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Separation of calcium carbonate particles in the presence of dispersant

Report convention CIFRE. Separation of calcium carbonate particles in the presence of dispersant. Liem Chau PHAM TRONG. Molde, June-09-2009. Outlook. Introduction. Objectives Analyze the sedimentation of calcium carbonate suspensions in the presence of dispersants

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Separation of calcium carbonate particles in the presence of dispersant

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  1. Report convention CIFRE Separation of calcium carbonate particles in the presence of dispersant Liem Chau PHAM TRONG Molde, June-09-2009

  2. Outlook

  3. 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

  4. 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

  5. Methods • Dispersion • Sedimentation experiments • Particle size characterization • Centrifugation • Scanning electron microscopy (SEM)

  6. Dispersion method • Mixer : Supertest from VMI • Beaker (stainless steel) • Volume = 1 liter • Diameter =10 cm • Turbine • Type : Deflocculator • Diameter = 35mm d=35mm

  7. Sedimentation Under gravity, T=30°C Turbiscan with Cooler (Formulaction) Transmission detector Laser source λ=850nm Backscattering detector

  8. Particle size characterization • 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 :

  9. Centrifugation • Equipement: Allegra 64 with Cooler (Beckman) • Rotor: S0410 swinging-bucket rotor (4x10ml) • Relative centrifugal force: 500g to 8000g • Temperature : 30°C

  10. 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

  11. 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

  12. Sedimentation under gravity: picture taken after 1 day Initial solid concentration : 15wt% DV-61 concentration between 0% and 0.7% Dispersant /solid concentration (wt% )

  13. 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

  14. t=0 : initial suspension Surface Homogeneous suspension Tube

  15. t=4h : formation of different layers Surface Meniscus Dilute suspension (Low BS and high Trans) Semi-dilute suspension (Low BS and low Trans) Dense suspension (High BS, Trans=0) Tube

  16. t=24h : change of different layers Surface Meniscus Dilute suspension with gradient concentration (Low BS, high Trans) Semi-dilute suspension Low BS, low Trans Flowable layer: Sediment High BS, Trans=0 Tube

  17. t=65h : constant height of compact sediment Surface Meniscus Very dilute suspension without concentration gradient) (Low BS, High Trans) Compact sediment (High BS, Trans=0) Tube

  18. Sedimentation height and velocity based on Backscattering Sample 1 csolide= 20wt% cdispersant= 0.7wt%

  19. Dilute suspension (csolid=0.5wt%, cdispersant=0.5wt%) Backscattering Constant sediment height reached after 24mn

  20. Sediment volume fraction after 1 week Effect of dispersants : DV61 vs DV1181

  21. Summary 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

  22. 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

  23. 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

  24. Particle size distribution without dispersant Initial solid concentration: 20wt%

  25. Particle size distribution with dispersant Effect of dispersant  Detection of particles smaller than 1µm with in presence of dispersant

  26. 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

  27. 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

  28. 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

  29. Size distribution in the supernatant Effect of centrifugation time  Shift of size distribution with increasing centrifugation time

  30. Size distribution after centrifugation for 11mn Initial suspension, sediment and supernatant Separation of sizes distribution. The sediment still contains particles smaller than 1µm

  31. 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 ?

  32. Effect of dispersant concentrations Centrifugation at 500g during 11mn Yield 10wt% Particle sizes in the supernatant are always smaller than 1µm Supernatant contains probably dispersant in excess

  33. Successive centrifugations Protocol A: Supernatant is removed after each centrifugation Supernatant is removed and replaced by deionized water at the same pH of initial suspension. The sediment +water is redispersed 1st centrifugation 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 Measurement of particle size distribution of suspension, supernatant and sediment after each operation centrifugation redispersion

  34. Successive centrifugations Protocol B : Supernatant is not removed after each centrifugation Alternate centrifugation and redispersion redispersion redispersion centrifugation centrifugation centrifugation initial suspension Measurement of particle size distribution of suspension after each operation centrifugation redispersion

  35. Protocol A Yield in the supernatant Tubes containing the supernatant after centrifugation csuspension=20wt% cdispersant=0.5wt% adding dispersant during redispersion of the sediment ( 0.5wt% of solid)

  36. Protocol A Cumulative yield in the supernatant

  37. Protocol A Different dispersant concentrations

  38. Observation by SEM suspension sediment supernatant cdispersant=0.5wt% cdispersant=1wt%

  39. Protocol B Height and volume fraction of sediment Yield in the supernatant is not yet determined

  40. Protocol B Particle size distribution in suspension after different redispersions

  41. 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 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

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