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
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
- 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=4h : formation of different layers t=4h : formation 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
Initial solid concentration: 20wt% Initial solid concentration: 20wt%
Effect of dispersant
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
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
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%)
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