Report convention CIFRE
Separation of calcium carbonate
particles in the presence of
dispersant
Liem Chau PHAM TRONG
Molde, June-09-2009
Outlook
Introduction
Materials and methods
• Materials
• Methods
Results
• Sedimentation
• Particle size distribution
• Particle size separation by centrifugation
Conclusions
2
Introduction
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
3
Materials
●
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
4
Methods
• Dispersion
• Sedimentation experiments
• Particle size characterization
• Centrifugation
• Scanning electron microscopy (SEM)
5
Dispersion method
●
Mixer : Supertest from VMI
●
Beaker (stainless steel)
●
➔
Volume = 1 liter
➔
Diameter =10 cm
Turbine
➔
Type : Deflocculator
➔
Diameter = 35mm
d=35mm
6
Sedimentation
Under gravity, T=30°C
Turbiscan with Cooler (Formulaction)
Laser
source
λ=850nm
Transmission
detector
Backscattering
detector
7
Particle size characterization
• Granulometer: Mastersizer 2000, Malvern
• Wet dispersion unit by Hydro SM (rotational velocity 1000 rpm)
• Choice of optical parameters for CaCO3:
➔
➔

1
n
Mean refractive indexes : n  no  ne   
2

n
Absorption indexes : k
red
 k
blue
0
red
blue
 1.57033
 1.58098
8
Centrifugation
• Equipement: Allegra 64 with Cooler (Beckman)
• Rotor: S0410 swinging-bucket rotor (4x10ml)
• Relative centrifugal force: 500g to 8000g
• Temperature : 30°C
9
Scanning Electron Microscopy
– 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
10
Results
•
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
11
Sedimentation under gravity: picture taken after 1 day
Initial solid concentration : 15wt%
DV-61 concentration between 0% and 0.7%
0%
0.1%
0.2%
0.3%
0.4%
0.5%
0.6%
0.7%
Dispersant /solid concentration (wt% )
12
Sedimentation during 65 hours
Under gravity (1g): csolid=20wt%, cdispersant=0.7wt%
Transmission
time
sedimentation
front
time
Backscattering
tube
top
bottom
gravity
Animation: Turbiscan, Easysoft
12
t=0 : initial suspension
h (mm)
50
50
Surface
40
40
30
30
Homogeneous
suspension
20
20
10
10
0
100
0
Transmission
100
0
Backscattering
0
Tube
14
t=4h : formation of different layers
h (mm)
50
50
Surface
Meniscus
40
40
Dilute suspension
(Low BS and high Trans)
30
30
20
20
Semi-dilute suspension
(Low BS and low Trans)
Dense suspension
(High BS, Trans=0)
10
10
0
100
0
Transmission
100
0
Backscattering
0
Tube
15
t=24h : change of different layers
h (mm)
50
50
Surface
Meniscus
40
40
30
30
20
20
10
10
Dilute suspension
with gradient concentration
(Low BS, high Trans)
Semi-dilute suspension
Low BS, low Trans
Flowable layer:
Sediment
High BS, Trans=0
0
100
0
Transmission
100
0
Backscattering
0
Tube
16
t=65h : constant height of compact sediment
h (mm)
50
50
Surface
40
40
30
30
20
20
10
10
Meniscus
Very dilute suspension
without concentration
gradient)
(Low BS, High Trans)
Compact sediment
(High BS, Trans=0)
0
100
0
Transmission
100
0
Backscattering
0
Tube
17
Sedimentation height and velocity based on Backscattering
45
Front height (mm)
35
5
4
30
Sample 1
csolide= 20wt%
cdispersant= 0.7wt%
25
3
20
2
15
1
10
5
Sedimentation velocity (mm/h)
Sedimentation front
Sedimentation velocity
40
0
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
Times (h)
18
Dilute suspension (csolid=0.5wt%, cdispersant=0.5wt%)
Backscattering
Constant sediment height reached after 24mn
19
Sediment volume fraction after 1 week
Effect of dispersants : DV61 vs DV1181
32
30
28
DV1182
DV61
26
cdispersant optimum
24
cake(%)
22
20
18
cake  CaCO
16
14
h suspension
3
h sediment
12
10
8
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Dispersant concentration (%)
20
Summary
Sedimentation
●
●
●
Dispersants allow to obtain a
compact sediment and a
dispersed suspension
Dispersant DV-61 gives a
better compaction under
gravity
Difficulties
●
●
Variation of pH with
dispersant concentration and
with time
Initial particle size distribution
was not controlled
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
21
Results
•
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
22
Particle size distribution
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
23
Particle size distribution without dispersant
Initial solid concentration: 20wt%
11
10
9
8
Volume(%)
7
6
5
4
3
2
1
0
0,01
0,1
1
10
100
1000
particle size (µm)
24
Particle size distribution with dispersant
Effect of dispersant
11
cdispersant(%)
10
0
0.05
0.1
0.15
0.2
0.3
0.5
1
2
4
9
Volume (%)
8
7
6
5
4
3
2
cdispersant
1
0
-2
10
-1
10
0
10
1
10
2
10
Particle size (µm)
 Detection of particles smaller than 1µm with in presence of dispersant
25
Particle size distribution
Effect of dispersant observed by SEM
cdispersant=0%
cdispersant=1%
 Initial suspensions contain mostly aggregated small particles (0.04-1µm)
 Dispersant helps to separate these aggregates
26
Results
•
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
27
Particle separation by centrifugation
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
28
Size distribution in the supernatant
Effect of centrifugation time
8
suspension=8.45vol%
7
cdispersant=0.5wt%
Volume (%)
6
Suspension
500g 2mn
500g 4mn
500g 10mn
500g 11mn
5
4
3
2
1
0
0,01
centrifugation
time
0,1
1
10
100
Particle size (µm)
 Shift of size distribution with increasing centrifugation time
29
Size distribution after centrifugation for 11mn
Initial suspension, sediment and supernatant
8
Volume (%)
6
Suspension
Sediment
Supernatant
4
2
0
0,01
0,1
1
10
100
Particle size (µm)
Separation of sizes distribution.
The sediment still contains particles smaller than 1µm
30
Questions
●
Improve the yield of small particles by adding more dispersant ?
●
Use successive centrifugations to increase the yield of the
separation?
●
Combine these two methods ?
31
Effect of dispersant concentrations
Centrifugation at 500g during 11mn
12
Yield 10wt%
Yield dry supernatant (wt%)
10
8
Particle sizes in the supernatant
are always smaller than 1µm
Supernatant contains probably
dispersant in excess
6
4
2
Yield
0
0
1
2
3
4
5
6
7
8
Dispersant concentration (solid wt%)
32
Successive centrifugations
Protocol A: Supernatant is removed after each centrifugation
1st centrifugation
Supernatant is removed and replaced by
deionized water at the same pH of initial
suspension.
The sediment +water is redispersed
initial
suspension
After centrifugation, if supernatant
is clear, dispersant is added
during the redispersion with
water at the same pH as initial
suspension
2nd centrifugation
3rd centrifugation
centrifugation
redispersion
Measurement of particle size
distribution of suspension, supernatant
and sediment after each operation
33
Successive centrifugations
Protocol B : Supernatant is not removed after each centrifugation
centrifugation
redispersion
redispersion
centrifugation
initial
suspension
centrifugation
Alternate centrifugation and redispersion
Measurement of particle size
distribution of suspension after
each operation
centrifugation
redispersion
34
Protocol A
Yield in the supernatant
csuspension=20wt%
cdispersant=0.5wt%
Tubes containing the supernatant after centrifugation
0.35% 6.58% 0.27% 5.56% 4.1%
0.59% 2.73% 2.15% 0.11%
adding dispersant during
redispersion of the sediment
( 0.5wt% of solid)
35
Protocol A
Cumulative yield in the supernatant
8
22wt%
22
7
20
6
18
16
5
14
4
12
10
3
8
2
6
Cumulative yield (%)
Yield of dry supernatant (wt%)
24
4
1
2
0
0
1
2
3
4
5
6
7
8
9
0
10
Centrifugation step
36
Protocol A
Different dispersant concentrations
25
Step 1
Step 2
Step 3
Total Yield
Supernatant dry mass (%)
20
15
10
5
0
0
1
2
3
4
5
6
Dispersant concentration (%)
37
Observation by SEM
suspension
sediment
supernatant
cdispersant=0.5wt%
cdispersant=1wt%
38
Protocol B
Height and volume fraction of sediment
Yield in the supernatant is not yet determined
39
Protocol B
Particle size distribution in suspension after different redispersions
14
12
initial suspension
1st redispersion
2nd redispersion
3th redispersion
4th redispersion
Volume (%)
10
8
6
4
2
0
-2
10
-1
10
0
10
1
10
2
10
3
10
Size (µm)
40
Conclusions and outlook
• 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
• 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
polymer adsorption through the
rheology of sediment, suspension
sediment height at different steps
made of small particles
(DV61 at 0.5wt% and( 2wt%)
41