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Separation of calcium carbonate particles in the presence of
dispersant
Liem Chau PHAM TRONG
Molde, June-09-2009
Report convention CIFRE
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Outlook
2
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Introduction
3
Objectives
Analyze the sedimentation of calcium carbonate suspensions in
the presence of dispersants
Verify the existence of small particles (≤1µm) and effects of
dispersants : size distribution, sedimentation et centrifugation
Separation and recovery of these particles by centrifugation
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Materials
4
● CaCO3 humid cakes :75%<1µm (according to Coatex)
● Dispersants ➔ DV61 :
Polyelectrolyte : Sodium polycarboxylate
Mw=15000-18000g/mol
➔ DV1182 : Comb-like structure polymer carrying POE side chains
Mw=40000g/mol
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Methods
5
• Dispersion
• Sedimentation experiments
• Particle size characterization
• Centrifugation
• Scanning electron microscopy (SEM)
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Dispersion method
6
● Mixer : Supertest from VMI
● Beaker (stainless steel)
➔ Volume = 1 liter➔ Diameter =10 cm
● Turbine
➔ Type : Deflocculator➔ Diameter = 35mm
d=35mm
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Sedimentation
7
Under gravity, T=30°C
Turbiscan with Cooler (Formulaction)
Laser sourceλ=850nm
Transmission detector
Backscattering detector
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Particle size characterization
8
• Granulometer: Mastersizer 2000, Malvern
• Wet dispersion unit by Hydro SM (rotational velocity 1000 rpm)
• Choice of optical parameters for CaCO3:
➔ Mean refractive indexes :
➔ Absorption indexes :
58098.1
57033.1
2
1
blue
red
n
nnnn eo
0bluered
kk
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Centrifugation
9
• Equipement: Allegra 64 with Cooler (Beckman)
• Rotor: S0410 swinging-bucket rotor (4x10ml)
• Relative centrifugal force: 500g to 8000g
• Temperature : 30°C
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Scanning Electron Microscopy
10
– Very dilute suspensions obtained from initial suspension,
sediments or supernatants in water at pH=9.7 (slightly turbid by
eye)
– 1µl drop deposited on the microscope slide
– Drying at room temperature for at least 24h
– Metal deposit under vacuum
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Results
11
• Sedimentation with Turbiscan
– CaCO3 concentration: 0.5wt% to 20wt%
– Dispersant: DV61, DV1182 (0 to 0.7 vs CaCO3 wt% )
Visual observation of the sedimentation
Measurement of the position of the interface vs time
• Particle size distribution
Measurement by granulometer
Obsevation by Scanning electron microscopy
• Particle size separation by centrifugation
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Sedimentation under gravity: picture taken after 1 day
12
Initial solid concentration : 15wt%DV-61 concentration between 0% and 0.7%
Dispersant /solid concentration (wt% )
0% 0.1% 0.2% 0.3% 0.4% 0.5% 0.6% 0.7%
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Sedimentation during 65 hours
12
Under gravity (1g): csolid=20wt%, cdispersant=0.7wt%
time
time
Transmission
Backscattering
sedimentation front
gravity
tube
bottom top
Animation: Turbiscan, Easysoft
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100 00
10
20
30
40
50
Backscattering
h (mm)
0
10
20
30
40
50
100 0
Transmission
Surface
Tube 14
t=0 : initial suspension
Homogeneous suspension
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100 00
10
20
30
40
50
Backscattering
h (mm)
0
10
20
30
40
50
100 0
Transmission 15
t=4h : formation of different layers
Surface
Tube
Semi-dilute suspension(Low BS and low Trans)
Dense suspension(High BS, Trans=0)
Dilute suspension(Low BS and high Trans)
Meniscus
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100 00
10
20
30
40
50
Backscattering
h (mm)
0
10
20
30
40
50
100 0
Transmission
Surface
Semi-dilute suspensionLow BS, low TransFlowable layer:
SedimentHigh BS, Trans=0
Dilute suspensionwith gradient concentration(Low BS, high Trans)
Meniscus
Tube 16
t=24h : change of different layers
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Surface
Compact sediment(High BS, Trans=0)
Meniscus
Very dilute suspension without concentration gradient) (Low BS, High Trans)
100 00
10
20
30
40
50
Backscattering
h (mm)
0
10
20
30
40
50
100 0
TransmissionTube 17
t=65h : constant height of compact sediment
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0 5 10 15 20 25 30 35 40 45 50 55 60 650
5
10
15
20
25
30
35
40
45
Sedim
entation velocity (mm
/h)
Sedimentation front
Fro
nt h
eigh
t (m
m)
Times (h)
0
1
2
3
4
5
Sedimentation velocity
Sedimentation height and velocity based on Backscattering
18
Sample 1c
solide= 20wt%
cdispersant
= 0.7wt%
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Dilute suspension (csolid=0.5wt%, cdispersant=0.5wt%)
19
Constant sediment height reached after 24mn
Backscattering
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0,0 0,2 0,4 0,6 0,8 1,0 1,2
8
10
12
14
16
18
20
22
24
26
28
30
32 ca
ke(%
)
Dispersant concentration (%)
DV1182 DV61 c
dispersant optimum
Sediment volume fraction after 1 week
20
Effect of dispersants : DV61 vs DV1181
sediment
suspensionCaCOcake h
h3
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Summary
21
Sedimentation
● Dispersants allow to obtain a compact sediment and a dispersed suspension
● Dispersant DV-61 gives a better compaction under gravity
● Maximum volume fraction of sediment
max =0.30 (DV61,0.8wt%)
max = 0.24(DV1182, 0.6wt%)
● Presence of different layers during sedimentation due to the particle size distribution
Difficulties
● Variation of pH with dispersant concentration and with time
● Initial particle size distribution was not controlled
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Results
22
• Sedimentation with Turbiscan
– CaCO3 concentration: 5wt% to 20wt%
– Dispersant: DV61, DV1182 (0 to 0.7 dispersant vs CaCO3 wt% )
Visual observation
Measurement of the position of the interface vs time
• Particle size distribution
Measurement by granulometer Mastersizer 2000
Observation by Scanning electron microscopy
• Particle size separation by centrifugation
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Particle size distribution
23
Protocol
• pH of suspension : 9.7
• Initial solid concentration : 20wt%
• pH of water in the dispersion unit : 9.7
• Small amount of suspension is dispersed in the dispersion unit until an optimum measurement condition is reached
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Particle size distribution without dispersant
24
Initial solid concentration: 20wt%
0,01 0,1 1 10 100 10000
1
2
3
4
5
6
7
8
9
10
11V
olum
e(%
)
particle size (µm)
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10-2 10-1 100 101 102
0
1
2
3
4
5
6
7
8
9
10
11V
olum
e (%
)
Particle size (µm)
cdispersant(%) 0 0.05 0.1 0.15 0.2 0.3 0.5 1 2 4
cdispersant
Particle size distribution with dispersant
25
Effect of dispersant
Detection of particles smaller than 1µm with in presence of dispersant
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cdispersant
=0% cdispersant
=1%
Particle size distribution
26
Effect of dispersant observed by SEM
Initial suspensions contain mostly aggregated small particles (0.04-1µm)
Dispersant helps to separate these aggregates
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Results
27
• Sedimentation with Turbiscan
– CaCO3 concentration: 5wt% to 20wt%
– Dispersant: DV61, DV1182 (0 to 0.7 dispersant vs CaCO3 wt% )
Visual observation
Measurement of the position of the interface vs time
• Particle size distribution
Measurement by granulometer Mastersizer 2000
Obsevation by Scanning electron microscopy
• Particle size separation by centrifugation
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Particle separation by centrifugation
28
Protocol
● Dispersant concentration DV61 : 0.5wt%
● Initial solid concentration 20wt%
● Relative centrifugal force (RCF) fixed at 500g
● Centrifugation time : 2-11 minutes
● Centrifuge tube : ultra-clear polycarbonate, volume=10ml
● Characterization of the initial suspension, of the supernatant
and of the sediment by Mastersizer and SEM
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Size distribution in the supernatant
29
Effect of centrifugation time
Shift of size distribution with increasing centrifugation time
0,01 0,1 1 10 1000
1
2
3
4
5
6
7
8
Vol
ume
(%)
Particle size (µm)
Suspension 500g 2mn 500g 4mn 500g 10mn 500g 11mn
suspension
=8.45vol%
cdispersant
=0.5wt%
centrifugationtime
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0,01 0,1 1 10 1000
2
4
6
8
Vol
ume
(%)
Particle size (µm)
Suspension Sediment Supernatant
Size distribution after centrifugation for 11mn
30
Initial suspension, sediment and supernatant
Separation of sizes distribution.The sediment still contains particles smaller than 1µm
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Questions
31
● Improve the yield of small particles by adding more dispersant ?
● Use successive centrifugations to increase the yield of the
separation?
● Combine these two methods ?
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0 1 2 3 4 5 6 7 80
2
4
6
8
10
12
Yie
ld d
ry s
uper
nata
nt (w
t%)
Dispersant concentration (solid wt%)
Yield
Effect of dispersant concentrations
32
Centrifugation at 500g during 11mn
Particle sizes in the supernatant are always smaller than 1µmSupernatant contains probably dispersant in excess
Yield 10wt%
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After centrifugation, if supernatant is clear, dispersant is added during the redispersion with water at the same pH as initial suspension
Successive centrifugations
33
Protocol A: Supernatant is removed after each centrifugation
Measurement of particle size distribution of suspension, supernatant
and sediment after each operation centrifugation
redispersion
initialsuspension
1st centrifugation Supernatant is removed and replaced by deionized water at the same pH of initial suspension.The sediment +water is redispersed
2nd centrifugation
3rd centrifugation
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Successive centrifugations
34
Protocol B : Supernatant is not removed after each centrifugation
initialsuspension
centrifugation
redispersion
Measurement of particle size distribution of suspension after
each operation
cent
rifug
atio
n
cent
rifug
atio
n
cent
rifug
atio
n
redi
sper
sion
redi
sper
sion
Alternate centrifugation and redispersion
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0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
0.35%
6.58%
0.27%
5.56%
4.1%
0.59%
2.73%
2.15%
0.11%
Yie
ld D
ry s
uper
nata
nt (
wt%
)
Centrifugation step
adding dispersant during redispersion of the sediment
( 0.5wt% of solid)
0.35% 6.58% 0.27% 5.56% 4.1% 0.59% 2.73% 2.15% 0.11%
Protocol A
35
Yield in the supernatantTubes containing the supernatant after centrifugationcsuspension=20wt%
cdispersant=0.5wt%
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Protocol A
36
Cumulative yield in the supernatant
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
Cum
ulat
ive
yiel
d (%
)
Yie
ld o
f dry
sup
erna
tant
(w
t%)
Centrifugation step
0
2
4
6
8
10
12
14
16
18
20
22
2422wt%
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0 1 2 3 4 5 60
5
10
15
20
25S
uper
nata
nt d
ry m
ass
(%)
Dispersant concentration (%)
Step 1 Step 2 Step 3 Total Yield
Protocol A
37
Different dispersant concentrations
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Observation by SEM
38
suspension sediment supernatant
cdispersant=0.5wt%
cdispersant=1wt%
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0 1 2 3 4 5 6 720
30
40
50
60
Sed
imen
t heigh
t (cm)
cake
(%
)
Centrifugation step
cake
(dispersant 0.5%)
cake
(dispersant 2%)
1,0
1,5
2,0
2,5
3,0 0,5% Sediment height 2% Sediment height
Protocol B
39
Height and volume fraction of sediment
Yield in the supernatant is not yet determined
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10-2 10-1 100 101 102 103
0
2
4
6
8
10
12
14V
olum
e (%
)
Size (µm)
initial suspension 1st redispersion 2nd redispersion 3th redispersion 4th redispersion
Protocol B
40
Particle size distribution in suspension after different redispersions
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Conclusions and outlook
41
• Recovery of particles smaller than
1µm was obtained by different
ways:
– Increase the dispersant concentration
(up to 7wt%)
– Successive centrifugations with different
protocols.
– Maximum yield : 22wt%
• Successive centrifugations show
probably an improvement of
polymer adsorption through the
sediment height at different steps
(DV61 at 0.5wt% and( 2wt%)
• Consider a pilot test for separation
of small particle with protocol A or B
• Optimize the yield of small particles
• Characterize the absorption of
dispersant at solid surfaces after
successive centrifugations : NEW
MECHANISM ?
• Characterize the sedimentation, the
rheology of sediment, suspension
made of small particles