Aluminum Electrorefining and Electrowinning
in Ionic Liquid Electrolytes
Mingming Zhang1 and Ramana G. Reddy2
1Graduate Student, 2ACIPCO
Professor
Department of Metallurgical
and Materials Engineering,
The University of Alabama,
Tuscaloosa, AL 35487, USA
Aluminum Electrorefining and
Electrowinning
─
+
Cathode
Hot plate
Stirrer
Anode
Thermometer
Inert gas inlet
Reference
electrode
Electrolyte
Gas outlet
Chlorination
Electrolysis in ionic
liquid
Aluminum
Electrorefining/electrowinning Parameters
Proposed Al extraction process
1.5 - 2.5
0
CF4emission, kg/ton-Al
340
0
CO emission, kg/ton-Al
850 - 1000
25 - 150
Temperature, °C
100
5 – 20
Electrode distance, mm
-
200-700
Current density, A/m2
6.0 - 8.5
3.0 - 4.0
Energy consumption, KWh/lb
4.2 - 5.0
1.5 - 3.5
Cell
voltage, V
Current
Industrial Electrolysis
Electrolysis
in Ionic Liquid
Parameters
Laboratory Aluminum Electrowinning in
Ionic Liquids
Conclusions
uThe optimum electrowinning parameters are
determined as followings: Temperature range: 100-130°C; Applied cell
voltage:3.0-3.5V; Electrolyte concentration: ~1:1.7 (molar ratio)
uCurrent densities of 200-700A/m2,
current efficiencies of about 99% and aluminum deposit thickness of about
0.1-0.2 mm were obtained.
uAluminum production in ILs has an advantage of low
temperature, low energy consumption and low pollutants emission in laboratory
scale.
Batch
Recirculation and Pilot Electrowinning in Ionic Liquids
Batch
electrowinning experiment results
uCurrent
densities of batch recirculation were comparable with that of laboratory
experiments in similar conditions.
uCurrent
density and current efficiency increase when electrolyte circulation rate and
cell voltage increase.
uMaximum
current efficiencies were obtained at circulation rate of 20 ml/min and 3.5
V.
uCurrent
densities were in the range of 200-400A/m2, over 80% current efficiencies
can be obtained.
Conclusions
[1]. E.A. Brandes, et al., eds, Smithells Metals
Reference Book (7th Ed), 1998.
[2]. ASM Engineered Materials Reference Book (2nd Ed),
1994.
[3]. M. Zhang, V. Venkat and R. Reddy, JOM, 11, 2003.
uThe computed current densities were
in good agreement with experimental data when applied cell voltage was less
than 3.5 V.
uOptimum electrode distance was
determined to be 1.0-1.5 cm based electrical field distribution modeling.
Conclusions
Comparison
of experimental and modeling results
Modeling of Aluminum Electrowinning in
Ionic Liquids
Electrochemical capacitors
Extraction of light metals
Thermal storage fluids
Research Interests
Porous
carbon
electrode
Separator
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– +
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Electrolyte
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Acknowledgements
We
would like to acknowledge the support from the following organizations
u NSF
(NSF-EPS-9977239)
u DOE
(DE-FC07-02ID14397)
u The
University of Alabama (UA)
u Alabama
Supercomputer Center (ASC)
u TMS Student
Travel Grant
27
-
-
cp
Viscosity
0.186
24
295
W/K m
Thermal Conductivity
0.6~2.0
2.8x104
6.3x107
S/m
Conductivity
1800
0.5~1.7
1238
C6mimCl+AlCl3 electrolyte
(MR:1:1.7)[3]
3.5x105
1.68x10-8
Ωm
Electrical Resistivity
J/kg K
kg/m³
669
385
Specific Heat
2250
8940
Density
Graphite anode[2]
Cu cathode[1]
Properties
(room temp.)
Modeling Objectives
Assumptions
Modeling Results
Parameters
Used in Modeling
3-D Meshing of
Electrolyte cell
Cell
design and Operating Variables Optimization
lLaboratory scale
models which are generally associated with the effects of electrolytic
processing variables.
lMagneto-hydro-dynamic
(MHD) models which are generally associated with the problem of cell
stability.
lThermal-electric
models which are generally associated with the problem of cell heat balance.
Average velocity vector
u A steady state laminar fluid, i.e., no
ends effect
u No bubble generation from the electrode
surface
u Electrolyte volume changes are
neglected
u Constant values for transport and phase
diffusivity
Pilot Electrowinning Setup
0.1
20
18
1.5
1.5
1.5
0.6
20
Copper cathode
Graphite anode
* Dimension unit in
centimeter
Schematic for
Batch Recirculation Electrowinning
Mixed
electrolyte
reservoir
Anode
(Graphite plate)
Cathode
(Pure copper plate)
Inert
Gas
─
+
Hot plate
Thermometer
* Average current density ** Current efficiency
Copper cathode and graphite anode after
electro winning
Advantages of this
process
u Low energy
consumption (3.0 – 4.0 kWh/lb - Al)
u High
purity Al produced (99.89% Al) for Al electro winning/refining
u No
pollutant emission
u To determine the
feasibility of using ionic liquids for the electrolytic reduction of aluminum
at low temperatures.
u To provide
insights into the potential for ionic liquids as electrolytes for the
production of primary or secondary aluminum.
Copper cathode and Al-MMC anode after
electro refining