Objectives



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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%)




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