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BaCO3CaO and Acid Leaching Technology .pdf



Nom original: BaCO3CaO and Acid Leaching Technology.pdf
Titre: Mechanisms of Vanadium Recovery from Stone Coal by Novel BaCO3/CaO Composite Additive Roasting and Acid Leaching Technology
Auteur: Zhenlei Cai, Yimin Zhang, Tao Liu and Jing Huang

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minerals
Article

Mechanisms of Vanadium Recovery from Stone Coal
by Novel BaCO3/CaO Composite Additive Roasting
and Acid Leaching Technology
Zhenlei Cai 1,2,3, *, Yimin Zhang 1,2,3, *, Tao Liu 1,2,3 and Jing Huang 1,2,3
1
2
3

*

School of Resource and Environmental Engineering, Wuhan University of Science and Technology,
Wuhan 430081, China; liutao781019@126.com (T.L.), jing_huang81@126.com (J.H.)
Hubei Provincial Engineering Technology Research Center of High Efficient Cleaning Utilization for Shale
Vanadium Resource, Wuhan 430081, China
Hubei Collaborative Innovation Center for High Efficient Utilization of Vanadium Resources,
Wuhan 430081, China
Correspondence: caizhenlei@wust.edu.cn or ande559@163.com (Z.C.); zym126135@126.com (Y.Z.)

Academic Editor: William Skinner
Received: 14 December 2015; Accepted: 22 March 2016; Published: 29 March 2016

Abstract: In this report, the vanadium recovery mechanisms by novel BaCO3 /CaO composite
additive roasting and acid leaching technology, including the phase transformations and the
vanadium leaching kinetics, were studied. The purpose of this manuscript is to realize and improve
the vanadium recovery from stone coal using BaCO3 /CaO as the composite additive. The results
indicated that during the composite additive BaCO3 /CaO roasting process, the monoclinic crystalline
structure of muscovite (K(Al,V)2 [Si3 AlO10 ](OH)2 ) was converted into the hexagonal crystalline
structure of BaSi4 O9 and the tetragonal crystalline structure of Gehlenite (Ca2 Al2 SiO7 ), which could,
therefore, facilitate the release and extraction of vanadium. Vanadium in leaching residue was
probably in the form of vanadate or pyrovanadate of barium and calcium, which were hardly
extracted during the sulfuric acid leaching process. The vanadium leaching kinetic analysis indicated
that the leaching process was controlled by the diffusion through a product layer. The apparent
activation energy could be achieved as 46.51 kJ/mol. The reaction order with respect to the sulfuric
acid concentration was 1.1059. The kinetic model of vanadium recovery from stone coal using novel
composite additive BaCO3 /CaO could be finally established.
Keywords: vanadium recovery; stone coal; novel composite additive; BaCO3 /CaO; phase
transformations; kinetics

1. Introduction
Vanadium plays important roles in many fields, such as ferrous and nonferrous alloy
production [1], thermistors [2], and catalysts [3]. More than 87% of the vanadium resources exist in
the form of stone coal in China [4]. To meet the ever-increasing demand of vanadium resources and
the exhaustion of stone coal with high-grade vanadium, the utilization, and exploitation of refractory
stone coal becomes more and more important.
There are two different kinds of additives utilized for vanadium recovery: roasting additives and
leaching additives. Compared to the leaching additives, including Na2 CO3 [5,6], H2 O2 [7,8], FeSO4 [9],
NaClO [10], CaF2 [11], and H2 SiF6 [12], the roasting additives are more effectively employed due to
their good applicability and availability.
Wang [13] studied different effects on the vanadium leaching efficiency of stone coal. The results
indicate that the roasting additive NaCl must be added to destroy vanadium-bearing crystalline form
so as to acquire high vanadium leaching efficiency. Zeng [14] studied the NaCl/CaO oxidizing roasting
Minerals 2016, 6, 26; doi:10.3390/min6020026

www.mdpi.com/journal/minerals

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in a laboratory fluidized bed reactor for stone coal. The results indicated that the maximum vanadium
oxidizing
roasting
in a91%
laboratory
fluidized
reactor for
stone coal. The results
indicated
thatCO
the
leaching rate
reached
under the
optimalbed
conditions.
Aarabi-Karasgani
[15] studied
the Na
2
3
maximum
vanadium leaching
reachedfor
91%
under the
optimalfrom
conditions.
Aarabi-Karasgani
[15]
alkaline roasting-acid
leaching rate
technology
vanadium
recovery
LD (Linz–Donawitz)
converter
studied
Na2CO
3 alkaline roasting-acid leaching technology for vanadium recovery from LD
slag. Thethe
results
indicated
that the maximum vanadium recovery of 95% was achieved under the
(Linz–Donawitz)
converter
slag. The results indicated that the maximum vanadium recovery of 95%
optimum conditions.
was achieved
the optimum
conditions.
Althoughunder
the results
of the above
investigations are convincing, a novel composite additive is
Although
the
results
of
the
above
investigations
convincing,
a novel
composite
additive
is
expected to be found for the high effective
extraction of are
vanadium,
especially
from
the refractory
stone
expected
to same
be found
the high
effective
extraction of
vanadium,
especially
the refractory
coal. At the
time,for
it should
have
good availability
and
be favorable
for the from
optimization
of the
stone
coal.
At
the
same
time,
it
should
have
good
availability
and
be
favorable
for
the
optimization
whole extraction process.
of theInwhole
process.a novel composite additive BaCO /CaO, based on their similar
our extraction
previous report,
3
In our previous
report,
a novel
additive
3/CaO, based on their similar
characteristics
in the same
main
groupcomposite
element, was
used BaCO
for the
vanadium recovery from the
characteristics
in
the
same
main
group
element,
was
used
for
the
vanadium
recovery from
the
representative refractory stone coal [16]. However, further investigations
on the vanadium
recovery
representative
refractory
stone
coal
[16].
However,
further
investigations
on
the
vanadium
recovery
mechanisms, based on the intensive systematic discussion of the experimental conditions, are definitely
mechanisms,
basedand
on promote
the intensive
systematicof discussion
of the
experimental
required to explain
the application
the composite
additive,
includingconditions,
the analysisare
of
definitely
required
to
explain
and
promote
the
application
of
the
composite
additive,
including the
the crystal transformation relationship and the vanadium leaching kinetics.
analysis
the crystal
transformation
relationship
andthe
thedifferent
vanadium
leaching
kinetics.
Theof
main
purpose
of this paper is
to investigate
effects
on the
vanadium leaching
The main
of stone
this paper
is tothe
investigate
the different
effects on the during
vanadium
efficiency
frompurpose
refractory
coal for
rate-controlling
step determination
the leaching
leaching
efficiency
from
refractory
stone
coal
for
the
rate-controlling
step
determination
during
the
leaching
process. Meanwhile, the phase transformations were studied and the leaching kinetic model
was
process.
Meanwhile,
the
phase
transformations
were
studied
and
the
leaching
kinetic
model
was
established to reveal the vanadium recovery mechanisms and, thus, further improve the recovery effect.
established to reveal the vanadium recovery mechanisms and, thus, further improve the recovery effect.
2. Materials and Methods
2. Materials and Methods
2.1. Materials
2.1. Materials
The sample of raw stone coal was obtained from Hubei, China. The ore sample was crushed and
Theinto
sample
of raw
stone
coal wassize
obtained
from
Hubei,
China. The
ore sample was
crushed
ground
powder
with
the particle
of ´0.106
mm.
The chemical
multi-elemental
analysis
of
and
ground
into
powder
withinthe
particle
size
of −0.106
mm.
Thecompositions
chemical multi-elemental
the raw
stone
coal
was listed
Table
1. The
main
mineral
phase
of the raw oreanalysis
sample,
of
the raw
coal was
Table 1. analysis
The main
mineral
phase2500PC,
compositions
the raw
ore
which
werestone
determined
by listed
X-ray in
diffraction
(XRD,
D/MAX
Rigaku,ofTokyo,
Japan)
sample,
which
were quartz,
determined
by X-ray
diffractioncalcite,
analysis
(XRD,
D/MAX 2500PC, Rigaku, Tokyo,
(Figure 1),
included
muscovite,
phlogopite,
and
pyrite.
Japan) (Figure 1), included quartz, muscovite, phlogopite, calcite, and pyrite.
Table 1. Chemical multi-elemental analysis of stone coal wt % [16].

Table 1. Chemical multi-elemental analysis of stone coal wt % [16].
Element V2 O5 SiO2 Al2 O3 CaO Fe2 O3 K2 O MgO Na2 O SO3

Element V2O5 SiO2
Content 0.77
51.15
Content 0.77 51.15

P2 O5

Al2O3 CaO Fe2O3 K2O MgO Na2O SO3 P2O5
9.08
8.33
2.44
1.97
1.82
0.45
3.55
1.29
9.08
8.33
2.44
1.97 1.82
0.45 3.55 1.29

Figure 1. XRD image of stone coal [16].
Figure 1. XRD image of stone coal [16].

The elemental distribution of raw stone coal, which was analysed by energy disperse X-ray
spectrometry (EDS or BEI, INCA Energy 350, Oxford Instruments, Oxford, UK), is shown in
Figure 2. The EDS spectra analysis of the (i) point showed that the aluminium content was 10.67%,
which was close to the theoretical aluminium content 12.80% of muscovite containing vanadium.

Minerals 2016, 6, 26

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The elemental distribution of raw stone coal, which was analysed by energy disperse X-ray
spectrometry (EDS or BEI, INCA Energy 350, Oxford Instruments, Oxford, UK), is shown in Figure 2.
The
EDS
spectra
Minerals
2016,
6, 26 analysis of the (i) point showed that the aluminium content was 10.67%, which3 was
of 13
close to the theoretical aluminium content 12.80% of muscovite containing vanadium. Meanwhile, the
Meanwhile,
relevance
of V,
O,the
Al,raw
Si, and
K coal
in the
raw stone
coal
that
the vanadium
relevance
of the
V, O,
Al, Si, and
K in
stone
indicated
that
theindicated
vanadium
probably
existed
probably
existed in muscovite.
in
muscovite.

Figure 2. (a) BEI of raw stone coal; EDS elemental distribution: (b) O; (c) Al; (d) Si; (e) K; (f) V; (i) EDS
Figure 2. (a) BEI of raw stone coal; EDS elemental distribution: (b) O; (c) Al; (d) Si; (e) K; (f) V; (i) EDS
spectra marked from BEI by circle.
spectra marked from BEI by circle.

Chemical compositions of samples were determined by X-ray Fluorescence (XRF, XRF-1800,
Chemical
compositions
of samples Coupled
were determined
by X-ray
Fluorescence
(XRF, (ICP-AES,
XRF-1800,
Shimadzu,
Kyoto,
Japan) or Inductively
Plasma-Atomic
Emission
Spectroscopy
Shimadzu,
Kyoto,
Japan)
or
Inductively
Coupled
Plasma-Atomic
Emission
Spectroscopy
(ICP-AES,
Optima-4300DV, PerkinElmer, Boston, MA, USA). Phase compositions of solid samples
were
Optima-4300DV,
PerkinElmer,
Boston,
MA,
USA).
Phase
compositions
of
solid
samples
were
identified
identified by X-ray diffraction analysis (XRD, D/MAX 2500PC, Rigaku, Tokyo, Japan) using Cu Kα
by
X-ray diffraction
analysis
(XRD, and
D/MAX
2500PC,
Rigaku,
Tokyo, Japan)
using Cu
Kαconducted
radiation.
radiation.
Microscopic
observation
analysis
of element
distribution
in samples
were
Microscopic
and analysis
of element
in samples
conducted
scanning
by scanningobservation
electron microscopy
(SEM,
VEGAdistribution
III, TESCAN,
Brno, were
Czech
Republic)byequipped
electron
microscopy
(SEM,
VEGA
III,
TESCAN,
Brno,
Czech
Republic)
equipped
with
energy
disperse
with energy disperse X-ray spectrometry (EDS or BEI, INCA Energy 350, Oxford Instruments).
X-ray spectrometry (EDS or BEI, INCA Energy 350, Oxford Instruments).
2.2. Experimental Procedure
2.2. Experimental Procedure
Twenty grams of stone coal (with a fixed particle size fraction, except for its effect study) was
Twenty grams of stone coal (with a fixed particle size fraction, except for its effect study) was
added into the corundum crucible. Then, a certain amount of BaCO3 and CaO was put into it and
added into the corundum crucible. Then, a certain amount of BaCO3 and CaO was put into it and
mixed completely. After the crucible was placed into the muffle furnace, the roasting process started
mixed completely. After the crucible was placed into the muffle furnace, the roasting process started
at a required temperature for a certain period of time. When the roasting process was complete, the
at a required temperature for a certain period of time. When the roasting process was complete, the
roasted product was transferred into a leaching pod containing a required amount of sulfuric acid
roasted product was transferred into a leaching pod containing a required amount of sulfuric acid
solution according to the liquid-to-solid ratio of 5 mL/g. This ratio refers to the ratio of the leaching
solution according to the liquid-to-solid ratio of 5 mL/g. This ratio refers to the ratio of the leaching
agent (mL) to the raw material (g). This means that the volume of the leaching agent was always
agent (mL) to the raw material (g). This means that the volume of the leaching agent was always fixed
fixed at 100 mL during the experiments. The solution was stirred continuously for a certain period.
at 100 mL during the experiments. The solution was stirred continuously for a certain period. After the
After the sample was filtrated, vanadium in filtrate was analyzed to calculate the vanadium leaching
efficiency. The vanadium leaching efficiency can be calculated as follows:

η=


× 100%


(1)

Minerals 2016, 6, 26

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sample was filtrated, vanadium in filtrate was analyzed to calculate the vanadium leaching efficiency.
The vanadium leaching efficiency can be calculated as follows:
η“


ˆ 100%


(1)

where η is the vanadium leaching efficiency (wt %), V is the volume of the filtrate (mL), β is the
vanadium content in filtrate (g/mL), m is the mass of raw stone coal (g), and α is the vanadium content
in raw stone coal (wt %).
Although the mass change occurred through the roasting process, the vanadium total content
was not changed after the roasting process. This means it did not take effect to the investigation of the
vanadium leaching efficiency. When the leaching conditions were studied, the change of the mass after
the roasting process didn’t need to be adjusted. Therefore, the vanadium leaching efficiency was only
investigated for the whole process (from the roasting process to the leaching process).
3. Results and Discussion
3.1. Roasting Process
3.1.1. Effect of BaCO3 /CaO Total Weight on Vanadium Leaching Efficiency
The effect of BaCO3 /CaO total weight from 1 to 9 wt % on the vanadium leaching efficiency was
studied (Figure 3), with the BaCO3 /CaO mass ratio at 1:9, the roasting temperature at 850 ˝ C, the
roasting time for 2 h, the sulfuric acid concentration at 10% (v/v), the leaching temperature at 80 ˝ C, the
leaching time for 3 h, and the liquid-to-solid ratio at 5 mL/g. The results indicated that the vanadium
leaching efficiency increased with the increase of the BaCO3 /CaO total weight from 1 to 5 wt %.
A further increase of the BaCO3 /CaO total weight will result in the sharp decrease of the vanadium
leaching efficiency. The reason was probably that the vanadate or pyrovanadate of barium and calcium
were formed, which prohibited the vanadium from being effctively extracted in the following sulfuric
Minerals
2016, 6, process.
x
5 of 16
acid
leaching
Thus, the optimum BaCO3 /CaO total weight should be 5 wt %.

Figure3.3.Effect
Effectof
ofBaCO
BaCO33/CaO
/CaO total
Figure
total weight
weight on
on vanadium
vanadium leaching
leaching efficiency.
efficiency.

3.1.2. Effect of Mass Ratio of BaCO3 to CaO on Vanadium Leaching Efficiency
The effect of the mass ratio of BaCO3 to CaO from 1:9 to 9:1 on the vanadium leaching efficiency
was studied, with the BaCO3 /CaO total weight at 5 wt % and the roasting temperature at 850 ˝ C.
From Figure 4, it can be observed that when the mass ratio increased from 1:9 to 9:1 for 4 h, it had

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2016,
x
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2016,6,6,
6,26
x
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55ofof1415

From Figure 4, it can be observed that when the mass ratio increased from 1:9 to 9:1 for 4 h, it had
trival
Meanwhile,
thethe
increase
of the
mass
ratioratio
means
the
trivalimpact
impacton
onthe
thevanadium
vanadiumleaching
leachingefficiency.
efficiency.
Meanwhile,
increase
of the
mass
means
the greater
utilization
of BaCO
3
,
which
will
bring
more
difficult
operations
and
environmental
risks.
greater
utilization
of BaCO
,
which
will
bring
more
difficult
operations
and
environmental
risks.
With
3
3
With
the increase
of the roasting
time0.5from
to 2vanadium
h, the vanadium
the
increase
of the roasting
time from
to 2 0.5
h, the
leachingleaching
efficiencyefficiency
increasedincreased
sharply
from
30.71%
52.16%towith
the mass
of 1:9,
but of
no1:9,
significant
improvement
on the vanadium
sharply
fromto30.71%
52.16%
with ratio
the mass
ratio
but no significant
improvement
on the
vanadium
leachingcould
efficiency
could bewhen
obtained
when the
roasting
time2was
over 2 h. Therefore,
the
leaching
efficiency
be obtained
the roasting
time
was over
h. Therefore,
the optimum
mass
ratio mass
of BaCO
should
be should
1:9, andbe
the
optimum
should
be 2should
h.
optimum
ratio
ofCaO
BaCO
33 to CaO
1:9,
and the roasting
optimumtime
roasting
time
be 2 h.
3 to

Figure 4.
4. Effect
Effect of
of mass
mass ratio
ratio of
of BaCO
BaCO333 to
to CaO
CaO on
on vanadium
vanadium leaching
leaching efficiency.
efficiency.
Figure

3.1.3. Effect
Effect of
of Roasting
Roasting Temperature
Temperatureon
onVanadium
VanadiumLeaching
LeachingEfficiency
Efficiency
3.1.3.
The effect
effectof
ofthe
theroasting
roastingtemperature
temperaturefrom
from550
550toto950
950˝°C,
withthe
theBaCO
BaCO
33/CaO total
total weight
weight at
at
The
C, with
3 /CaO
wt.%%and
andthe
theBaCO
BaCO
33/CaO mass
mass ratio
ratioat
at1:9,
1:9,on
onthe
thevanadium
vanadiumleaching
leaching efficiency
efficiencywas
wasinvestigated
investigated
55 wt
3 /CaO
(Figure
5).
The
results
indicated
that
the
vanadium
leaching
efficiency
increased
remarkably
from
(Figure 5). The results indicated that the vanadium leaching efficiency increased remarkably from
˝
19.35% to
to 52.16%
52.16% as
as the
the roasting
roasting temperature
temperature increased
increased from
from 550
550 to
to 850
850 °C
for 22 h,
h, but
but when
when the
the
19.35%
C for
˝
roasting
temperature
exceeded
850
°C
for
2
h,
only
a
slight
improvement
of
the
vanadium
leaching
roasting temperature exceeded 850 C for 2 h, only a slight improvement of the vanadium leaching
efficiency could
could be
be observed.
observed. The
The vanadium
vanadium leaching
leaching efficiency
efficiency increased
increased with
with the
the increase
increase of
of the
the
efficiency
˝
roastingtime
timefrom
from0.5
0.5toto2 2h hatat
850C.
°C.
further
increase
of the
roasting
time
made
impact
on
roasting
850
AA
further
increase
of the
roasting
time
made
littlelittle
impact
on the
˝
˝
the
vanadium
leaching
efficiency
at
850
°C.
Hence,
the
optimum
roasting
temperature
should
be
vanadium leaching efficiency at 850 C. Hence, the optimum roasting temperature should be 850 C,
850
°C,
and
the
optimum
roasting
time
should
be
2
h.
and the optimum roasting time should be 2 h.

Figure 5.
5. Effect
Effect of
of roasting
roasting temperature
temperature on
on vanadium
vanadium leaching
leaching efficiency.
efficiency.
Figure

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3.1.4. Phase Transformation of Stone Coal during the Roasting Process
The crystal transformation relationship of muscovite (K(Al,V)2[Si3AlO10](OH)2), BaSi4O9,
study the(Ca
behavior
of the stone coal during the roasting process with the BaCO /CaO total
and To
Gehlenite
2Al2SiO7) is shown in Figure 7. The crystalline structure of3 muscovite
weight
at
5
wt
%,
the
mass
of BaCO
CaO at and
1:9, the
andunit
thecell
roasting
time are:
of 2ah,
the phase
3 to system,
(K(Al,V)2[Si3AlO10](OH)2) is aratio
monoclinic
crystal
parameters
= 0.5193
nm,
˝ C, were
transformation
of
the
roasting
samples,
with
the
roasting
temperature
from
650
to
950
b = 0.9045 nm, c = 2.0044 nm, α = γ = 90°, and β = 95.8°. During the BaCO3/CaO composite additive
analyzedprocess,
by XRD.Si–O
The and
XRDAl–O
patterns
arewere
shown
in Figure
6. The results
indicatedstructure
that the muscovite
roasting
bonds
broken.
Meanwhile,
the hexagonal
of BaSi4O9
and
phlogopite
crystalline
phase
were
weakened,
and
the
new
crystalline
phase
of BaSi
4 O9 and
and the tetragonal structure of Gehlenite (Ca2Al2SiO7) were formed. The crystalline
structure
of
˝ C.
Gehlenite
were
presented
in
the
roasting
sample
with
the
roasting
temperatures
of
650
and
750
BaSi4O9 is with the P3 space group and the unit cell parameters are a = b = 1.1247 nm, c = 0.4485 nm,
˝
When
reached
the muscovite
phlogopite
crystalline
phases
α = β =the
90°,roasting
and γ = temperature
120°. The Si–O
oxides850
formC,a close
circle typeand
array
and surround
Ba2+ ion
with
disappeared,
indicating
that
the
structure
of
muscovite
or
phlogopite
was
destroyed.
Moreover,
the
hexagonal coordination. The crystalline structure of Gehlenite (Ca2Al2SiO7) is with the P-421m space
V(III),
was
an cell
isomorphism
replacement
Al(III)
alumina
group which
and the
unit
parameters
are a = b =with
0.7693
nm,or
c =Mg(III)
0.5072innm,
α = βoctahedral
= γ = 90°. structure
The Al3+
of
mica
in
stone
coal,
could
be
released
from
the
crystal
lattice
and
oxidized
into
V(IV)
or
V(V)
for the
ion and the Si4+ ion are located at the same position in the unit cell with different occupancy.
˝
preparation
of oxides
the following
When the
temperature
reachedof950
C, through
the new
The Al–Si–O
form aleaching
doubleprocess.
close-packed
typeroasting
array with
the inclusion
Ca2+
crystalline
phase
of
diopside
started
to
present
in
the
roasting
sample.
tetragonal coordination.

Figure 6. XRD patterns of roasting samples at different roasting temperature. (A) Roasting at 650 ˝°C;
Figure 6. XRD patterns of roasting samples at different roasting temperature. (A) Roasting at 650 C;
(B) Roasting at 750 ˝°C; (C) Roasting at 850 °C;
(D) Roasting at 950 °C.
(B) Roasting at 750 C; (C) Roasting at 850 ˝ C; (D) Roasting at 950 ˝ C.

The crystal transformation relationship of muscovite (K(Al,V)2 [Si3 AlO10 ](OH)2 ), BaSi4 O9 ,
and Gehlenite (Ca2 Al2 SiO7 ) is shown in Figure 7. The crystalline structure of muscovite
(K(Al,V)2 [Si3 AlO10 ](OH)2 ) is a monoclinic crystal system, and the unit cell parameters are:
a = 0.5193 nm, b = 0.9045 nm, c = 2.0044 nm, α = γ = 90˝ , and β = 95.8˝ . During the BaCO3 /CaO
composite additive roasting process, Si–O and Al–O bonds were broken. Meanwhile, the hexagonal
structure of BaSi4 O9 and the tetragonal structure of Gehlenite (Ca2 Al2 SiO7 ) were formed. The
crystalline structure of BaSi4 O9 is with the P3 space group and the unit cell parameters are
a = b = 1.1247 nm, c = 0.4485 nm, α = β = 90˝ , and γ = 120˝ . The Si–O oxides form a close circle
type array and surround Ba2+ ion with hexagonal coordination. The crystalline structure of Gehlenite
(Ca2 Al
is withtransformation
the P-421m space
group of
and
the unit(K(Al,V)
cell parameters
are 2a), =BaSi
b =4O0.7693
Figure
relationship
muscovite
2[Si3AlO10](OH)
9, and nm,
2 SiO77.) Crystal
˝ . roasting
the
process.
Gehlenite
c = 0.5072
nm,(Ca
α =2Al
β2SiO
= γ7)=in90
The Al3+
ion and the Si4+ ion are located at the same position in the
unit cell with different occupancy. The Al–Si–O oxides form a double close-packed type array with the
2+ through tetragonal coordination.
3.2.
Leaching
Process
inclusion
of Ca

3.2.1. Effect of Sulfuric Acid Concentration on Vanadium Leaching Efficiency
Effect of sulfuric acid concentration from 5% (v/v) to 25% (v/v) on the vanadium leaching
efficiency is shown in Figure 8, with fixing the BaCO3/CaO total weight at 5 wt %, the mass ratio of
BaCO3 to CaO at 1:9, the roasting temperature at 850 °C, the roasting time at 2 h, the leaching
temperature at 80 °C, and the liquid-to-solid ratio at 5 mL/g. When the sulfuric acid concentration
increased from 5% (v/v) to 25% (v/v) for 4 h, significant improvement of the vanadium leaching
efficiency could be achieved. The possible reasons were that the H+ concentration increased with the
increase of the sulfuric acid concentration, which could intensify the reaction with the target
minerals and the vanadium dissolution completely. Considering that the disadvantageous resulted

Figure
XRD patterns of roasting samples at different roasting temperature. (A) Roasting at 650 °C;7 of 14
Minerals
2016, 6.
6, 26
(B) Roasting at 750 °C; (C) Roasting at 850 °C; (D) Roasting at 950 °C.

Figure 7.
7. Crystal
Crystal transformation
transformationrelationship
relationshipofofmuscovite
muscovite(K(Al,V)
(K(Al,V)
2[Si
3AlO
](OH)22), BaSi
BaSi44O99,, and
2 [Si
3 AlO
1010](OH)
Gehlenite (Ca22Al
Al22SiO
SiO77) )ininthe
theroasting
roastingprocess.
process.

3.2. Leaching
3.2.
Leaching Process
Process
Vanadium Leaching
Leaching Efficiency
Efficiency
3.2.1. Effect of Sulfuric Acid Concentration on Vanadium
Effect of sulfuric
sulfuric acid
acid concentration
concentration from
from 5%
5% (v/v)
(v/v) to 25%
25% (v/v)
(v/v) on the vanadium leaching
total
weight
at at
5 wt
%,%,
thethe
mass
ratio
of
efficiency is shown
shown in
in Figure
Figure8,8,with
withfixing
fixingthe
theBaCO
BaCO3/CaO
/CaO
total
weight
5 wt
mass
ratio
3
˝ C,the
BaCO
3 to
CaO
at
1:9,
the
roasting
temperature
at
850
°C,
roasting
time
at
2
h,
the
of
BaCO
to
CaO
at
1:9,
the
roasting
temperature
at
850
the
roasting
time
at
2
h,
leaching
3
liquid-to-solid ratio
ratio at
at 55 mL/g.
mL/g. When the sulfuric acid concentration
temperature at 80 ˝°C,
C, and the liquid-to-solid
(v/v) to
(v/v) for
increased from 5% (v/v)
to 25% (v/v)
for 44 h,
h, significant
significant improvement
improvement of the vanadium leaching
+ concentration
that
thethe
H+Hconcentration
increased
withwith
the
efficiency could
could be
be achieved.
achieved.The
Thepossible
possiblereasons
reasonswere
were
that
increased
increase
of
the
sulfuric
acid
concentration,
which
could
intensify
the
reaction
with
the
the
increase
of
the
sulfuric
acid
concentration,
which
could
intensify
the
reaction
with
the
target
Minerals 2016, 6, 26
7 of 13
vanadium dissolution
dissolution completely.
completely. Considering
Considering that
that the
the disadvantageous
disadvantageous resulted
minerals and the vanadium
from the excessive acid consumption,
of the
the sulfuric
sulfuric acid concentration was selected. With
consumption, 15%
15% (v/v)
(v/v) of
the increase of the leaching time from 0.5 to 3 h, the vanadium leaching efficiency sharply increased
with the sulfuric
sulfuric acid
acid concentration
concentration at
at 15%
15% (v/v),
(v/v), but no significant increasement on the vanadium
leaching efficiency could be obtained with the leaching time at 4 h. Therefore, the optimum leaching
time should be 3 h.

Figure
Figure 8.
8. Effect
Effect of
of sulfuric
sulfuric acid
acid concentration
concentration on
on vanadium
vanadium leaching
leaching efficiency.
efficiency.

3.2.2. Effect of Leaching Temperature on Vanadium Leaching Efficiency
3.2.2. Effect of Leaching Temperature on Vanadium Leaching Efficiency
The effect of leaching temperature from 50 to 95 ˝°C on the vanadium leaching efficiency is
The effect of leaching temperature from 50 to 95 C on the vanadium leaching efficiency is
shown in Figure 9, with the sulfuric acid concentration at 15% (v/v) and the liquid-to-solid ratio at
shown in Figure 9, with the sulfuric acid concentration at 15% (v/v) and the liquid-to-solid ratio at
5 mL/g. When the leaching temperature increased from 50 to 95 °C for 4 h, the vanadium leaching
5 mL/g. When the leaching temperature increased from 50 to 95 ˝ C for 4 h, the vanadium leaching
efficiency improved continuously. The possible reasons could be that the viscosity of the reaction
efficiency improved continuously. The possible reasons could be that the viscosity of the reaction
system decreased with the increase of the leaching temperature. Therefore, the H+ diffusion rate
system decreased with the increase of the leaching temperature. Therefore, the H+ diffusion rate
increased, which promoted the accessibility and the reaction with the target minerals, and finally
improved the vanadium leaching efficiency. 88.50% of the vanadium leaching efficiency could be
obtained at 95 °C for 4 h. When the leaching time increased from 0.5 to 3 h at 95 °C, the maximum
vanadium leaching of 84.98% could be achieved. Thus, the optimum leaching temperature should be
95 °C, and the leaching time should be 3 h.

3.2.2. Effect of Leaching Temperature on Vanadium Leaching Efficiency
The effect of leaching temperature from 50 to 95 °C on the vanadium leaching efficiency is
shown in Figure 9, with the sulfuric acid concentration at 15% (v/v) and the liquid-to-solid ratio at
5Minerals
mL/g.2016,
When
6, 26the leaching temperature increased from 50 to 95 °C for 4 h, the vanadium leaching
8 of 14
efficiency improved continuously. The possible reasons could be that the viscosity of the reaction
system decreased with the increase of the leaching temperature. Therefore, the H+ diffusion rate
increased, which
which promoted
promoted the
the accessibility
accessibility and
and the
the reaction
reaction with
with the
the target
target minerals,
minerals, and
and finally
finally
increased,
improved
the
vanadium
leaching
efficiency.
88.50%
of
the
vanadium
leaching
efficiency
could
improved the vanadium leaching efficiency. 88.50% of the vanadium leaching efficiency could be
be
˝ C for 4 h. When the leaching time increased from 0.5 to 3 h at 95 ˝ C, the maximum
obtained
at
95
obtained at 95 °C for 4 h. When the leaching time increased from 0.5 to 3 h at 95 °C, the maximum
vanadium
leaching of
of 84.98%
vanadium leaching
84.98% could
could be
be achieved.
achieved. Thus,
Thus, the
the optimum
optimum leaching
leaching temperature
temperature should
should be
be
˝ C, and the leaching time should be 3 h.
95
95 °C, and the leaching time should be 3 h.

Figure
Figure 9.
9. Effect
Effect of
of leaching
leaching temperature
temperature on
on vanadium
vanadium leaching
leaching efficiency.
efficiency.

3.2.3.
of Roasting
Roasting Samples
Samples during
during the
the Leaching
Leaching Process
Process
3.2.3. Phase
Phase Transformation
Transformation of
The
phase transformation
transformation of
roasting samples
samples during
during the
the leaching
leaching process
process was
was investigated
investigated
The phase
of roasting
according
to
the
XRD
analysis
of
the
leaching
residuals
from
60
to
95
°C,
while
fixing
the sulfuric
according to the XRD analysis of the leaching residuals from 60 to 95 ˝ C, while fixing the sulfuric
acid
acid
concentration
at (v/v)
15% (v/v)
and
the leaching
time
at 3The
h. The
XRD
patterns
are shown
in Figure
10.
concentration
at
15%
and
the
leaching
time
at
3
h.
XRD
patterns
are
shown
in
Figure
10.
The
Minerals
2016, 6,indicated
26
8 of 13
The
results
that
the
calcite
and
hematite
crystalline
phases
in
the
roasting
samples
results indicated that the calcite and hematite crystalline phases in the roasting samples disappeared,
disappeared,
while the
diffraction
peaks of phases
the crystalline
phases
of quartz,
BaSi4O9, and Gehlenite,
while
diffraction
of the crystalline
quartz,
BaSi
and Gehlenite,
left
4 O9 , the
whichthe
were
left inpeaks
the leaching
residue, were ofintensified
with
increase ofwhich
the were
leaching
˝ C.
in
the
leaching
residue,
were
intensified
with
the
increase
of
the
leaching
temperature
from
60
to
95
temperature from 60 to 95 °C. The reasons were probably that the calcite and hematite reacted with
The
reasons
that
thethe
calcite
and hematite
with sulfuric
acid
and dissolved
into
sulfuric
acidwere
andprobably
dissolved
into
solution
during reacted
the leaching
process,
whereas
the quartz,
the
the were
leaching
process, whereas the quartz, BaSi4 O9 , and Gehlenite were inactive.
BaSisolution
4O9, andduring
Gehlenite
inactive.

Figure 10.
10. XRD
of leaching
leaching samples
samples at
at different
different leaching
leaching temperature.
temperature. (A)
(A) Leaching
Leaching at
at 60
60 ˝°C;
Figure
XRD patterns
patterns of
C;
˝ C; (D)
˝ C.
(B) Leaching
Leaching at
at 70
70 ˝°C;
(B)
C; (C)
(C) Leaching
Leaching at
at 80
80 °C;
(D) Leaching
Leaching at
at 95
95 °C.

The BEI and EDS elemental distribution of leaching residual is shown in Figure 11. The results
The BEI and EDS elemental distribution of leaching residual is shown in Figure 11. The results
indicated that the element distribution of O, Si, Ba, and Ca had obvious relevance. Combined with
indicated that the element distribution of O, Si, Ba, and Ca had obvious relevance. Combined with the
the XRD analysis of the leaching residual, the BaSi4O9 and Gehlenite indeed existed after the
XRD analysis of the leaching residual, the BaSi4 O9 and Gehlenite indeed existed after the BaCO3 /CaO
BaCO3/CaO composite additive roasting and leaching process. Meanwhile, the relevance of V, O, Ba,
composite additive roasting and leaching process. Meanwhile, the relevance of V, O, Ba, and Ca in
and Ca in the leaching residue indicated that the vanadium in the leaching residue was probably in
the form of vanadate or pyrovanadate of barium and calcium, which were hardly extracted during
the sulfuric acid leaching process.

Figure 10. XRD patterns of leaching samples at different leaching temperature. (A) Leaching at 60 °C;
(B) Leaching at 70 °C; (C) Leaching at 80 °C; (D) Leaching at 95 °C.

The BEI and EDS elemental distribution of leaching residual is shown in Figure 11. The results
indicated
that
Minerals 2016,
6, 26the element distribution of O, Si, Ba, and Ca had obvious relevance. Combined9 with
of 14
the XRD analysis of the leaching residual, the BaSi4O9 and Gehlenite indeed existed after the
BaCO3/CaO composite additive roasting and leaching process. Meanwhile, the relevance of V, O, Ba,
the
indicated
the vanadium
the leaching
residue
wasresidue
probably
in probably
the form of
andleaching
Ca in theresidue
leaching
residuethat
indicated
that the in
vanadium
in the
leaching
was
in
vanadate
or
pyrovanadate
of
barium
and
calcium,
which
were
hardly
extracted
during
the
the form of vanadate or pyrovanadate of barium and calcium, which were hardly extractedsulfuric
during
acid
leachingacid
process.
the sulfuric
leaching process.

Figure
11. (a)
elemental distribution:
distribution: (b)
Si; (d)
(d) V;
V; (e)
(e) Ba;
Ba; (f)
(f) Ca.
Ca.
Figure 11.
(a) BEI
BEI of
of leaching
leaching residual,
residual, EDS
EDS elemental
(b) O;
O; (c)
(c) Si;

3.3. Kinetic Analysis
3.3. Kinetic Analysis
Assuming that the particles are spherical, the reaction is irreversible and the loose ash layers
Assuming that the particles are spherical, the reaction is irreversible and the loose ash layers
could form after the reaction. The experimental data could be analyzed using the shrinking core
could form after the reaction. The experimental data could be analyzed using the shrinking core model
model (SCM) [17]. The shrinking core model considers that the rate-controlling step of the leaching
(SCM) [17]. The shrinking core model considers that the rate-controlling step of the leaching process is
process is either the diffusion of the reactant through the solution boundary, or through a solid
either the diffusion of the reactant through the solution boundary, or through a solid product layer, or
product layer, or the surface chemical reaction [18].
the surface chemical reaction [18].
As the shrinking core model (SCM) is valid only for mono-sized particles, the practical way of
As the shrinking core model (SCM) is valid only for mono-sized particles, the practical way of
doing the kinetic analysis is by limiting the particle size to a narrow size. Therefore, we divided the
doing the kinetic analysis is by limiting the particle size to a narrow size. Therefore, we divided the
roasting sample into three particle size fractions: 0.038–0.044, 0.044–0.075, and 0.075–0.106 mm. The
roasting sample into three particle size fractions: 0.038–0.044, 0.044–0.075, and 0.075–0.106 mm. The
effect of particle size on the vanadium leaching efficiency is shown in Figure 12. It could be seen
effect of particle size on the vanadium leaching efficiency is shown in Figure 12. It could be seen that
that the vanadium leaching efficiency increased with the decrease of the particle size. A shrinking
the vanadium
leaching efficiency increased with the decrease of the particle size. A shrinking9 core
Minerals
2016, 6,(SCM)
26
of 13
core model
was utilized to analyze the experimental data (Figure 13). The linear relation
model (SCM) was utilized to analyze the experimental data (Figure 13). The linear relation between the
reaction rate
inverse
initial
d´1 confirmed
the reactionthat
ratethe
controlling
0 and therate
between
the kreaction
k0 and
the particle
inverse diameter
initial particle
diameter that
d−1 confirmed
reaction
step controlling
was probably
the
diffusion
through
a solid product
(Figure
14).layer (Figure 14).
rate
step
was
probably
the diffusion
throughlayer
a solid
product

Figure 12. Effect of particle size on vanadium leaching efficiency.
Figure 12. Effect of particle size on vanadium leaching efficiency.

Minerals 2016, 6, 26

10 of 14

Figure 12. Effect of particle size on vanadium leaching efficiency.
Figure 12. Effect of particle size on vanadium leaching efficiency.

2/3
Figure
Fitting
plots
1 − 2α/3´− (1
(1 − α)
leaching
time
Figure
13.13.
Fitting
plots
of of

α)2/32/3versus
versus
leaching
timet at
t atdifferent
differentparticle
particlesizes.
sizes.
Figure
13.
Fitting
plots
of
1 −2α/3
2α/3 − (1 −´α)
versus
leaching
time
t at
different
particle
sizes.

Figure 14. Fitting plot of k0 as a function of d−1.
−1.
Figure14.
14.Fitting
Fittingplot
plotofofkk0as
asaafunction
functionof
ofdd´1
Figure
.
0

In order to determine if the mass transfer was the possible rate-controlling step, the effect of
In order
toatdetermine
if the
mass
transfer
was
the possible
rate-controlling
step,
the effect
of
stirring
speedto
600, 800, and
1000
rpm
on thewas
vanadium
leaching
efficiency was
studied.
It was
In order
determine
if the
mass
transfer
the possible
rate-controlling
step,
the effect
of
stirring
speed
at
600,
800,
and
1000
rpm
on
the
vanadium
leaching
efficiency
was
studied.
It
was
found that
the at
stirring
speed
a slight
effect
the vanadium
leaching
efficiency.
Therefore,
the
stirring
speed
600, 800,
andhad
1000
rpm on
the on
vanadium
leaching
efficiency
was studied.
It was
found
that
the
stirring
speed
had
a
slight
effect
on
the
vanadium
leaching
efficiency.
Therefore,
the
following
investigations
theon
diffusion
throughleaching
a solid efficiency.
product and
the surface
found
thatkinetic
the stirring
speed hadfocused
a slight on
effect
the vanadium
Therefore,
the
following
kinetic investigations focused on the diffusion through a solid product and the surface
chemical
reaction.
following kinetic investigations focused on the diffusion through a solid product and the surface
chemical reaction.
chemical reaction.
As for the vanadium leaching process, if the process is controlled by the chemical reaction, the
following expression of shrinking core model could be used to describe the vanadium dissolution
kinetics of the process [18,19]:
1 ´ p1 ´ αq1{3 “ k1 t
(2)
Similarly, when the diffusion of the reagent (sulfuric acid) through a product layer is the
controlling step, the following expression of the shrinking core model could be used [18,19]:
2
1 ´ α ´ p1 ´ αq2{3 “ k2 t
3

(3)

where α is the vanadium leaching efficiency (wt %); k1 and k2 are the rate constants of the chemical
reaction and the diffusion through a product layer, respectively; and t is the leaching time (h).
Based on the experimental results provided in Figure 9, a fitting plot of 1 ´ (1 ´ α)1/3 vs. t is
given in Figure 15. It can be seen that the linear correlation was relatively low, indicating that the
vanadium leaching reaction was probably not controlled by the chemical reaction.

where α is the vanadium leaching efficiency (wt %); k11 and k22 are the rate constants of the chemical
reaction and the diffusion through a product layer, respectively; and t is the leaching time (h).
1/3
Based on the experimental results provided in Figure 9, a fitting plot of 1 − (1 − α)1/3
vs. t is given
in Figure
15.
It
can
be
seen
that
the
linear
correlation
was
relatively
low,
indicating
that
Minerals 2016, 6, 26
11 of
14 the
vanadium leaching reaction was probably not controlled by the chemical reaction.

1/31/3
1/3
Figure
15.15.
Fitting
plots
versus
differentleaching
leaching
temperatures.
Figure
Fitting
plotsofof11−´(1(1−´α)α)
versusleaching
leachingtime
time tt at
at different
temperatures.

2/3 vs.
2/3
A fitting
plotplot
of 1of− 12α/3
− (1´− (1
α)´
t is
in Figure
16. It
be observed
that
the
linear
A fitting
´ 2α/3
α)2/3
vs.shown
t is shown
in Figure
16.can
It can
be observed
that
the
correlation
was great
during
the whole
leaching
time,
indicating
theleaching
leaching
process
linear correlation
was
great during
the whole
leaching
time,
indicating that
that the
process
was was
controlled
by the
diffusion
throughaaproduct
product layer.
layer.
controlled
by the
diffusion
through

2/3 versus leaching time t at different leaching temperatures.
Figure
16. Fitting plots of 1 − 2α/3 − (1 − α)2/3
Figure 16. Fitting plots of 1 ´ 2α/3 ´ (1 ´ α)2/3 versus leaching time t at different leaching temperatures.

3.3.1.3.3.1.
Calculation
of Reaction
Orders
Calculation
of Reaction
Orders
2/3 2/3
A fitting
plotplot
of 1of−12α/3
− (1´−(1α)´2/3
respect
to the
leaching
time
under the
A fitting
´ 2α/3
α)withwith
respect
to the
leaching
time(t)(t)was
wasobtained
obtained under
different
sulfuric
acid
concentrations.
From
the
slopes
of
the
fitting
lines
in
Figure
17,
the
apparent
the different sulfuric acid concentrations. From the slopes of the fitting lines in Figure 17, the apparent
rate constant
(k) values
were
determined.AAfitting
fittingplot
plot of
of lnk
lnk vs.
vs. ln[H
ln[H222SO
rate constant
(k) values
were
determined.
SO444]] is
is shown
shownininFigure
Figure1818 to

to achieve the order of dependency with respect to the sulfuric acid concentration. The result from
the slope of the fitting line indicated that the empirical reaction order with respect to the sulfuric
concentration is 1.1059.

Minerals 2016, 6, 26
Minerals 2016, 6, 26

11 of 13
11 of 13

achieve the order of dependency with respect to the sulfuric acid concentration. The result from the
achieve2016,
the
of line
dependency
with
to the sulfuric
acidorder
concentration.
The to
result
the
slope
the6,order
fitting
indicated
thatrespect
the empirical
reaction
with respect
the from
sulfuric
Mineralsof
26
12 of 14
slope
of
the
fitting
line
indicated
that
the
empirical
reaction
order
with
respect
to
the
sulfuric
concentration is 1.1059.
concentration is 1.1059.

Figure 17. Fitting plots of 1 − 2α/3 − (1 − α)2/3 versus
leaching time t at different sulfuric acid concentrations.
Figure 17. Fitting plots of 1 ´ 2α/3 ´ (1 ´ α)2/3 versus leaching time t at different sulfuric acid concentrations.
Figure 17. Fitting plots of 1 − 2α/3 − (1 − α)2/3 versus leaching time t at different sulfuric acid concentrations.

Figure 18. Fitting plot of lnk as a function of ln[H2SO4].
Figure 18. Fitting plot of lnk as a function of ln[H2SO4].
Figure 18. Fitting plot of lnk as a function of ln[H2 SO4 ].

3.3.2. Calculation of Apparent Activation Energy
3.3.2. Calculation of Apparent Activation Energy
3.3.2.According
Calculation
Apparent
Activation
toofthe
slopes of
the fittingEnergy
lines in Figure 16, the apparent rate constant (k2) values
According
to the
slopesplot
of the
fitting
in Figure 16, theinapparent
rate
constant
(k2) values
wereAccording
obtained and
a
fitting
of
lnk
2 vs.lines
Figure
With
the
the
to the slopes of the fitting lines1/(1000T)
in Figureis16,shown
the apparent
rate19.
constant
(k2 ) slope
valuesofwere
were
obtained
and
a
fitting
plot
of
lnk
2
vs.
1/(1000T)
is
shown
in
Figure
19.
With
the
slope
of
the
fitting
line
above,
the plot
apparent
energy
(E) could
be calculated
the
obtained
and
a fitting
of lnk2activation
vs. 1/(1000T)
is shown
in Figure
19. Withas
the46.51
slopekJ/mol
of the by
fitting
fitting
line
above,
the
apparent
activation
energy
(E)
could
be
calculated
as
46.51
kJ/mol
by
the
Arrhenius
as follows:
line above,equation
the apparent
activation energy (E) could be calculated as 46.51 kJ/mol by the Arrhenius
Arrhenius equation as follows:
equation as follows:
ln k = − E / ( RT ) + ln A
(4)
(4)
lnlnk
k =“−´E{pRTq
E / ( RT`) +lnA
ln A
(4)
Meanwhile, the reaction constant (A) could also calculated as 1.5374 × 1055 with the intercept of
5 with the
Meanwhile,
the
constant
could
calculated
as
of
Meanwhile,
the reaction
reaction
constant (A)
(A)
could also
also
calculated
as1.5374
1.5374ˆ
× 10
10
the intercept
intercept
the fitting
line. Therefore,
the vanadium
leaching
kinetic
model controlled
by
thewith
diffusion
throughof
a
the
fitting
line.
Therefore,
the
vanadium
leaching
kinetic
model
controlled
by
the
diffusion
through
the fitting
line.could
Therefore,
the vanadium
leaching kinetic model controlled by the diffusion through aa
product
layer
be expressed
as follows:
product
product layer
layer could
could be
be expressed
expressed as
as follows:
follows:

2
1.1059
1 − 2 α −2 (1 − α) 2/3
=2{3(1.5374 × 1055 )5[ H 2 SO4 ]1.1059
exp [ −46510 / ( RT ) ] t
2/3
“ p1.5374
ˆ 10) [q H
rH2SO
SO4 s]1.1059 exp
t )] t
1 − 31 ´
α −3 α(1´−p1α)´ αq= (1.5374
× 10
expr´46510{pRTqs
[ −46510 / ( RT
2
4
3

(5)
(5)
(5)

2KAl pSiO3 q2 ` 4H2 SO4 Ñ 4H2 SiO3 ` K2 SO4 ` Al2 pSO4 q3

(6)

The
The leaching
leaching system
system for
for the
the vanadium
vanadium recovery
recovery from
from the
the refractory
refractory stone
stone coal
coal was
was very
very
The
leaching
system
for
the
vanadium
recovery
from
the
refractory
stone
coal
was
very
complicated,
because
vanadium
existed
in
the
mica
(a
kind
of
aluminosilicate)
of
this
stone
coal.
complicated, because vanadium existed in the mica (a kind of aluminosilicate) of this stone coal.
complicated,
because
vanadium
existed
in
the
mica
(a
kind
of
aluminosilicate)
of
this
stone
coal.
The
indicated that
activation energy
a chemical
chemical reaction
reaction was
was
The typical
typical kinetic
kinetic theory
theory [20]
[20] indicated
that the
the activation
energy for
for a
The typical
kinetic
theory energy
[20] indicated
that the activation
energyIn
forthis
a chemical
reaction
was
>40
kJ/mol,
and
the
activation
for
a
diffusion
was
<40
kJ/mol.
study,
the
activation
>40 kJ/mol, and the activation energy for a diffusion was <40 kJ/mol. In this study, the activation
>40
kJ/mol,
and
the
activation
energy
for
a
diffusion
was
<40
kJ/mol.
In
this
study,
the
activation
energy
was calculated
calculated as
as 46.51
46.51 kJ/mol.
kJ/mol. Our
reaction
energy was
Ourresearch
research team
team [21]
[21] concluded
concluded that
that there
there is
is aa reaction
energy was
calculated as 46.51
kJ/mol.
Our
research
teamas[21]
concluded that there is a reaction
between
the
aluminosilicate
in
stone
coal
and
sulfuric
acid
follows:
between the aluminosilicate in stone coal and sulfuric acid as follows:
between the aluminosilicate in stone coal and sulfuric acid as follows:

Minerals 2016, 6, 26
Minerals 2016, 6, 26

12 of 13

2KAl ( SiO3 )2 + 4H 2SO 4 → 4H 2SiO3 + K 2SO 4 + Al 2 ( SO 4 )3

13 of 14

(6)

The
is insoluble
SiO33 is
insoluble and
and very
very compact,
compact, which
which will
will cover
cover the
the surface
surface of
of the
the
The production
production of
of H
H22SiO
reaction
particle
and
significantly
increase
the
resistance
of
diffusion.
This
is
why,
although
reaction particle and significantly increase the resistance of diffusion. This is why, although the
the
activation
leaching
process
was
stillstill
controlled
by the
diffusion
through
the
activationenergy
energywas
wasvery
veryhigh,
high,the
the
leaching
process
was
controlled
by the
diffusion
through
product
layer.
The
reaction
mechanisms
in
this
study
were
similar
to
the
“Shrinking
Core–Shrinking
the product layer. The reaction mechanisms in this study were similar to the “Shrinking Core–Shrinking
Particle”
Particle” model
model used
used by
by Safari
Safarietetal.
al.[22],
[22],and
andititwas
wasalso
alsoillustrated
illustratedand
andproved
provedby
byJu
Juetetal.
al.[19].
[19].

Figure19.
19.Arrhenius
Arrheniusfitting
fittingplot
plotofoflnk
lnk2as
asaafunction
functionof
of1/(1000T).
1/(1000T).
Figure
2

4. Conclusions
4. Conclusions

The novel BaCO3/CaO composite additive roasting and acid leaching technology was proved

The novel BaCO3 /CaO composite additive roasting and acid leaching technology was proved to
to be feasible for the vanadium recovery from refractory stone coal.
be feasible for the vanadium recovery from refractory stone coal.

According to the phase transformation analysis, the monoclinic crystalline structure of
According to the phase transformation analysis, the monoclinic crystalline structure of muscovite

muscovite (K(Al,V)2[Si3AlO10](OH)2) was converted into the hexagonal crystalline structure of
(K(Al,V)2 [Si3 AlO10 ](OH)2 ) was converted into the hexagonal crystalline structure of BaSi4 O9
BaSi4O9 and the tetragonal crystalline structure of Gehlenite (Ca2Al2SiO7) during the composite
and the tetragonal crystalline structure of Gehlenite (Ca2 Al2 SiO7 ) during the composite additive
additive BaCO3/CaO roasting process, which could, therefore, facilitate the release and
BaCO3 /CaO roasting process, which could, therefore, facilitate the release and extraction of
extraction of vanadium. Vanadium in leaching residue was probably in the form of vanadate or
vanadium. Vanadium in leaching residue was probably in the form of vanadate or pyrovanadate
pyrovanadate of barium and calcium, which were hardly extracted during the sulfuric acid
of barium and calcium, which were hardly extracted during the sulfuric acid leaching process.
leaching process.
According to the vanadium leaching kinetic analysis, the process was controlled by the diffusion


According to the vanadium leaching kinetic analysis, the process was controlled by the
through a product layer. The apparent activation energy could be achieved as 46.51 kJ/mol.
diffusion through a product layer. The apparent activation energy could be achieved as
The reaction order with respect to the sulfuric acid concentration was 1.1059. The kinetic model
46.51 kJ/mol. The reaction order with respect to the sulfuric acid concentration was 1.1059. The
of vanadium recovery from stone coal using novel composite additive BaCO3 /CaO could be
kinetic model of vanadium recovery from stone coal using novel composite additive
finally established.
BaCO3/CaO could be finally established.
Acknowledgements: This work was financially supported by the National Natural Science Foundation of
Acknowledgments:
Thisand
work
was financially
supported
theTechnology
National Natural
Science
Foundation
of China
China (Nos. 51474162
51404174),
and the
Science by
and
Research
Program
of Ministry
of
(Nos. 51474162 and 51404174), and the Science and Technology Research Program of Ministry of Education of
Education
of
China
(No.
213025A).
China (No. 213025A).
Author Contributions:
Contributions: Zhenlei
Zhenlei Cai
Cai and
and Yimin
Yimin Zhang
Zhangconceived
conceived and
and designed
designed the
the experiments;
experiments; Zhenlei
Zhenlei Cai
Cai
Author
performed the
the experiments;
experiments; Zhenlei
Zhenlei Cai
Cai analyzed
analyzed the
the data;
data; Yimin Zhang,
Zhang, Tao
Tao Liu,
Liu,and
andJing
JingHuang
Huangcontributed
contributed
performed
reagents/materials/analysis
tools;Zhenlei
ZhenleiCai
Caiwrote
wrotethe
thepaper.
paper.
reagents/materials/analysis tools;
Conflicts
Conflictsof
ofInterest:
Interest:The
Theauthors
authorsdeclare
declareno
noconflict
conflictof
ofinterest.
interest.

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© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons by Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).


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