Nickel
Ni
k lP
Production
d ti th
through
h
The Caron Process
M.A. Rhamdhani1, E. Jak2, P.C. Hayes2
1
FEIS, Swinburne University of Technology
2
Pyrometallurgy Research Centre, The University of Queensland
Nickel Production
Main driving force:
… European Union’s new chemical policy regulations
Oxygen content of nickel product (<0.1wt% as NiO)
… Minimise the generation of residual NiO dust (carcinogenic substance)
… Improvement of the overall process
Principal sources of nickel:
… Ni-sulphide ores (700 kilo tonnes Ni/ year)
… Ni-laterite ores (500 kilo tonnes Ni/ year)
Major Process Æ Caron Process (combinations of hydro and
pyrometallurgical processes)
2
© Swinburne University of Technology
Schematic of Nickel Production (Modified Caron Process)
1
2
3
Image is from BHP Billiton, Yabulu refinery
© Swinburne University of Technology
Approach of the present study
Final goal: to reduce the final oxygen content (<0.1%NiO) in the final
Ni product
Approach:
1.
Systematic investigation of the modes of occurrences of residual
NiO in the plant samples
2.
Systematic lab experiments to investigate the fundamental
phenomena and reactions
3.
4
-
(I) BNC reduction/oxidation studies
-
( ) Synthetic
(II)
y
NiO reduction studies ((microstructures and
kinetics)
Relate ((1)) and (2)
( ) to suggest
gg process
p
strategies
g
© Swinburne University of Technology
Types of residual NiO in plant samples
Type 1: Trapped round particles
surrounded by: (1a) thick or (1b)
thin dense Ni
Type 2: Trapped blocky form
surrounded by porous Ni
Type 3: Surface layer of a NiO on
Ni particle:
ti l (3
(3a)) with
ith or (3b)
without a fine layer of Ni on
oxide surface
Type 4: Bulky NiO: 4(a) with or 4(b)
without dense Ni inside
Type 5: Fine partially reduced NiO
particles with individual particle
size of 1 to 5µm
5
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BNC reduction/oxidation studies
„
Replicate the conditions in industrial process
„
Study the microstructure changes of the BNC during controlled reduction and
oxidation
id i processes
„
Identify the conditions in which a residual NiO maybe forming
Experimental apparatus
… A top blown fluidising particle technique
… Gas
G flflow rate:
t 500-1000
500 1000 ml/min
l/ i
… Sample: Pre-dried BNC at 100oC for 16 hrs
… Sample is cooled by removing the tube from the
ffurnace andd flowing
fl i N2 gas, andd water
t outside
t id th
the
tube
Characterisations
‰ SEM, EDS, EPMA, XRD, TGA/DTA
‰ Chemical bulk O and S analyses.
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Detailed Experimental Conditions
(1) BNC Calcined in air
30-120 min at T = 100oC – 900oC, Heating rate 10oC/min
(2) BNC Reduced in 15%H2-N2
30-120
30
120 min at T = 100oC – 900oC, Heating rate 10oC/min
(3) BNC Reduced in 1.5%H2-N2
30 120 min
30-120
i at T = 500
00oC – 900oC,
C H
Heating
i rate 10oC/min
C/ i
(4) Pre-oxidised BNC (30 min 900oC) reduced in 15%H2-N2
30 min at T = 100oC – 900oC, Heating rate 10oC/min
(5) Pre
Pre-oxidised
oxidised BNC (30 min 500oC and 700oC) reduced in 15%H2-N
N2
30 min at T = 500oC – 900oC, Heating rate 10oC/min
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(1) BNC Calcined in air
200oC
30 min at T = 110oC to 900oC
Heating
g rate 10oC/min
25oC-300oC
D
Decomposition
iti off BNC
400oC
300oC-400oC
Transformation of 1-10µm amorphous
( ultrafine)
(or
lt fi ) Æcrystalline
Æ
t lli NiO
600oC
400oC-600oC
A concentric layered structure within
each particle becomes evident
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(1) BNC Calcined in air
700oC
700oC-800oC
800oC
•Agglomeration of particles are evident
•Concentric layers more distinct
800oC-900oC
900oC
9
•Recrystallisation NiO begins 0.1µmsized grains forms
•NiO sintering and agglomeration
becomes significant
© Swinburne University of Technology
(1) BNC Calcined in air
10
© Swinburne University of Technology
(2) BNC Reduced in 15%H2-N2
200oC
30 min at T = 110oC to 900oC
Heating
g rate 10oC/min
25oC-300oC
Amorphous BNC transformed to
crystalline NiO
340oC
300oC-400oC
•Initial
Initial nucleation and growth of a
porous Ni metal
•Agglomeration starts
400oC
400oC-500oC
•Reduction to Ni almost complete
gg
through
g Ni
•More agglomeration
sintering
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(2) BNC Reduced in 15%H2-N2
600oC
600oC-700oC
•Reduction to Ni complete
•Growth
G th off Ni subgrains,
b i 00.05-0.1µm
05 0 1
800oC
700oC-800oC
•Coarseningg of Ni subgrains,
g
0.20.5µm
•Particle sintering/agglomeration
•Recrystallisation
Recrystallisation of subgrains
900oC
800oC-900oC
•Subgrains
S b i fform 00.5-2µm
5 2 dense
d
grains, within fully recrystallised Ni
particles
•No evidence of residual NiO
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© Swinburne University of Technology
(2) BNC Reduced in 15%H2-N2
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(3) BNC Reduced in 1.5%H2-N2
T = 500oC to 900oC
Heating rate 10oC/min
The effect
Th
ff t off reduction
d ti time
ti andd reduction
d ti rate
t
At T = 700oC and above, there is a formation of trapped residual nickel oxide
120 min
30 min
i
14
600oC
700oC
800oC
900oC
© Swinburne University of Technology
(4) Pre-oxidised BNC (at 900oC) reduced in 15%H2-N2
340oC
30 min at T = 110oC to 900oC
Heating rate 10oC/min
25oC
C-300
300oC
•Fine grained (0.1-0.5µm) NiO crystalline
500oC
300oC-500oC
•Nucleation
Nucleation and growth of porous Ni
•Bridging between particles
•Agglomeration of particles
600oC
500oC-600
C 600oC
•Majority of NiO is reduced
•Some residual NiO
•Pitting/pores
Pitti /
evidence
id
on surface
f
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(4) Pre-oxidised BNC (at 900oC) reduced in 15%H2-N2
700oC
700oC
•Substantial recrystallisation of Ni subgrains
•Formation of dense Ni layers on the
surface
800oC
800oC
•Formation of dense polycrystalline Ni
•Residual NiO trapped
•Agglomeration of dense grains
900oC
900oC
•Further
Further agglomeration of dense Ni
product grains
•Residual NiO remains in some of the
particles
i l
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© Swinburne University of Technology
(4) Pre-oxidised BNC (at 900oC) reduced in 15%H2-N2
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© Swinburne University of Technology
(5) Pre-oxidised BNC (at 500oC & 700oC) reduced in 15%H2-N2
The effect
Th
ff t off pre-oxidation
id ti ttemperature
t
Pre-oxidation at T = 700oC and below, does not lead to the formation of trapped
residual nickel oxide
Pre-oxidised
@ 700oC
Pre-oxidised
@ 500oC
18
600oC
700oC
800oC
900oC
© Swinburne University of Technology
(5) Pre-oxidised BNC (at 500oC & 700oC) reduced in 15%H2-N2
Comparison
C
i
off final
fi l microstructure
i
t t off pre-oxidised
idi d BNC (at
( t 500oC,
C 700oC andd
900oC) reduced in 15%H2-N2 at 900oC for 30 minutes.
Pre-oxidised
@ 500oC
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Pre-oxidised
@ 700oC
Pre-oxidised
@ 900oC
© Swinburne University of Technology
Summary (1)
„
Between 100oC-400oC
Two steps decomposition of BNC to NiO
In a reducing condition, Ni immediately nucleates
„
Between 700oC-800oC
Various competing phenomena affecting microstructures:
- Ni recrystallisation and grain growth
- NiO recrystallisation and grain growth
- Ni sintering and densification
- NiO sintering and densification
Complicated to control, need some strategies in processing at this T range
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© Swinburne University of Technology
Summary (1)
The findings have clear implications for industrial practice
The key to achieve complete reduction of NiO by H2 gas is
by controlling the relative rates of densification of Ni
product and the overall reduction rate of NiO
High extent of NiO reduction favored by:
1
1.
Maintaining a high-NiO,
high-NiO specific surface area
Avoiding NiO and Ni recrystallisation and densification (carrying out
reduction at T < 600oC)
2.
Maintaining a high chemical rate
High pH2 and high H2/H2O ratios
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© Swinburne University of Technology
Overall Summary
„
A range of microstructures can develop depending on the thermal and chemical histories
of the materials in the process
„
The microstructures created depends
p
on the reduction conditions, i.e. temperature,
p
partial
p
pressure of H2 (kinetics driving force), and H2/H2O ratio (thermodynamic driving force)
„
The following phenomena affect the final-product microstructure:
… Chemical changes, i.e. decomposition, reduction and oxidation reactions
… NiO and Ni recrystallisation and grain growth
… NiO and Ni sintering and densification;
… Agglomeration of the NiO and Ni particles
„
NiO remains unreduced because it has not been efficiently exposed to reduction conditions:
… Surrounded by an impervious nickel product layer formed
… Due to the lack of porosity Æ low supply of reduction gas
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© Swinburne University of Technology
Acknowledgements
„
John Fittock and Dr Joy Morgan, BHP Billiton, Yabulu refinery
„
Australian Research Council
The materials on this presentation are extracted from:
„
Rhamdhani, M.A.,
Rhamdhani
M A Jak.
Jak E
E., and Hayes
Hayes, P
P.C.,
C “Basic
Basic nickel carbonate.
carbonate Part I.I Microstructure and phase changes during oxidation
and reduction processes”, Metallurgical and Materials Transactions B, Vol. 39B, April 2008, pp.218-33.
„
Rhamdhani, M.A., Jak. E., and Hayes, P.C., “Basic nickel carbonate. Part II. Microstructure evolution during industrial nickel
production from basic nickel carbonate”, Metallurgical and Materials Transactions B, Vol. 39B, April 2008, pp.234-45.
„
Hidayat, T., Rhamdhani, M.A., Jak, E., and Hayes, P.C., “The kinetics of reduction of dense synthetic NiO in H2/N2 and H2/H2O
atmospheres”, under review (submitted 18 May 2008), Metallurgical and Materials Transactions B, 2008.
„
Hidayat, T., Rhamdhani, M.A., Jak, E., and Hayes, P.C., “Microstructures Developing during the Reduction of Dense Synthetic
Ni k l Oxide
Nickel
O id using
i Hydrogen
H d
Gas
G Mi
Mixtures”,
t
” under
d preparation
ti ffor Metallurgical
M t ll i l andd M
Materials
t i l TTransactions
ti
B
B, 2008.
2008
„
Hidayat, T., Rhamdhani, M.A., Jak, E., and Hayes, P.C., “The characterization of nickel metal pore structures and the
measurement of intrinsic reaction rate during reduction of nickel oxide in H2-N2 and H2-H2O atmospheres”, Minerals Engineering,
Vol.21,, 2008,, pp
pp. 157-66
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