minerals
Article
Recovery Process of Li, Al and Si from Lepidolite by
Leaching with HF
Gustavo D. Rosales, Eliana G. Pinna, Daniela S. Suarez and Mario H. Rodriguez *
Laboratorio de Metalurgia Extractiva y Síntesis de Materiales (MESiMat), Facultad de Ciencias Exactas y
Naturales, Universidad Nacional de Cuyo, Mendoza 5500, Argentina; [email protected] (G.D.R.);
[email protected] (E.G.P.); [email protected] (D.S.S.)
* Correspondence: [email protected]; Tel.:+54-9261-337-9329
Academic Editor: William Skinner
Received: 5 January 2017; Accepted: 1 March 2017; Published: 3 March 2017
Abstract: This work describes the development of a new process for the recovery of Li, Al and Si
along with the proposal of a flow sheet for the precipitation of those metals. The developed process is
comprised of lepidolite acid digestion with hydrofluoric acid, and the subsequent precipitation of the
metals present in the leach liquor. The leaching operational parameters studied were: reaction time,
temperature and HF concentration. The experimental results indicate that the optimal conditions to
achieve a Li extraction higher than 90% were: solid-liquid ratio, 1.82% (w/v); temperature, 123 ◦ C;
HF concentration, 7% (v/v); stirring speed, 330 rpm; and reaction time, 120 min. Al and Si can be
recovered as Na3 AlF6 and K2 SiF6 . LiF was separated from the leach liquor during water evaporation,
with recovery values of 92%.
Keywords: lithium; aluminum; silicon; extraction; hydrofluoric acid
1. Introduction
Fluorides and fluorinated materials appear in various aspects of modern life. The strategic
role of fluoride materials involves diverse research fields and applications in areas such as energy
production, microelectronics and photonics, catalysis, pigments, textiles, cosmetics, plastics, domestic
wares, automotive technology and the construction industry.
One of the most commonly used lithium salts is LiF, which is utilized as a flux in the ceramics
and glass industries, as well as in light metals welding [1,2]. It is especially used in the manufacture of
optical components for analysis equipments (IR and UV spectroscopies). Also, it has recently been
used in the fabrication of new cathodes for lithium-ion batteries, in the LiF-Fe ones [3]. A potentially
important use of LiF is represented by atomic fusion, where it would be employed as a source of 6 Li
isotopes [4,5].
The fluorometalates of K, and particularly fluorosilicates, have applications in the field of
Al brazing. Firstly, the corresponding reaction gives rise to the formation of elemental Si and K
fluoroaluminate, which act as a fluxing agent. The elements formed combine and alloy with Al,
diffusing through the base material so as to reach the corresponding eutectics mixtures, thereby locally
lowering the melting point of the Al and thus acting as a metal fillet or clad, which forms the joint [6].
Synthetic cryolite is a very important fluoroaluminate regarding to its industrial applications.
Probably its most important and best-known application is in the production and refining of aluminum
in combination with other fluorides, the so-called Hall-Heroult process [7]. Cryolite is also employed
in grinding applications as an abrasive aid in the polymeric matrix of phenolics resins [4]. Other uses,
dealing with lower volumes, include solid lubricant for brakes in heavy-duty applications, and in the
production of welding agents, pyrotechnics and metal surface treatments.
Minerals 2017, 7, 36; doi:10.3390/min7030036
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Lepidolite (KLiAl2 Si3 O10 (OH,F)3 ) is a mica with a complex and variable formula. Its Li
concentration ranges from 1.39% (3.0% Li2 O) to a theoretical maximum of 3.58% Li (7.7% Li2 O).
The major commercial deposits of lepidolite are in: Bikita, Zimbabwe; Bernie Lake, Manitoba, Canada;
Karibib, Namibia; and Mina Gerais, Brazil [1]. In Argentina, the main deposits of lepidolite are found
in the San Luis, Salta and Catamarca provinces [8,9].
The most significant processes for the extraction of Li from lepidolite are the “sulfate acid” and
“lime” methods. Acid digestion is carried out with concentrated sulphuric acid at temperatures higher
than 250 ◦ C, whereas the lime method is carried out with CaCO3 at 1040 ◦ C. The products obtained
through these methods are Li2 CO3 and LiOH, respectively [1,2].
Relevant findings about the dissolution of lepidolite with a combination of both pyro and
hydrometallurgical routes have been published. In such processes, lepidolite is firstly calcined together
with Na2 SO4 , K2 SO4 , FeSO4 or FeS, at temperatures higher than 800 ◦ C. Then, the obtained mixture is
leached with water [10–14]. In the whole process mentioned before, the only valuable metal recovered
is Li. Al and Si are lost with the waste generated during the Li recovery process.
The aim of this paper is to describe a process to recover Li, Si and Al from lepidolite and to
highlight the controlling parameters of the process, including the best operational conditions.
2. Materials and Methods
The leaching agent was HF (40% w/w), with analytical grade. The reagents used for the recovery
assays were KOH and NaOH, both of analytical grades. The employed mineral was lepidolite,
extracted from the mine “Las Cuevas”, located in the department of San Martín, San Luis, Argentina.
The ore was concentrated by hand sorting, then grounded in a ring mill and sieved to a particle size of
<45 µm.
Characterization of the ore and products was performed by X-ray fluorescence (XRF) on a Philips
PW 1400 instrument (Philips, Amsterdam, The Netherlands) and by X-ray diffraction (XRD) in a
Rigaku D-Max III C diffractometer (Rigaku, Osaka, Japan), operated at 35 kV and 30 mA. The Kα
radiation of Cu and the filter of Ni, λ = 0.15418 nm were used. Morphological analysis was done by
scanning electron microscopy (SEM), in an equipment LEO 1450 VP (Zeiss, Jena, Germany) which
was equipped with an EDAX Genesis 2000 X-ray dispersive spectrometer (EDAX, Mahwah, NJ, USA),
used to determine the semi-quantitative composition of the residues obtained through the leaching of
the minerals by electron probe microanalysis (EPMA).
Determination of lithium content in the ore was performed by atomic absorption spectroscopy
(AAS) using a Varian SpectrAA 55 spectrometer (Palo Alto, Santa Clara, CA, USA) with a
hollow-cathode lamp (analytical error 1.5%). Previously, the sample (lepidolite) was dissolved using a
concentrated mixture of sulfuric acid and hydrofluoric acid, according to the method of Brumbaugh
and Fanus, 1954 [15]. The bulk composition of the ore is shown in Table 1, determined by AAS (Li and
Na) and XRF (Si, Al, Fe, Ca, Mg, K and Ti). The results of the characterization of the ore by XRD are
shown in Figure 1.
Table 1. The bulk composition of the ore by AAS and XRF.
Component
% w/w
SiO2
Al2 O3
Fe
Ca
Mn
K
Na
Li
Others
50.78
26.93
0.13
0.14
0.24
6.5
1.25
2.00
5.87
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Figure
Figure 1.
1. XRD
XRD pattern
pattern of
of the
the lepidolite
lepidolite concentrate.
concentrate.
The XRD
XRD patterns
patterns in
in Figure
Figure 11 show
show that
that the
the sample
sample is
is mainly
mainly composed
composed of
of lepidolite
lepidolite (ICDD
(ICDD
The
01-085-0398), with
with the
the presence
presence of
of albite
albite (ICDD
(ICDD96-900-1631)
96-900-1631)and
andquartz
quartz(JCPDS
(JCPDS33-1161)
33-1161)as
asgangue.
gangue.
01-085-0398),
2.1.
2.1. Experimental Equipment
Equipment and
and Procedure
Procedure
2.1.1.
2.1.1. Leaching
Leaching Assays
Assays
The
a steel
closed
vessel
of 500
mL mL
coated
withwith
Teflon
and
The experimental
experimentaltests
testswere
wereperformed
performedinin
a steel
closed
vessel
of 500
coated
Teflon
equipped
with
magnetic
stirring
and
temperature
control
systems.
and equipped with magnetic stirring and temperature control systems.
For
test, aamass
massofofthe
theore
oreand
and
a volume
of distilled
water
were
placed
the reactor.
For each
each test,
a volume
of distilled
water
were
placed
intointo
the reactor.
The
The
mixture
was
subsequently
heated
in
an
oil
bath,
with
stirring
until
the
final
work
temperature
mixture was subsequently heated in an oil bath, with stirring until the final work temperature was
was
reached.
Once
desired
temperature
was
achieved,
appropriateamount
amountof
ofHF
HF was
was added
added to
reached.
Once
the the
desired
temperature
was
achieved,
ananappropriate
to
the
mixture,
so
as
to
obtain
different
acid
concentrations.
From
that
moment,
the
reaction
time
was
the mixture, so as to obtain different acid concentrations. From that moment, the reaction time was
calculated.
waswas
finished,
the solid
was filtered,
dried atdried
75 ◦ C,atand
weighed.
calculated. Once
Oncethe
theexperiment
experiment
finished,
the solid
was filtered,
75 then
°C, and
then
Li was analyzed by atomic absorption to calculate the extraction percentage in all the experiments
weighed.
by theLifollowing
equation:
was analyzed
by atomic absorption to calculate the extraction percentage in all the
Li
experiments by the following equation: X = s × 100%
(1)
Lim
Lis
where: Lim is the initial amount of lithium in
the
X the
= mineral
× 100%and Lis is the amount of the element in (1)
Li
m
leach liquor [16,17].
TheLiexperimental
study of this work was performed by univariate analysis. In order to evaluate
where:
m is the initial amount of lithium in the mineral and Lis is the amount of the element in the
the
experimental
error,
each test was replicated three times. The average extraction efficiency and
leach liquor [16,17].
standard
were
calculated
each
parameter
studied.
The deviation
experimental
study
of thisfor
work
was
performed
by univariate analysis. In order to evaluate
The
operational
studied
parameters
were:
temperature,
reaction
time
and HF concentration.
the experimental error, each test was replicated three times. The
average
extraction
efficiency and
The
following
parameters
were
kept
constant:
particle
size,
<45
µm;
solid-liquid
ratio, 1.82% (w/v);
standard deviation were calculated for each parameter studied.
and stirring
speed, 330studied
rpm. parameters were: temperature, reaction time and HF concentration.
The operational
The following parameters were kept constant: particle size, <45 μm; solid-liquid ratio, 1.82% (w/v);
2.1.2. Recovery Assays
and stirring speed, 330 rpm.
The residual Si and Al in the liquor obtained after the leaching of the mineral were removed as
the
compounds
K2 SiF6 and Na3 AlF6 , by using KOH and NaOH, respectively. The reactions proposed
2.1.2.
Recovery Assays
for obtaining these compounds are the following [16–18]:
The residual Si and Al in the liquor obtained after the leaching of the mineral were removed as
the compounds K2SiF6 and Na3AlF6, by using KOH and NaOH, respectively. The reactions proposed
2KOH(aq) + H2 SiF6(aq) → K2 SiF6(s) + 2H2 O
(2)
for obtaining these compounds are the following [16–18]:
AlF
→ Na3 AlF
+ 23H
3NaOH
+H
(aq) (aq)
6(aq)
2KOH
+3H
2SiF
6(aq) → K2SiF
6(s)6(s)
+ 2H
O 2O
(3)
(2)
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3NaOH(aq) + H3AlF6(aq) → Na3AlF6(s) + 3H2O
(3)
The
The recovery
recovery of
of Li
Li from
from the
the resulting
resulting solution
solution after
after the
the precipitation
precipitation of
of Al
Al and
and Si
Si can
can be
be carried
carried
out
by
one
of
the
many
known
methods.
In
this
case,
lithium
was
precipitated
as
LiF,
evaporating
the
out by one of the many known methods. In this case, lithium was precipitated as LiF, evaporating
solutions
above
the the
solubility
product
constant
(Ksp)
of LiF
[16,17,19–23].
TheThe
recovery
efficiency
of
the solutions
above
solubility
product
constant
(Ksp)
of LiF
[16,17,19–23].
recovery
efficiency
each
element
was
calculated
by
gravimetric
analysis.
of each element was calculated by gravimetric analysis.
In
In Figure
Figure 22 itit is
is presented
presented the
the process
process flow
flowsheet
sheetfor
forLi,
Li,Si
Siand
andAl
Alrecovery.
recovery.
Figure 2.
2. Generalized
Generalized process
process flow
flow sheet
sheet for
for Li,
Li, Si
Si and
and Al
Al recovery
recovery from
from lepidolite.
lepidolite.
Figure
3. Results
3. Results
3.1. Leaching
Leaching of
of Li
Li from
from Lepidolite
Lepidolite
3.1.
The
The lepidolite
lepidolite dissolution
dissolution with
with HF
HF can
can be
be represented
representedby
bythe
thefollowing
followingreaction
reaction[16–18]:
[16–18]:
KLi2KLi
AlSi2AlSi
→→
2LiF
+ H33AlF
+ 4H SiF
SiF6(aq)
+ KF
+ 11H
O
4 O104F(OH)
(s) +(s)32HF
(aq)(aq)
(aq)
6(aq)
O10F(OH)
+ 32HF
2LiF
(aq) + H
AlF6(aq)
6(aq) + 4H22
+ KF
(aq)(aq)
+ 11H
2O 2
(4)
(4)
3.1.1. Effect of Temperature
3.1.1. Effect of Temperature
In order to investigate the effect of the leaching temperature on the Li extraction, a series of
In order
to investigate
the effect of
the 75
leaching
on of
thethe
Lileaching
extraction,
a series
of
◦ C. Conditions
leaching
experiments
were performed
from
to 220 temperature
process
were
leaching
experiments
were
performed
from
75
to
220
°C.
Conditions
of
the
leaching
process
were
as
as follows: solid-liquid ratio, 1.82% (w/v); HF concentration, 7% (v/v); stirring speed, 330 rpm; and
follows: time,
solid-liquid
1.82% are
(w/v);
HF concentration,
7% which
(v/v); stirring
330 rpm;
reaction
120 min.ratio,
The results
presented
in Figure 3 from
it can bespeed,
appreciated
fromand
the
reaction
time,
120
min.
The
results
are
presented
in
Figure
3
from
which
it
can
be
appreciated
from
error bars that the largest standard deviation in the experimental data is about ±2.5%.
the error
bars
that the largest
standard
deviation
in thehas
experimental
is on
about
Figure
3 illustrates
that the
reaction
temperature
an obviousdata
effect
the ±2.5%.
leaching process.
Figure
3
illustrates
that
the
reaction
temperature
has
an
obvious
effect
on
the
process.
The extraction efficiency increases significantly when the leaching temperature isleaching
increased
from
The
extraction
efficiency
increases
significantly
when
the
leaching
temperature
is
increased
from 75
◦
75 to 123 C. This coincides with the results of Rosales et al. (2014 and 2016), who determined
to 123
This coincides
with the
results of Rosales
et al. (2014 and
2016),
determined
that the
that
the°C.
dissolution
of lithium
aluminosilicates
(β-spodumene)
with
HF iswho
strongly
dependent
on
dissolution
of
lithium
aluminosilicates
(β-spodumene)
with
HF
is
strongly
dependent
on
the
the temperature [17,18]. The extraction efficiency was 90% when the reaction temperature was
temperature
[17,18].
extraction
efficiency
was 90% when
was 123
°C.
◦ C. However,
123
a The
further
increase
of the temperature
did the
notreaction
result intemperature
a clear increase
of the
However, efficiency
a further (92%).
increase
of optimum
the temperature
did not
in to
a be
clear
of economic
the extraction
◦ C for the
extraction
The
temperature
wasresult
chosen
123increase
and
efficiency
(92%).
The
optimum
temperature
was
chosen
to
be
123
°C
for
the
economic
and
industrial
industrial applications.
applications.
Minerals 2017, 7, 36
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55 of
Figure
Figure 3.
3. Effect
Effectof
ofthe
thetemperature
temperature on
on the
the Li
Li extraction
extraction efficiency.
efficiency.
3.1.2.
3.1.2. Effect
Effect of
of Reaction
Reaction Time
Time
To
of the
the reaction
reaction time
time on
on the
the Li
Li extraction,
extraction, experiments
experiments were
To study
study the
the effect
effect of
were conducted
conducted at
at
◦ C; and
conditions
of
solid-liquid
ratio,
1.82%
(w/v);
HF
concentration,
7%
(v/v);
temperature,
conditions of solid-liquid ratio, 1.82% (w/v); HF concentration, 7% (v/v); temperature, 123
123 °C;
and
stirring
stirring speed,
speed, 330
330 rpm.
rpm.
The
results
are
plottedin
inFigure
Figure4,4,which
whichshows
showsthat
that
leaching
time
a remarkable
effect
on
The results are plotted
leaching
time
hashas
a remarkable
effect
on the
the
dissolution
of
the
mineral.
As
the
time
increased
from
10
to
240
min,
the
lithium
extraction
dissolution of the mineral. As the time increased from 10 to 240 min, the lithium extraction efficiency
efficiency
increased
from
due to time
the reaction
favoring
the contact
between
the
increased from
37% to
95%,37%
duetoto95%,
the reaction
favoringtime
the contact
between
the leaching
agent
leaching
agent
and
the
mineral,
improving
the
extraction
efficiency.
As
the
reaction
time
increased
and the mineral, improving the extraction efficiency. As the reaction time increased up to 120 min,
up
120 min,percentage
the extraction
of Li remained
constant.
Statistical
analysis
of the
the to
extraction
of Lipercentage
remained almost
constant.almost
Statistical
analysis
of the results
indicates
results
indicates
that
there
is
a
standard
deviation
of
1.6%.
that there is a standard deviation of 1.6%.
Figure
Figure 4.
4. Effect
Effectof
ofreaction
reaction time
time on
on the
the Li
Li extraction
extraction efficiency.
efficiency.
3.1.3.
3.1.3. Effect
Effect of
of HF
HF Concentration
Concentration
In
order
to
investigate
In order to investigate the
the effect
effect of
of the
the HF
HF concentration
concentration on
on the
the Li
Li extraction,
extraction, aa series
series of
of leaching
leaching
experiments
were
performed
ranging
from
7%
to
20%
(v/v)
of
HF.
The
conditions
of
the
leaching
experiments were performed ranging from 7% to 20% (v/v) of HF. The conditions of the leaching
process were as follows: solid-liquid ratio, 1.82% (w/v); stirring speed, 330 rpm; temperature, 123 °C;
and reaction time, 60 min. The results are plotted in Figure 5.
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process were as follows: solid-liquid ratio, 1.82% (w/v); stirring speed, 330 rpm; temperature, 123 ◦ C;
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10
and
reaction
60 min. The results are plotted in Figure 5.
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Figure 5. Effect
Effect of HF
HF concentration on
on the Li
Li extraction efficiency.
efficiency.
Figure
Figure 5.
5. Effect of
of HF concentration
concentration on the
the Li extraction
extraction efficiency.
Figure 55 illustrates
illustrates that
that the
the HF
HF concentration
concentration has
has aa notorious
notorious effect
effect on
on the
the leaching
leaching process.
process. The
The
Figure
Figure
5
illustrates
that
the
HF
concentration
has
a
notorious
effect
on
the
leaching
process.
extraction efficiency
efficiency increased
increased significantly
significantly when
when the
the HF
HF concentration
concentration was
was increased
increased from
from 7%
7% to
to
extraction
The
extraction
efficiency
increased
significantly
when
the
HFachieved
concentration
was increased
from
7%
to
20%
(v/v).
The
maximum
extraction
value
of
Li
(95%)
was
by
working
with
HF
15%
(v/v).
20% (v/v). The maximum extraction value of Li (95%) was achieved by working with HF 15% (v/v).
20%
(v/v).
The
maximum
extraction
value of
Li (95%) was
achieved
by working
with HF 15%of(v/v).
Above
15%
(v/v)
of HF,
HF, the
the
Li extraction
extraction
percentage
decreased,
since
high concentrations
concentrations
HF
Above
15%
(v/v)
of
Li
percentage
decreased,
since
high
of HF
Above
15%
(v/v)
of
HF,
the
Li
extraction
percentage
decreased,
since
high
concentrations
of
HF
produce
produce aa precipitation
precipitation of
of Li
Li alkali
alkali fluorides
fluorides (e.g.,
(e.g., Li
Li33Na
Na33Al
Al22FF1212)) [17].
[17].
produce
a precipitation of Li alkali fluorides (e.g., Li3 Na3 Al2 F12 ) [17].
3.1.4. Characterization
Characterization of
of the
the Residue
Residue
3.1.4.
3.1.4. Characterization of the Residue
Figure 66 presents
presents the
the diffractograms
diffractograms of
of the
the leaching
leaching residues
residues obtained
obtained at
at 123
123 and
and 160
160 ◦°C
°C
with
C with
Figure
extractions of
of 90%
90%
and
95%
ofofLi,
Li,
respectively,
under
thethe
following
experimental
conditions:
HF,HF,
7%
90%and
and95%
95%of
Li,respectively,
respectively,
under
following
experimental
conditions:
extractions
under
the
following
experimental
conditions:
HF,
7%
(v/v)
and
time,
120
min.
7% (v/v)
time,
(v/v)
andand
time,
120 120
min.min.
Figure 6.
6. XRD
XRD patterns
patterns of
of the
the leaching
leaching residue
residue obtained
obtained at
at 123
123 and
and 160
160 ◦°C.
°C.
C.
Figure
From Figure
Figure 66 itit can
can be
be inferred
inferred that
that the
the dissolution
dissolution of
of the
the lepidolite
lepidolite present
present in
in the
the ore
ore occurs,
occurs,
From
and
even
more,
it
enhances
the
intensity
of
the
diffraction
lines
of
albite
and
quartz.
This
indicates
and even more, it enhances the intensity of the diffraction lines of albite and quartz. This indicates
that, working
working at
at 123
123 °C,
°C, the
the dissolution
dissolution reaction
reaction is
is preferential
preferential for
for lepidolite.
lepidolite. Meanwhile,
Meanwhile, the
the
that,
dissolution
of
lepidolite
and
albite
is
achieved
at
160
°C,
leaving
quartz
in
the
leaching
residue.
dissolution of lepidolite and albite is achieved at 160 °C, leaving quartz in the leaching residue.
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From Figure 6 it can be inferred that the dissolution of the lepidolite present in the ore occurs, and
even more, it enhances the intensity of the diffraction lines of albite and quartz. This indicates that,
working at 123 ◦ C, the dissolution reaction is preferential for lepidolite. Meanwhile, the dissolution of
Minerals 2017, 7, 36
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lepidolite
and albite is achieved at 160 ◦ C, leaving quartz in the leaching residue.
3.2. Recovery of Si, Al and Li
3.2. Recovery of Si, Al and Li
3.2.1. Recovery of Silicon as K2SiF6
3.2.1. Recovery of Silicon as K2 SiF6
The leach liquor obtained after the first filtration was treated with KOH to precipitate the
The
leach liquor obtained after the first filtration was treated with KOH to precipitate the residual
residual Si according to Equation (2). The amount of KOH used was equal to the stoichiometric
Si according
to Equation
The amount
ofresult
KOH of
used
to the stoichiometric
valuesolid
calculated
value calculated
from(2).
Equation
(2). The
the was
XRDequal
characterization
of the obtained
is
from shown
Equation
(2).
The
result
of
the
XRD
characterization
of
the
obtained
solid
is
shown
in
Figure 7.
in Figure 7.
Figure
7. 7.
XRD
Figure
XRDpattern
patternof
of the
the precipitated
precipitated KK
2SiF
6. 6 .
2 SiF
Figure 7 shows the appearance of diffraction lines that correspond to the structure of K2SiF6
Figure 7 shows the appearance of diffraction lines that correspond to the structure of K2 SiF6
(JCPDS 7-217), which is in agreement with the proposed Equation (2). By gravimetry, it was
(JCPDS
7-217), which is in agreement with the proposed Equation (2). By gravimetry, it was determined
determined that the recovery of Si was 93%.
that the recovery
of6 precipitate
Si was 93%.
The K2SiF
was analyzed by microanalysis EDS and XRF to determine the purity of
The
K
SiF
precipitate
was analyzed
bythe
microanalysis
2
6
the precipitate.
Table 2 shows
the purity of
compound. EDS and XRF to determine the purity of
the precipitate. Table 2 shows the purity of the compound.
Table 2. Purity of K2SiF6.
Table 2. Purity of K2 SiF6 .
Elemental Composition (wt %)
Si
K
F
Na
Al
O
Mn
Fe
Others
Elemental Composition (wt %)
98.8
16.9
35.1
46.8
0.2
0.2
0.8
Purity of K2 SiF6 (wt %)
Si
K
F
Na
Al
O
Mn
Fe
Others
The results
Figure35.1
7 and46.8
Table 2 -indicate
98.8 obtained from
16.9
0.2 that the
- precipitation
0.2 reaction
0.8 was
highly selective to Si, seeing that there was no formation of any Al and Li compound.
Purity of K2SiF6 (wt %)
The
obtained
from Figure
and
Table 2 indicate that the precipitation reaction was highly
3.2.2.results
Recovery
of Aluminum
as Na37AlF
6
selective to
Si,
seeing
that
there
was
no
formation
of any Al and Li compound.
To precipitate Al as Na3AlF6, the liquor obtained after the recovery of Si was treated with NaOH
according to Equation (3) (Rosales et al., [16,17]). The amount of NaOH used was equal to the
stoichiometric value calculated from Equation (3). After the addition of NaOH, the appearance of a
white
precipitate
3AlF6 was
observed.
The
was filtered
and dried
forwith
To
precipitate
Alcorresponding
as Na3 AlF6 , to
theNaliquor
obtained
after
thesolid
recovery
of Si was
treated
characterization.
NaOH according to Equation (3) (Rosales et al., [16,17]). The amount of NaOH used was equal to
Figure 8 shows
diffractogram
the solid obtained
after
additionofofNaOH,
NaOH. the appearance
the stoichiometric
valuethe
calculated
fromofEquation
(3). After
thethe
addition
3.2.2. Recovery of Aluminum as Na3 AlF6
of a white precipitate corresponding to Na3 AlF6 was observed. The solid was filtered and dried
for characterization.
Figure 8 shows the diffractogram of the solid obtained after the addition of NaOH.
Minerals 2017, 7, 36
8 of 10
Minerals 2017, 7, 36
8 of 10
Minerals 2017, 7, 36
8 of 10
Figure 8. XRD pattern of the precipitated Na3AlF6.
Figure 8. XRD pattern of the precipitated Na3 AlF6 .
The diffractogram in Figure 8 indicates that the formation of solid Na3AlF6 has taken place
The
diffractogram
in Figure
88.indicates
that
theprecipitated
formation
of solid Na3 AlF6 has taken place
according
to Equation
(3),Figure
without
other
phases
detected
as impurities.
XRD
pattern
of the
Na3AlF6.
3 shows
purity of
the compound
Na3AlF6as
, obtained
by microanalysis EDS and XRF.
according toTable
Equation
(3),the
without
other
phases detected
impurities.
diffractogram
in Figure
8 indicates that
of
solid
Na3AlF6 has EDS
takenand
place
TableThe
3 shows
the purity
of the compound
Na3the
AlFformation
,
obtained
by
microanalysis
XRF.
6
3. detected
Purity of Na
AlF6.
according to Equation (3), without other Table
phases
as 3impurities.
Table 3. Purity
of Na
AlF
Table 3 shows the purity of the compound
Na3AlF
6, obtained
by microanalysis
3
6 .Composition
Elemental
(wt %)EDS and XRF.
Purity of Na3AlF6 (wt %)
Al
Na
F
K
Si
O
Mn
Fe
Others
Elemental
Composition
(wt %)
Table 3. Purity
of Na3AlF
6.
15.7 34.6 39.2
1.8
2.5
4.2
0.21
1.79
Purity of 89.5
Na3 AlF6 (wt %)
Al
Na
F
K
Si
O
Mn
Others
Elemental
Composition
(wt %)Fe
Purity
of appearence
Na3AlF
%)Na2SiF15.7
89.56 (wtof
34.6
39.2
1.8
2.5
4.2
0.21Fe
1.79presence
The
6 in the
diffractogram
but the
Al
Na
F
Kof Figure
Si 8 is
Onot observed,
Mn
Others of
Si (2.5%) by
detected.
indicates
the Si,
89.5EDS analysis is 15.7
34.6This39.2
1.8 that2.5
4.2which- was not
0.21recovered
1.79in the
previous
step, was
precipitated
asdiffractogram
Na2SiF6 in amounts
below8the
detection
limit but
of XRD.
For further
The
appearence
of Na
SiF
in
the
of
Figure
is
not
observed,
the
presence
of Si
2
6
purification
the solid
can
with solutions
at different
pH values
[20].
The achieved
The
appearence
of
Na
2SiFbe
6 inwashed
the
diffractogram
of
Figure
8
is
not
observed,
but
the
presence
of
(2.5%) by EDS analysis is detected. This indicates that the Si, which was not recovered in the previous
recovery
of Aliswas
95%. This indicates that the Si, which was not recovered in the
(2.5%) bypercentage
EDS analysis
detected.
step, Si
was
precipitated
as Na2 SiF
6 in amounts below the detection limit of XRD. For further purification
previous step, was precipitated as Na2SiF6 in amounts below the detection limit of XRD. For further
the solid
canRecovery
be washed
with solutions
different pH values [20]. The achieved recovery percentage
3.2.3.
of Lithium
LiF at with
purification
the solid
can beaswashed
solutions at different pH values [20]. The achieved
of Alrecovery
was 95%.
percentage
of
Al
was
95%.
The liquor obtained after the recovery of Al and Si was evaporated (at 75 °C) until the
appearance
a gelatinous
white precipitate that corresponded to LiF [23]. The obtained solid was
3.2.3.3.2.3.
Recovery
of of
Lithium
as as
LiF
Recovery
of Lithium
LiF
washed and dried at 75 °C for further characterization. The total lithium precipitation, obtained by
The
liquor
obtained
after
theabout
recovery
Al of
and
wasSi
evaporated
75 ◦(at
C) 75
until
the
appearance
gravimetric
analisys,
was
92%.ofFigures
and
10
showevaporated
the (at
diffractogram
and
the the
SEM
The liquor
obtained
after
the recovery
Al9Siand
was
°C)
until
micrograph
the
obtained
LiF,
respectively.
of a gelatinous
white
precipitate
that
corresponded
to LiF [23]. to
The
wassolid
washed
appearance
of of
a gelatinous
white
precipitate
that corresponded
LiFobtained
[23]. The solid
obtained
was and
and
at 75characterization.
°C for further characterization.
The total
lithium precipitation,
by
driedwashed
at 75 ◦ C
fordried
further
The total lithium
precipitation,
obtainedobtained
by gravimetric
gravimetric
analisys,
was
about
92%.
Figures
9
and
10
show
the
diffractogram
and
the
SEM
analisys, was about 92%. Figures 9 and 10 show the diffractogram and the SEM micrograph of the
micrograph
of the obtained LiF, respectively.
obtained
LiF, respectively.
Figure 9. Diffractogram of the precipitated LiF.
Figure9.9.Diffractogram
Diffractogram of
LiF.
Figure
of the
theprecipitated
precipitated
LiF.
Minerals 2017, 7, 36
9 of 10
Minerals 2017, 7, 36
9 of 10
Figure
Figure 10.
10. SEM
SEM micrograph
micrograph of
of the
the precipitated
precipitated LiF.
LiF.
Figure
Figure 99 shows
shows that
that the
the compound
compound LiF
LiF was
was obtained
obtained without
without other
other phases
phases as
as impurities.
impurities.
Frontino
et
al.
(2008),
obtained
a
similar
diffractogram
for
the
precipitation
of
LiF
from
spent
Frontino et al. (2008), obtained a similar diffractogram for the precipitation of LiF from spent Li-ion
Li-ion
batteries
batteries [23].
[23].
In
Figure10
10it itcan
can
theparticles
LiF particles
a well-defined
crystal structure
and
In Figure
be be
seenseen
thatthat
the LiF
have ahave
well-defined
crystal structure
and coincided
coincided
with
the
cubic
shape
of
LiF
particles
found
in
the
literature.
with the cubic shape of LiF particles found in the literature.
The
The resulting
resulting LiF
LiF was
was analyzed
analyzed by
by AAS
AAS and
and EDS
EDS to
to determine
determine the
the concentration
concentration of
of major
major
impurities
in
the
sample.
The
results
are
presented
in
Table
4.
impurities in the sample. The results are presented in Table 4.
Table
Table 4. Purity
Purity of LiF.
Purity
of LiF
(wt(wt
%)%)
Purity
of LiF
99.199.1
Elemental
Composition
Elemental Composition
(wt(wt
%) %)
LiLi
26.7
26.7
F F Na Na K
K Ca Ca
72.572.5 0.08 0.08 0.05 0.05 0.02 0.02
Mn
Mn
Others
Others
0.03
0.03
0.590.59
Table
that the
the purity
purity of
of the
the LiF
LiF precipitated
precipitated was
was 99.1%.
99.1%.
Table 44 indicates
indicates that
4. Conclusions
Conclusions
In summary,
summary, aaprocess
processthat
thatincludes
includes
leaching
with
employed
to extract
Li,and
Al Si
and
Si
leaching
with
HFHF
waswas
employed
to extract
Li, Al
from
from
lepidolite.
The experimental
the optimal
conditions
toa achieve
a Li
lepidolite.
The experimental
resultsresults
indicateindicate
that thethat
optimal
conditions
to achieve
Li extraction
extraction
90% are:
solid-liquid
1.82% (w/v);
123 7%
°C; (v/v);
HF
higher thanhigher
90% are:than
solid-liquid
ratio,
1.82% (w/v);ratio,
temperature,
123 ◦ C;temperature,
HF concentration,
concentration,
7%
(v/v);
stirring
speed,
330
rpm;
and
reaction
time,
120
min.
The
compounds
K
2
SiF
stirring speed, 330 rpm; and reaction time, 120 min. The compounds K2 SiF6 and Na3 AlF6 can be6
and
Na3AlF
6 can be obtained
as subproducts
of the of
process,
recovery ofThe
93%Li and
95%,
obtained
as subproducts
of the process,
with a recovery
93% andwith
95%,arespectively.
dissolved
respectively.
Theby
Li chemical
dissolvedprecipitation
can be separated
chemical
precipitation
as and
LiF, awith
a recovery
can be separated
as LiF, by
with
a recovery
value of 92%
purity
of 99.1%.
value
of 92% and
a purity
99.1%. Furthermore,
Al and Si are
recovered the
as valuable
subproducts,
Furthermore,
Al and
Si are of
recovered
as valuable subproducts,
diminishing
generation
of residues
diminishing
the generation
of of
residues
during
the
resultseconomic
of the current
work way
can
during the process.
The results
the current
work
canprocess.
provideThe
a simple,
and effective
provide
a
simple,
economic
and
effective
way
to
recover
Li
from
lepidolite.
to recover Li from lepidolite.
The financial
financial support
support from
from the
the Universidad
Universidad Nacional
Nacional de
de Cuyo,
Cuyo, Secretaría
Secretaría de
de Ciencia,
Ciencia,
Acknowledgments: The
Técnica yy Posgrado,
Posgrado, is
is gratefully
gratefully acknowledged.
acknowledged. Two
Two anonymous
anonymous referees
referees provided
provided constructive
constructive and
and helpful
helpful
Técnica
reviews, corrections and comments. Many thanks are due to the editorial staff of Minerals.
reviews, corrections and comments. Many thanks are due to the editorial staff of Minerals.
Author Contributions: Gustavo D. Rosales, Eliana G. Pinna, Daniela S. Suarez and Mario H. Rodriguez conceived
Author
Contributions:
GustavoGustavo
D. Rosales,
Eliana Eliana
G. Pinna,
Daniela
Suarez
Mario performed
H. Rodriguez
and designed
the experiments;
D. Rosales,
G. Pinna
andS.Mario
H. and
Rodriguez
the
conceived
and
designed
D. Rosales,
Elianareagents,
G. Pinna
and Mario
Rodriguez
experiments
and
analyzedthe
theexperiments;
data; Mario Gustavo
H. Rodriguez
contributed
materials
and H.
analysis
tools;
Gustavo D.the
Rosales,
Eliana G.and
Pinna,
Danielthe
S. Suarez
and Mario
H. Rodriguez
wrote the
paper. materials and
performed
experiments
analyzed
data; Mario
H. Rodriguez
contributed
reagents,
analysis
tools;
Gustavo
D.
Rosales,
Eliana
G.
Pinna,
Daniel
S.
Suarez
and
Mario
H.
Rodriguez
wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
Conflicts of Interest: The authors declare no conflict of interest.
Minerals 2017, 7, 36
10 of 10
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