.
The
composition
of
the
vanadium
pentoxide
product
is
shown
in
Table
4
and
compared
well. The composition of the vanadium pentoxide product is shown in Table 4 and compared withwith
the
the requirements of the relevant industry standard in China (YB/T5304-2011) [34]. As shown, the purity
the requirements
of the
relevant
industry
standard
in China
(YB/T5304-2011)[34].
[34].As
Asshown,
shown,the
thepurity
purity
requirements
of the
relevant
industry
standard
in China
(YB/T5304-2011)
of the product reached 99.52% V2O5, with trace amounts of sodium, iron, and phosphorus impurities.
of the
the product
product reached
amounts
ofof
sodium,
iron,
and
phosphorus
impurities.
of
reached 99.52%
99.52%V
V22OO5,5with
, withtrace
trace
amounts
sodium,
iron,
and
phosphorus
impurities.
Metals 2016, 6, 63
Metals 2016, 6, 63
10 of 13
10 of 13
7000
∆
6000
∆-V2O5
5000
Intensity
4000
3000
∆
∆
∆
2000
∆
1000
∆
∆
∆
∆ ∆ ∆ ∆ ∆ ∆∆
∆∆
0
10
20
30
40
50
60
70
80
90
2-Theta(°)
Figure9.9.XRD
XRDpattern
patternof
ofthe
theVV22O
O55 product.
product.
Figure
Table4.4. Chemical
Chemicalanalysis
analysisof
ofvanadium
vanadiumpentoxide.
pentoxide.
Table
Component (%)
Product
Product
V2O5 99
YB/T 5304-2011 V2 O5 99
V2O5 98
YB/T 5304-2011
V2O5
V2 O5
99.52
99.52
≥99.0
ě99.0
≥98.0
Si
Si
0.005
0.005
≤0.20
ď0.20
≤0.25
Fe
P
S
As
K2O + Na2O
Fe
P
S
As
K2 O + Na2 O
0.08
0.01 0.007 0.006
0.15
0.08
0.01
0.007
0.006
0.15
≤0.20 ≤0.03 ≤0.01 ≤0.01
≤1.0
ď0.20 ≤0.05
ď0.03 ≤0.03
ď0.01 ≤0.02
ď0.01
ď1.0
≤0.30
≤1.5
V2 O5 98
ě98.0
ď0.25
ď0.30
Component (%)
ď0.05
ď0.03
ď0.02
ď1.5
3.5. Development of a Process Flow Sheet to Recover Vanadium
3.5. Development
of ainvestigation
Process Flow Sheet
to Recover Vanadium
Based on the
and discussion
above, a process flow sheet to extract and recover
vanadium
theinvestigation
H2SO4-HF solution
generatedabove,
by thealeaching
black
shale
solvent
extraction
Based from
on the
and discussion
processof
flow
sheet
toby
extract
and
recover
and precipitation
proposed
in
Figure
10.
In
this
flow
sheet,
vanadium
(IV)
in
the
leach
solution
can
vanadium
from theisH
SO
-HF
solution
generated
by
the
leaching
of
black
shale
by
solvent
extraction
2
4
be
effectively
extracted
using
10%
(v/v)
D2EHPA
with
5%
(v/v)
TBP
at
an
aqueous
pH
of
2.5
and
an
and precipitation is proposed in Figure 10. In this flow sheet, vanadium (IV) in the leach solution can be
O/A phaseextracted
ratio of using
1/1. With
six counter-current
extraction
stages,
96.7% vanadium
is extracted.
effectively
10% (v/v)
D2EHPA with 5%
(v/v) TBP
at an aqueous
pH of 2.5 and
an O/A
Vanadium
in1/1.
the loaded
phase can
be completely
by 1.5 mol/L
H2SO4 Vanadium
at an O/A
phase
ratio of
With sixorganic
counter-current
extraction
stages, stripped
96.7% vanadium
is extracted.
phase
ratio oforganic
8/1. Then,
about
times of thestripped
stoichiometric
requirement
2OO/A
2 is added
the
in
the loaded
phase
can six
be completely
by 1.5 mol/L
H2 SO4ofatHan
phaseto
ratio
stripping
solution
(IV) to vanadium
(V)of at
°Cadded
for 1 to
h.the
Ammonium
of
8/1. Then,
aboutto
sixoxidize
times ofvanadium
the stoichiometric
requirement
H250
O2 is
stripping
polyvanadate
can vanadium
be successfully
precipitated
oxidized
solution polyvanadate
by adding aqueous
solution
to oxidize
(IV) to vanadium
(V)from
at 50 ˝the
C for
1 h. Ammonium
can be
ammonia to precipitated
adjust the pH
to 1.8–2.2,
at 90 °C
for 2 h.byThe
driedaqueous
ammonium
polyvanadate
calcined
successfully
from
the oxidized
solution
adding
ammonia
to adjustisthe
pH to
at 550 °C
to obtain
a high
of V2O5polyvanadate
product.
1.8–2.2,
at for
90 ˝2Ch for
2 h. The
driedpurity
ammonium
is calcined at 550 ˝ C for 2 h to obtain a
high purity of V2 O5 product.
Metals
2016,
Metals
2016,
6,6,
6363
1111ofof1313
Figure
flow sheet
sheetfor
for
extraction
recovery
of vanadium
from
2SO
4-HFsolution
leach
Figure10.
10. Proposed
Proposed flow
extraction
andand
recovery
of vanadium
from H
-HF
leach
2 SO4H
solution
fromshale
blackbyshale
by solvent
extraction
and precipitation.
from black
solvent
extraction
and precipitation.
4.4.Conclusions
Conclusions
Based
in this
thispaper,
paper,a aprocess
process
extraction
and
recovery
of vanadium
Basedon
onthe
thedata
data presented
presented in
forfor
extraction
and
recovery
of vanadium
from
from
H
2
SO
4
-HF
solutions
generated
by
the
leaching
of
black
shale
is
suggested.
The
conclusions
H2 SO4 -HF solutions generated by the leaching of black shale is suggested. The conclusions from the
from
test
work
are presented
test the
work
are
presented
below: below:
(1) A vanadium extraction efficiency of 96.7% was achieved using 10% (v/v) D2EHPA with 5%
(1) TBP
A vanadium
extraction
efficiency
96.7%
achieved using
10% (v/v)
with 5%
(v/v)
in sulfonated
kerosene
in six of
stages
ofwas
counter-current
extraction
at D2EHPA
an equilibrium
pH(v/v)
of
TBP
in
sulfonated
kerosene
in
six
stages
of
counter-current
extraction
at
an
equilibrium
pH
of
2.5
2.5 and an O/A phase ratio of 1/1. Fluoride ions in the leaching solution had almost no effect on
and an
phase ratio of 1/1. Fluoride ions in the leaching solution had almost no effect on
vanadium
(IV)O/A
extraction.
vanadium
(IV)
extraction.
(2) 99.7% of the loaded
vanadium was stripped from the organic phase by 1.5 mol/L H2SO4 in
(2)
99.7%
of
the
loaded
vanadium
stripped
five counter-current stages at an O/A was
phase
ratio offrom
8/1. the organic phase by 1.5 mol/L H2 SO4 in five
counter-current
stages
at
an
O/A
phase
ratio
of
8/1.
(3) 98% of vanadium was precipitated as ammonium
polyvanadate by oxidation and
(3)
98%
of
vanadium
was
precipitated
as
ammonium
polyvanadate
by oxidation
precipitation. Following calcination of the dried ammonium polyvanadate
at 550 °Cand
forprecipitation.
2 h, a high
˝ C for 2 h, a high purity
Following
calcination
of
the
dried
ammonium
polyvanadate
at
550
purity 99.52% V2O5 product was obtained.
99.52%
V2sheet
O5 product
obtained.
(4)
A flow
for thewas
extraction
and recovery of vanadium from a H2SO4-HF mixed leach
A
flow
sheet
for
the
extraction
and
recovery
vanadium from a H2 SO4 -HF mixed leach solution
(4)
solution by solvent extraction and precipitation is of
proposed.
by solvent extraction and precipitation is proposed.
Acknowledgments: This work has been supported by the National Basic Research Program of China (Grant
No.
2014CB643404), NSFC
Foundation
of China,
Grant
No.
51174104,
51304093
and 51474115).
Acknowledgments:
This (Natural
work hasScience
been supported
by the
National
Basic
Research
Program
of China
(Grant No.
2014CB643404),
NSFC Xingbin
(Natural Li
Science
Foundation
of China, Grant
No. 51174104,
51304093
Author
Contributions:
conducted
the experiments
and wrote
the initial
draft ofand
the51474115).
manuscript.
Author
Contributions:
Li conducted
experiments
the initial
draft of the
Chang
Chang
Wei
designed the Xingbin
experiments.
Zhigan the
Deng,
Cunxiongand
Li wrote
and Gang
Fan analyzed
themanuscript.
data and wrote
Wei
designed
the experiments.
Zhigan
Cunxiong
andcontributed
Gang Fan analyzed
therevised
data and
wrote the All
final
the
final
manuscript.
Minting Li and
HuiDeng,
Huang
reviewedLiand
to the final
manuscript.
manuscript.
Minting
Li and
Hui Huang
reviewed
andthe
contributed
to the final revised manuscript. All authors
authors
contributed
to the
analysis
of the data
and read
final paper.
contributed to the analysis of the data and read the final paper.
Conflicts of Interest: The author declares no conflict of interest.
Metals 2016, 6, 63
12 of 13
Conflicts of Interest: The author declares no conflict of interest.
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