minerals
Article
Optimal Location of Vanadium in Muscovite and
Its Geometrical and Electronic Properties by
DFT Calculation
Qiushi Zheng 1,2,3 , Yimin Zhang 1,2,3, *, Tao Liu 1,2,3 , Jing Huang 1,2,3 , Nannan Xue 1,2 and
Qihua Shi 1,2
1
2
3
*
School of Resource and Environmental Engineering, Wuhan University of Science and Technology,
Wuhan 430081, China; [email protected] (Q.Z.); [email protected] (T.L.);
[email protected] (J.H.); [email protected] (N.X.); [email protected] (Q.S.)
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: [email protected]; Tel.: +86-27-6886-2057
Academic Editor: Shifeng Dai
Received: 26 December 2016; Accepted: 17 February 2017; Published: 24 February 2017
Abstract: Vanadium-bearing muscovite is the most valuable component of stone coal, which is a unique
source of vanadium manufacture in China. Numbers of experimental studies have been carried out to
destroy the carrier muscovite’s structure for efficient extraction of vanadium. Hence, the vanadium
location is necessary for exploring the essence of vanadium extraction. Although most infer that
vanadium may substitute for trivalent aluminium (Al) as the isomorphism in muscovite for the similar
atomic radius, there is not enough experimental evidence and theoretical supports to accurately locate
the vanadium site in muscovite. In this study, the muscovite model and optimal location of vanadium
were calculated by density functional theory (DFT). We find that the vanadium prefers to substitute
for the hexa-coordinated aluminum of muscovite for less deformation and lower substitution energy.
Furthermore, the local geometry and relative electronic properties were calculated in detail. The basal
theoretical research of muscovite contained with vanadium are reported for the first time. It will make
a further influence on the technology development of vanadium extraction from stone coal.
Keywords: vanadium; muscovite; stone coal; substitution; geometry; electronic property; DFT
1. Introduction
Vanadium (V), as a steel alloy additive, is widely used in refining high-strength steels,
titanium–aluminum alloys and oxidation catalysts [1], whilst its polyvalence gives it potential for
development of a vanadium redox battery [2,3]. In China, V-bearing stone coal is a significant source to
product vanadium compounds. The gross reserves of stone coal in China are about 61.88 billion tons,
in which the V grade generally ranges from 0.01% to 1.3% [1,4]. The process mineralogy shows that the
main minerals in stone coal include quartz (SiO2 ), muscovite (KAl2 (Si3 Al)O10 (OH)2 ), calcite (CaCO3 ),
and pyrite (FeS2 ). Most V in stone coal exists in the dioctahedral sheet of mica-group minerals, such as
muscovite [5]. Most investigations of V extraction from stone coal essentially aim to destroy the
structure of muscovite to liberate V. In the traditional process, roasting and leaching play a significant
role in increasing the leaching rate of V, while the mechanism study of them needs to clarify the
target site of the high temperature destruction and hydrion exchange. The accurate location of V in
muscovite lattice is indispensable for further exploring the essence of V extraction from stone coal.
Many V-extracting experiments of stone coal have put forward the inference that V may substitute
Minerals 2017, 7, 32; doi:10.3390/min7030032
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trivalent aluminium (Al) as the isomorphism in muscovite, based on the similar ratio of charge to
atomic radius [6,7], which is similar to the cation substitutions of Al3+ by Mg2+ and Fe3+ in the
Mineralssheet.
2017, 7, 32
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octahedral
However, there is not enough evidence to sustain this point in direct experimental
characterization or instrument tests, due to the complexity of natural V-bearing muscovite, which is
(Al) as the isomorphism in muscovite, based on the similar ratio of charge to
finelytrivalent
grainedaluminium
and poorly
crystallized in stone coal [8]. Therefore, the introduction of simulating
atomic radius [6,7], which is similar to the cation substitutions of Al3+ by Mg2+ and Fe3+ in the
calculation by quantum chemistry makes it possible to distinguish the optimal location of V and obtain
octahedral sheet. However, there is not enough evidence to sustain this point in direct experimental
the related
physical and chemical properties.
characterization or instrument tests, due to the complexity of natural V-bearing muscovite, which is
In
recent
years,and
thepoorly
ab initio
methodsinorstone
density
theory
with periodic
boundary
finely
grained
crystallized
coalfunctional
[8]. Therefore,
the(DFT)
introduction
of simulating
conditions
and by
pseudopotential
havemakes
applied
to the study
of crystallographic,
elastic of
and
thermal
calculation
quantum chemistry
it possible
to distinguish
the optimal location
V and
properties
aluminosilicate
Especially,
surfaces and interlayers of phyllosilicate were studied
obtainofthe
related physical[9–12].
and chemical
properties.
In recent years,
the ab The
initioquantum
methods or
density functional
theory
(DFT)
with periodic
by DFT calculations
[13–15].
chemical
calculations
can
identify
the mostboundary
steady state
conditionsthe
andtotal
pseudopotential
have applied
to the study
of crystallographic,
elastic and
thermal
by comparing
energies of different
structures,
and analyzing
the interaction
between
V and
properties
of aluminosilicate
[9–12].
Especially,
surfaces
and interlayers
of phyllosilicate
were
oxygen
in the lattice,
which further
affects
the related
physical
and chemical
properties
ofstudied
muscovite.
by DFT calculations [13–15]. The quantum chemical calculations can identify the most steady state
In this paper, we presented a detailed DFT study of muscovite modified by the substitution of V,
by comparing the total energies of different structures, and analyzing the interaction between V and
and resolved its optimal location in the view of energy and local structure. In addition to its reliable
oxygen in the lattice, which further affects the related physical and chemical properties of muscovite.
crystallography,
we also
the
difference
the muscovite’s
properties
and theofbond
In this paper,
werevealed
presented
a detailed
DFTofstudy
of muscoviteelectronic
modified by
the substitution
natureV,as
the
V
exists.
Hence,
it
can
provide
a
theoretical
basis
and
experimental
instruction
for further
and resolved its optimal location in the view of energy and local structure. In addition to its reliable
destruction
of
V–O
bond
and
the
process
of
V
dissolution
from
muscovite.
crystallography, we also revealed the difference of the muscovite’s electronic properties and the bond
nature as the V exists. Hence, it can provide a theoretical basis and experimental instruction for
2. Methods
further destruction of V–O bond and the process of V dissolution from muscovite.
2.1. Structure
and Models
2. Methods
Initial atomic coordinates for the crystal structure of muscovite is taken from the Catti et al. [16]
2.1. Structure and Models
basing on powder neutron diffraction, where the lattice parameters are a = 5.2108 Å, b = 9.0399 Å,
atomic
for the
crystal
structure
of muscovite
is taken from
the Catti
et al. [16]
c = 20.021Initial
Å, and
β =coordinates
95.76◦ . The
ideal
chemical
formula
of muscovite
is KAl
2 (Si3 Al)O10 (OH)2 .
basing on powder neutron diffraction, where the lattice parameters are a = 5.2108 Å, b = 9.0399 Å, c =
The unit cell of muscovite is stacked by two 2:1 layers, which contains two tetrahedral sheets (T)
20.021 Å, and β = 95.76°. The ideal chemical formula of muscovite is KAl2(Si3Al)O10(OH)2. The unit
and one octahedral sheet (O) (Figure 1a) [13,16]. The tetrahedral sheet consists of many SiO4 units
cell of muscovite is stacked by two 2:1 layers, which contains two tetrahedral sheets (T) and one
bonded
with each
by the1a)
triangular
basal
oxygens
of the
tetrahedron.
Six4 units
SiO4 bonded
units form
octahedral
sheetother
(O) (Figure
[13,16]. The
tetrahedral
sheet
consists
of many SiO
a ringwith
of quasi-hexagonal
symmetry
(Figure
1b).
Then,
those
quasi-hexagonal
rings
bond
with each
each other by the triangular basal oxygens of the tetrahedron. Six SiO4 units form a ring of quasiother,hexagonal
forming symmetry
a plane of(Figure
infinite1b).
extension.
The
central
atoms
of
O
sheets
are
six-coordinated
Then, those quasi-hexagonal rings bond with each other, formingwith
octahedron
detail, the
octahedral
polyhedron
is formed
by four oxygens,
belong to
a planegeometry.
of infiniteIn
extension.
The
central atoms
of O sheets
are six-coordinated
withwhich
octahedron
geometry.
In detail,
thetwo
octahedral
formed bygroups
four oxygens,
which belong
to the apices
the apices
of T sheets
and
verticespolyhedron
which areishydroxyl
in the center
of the quasi-hexagonal
T sheets
and two
which are
hydroxyl groups
in the
the quasi-hexagonal
ring. The are
ring. of
The
muscovite
is vertices
dioctahedral
phyllosilicate
series
andcenter
only of
two-thirds
of the octahedron
muscovite
is
dioctahedral
phyllosilicate
series
and
only
two-thirds
of
the
octahedron
are
occupied
occupied in O sheets. Meanwhile, the presence of substitution of Al(III) for the quarter ofinSi(IV)
O sheets. Meanwhile, the presence of substitution of Al(III) for the quarter of Si(IV) (tetravalent
(tetravalent silicium) results in a net negative charge that is compensated by a sheet of K cations
silicium) results in a net negative charge that is compensated by a sheet of K cations between two
between two layers. All sheets are parallel to the (001) plane. Thus, it is necessary to build a muscovite
layers. All sheets are parallel to the (001) plane. Thus, it is necessary to build a muscovite model with
modelexplicit
with explicit
arrangement
of Al for comprehensive
of V substitution.
arrangement
of Al for comprehensive
investigationinvestigation
of V substitution.
Figure 1. The structure of (a) unit cell and (b) quasi-hexagonal ring of SiO4 units.
Figure 1. The structure of (a) unit cell and (b) quasi-hexagonal ring of SiO4 units.
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The
The isomorphic
isomorphic substitutions
substitutions in
in 2:1 dioctahedral
dioctahedral phyllosilicates
phyllosilicates show
show a considerable
considerable short-range
short-range
order
but
no
long-range
order
[17,18].
Previous
theoretical
and
experimental
studies
on
order but no long-range order [17,18]. Previous theoretical and experimental studies on muscovite
muscovite
found
ordered distribution
distributionofofthe
thecations
cationsinin
T sheet
with
Loewenstein
Al-avoidance
found an ordered
thethe
T sheet
with
the the
Loewenstein
Al-avoidance
rule
rule
[19–21].
distribution
investigated
by combining
quantum
mechanics
methods
[19–21].
ThisThis
distribution
was was
also also
investigated
by combining
quantum
mechanics
methods
with
with
empirical
models
to reduce
number
differentatomic
atomicconfigurations,
configurations,which
which consume vast
empirical
models
to reduce
thethe
number
of of
different
vast
computing
computing resources
resources [22,23].
[22,23]. In many pieces of literature, the arrangements
arrangements are often
often presumed
presumed
without
without direct
direct supporting
supporting evidence
evidence [24].
[24]. For
For getting
getting the reliable
reliable muscovite
muscovite model,
model, we
we elucidated
elucidated any
such
such effects
effects by
by comparing
comparing several
several Al
Al arrangements.
arrangements.
Considering
cell
of muscovite
withwith
84 atoms,
doubling
the size
the supercell
would
Consideringthe
theone
oneunit
unit
cell
of muscovite
84 atoms,
doubling
theofsize
of the supercell
make
DFT
calculations
prohibitively
expensive.
We
consequently
used
one
unit
cell
for
muscovite
would make DFT calculations prohibitively expensive. We consequently used one unit cell for
model
calculations.
In order to build
theto
conventional
unit cell, weunit
assumed
an assumed
equal tetra-coordinated
muscovite
model calculations.
In order
build the conventional
cell, we
an equal tetraIV ) concentration
aluminum
(Al
in each layer.inNamely,
there
is only one
to distribute
among
four
coordinated
aluminum
(AlIV) concentration
each layer.
Namely,
thereAlisIVonly
one AlIV to
distribute
sites
in
T
sheets.
For
simplicity,
we
artificially
rebuilt
the
crystal
symmetry
in
the
models,
in
which
the
among four sites in T sheets. For simplicity, we artificially rebuilt the crystal symmetry in the models,
IV
Al
substitute
insubstitute
the form of
center-symmetry
(Figure 2a).(Figure
Albeit2a).
maintaining
symmetrysymmetry
does not
in which
the AlIV
in the
form of center-symmetry
Albeit maintaining
consider
all
possible
aluminum
distributions
in
the
real
minerals,
it
is
a
good
initial
model
compared
does not consider all possible aluminum distributions in the real minerals, it is a good initial model
to
experimental
observations.
Finally, there
are sixteen
to elect the optimal
compared
to experimental
observations.
Finally,
there calculation
are sixteen configurations
calculation configurations
to elect
muscovite
the optimalmodel.
muscovite model.
Figure 2. (a) The AlIV substitution abided by center-symmetry; (b) the label of upper surface and lower
Figure 2. (a) The AlIV substitution abided by center-symmetry; (b) the label of upper surface and lower
surface beside interlayer.
surface beside interlayer.
Then, a 2 × 1 × 1 supercell containing 168 atoms was generated by the unite cell of the optimal
Then, model.
a 2 × The
1 × V1 substitution
supercell containing
168 atoms
was generated
unite cell
of the
muscovite
was achieved
by replacing
Si or Al inbythethe
supercell.
Thus,
we
optimal
muscovite
model.
The
V
substitution
was
achieved
by
replacing
Si
or
Al
in
the
supercell.
considered three categories for V substitution: (a) octahedral Al; (b) tetrahedral Al; and (c) tetrahedral
Thus,
categories
for V substitution:
octahedrallow
Al; level,
(b) tetrahedral
Al;
Si. Thewe
V considered
substitutionthree
in the
actual muscovite
presents at(a)
a relatively
and we only
and
(c)
tetrahedral
Si.
The
V
substitution
in
the
actual
muscovite
presents
at
a
relatively
low
level,
and
we
substituted the single 2:1 layer with one V atom. Thus, we identified the optimal location of V.
only substituted the single 2:1 layer with one V atom. Thus, we identified the optimal location of V.
2.2. DFT Calculations
2.2. DFT Calculations
The DFT calculations were performed with the Vienna ab initio simulation package (VASP)
The DFT calculations were performed with the Vienna ab initio simulation package
developed for periodical systems [25,26]. The exchange-correlation functional used the Perdew(VASP) developed for periodical systems [25,26]. The exchange-correlation functional used the
Burke-Ernzerhof (PBE)-version of the generalized gradient approximation (GGA) [27,28] and the
Perdew-Burke-Ernzerhof (PBE)-version of the generalized gradient approximation (GGA) [27,28] and
plane-wave basis set used projector augmented waves (PAW) [29,30]. These methods have provided
the plane-wave basis set used projector augmented waves (PAW) [29,30]. These methods have provided
close lattice parameters to experimental values of phyllosilicates [31]. In detail, the tested kinetic
close lattice parameters to experimental values of phyllosilicates [31]. In detail, the tested kinetic
energy cutoff value of 800 eV and a (8 × 4 × 2) Γ-point centered k-points mesh were accomplished to
energy cutoff value of 800 eV and a (8 × 4 × 2) Γ-point centered k-points mesh were accomplished to
truncate the plane-wave basis in the high-precision calculations of muscovite model. Considering the
truncate the plane-wave basis in the high-precision calculations of muscovite model. Considering the
double size of the a-axis in the supercell, the k-points were reduced to (4 × 4 × 2) in the calculations of
double size of the a-axis in the supercell, the k-points were reduced to (4 × 4 × 2) in the calculations of
V substitution. Meanwhile, other parameters were remained. Full geometry optimization
V substitution. Meanwhile, other parameters were remained. Full geometry optimization calculations
calculations were performed in which all structural parameters were relaxed without constraint of
were performed in which all structural parameters were relaxed without constraint of the space group
the space group symmetry. Namely, the space group was P1. All calculations were convergent until
Minerals 2017, 7, 32
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symmetry. Namely, the space group was P1. All calculations were convergent until the total energy
change of 10−4 eV and residual forces of 0.05 eV/Å, respectively. With these parameters, converged
total energies and lattice vectors were obtained.
3. Results and Discussion
3.1. Muscovite Model
We defined the surfaces beside interlayer with upper surface (U) and lower surface (L) (Figure 2a).
Every surface have four different substitutable sites, which were labelled 1–4 (Figure 2b). The sixteen
possible configurations were identified by combination, like CU , and the calculated crystallographic
parameters were compared with experimental values in Table 1.
Table 1. The calculated crystallographic parameters of sixteen configurations.
CUL
a (Å)
b (Å)
c (Å)
α (◦ )
β (◦ )
γ (◦ )
E (eV)
Exp
C11
C12
C13
C14
C21
C22
C23
C24
C31
C32
C33
C34
C41
C42
C43
C44
5.211
5.293
5.285
5.292
5.284
5.285
5.278
5.284
5.278
5.292
5.284
5.293
5.285
5.284
5.278
5.285
5.278
9.040
9.122
9.134
9.124
9.136
9.134
9.145
9.136
9.148
9.124
9.136
9.122
9.134
9.136
9.148
9.134
9.145
20.021
20.267
20.270
20.261
20.266
20.270
20.275
20.266
20.267
20.261
20.266
20.267
20.270
20.266
20.267
20.270
20.275
90.00
90.00
89.90
90.00
89.95
90.10
90.00
90.05
90.00
90.00
89.95
90.00
89.90
90.05
90.00
90.10
90.00
95.76
95.83
95.88
95.83
95.88
95.88
95.94
95.88
95.94
95.83
95.88
95.83
95.88
95.88
95.94
95.88
95.94
90.00
90.00
90.09
90.00
90.09
89.91
90.00
89.91
90.00
90.00
90.09
90.00
90.09
89.91
90.00
89.91
90.00
0.025
0.072
0
0.089
0.077
0.187
0.091
0.148
0
0.093
0.027
0.072
0.091
0.147
0.078
0.186
E is the relative total energy based on the lowest total energy, C13 (C31 ), thus the energy of C13 (C31 ) was returned
to zero.
For muscovite, we obtained fair agreement within the estimated experimental uncertainty of the
lattice parameters, which was determined in powder neutron diffraction experiment. The relative
deviations of cell parameters were reported (Figure 3). After substitution, the a-axis, b-axis and c-axis
expand less than 1.42%, 1.05% and 1.23%, respectively. Simultaneously, the average calculated Si–O
distance (1.641 Å) and Al–O distance (1.944 Å) have minor differences to the experimental bond length
(1.643 Å, 1.943 Å, respectively). While the average calculated O–H distance (0.972 Å) is 2.6% longer
than the experimental values (0.947 Å), it can be resulted from the dangling nature of O–H and the
hydrogen bonds of H atoms formed with the nearest O atoms [11]. Thus, these insignificant differences
prove the reliability of these DFT calculations. In the sixteen configurations, the relative deviations and
relative total energy of C13 are similar to C31 , the C24 is similar to C42 , and the C12 and C21 are similar to
C34 and C43 , respectively. Thus, they can be divided into six categories shown in Figure 3. It suggests
that the Al-substitutions of the 1 and 3 sites or 2 and 4 sites of Si in each T sheet are equivalent. It can
be ascribed to the similar environment of Si before substitution.
The most stable case is C13 and C31 , where Al atoms beside interlayer prefer a “W” shape for
the longer Al–Al distance (Figure 4). However, all categories differ in total energy by less than
0.2 eV/f.u. Such slight energy differences between the minimum energy and other suboptimum
structures demonstrate thermal disorder of the Al distribution in this material [32]. As a model
configuration, an Al distribution with the lowest total energy is assumed, C13 , with a = 5.292 Å,
b = 9.124 Å, c = 20.261 Å, and β = 95.83◦ .
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11
Figure
3.
The
relative
deviations
of
cell
parameters
and
total
energy
of
sixteen
configurations.
Figure
Figure3.
3.The
Therelative
relativedeviations
deviationsof
ofcell
cellparameters
parametersand
andtotal
totalenergy
energyof
ofsixteen
sixteenconfigurations.
configurations.
Figure
4.
One
layer
of
the
muscovite
model
along
the
a-axis.
Figure4.
4.One
Onelayer
layerof
ofthe
themuscovite
muscovitemodel
modelalong
alongthe
thea-axis.
a-axis.
Figure
3.2.
Optimal
Location
of
Vanadium
and
Local
Geometry
3.2.Optimal
OptimalLocation
Locationof
ofVanadium
Vanadiumand
andLocal
LocalGeometry
Geometry
3.2.
The
dissociation
and
liberation
of
cation
polyhedron
in
the
muscovite
need
to
absorb
enough
Thedissociation
dissociationand
andliberation
liberationof
ofcation
cationpolyhedron
polyhedronin
inthe
themuscovite
muscoviteneed
needto
toabsorb
absorbenough
enough
The
energy.
However,
the
different
cations
with
different
polyhedrons
reflect
different
inflexibility.
For
energy. However,
different
polyhedrons
reflect
different
inflexibility.
For
energy.
However, the
thedifferent
differentcations
cationswith
with
different
polyhedrons
reflect
different
inflexibility.
instance,
the
Si–O
tetrahedral
is
more
stable
than
the
Al–O
octahedral
and
it
is
difficult
to
be
instance,
the
Si–O
tetrahedral
is
more
stable
than
the
Al–O
octahedral
and
it
is
difficult
to
be
For instance, the Si–O tetrahedral is more stable than the Al–O octahedral and it is difficult to be
destroyed
because
of
the
hard
Si–O
bond
and
the
ring
of
the
quasi-hexagonal.
Thus,
the
location
of
destroyed
because
of
the
hard
Si–O
bond
and
the
ring
of
the
quasi-hexagonal.
Thus,
the
location
destroyed because of the hard Si–O bond and the ring of the quasi-hexagonal. Thus, the location ofof
will
directly
decide
whether
the
V
existing
in
muscovite
is
easy
to
be
extracted
or
not.
Vwill
willdirectly
directlydecide
decidewhether
whetherthe
theV
Vexisting
existingin
inmuscovite
muscoviteis
iseasy
easyto
tobe
beextracted
extractedor
ornot.
not. Hereinafter,
Hereinafter,
VV
Hereinafter,
we
compared
the
different
locations
where
V
substituted
in
the
aspects
of
energy
and
structure.
we
compared
the
different
locations
where
V
substituted
in
the
aspects
of
energy
and
structure.
we compared the different locations where V substituted in the aspects of energy and structure.
Due
to
the
reduced
overall
symmetry
for
the
Al
substitution,
the
Si–O
tetrahedral
sites
are
now
Dueto
tothe
thereduced
reducedoverall
overallsymmetry
symmetryfor
forthe
theAl
Alsubstitution,
substitution,the
theSi–O
Si–Otetrahedral
tetrahedralsites
sitesare
arenow
now
Due
split
into
three
non-degenerate
types
(Figure
5).
In
total,
we
calculated
the
five
cases
of
V
substitution
splitinto
intothree
threenon-degenerate
non-degeneratetypes
types(Figure
(Figure5).
5).In
Intotal,
total,we
wecalculated
calculatedthe
thefive
fivecases
casesof
ofV
Vsubstitution
substitution
split
in
the
2
×
1
×
1
supercell
of
muscovite.
The
V
substitution
assumes
the
reaction:
in
the
2
×
1
×
1
supercell
of
muscovite.
The
V
substitution
assumes
the
reaction:
in the 2 × 1 × 1 supercell of muscovite. The V substitution assumes the reaction:
M
(1)
MOO ++ V
V→
→M
MSS ++ Si(Al)
Si(Al)
(1)
MO + V → MS + Si(Al)
(1)
where
where M
MOO is
is the
the original
original muscovite
muscovite and
and M
MSS is
is the
the muscovite
muscovite with
with V
V substitution.
substitution. V
V is
is the
the vanadium
vanadium
atom
is
or
replaced
Thus,
the
(E
atom and
and
Si(Al)
is the
the silicium
silicium
or aluminum
aluminum
atom
replaced by
by V.
V.V
Thus,
the substitution
substitution
energy
(ESS))
where
MO Si(Al)
is
the original
muscovite
and MS isatom
the muscovite
with
substitution.
V is the energy
vanadium
can
be
defined
by
the
formula:
can be
defined
the silicium
formula:or aluminum atom replaced by V. Thus, the substitution energy (ES )
atom
and
Si(Al)by
is the
can be defined by the formula: ES = E[MS] + E[Si(Al)] − E[MO] − E[V]
(2)
ES = E[MS] + E[Si(Al)] − E[MO] − E[V]
(2)
where
muscovite
with
substitution.
where E[M
E[MSS]] is
is the
the total
total energy
energy
of=the
the
muscovite
with−V
VE[M
substitution.
E[MOO]] is
is the
the total
total energy
energy of
of the
the
ESof
E[M
(2)
S ] + E[Si(Al)]
O ] − E[V] E[M
original
original muscovite.
muscovite. E[Si(Al)]
E[Si(Al)] and
and E[V]
E[V] are
are the
the individual
individual ground
ground state
state energies
energies per
per atom
atom of
of Si
Si or
or Al
Al
where
E[M
energy of the
V of
substitution.
is
thereaction
total energy
the
and
respectively.
the
negative
value
that
can
occur
S ] is the totalTherefore,
O ] this
and V,
V,
respectively.
Therefore,
themuscovite
negative with
value
of EESS means
meansE[M
that
this
reaction
can of
occur
original
muscovite.
and
E[V]
are the value
individual
state
energies
per atomcan
of Sinot
or
and
spontaneously.
In
contrary,
the
positive
SS means
that
this
spontaneously.
InE[Si(Al)]
contrary,
the
positive
value of
of EEground
means
that
this reaction
reaction
can
notAloccur
occur
V,
respectively.
Therefore,
the
negative
value
of
E
means
that
this
reaction
can
occur
spontaneously.
spontaneously.
S
spontaneously.
In contrary,
the positive
of ES meansand
thatsubstitution
this reactionenergies
can not occur
The
of
cell
of
five
The values
values
of the
the value
cell parameters
parameters
and
substitution
energies
of the
thespontaneously.
five configurations
configurations were
were
The
values
of
the
cell
parameters
and
substitution
energies
of
the
five
configurations
were
displayed
in
Table
2.
The
calculated
cell
parameters
expand
in
the
c-axis
with
respect
to
previous
displayed in Table 2. The calculated cell parameters expand in the c-axis with respect to previous
displayed
in Table
2. The calculated
parameters
expand
the
c-axis withof
respect
to previous
model
Meanwhile,
ititpresents
aaslight
difference
within
the
substitution
non-degenerate
Simodelvalues.
values.
Meanwhile,
presentscell
slight
difference
withinin
the
substitution
of
non-degenerate
Simodel
values. Meanwhile,
it presents
a slight difference
within
the substitution
of non-degenerate
O
but
difference
between
The
of
O tetrahedral,
tetrahedral,
but aa non-ignorable
non-ignorable
difference
between three
three categories.
categories.
The substitution
substitution
of tetratetracoordinated
coordinatedsilicium
silicium(Si
(SiIVIV))and
andtetra-coordinated
tetra-coordinatedaluminum
aluminum(Al
(AlIVIV))to
toV
Vpresent
presentaalarger
largervalue
valueof
ofccthan
than
VI
hexa-coordinated
hexa-coordinated aluminum
aluminum (Al
(AlVI).). ItIt implies
implies that
that the
the substitution
substitution of
of Al
AlVIVI to
to V
V lead
lead to
to aa smaller
smaller
Minerals 2017, 7, 32
6 of 11
Si–O tetrahedral, but a non-ignorable difference between three categories. The substitution of
tetra-coordinated
silicium (SiIV ) and tetra-coordinated aluminum (AlIV ) to V present a larger value
of c
Minerals 2017, 7, 32
6 of 11
VI
VI
than hexa-coordinated aluminum (Al ). It implies that the substitution of Al to V lead to a smaller
IV ]1 <
VI]] <<
IV]1
expansion.
Furthermore,
<<V[Si
V[SiIVIV
V[Si
expansion.
Furthermore,the
theincreasing
increasingorder
orderofofsubstitution
substitutionenergy:
energy: V[Al
V[AlVI
]2]2< <
V[Si
<
IV ]IV< V[SiIVIV]3.
V[Al
V[Al ] < V[Si ]3.
Figure 5. The substituted location in muscovite.
Figure
5. The substituted location in muscovite.
Table 2. The cell parameters and substitution energies of five configurations.
Table 2. The cell parameters and substitution energies of five configurations.
Config
a (Å)
b (Å)
a (Å) 9.124
b (Å)
ModelConfig10.584
V[AlVI]Model10.543
9.124
10.584 9.124
V[AlVI]V[AlVI10.553
10.543 9.130
9.124
]
10.553 9.143
9.130
]
V[SiIV]1V[AlVI10.576
10.576 9.145
9.143
V[SiIV ]1
V[SiIV]2
10.571
10.571 9.147
9.145
V[SiIV ]2
V[SiIV]3
10.570
V[SiIV ]3
10.570
9.147
c (Å)
c (Å)
20.261
20.358
20.261
20.376
20.358
20.376
20.416
20.416
20.417
20.417
20.415
20.415
α (°)
β (°)
α (◦90.00
)
β (◦ ) 95.83
γ (◦ )
90.0090.0195.83
90.0190.0195.73
90.0190.0095.73
90.0090.0095.74
90.0089.9795.77
89.97
95.73
95.73
90.00
95.73
90.00
90.00
95.74
90.00
95.77
90.01
95.73
90.03
γ (°)
ES (eV)
90.00
90.00
90.00
−1.228
−0.344
90.00
−0.434
90.01
−0.519
90.03
−0.340
ES (eV)
−1.228
−0.344
−0.434
−0.519
−0.340
Figure 6 presents the bond distances and angles of the local geometry after substitution. For the
SiIVFigure
site, the
resultingthe
V–O
bond
lengths are
maximum
of 0.174
Å substitution.
resulting fromFor
thethe
6 presents
bond
distances
andincreased
angles ofby
thea local
geometry
after
larger
radius of V–O
V compared
to Si. However,
the bond
of neighboring
showthe
SiIV
site, ionic
the resulting
bond lengths
are increased
by alengths
maximum
of 0.174 Åtetrahedrals
resulting from
a slight
than 0.01
Å for
the purethe
tetrahedral
structure.
Consequentially,
the hard
larger
ionicdifference
radius ofof
V less
compared
to Si.
However,
bond lengths
of neighboring
tetrahedrals
show
bonds
of
Si–O
tetrahedral
slightly
pull
the
oxygen
atom
out
of
the
framework
into
the
interlayer
a slight difference of less than 0.01 Å for the pure tetrahedral structure. Consequentially, the hard
caused
by the
expansionslightly
of the V–O
decrease
the inter-tetrahedral
bond
angles about
bonds
of Si–O
tetrahedral
pulltetrahedral
the oxygenand
atom
out of the
framework into the
interlayer
caused
2.2°–8.3°. For the AlIV site, the V substitution shows the similar behavior to the SiIV site. In detail,◦the ◦
by the expansion of the V–O tetrahedral and decrease the inter-tetrahedral bond angles about 2.2 –8.3 .
resulting V–O bond lengths are increased about 0.117–0.138 Å, and the inter-tetrahedral bond angles
For the AlIV site, the V substitution showsVIthe similar behavior to the SiIV site. In detail, the resulting
decrease by about 3.0°–7.3°. For the Al site, the resulting V–O bond lengths are increased by
V–O bond lengths are increased about 0.117–0.138 Å, and the inter-tetrahedral bond angles decrease
maximum ◦ of 0.111
Å, and the inter-octahedral angles are changed less than 1.1°. Thus, the
by about 3.0 –7.3◦ . For the AlVI site, the resulting V–O bond lengths are increased by maximum of
substitution in octahedrals presents a smaller expansion than in tetrahedrals due to the plasticity of
0.111 Å, and the inter-octahedral angles are changed less than 1.1◦ . Thus, the substitution in octahedrals
Al–O octahedrals, which can endure a larger deformation.
presents
smaller expansion
thanthe
in shift
tetrahedrals
dueoxygens
to the plasticity
Al–O octahedrals,
which
Inatetrahedral
substitution,
of bridging
between of
tetrahedrons
along with
the c-can
endure
a
larger
deformation.
axis were investigated in Table 3. The bridging oxygens around substitution tetrahedron rise
In tetrahedral
substitution,
the shift
of bridging
oxygens
between
tetrahedrons
along with
obviously
more than
normal bridging
oxygens,
but some
shifts lose
the balance.
These lopsided
shiftsthe
c-axis
were
investigated
in
Table
3.
The
bridging
oxygens
around
substitution
tetrahedron
rise
of bridging oxygens present the torsional deformation of tetrahedron, which was evaluated by
IV
obviously
more
than
normal
bridging
oxygens,
but
some
shifts
lose
the
balance.
These
lopsided
variance. The lower variance of V[Si ]2 site substituting means smaller torsional deformation. On
shifts
bridging
present
the torsional
deformation
of tetrahedron,
which wasInevaluated
the of
contrary,
theoxygens
V[SiIV]3 site
substituting
reflects
a strong asymmetry
and deformation.
detail,
IV ]2 site substituting means smaller torsional deformation.
IV]2 < V[Si
IV]1
IV] < V[Si
byV[Si
variance.
The
lower
variance
ofIV]3,
V[Si
< V[Al
which
is consistent with the ordering of substitution energy.
thisthe
already
that the
stability
of V substitution
related
to the torsional
OnAltogether,
the contrary,
V[SiIVdemonstrates
]3 site substituting
reflects
a strong
asymmetry is
and
deformation.
In detail,
IV
IV
IV
IV
deformation
local
geometry.
In all,]3,the
V prefers
to substitute
aluminum
in
V[Si
]2 < V[Si of]1
< V[Al
] < V[Si
which
is consistent
withthe
thehexa-coordinated
ordering of substitution
energy.
muscovite.this
In other
words,
we can obtain
high
leaching
of V, as long
the octahedrals
are
Altogether,
already
demonstrates
that athe
stability
of rate
V substitution
is as
related
to the torsional
heavily dissociated
and liberated.
the effective
destruction
of the octahedrals
may be in
deformation
of local geometry.
In all, Thus,
the V prefers
to substitute
the hexa-coordinated
aluminum
meaningful
research
in
the
future.
muscovite. In other words, we can obtain a high leaching rate of V, as long as the octahedrals are
heavily dissociated and liberated. Thus, the effective destruction of the octahedrals may be meaningful
research in the future.
Minerals 2017, 7, 32
Minerals 2017, 7, 32
7 of 11
7 of 11
Figure
angles of
offive
fiveconfigurations
configurationsafter
aftersubstitution.
substitution.
Figure6.6.The
Thelocal
localbond
bonddistances
distances and angles
Table3.3.The
Theshift
shiftof
ofbridging
bridging oxygens
oxygens after
Table
aftervanadium
vanadiumsubstitution
substitution(Å).
(Å).
Site
O1
O2
O3
O4
O5
O6
(S*)2
V[SiIV]1
V[SiIV]2
V[SiIV ]1
V[SiIV ]2
0.158 *
0.090
O1 0.152 * 0.158 *
0.1890.090
*
O2 0.187 * 0.152 *
0.1970.189
* *
O3
0.187 *
0.197 *
0.031
0.180 *
O4
0.031
0.180 *
−0.008
0.0740.074
O5
−0.008
0.0730.073
O6 0.081 0.081
2
−4 × 10−44.824.82
× 10
× 10×−5 10−5
2.34
(S* )2.34
Site
V[SiIV]3
0.184 *
0.184
*
0.077
0.077
0.060
0.060
0.054
0.054
0.102
0.102 * *
0.232* *
0.232
−−3
3
2.88
2.88
××1010
V[SiIV ]3
V[AlIV]
0.063
0.063 0.057
0.057 0.056
0.056
0.115 *
0.115 *
0.157
*
0.157 *
*
0.131 0.131
*
3.00 ×3.00
10−4× 10−4
V[AlIV ]
∗
∗
* The
shift
substitutiontetrahedron.
tetrahedron.
The
variance
formula:
= O∑(O
−∗ O2∗.) .
∗
* The
shiftofofbridging
bridgingoxygens
oxygens around
around substitution
The
variance
formula:
(S∗ )(2 =) 13 ∑
i −O
ElectronicProperties
PropertiesofofVanadium-Bearing
Vanadium-Bearing Muscovite
Muscovite
3.3.3.3.
Electronic
Based on the optimal V-bearing muscovite, it is necessary to further calculate the physical and
Based on the optimal V-bearing muscovite, it is necessary to further calculate the physical and
chemical properties, which can guide either the beneficiation of V-bearing muscovite in the stone coal
chemical properties, which can guide either the beneficiation of V-bearing muscovite in the stone coal
or the breakage of V–O bond in the lattice.
or the breakage of V–O bond in the lattice.
Minerals 2017, 7, 32
8 of 11
3.3.1. Density of States (DOS) and Magnetism
Minerals 2017, 7, 32
11
The density
of states’ curves are shown in Figure 7, and the computed magnetic8 ofproperty
is also
summarized. The muscovite behaves as insulators, with a band gap of 4.83 eV. However, the band
3.3.1. Density of States (DOS) and Magnetism
gap of muscovite
has been verified to be around 5.09 eV [33]. This calculated value is typically
The density of states’ curves are shown in Figure 7, and the computed magnetic property is also
underestimated, due to well-known limitations in DFT calculations [34]. A finite density of doping
summarized. The muscovite behaves as insulators, with a band gap of 4.83 eV. However, the band
states can begap
observed
at Fermi
level
in to
majority
spin,
which
reflects
a metallic
of muscovite
has been
verified
be around
5.09 eV
[33]. This
calculated
value is nature,
typically whereas the
due
to well-known
in DFT
[34]. A suggests
finite density
of doping
Fermi level isunderestimated,
located in an
energy
gap oflimitations
minority
spincalculations
states, which
that
the existence of V
states can be observed at Fermi level in majority spin, which reflects a metallic nature, whereas the
does not disturb the insulating property of muscovite in the spin-down channel. Therefore, this
Fermi level is located in an energy gap of minority spin states, which suggests that the existence
material behaves
likenotobvious
spin
polarization.
the partial
density
of states (PDOS)
of V does
disturb the
insulating
property of Furthermore,
muscovite in the spin-down
channel.
Therefore,
this material
likeof
obvious
polarization.
partial density
of states
(PDOS)of V overlaps
curves with an
energybehaves
region
−1 tospin
4 eV
(FigureFurthermore,
8) clearlythe
shows
that the
3d-state
curves with an energy region of −1 to 4 eV (Figure 8) clearly shows that the 3d-state of V overlaps with
with the 2p-state
of O at Fermi level, which exhibits the slight p–d hybridization. However, the 3dthe 2p-state of O at Fermi level, which exhibits the slight p–d hybridization. However, the 3d-channel
channel of V ofcontributes
tothe
themajor
major
states.
V contributes to
states.
Figure 7. The density of states (DOS) curves of (a) muscovite and (b) muscovite doped with V.
Figure 7. The
density of states (DOS) curves of (a) muscovite and (b) muscovite doped with V.
Regarding the magnetic behavior of muscovite, the computed magnetic moment is zero because
Regarding
the magnetic
behavior
of muscovite,
computedNevertheless,
magnetic for
moment
is zero because
the total
DOS curve for
spin up–down
contributionthe
is symmetric.
muscovite
containing
an obvious
magnetic moment
can be noted,
a value of 1.998
µB because the
the total DOS
curveV,for
spin up–down
contribution
is with
symmetric.
Nevertheless,
for muscovite
total DOS curve is not symmetrical around the Fermi level. Consequently, the major contribution of
containing V, an obvious magnetic moment can be noted, with a value of 1.998 μB because the total
magnetism comes from the local magnetic moment of V atoms.
DOS curve is not symmetrical around the Fermi level. Consequently, the major contribution of
magnetism comes from the local magnetic moment of V atoms.
Minerals
Minerals 2017,
7, 32 2017, 7, 32
9 of 11
Minerals 2017, 7, 32
9 of 11
9 of 11
Figure 8. The local partial density of states (PDOS) curves (−1 to 4 eV).
The local
partial
density of
(PDOS)
curves
(−1 to(−1
4 eV).
Figure Figure
8. The8.local
partial
density
ofstates
states
(PDOS)
curves
to 4 eV).
3.3.2. Charge Transfer and Bond Analysis
3.3.2. Charge
Transfer and Bond
Analysis
three-dimensional
charge
density differences with isosurface value of 0.017 e/Å3 of V3.3.2. ChargeLocal
Transfer
and Bond Analysis
3 of
bearingLocal
muscovite
is displayedcharge
in Figure
9a, differences
which substantiates
the electron
transfer.
Blue
and
three-dimensional
density
with isosurface
value of
0.017 e/Å
3
Local
three-dimensional
charge
density
differences
with It
isosurface
0.017
yellow
colorsmuscovite
representislosing
and gaining
electrons,
respectively.
is
thatof
the
electrons
V-bearing
displayed
in
Figure
9a,
which
substantiates
theconspicuous
electronvalue
transfer.
Blue
ande/Å of Vto
O. Furthermore,
the unique
shaperespectively.
ofsubstantiates
isosurface
ofconspicuous
V the
suggests
that
the
p channels
yellowfrom
colorsV
losingin
and
gaining
electrons,
It is
that the
electrons
bearing transfer
muscovite
isrepresent
displayed
Figure
9a,
which
electron
transfer.
Blue and
from
V the
tolosing
O.d Furthermore,
unique
of isosurface
V
that results
the p channels
of transfer
O couple
with
channel
of V the
along
withshape
its coordinate
axis,ofconsistent
with
of PDOS.
yellow colors
represent
and gaining
electrons,
respectively.
It suggests
is conspicuous
that
the electrons
O couple study
with the
channel
of V along
with
its coordinate
axis,the
consistent
results of using
PDOS.an
Forofintensive
of dthe
characters
of V–O
bond,
we estimated
electronwith
distribution
transfer from
V to O. study
Furthermore,
the unique
shape we
of isosurface
of V suggests
that using
the p channels
For intensive
of the characters
of(Figure
V–O bond,
distribution
electron
localization function
(ELF) map
9b). 0–1 estimated
representsthe
theelectron
localized
level of electrons.
of O couple
with
the
d channel
of clearly
V(ELF)
along
with
coordinate
axis,the
consistent
results of PDOS.
an(001)
electron
localization
map
(Figure
9b).
0–1 represents
localized level
of compound.
electrons.
The
plane
in
the ELFfunction
map
shows
theits
ionic
nature
as highly
delocalized
inwith
the
The (001)
thecharacters
ELF
map clearly
shows
the
ionic
nature
as highly
delocalized
in the
compound. ofusing an
For intensive
study
of in
the
of V–O
we
estimated
the
electron
distribution
There
are plane
localized
electrons
around
Vbond,
originating
from
unshielded
inner
electrons
There
are
localized
electrons
around
V
originating
from
unshielded
inner
electrons
of
pseudopotential
of V. Therefore,
is responsible
for the
formation
of ionic
between
V and
electronpseudopotential
localization function
(ELF) itmap
(Figure 9b).
0–1
represents
thebonds
localized
level
of O.
electrons.
of
V.
Therefore,
it
is
responsible
for
the
formation
of
ionic
bonds
between
V
and
O.
Compared
to
the
Compared
to
the
covalent
bonds,
it
is
easier
for
ionic
bonds
to
be
broken
and
release
V
during
the
The (001) plane
inbonds,
the ELF
map clearly shows the ionic nature as highly delocalized in the compound.
covalent
it is easier for ionic bonds to be broken and release V during the leaching process.
leaching
process.
There are localized electrons around V originating from unshielded inner electrons of
pseudopotential of V. Therefore, it is responsible for the formation of ionic bonds between V and O.
Compared to the covalent bonds, it is easier for ionic bonds to be broken and release V during the
leaching process.
Figure
9. 9.(a)(a)Local
differenceof
ofV-bearing
V-bearingmuscovite;
muscovite;
electron
Figure
Localthree-dimensional
three-dimensionalcharge
charge density
density difference
(b)(b)
electron
localization
function
localization
functionmap
mapofof(001)
(001)plane.
plane.
4. Conclusions
As the foundation, the optimal muscovite model was tested from the sixteen configurations by
periodic DFT theory. After substitution with V, the lattice of muscovite has expanded for a larger
ionic radius of V. By employing substitution energy, the AlVI substitution possesses the lower
Figure
9. (a) Local
three-dimensional
density difference
V-bearing
muscovite;
(b) electron
substitution
energy.
In geometry, thecharge
AlVI substitution
presents aofsmaller
bond-angle
variation
than
Minerals 2017, 7, 32
10 of 11
4. Conclusions
As the foundation, the optimal muscovite model was tested from the sixteen configurations by
periodic DFT theory. After substitution with V, the lattice of muscovite has expanded for a larger ionic
radius of V. By employing substitution energy, the AlVI substitution possesses the lower substitution
energy. In geometry, the AlVI substitution presents a smaller bond-angle variation than AlIV and
SiIV , which further verifies the good plasticity of the Al–O octahedral. In summary, the V prefers
to substitute for the hexa-coordinated aluminum more than the tetra-coordinated aluminum or
silicium in muscovite. The focus of V extraction shall be concentrated on the effective destruction of
octahedrals. Meanwhile, the substitution of V makes this mineral perform narrower band gap and
finite magnetism. Combining PDOS with charge transfer, the interaction between V and O atom is
based on the p–d channel hybridization in muscovite. However, the V–O bonds perform an ionic nature
for the intense delocalization in the compound. In total, these theoretical data of V-bearing muscovite
have been obtained by the quantum chemistry method in detail. It will enhance the theoretical support
of V-bearing muscovite and guide the extraction of V from stone coal.
Acknowledgments: This research was financially supported by the National Natural Science Foundation of
China (No. 51474162, No. 51404174) and the National Key Science-Technology Support Programs of China
(No. 2015BAB18B01).
Author Contributions: Qiushi Zheng and Yimin Zhang conceived and designed the experiments; Qiushi Zheng,
Nannan Xue and Qihua Shi performed the calculations and analyzed the data; Yimin Zhang, Tao Liu and
Jing Huang contributed servers/softwares/analysis tools; and Qiushi Zheng wrote this paper.
Conflicts of Interest: The authors declare no conflict of interest.
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