Separation of calcium carbonate particles in the presence of

dispersant

Liem Chau PHAM TRONG

Molde, June-09-2009

Report convention CIFRE

Outlook

2

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

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

Methods

5

• Dispersion

• Sedimentation experiments

• Particle size characterization

• Centrifugation

• Scanning electron microscopy (SEM)

Dispersion method

6

● Mixer : Supertest from VMI

● Beaker (stainless steel)

➔ Volume = 1 liter➔ Diameter =10 cm

● Turbine

➔ Type : Deflocculator➔ Diameter = 35mm

d=35mm

Sedimentation

7

Under gravity, T=30°C

Turbiscan with Cooler (Formulaction)

Laser sourceλ=850nm

Transmission detector

Backscattering detector

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

Centrifugation

9

• Equipement: Allegra 64 with Cooler (Beckman)

• Rotor: S0410 swinging-bucket rotor (4x10ml)

• Relative centrifugal force: 500g to 8000g

• Temperature : 30°C

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

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

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%

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

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

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

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

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

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%

Dilute suspension (csolid=0.5wt%, cdispersant=0.5wt%)

19

Constant sediment height reached after 24mn

Backscattering

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

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

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

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

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)

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

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

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

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

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

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

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 ?

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%

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

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

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%

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%

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

Observation by SEM

38

suspension sediment supernatant

cdispersant=0.5wt%

cdispersant=1wt%

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

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

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