Objectives

Objectives

• 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

CaCO3 humid cakes :75%<1µm (according to Coatex)

• 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

Dispersion

• Dispersion

• Sedimentation experiments

• Particle size characterization

• Centrifugation

• Scanning electron microscopy (SEM)

Mixer : Supertest from VMI

• Mixer : Supertest from VMI

• Beaker (stainless steel)

• Volume = 1 liter
• Diameter =10 cm

• Turbine

• Type : Deflocculator
• Diameter = 35mm

Under gravity, T=30°C

• Under gravity, T=30°C

Granulometer: Mastersizer 2000, Malvern

• 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 :

Equipement: Allegra 64 with Cooler (Beckman)

• Equipement: Allegra 64 with Cooler (Beckman)

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

• Relative centrifugal force: 500g to 8000g

• Temperature : 30°C

Very dilute suspensions obtained from initial suspension, sediments or supernatants in water at pH=9.7 (slightly turbid by eye)

• 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

Sedimentation with Turbiscan

• 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

Initial solid concentration : 15wt%

• Initial solid concentration : 15wt%

• DV-61 concentration between 0% and 0.7%

Under gravity (1g): csolid=20wt%, cdispersant=0.7wt%

• Under gravity (1g): csolid=20wt%, cdispersant=0.7wt%

t=0 : initial suspension

• t=0 : initial suspension

t=4h : formation of different layers

• t=4h : formation of different layers

t=24h : change of different layers

• t=24h : change of different layers

t=65h : constant height of compact sediment

• t=65h : constant height of compact sediment

Effect of dispersants : DV61 vs DV1181

• Effect of dispersants : DV61 vs DV1181

Sedimentation

• 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

Sedimentation with Turbiscan

• 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

Protocol

• Protocol

Initial solid concentration: 20wt%

• Initial solid concentration: 20wt%

Effect of dispersant

• Effect of dispersant

Effect of dispersant observed by SEM

• Effect of dispersant observed by SEM

Sedimentation with Turbiscan

• 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

Protocol

• Protocol

Effect of centrifugation time

• Effect of centrifugation time

Initial suspension, sediment and supernatant

• Initial suspension, sediment and supernatant

Improve the yield of small particles by adding more dispersant ?

• Improve the yield of small particles by adding more dispersant ?

• Use successive centrifugations to increase the yield of the separation?

• Combine these two methods ?

Centrifugation at 500g during 11mn

• Centrifugation at 500g during 11mn

Protocol A: Supernatant is removed after each centrifugation

• Protocol A: Supernatant is removed after each centrifugation

Protocol B : Supernatant is not removed after each centrifugation

• Protocol B : Supernatant is not removed after each centrifugation

Yield in the supernatant

• Yield in the supernatant

Cumulative yield in the supernatant

• Cumulative yield in the supernatant

Different dispersant concentrations

• Different dispersant concentrations

Height and volume fraction of sediment

• Height and volume fraction of sediment

Particle size distribution in suspension after different redispersions

• Particle size distribution in suspension after different redispersions

Recovery of particles smaller than 1µm was obtained by different ways:

• 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%)