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Magnus Hedstr m, Emelie Hansen, Ola Karnland, Martin Birgersson, Ulf Nilsson

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Magnus Hedstr m, Emelie Hansen, Ola Karnland, Martin Birgersson, Ulf Nilsson

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    2. Turbidimetry (Nephelometry)

    3. Turbidimetry (Nephelometry)

    4. Experimental Considerations Under what circumstances do colloids form from montmorillonite? Time scales for swelling or sedimentation? Redesigned turbimeter: Sedimentation profiles in the vials. 1.5 mm resolution. What is the role of calcium? Can small quantities of Ca2+ prevent colloid formation? Different mineral: Wyoming contra Kutch (Asha) montmorillonite, Milos (Deponit CAN) The effect of excess NaCl Effect of NaOH

    5. Effect of Ca2+ on Colloid Formation Preparation of Material Only counter ions. No excess salt Ca and Na converted montmorillonite are mixed at various mass ratios with water 100/0 (pure Ca ), 80/20, 60/40, 40/60, 20/80, 0/100 (pure Na) Dispersed 15 min ultra sound 12 h mixing using magnet stirrer Oven dry at 60 °C

    6. Preparation of test

    7. The Setup

    8. Effect of Ca2+ on Colloid Formation

    9. Effect of Ca2+ on Colloid Formation

    10. Density profile within the vial

    11. Effect of Ca2+ on Colloid Formation

    12. Effect of Ca2+ on Colloid Formation

    13. Effect of Ca2+ on Colloid Formation

    16. Effect of NaCl on Swelling of Wy-Na

    17. Effect of NaCl on Swelling of Wy-Na

    18. Effect of NaCl on Sedimentation of Wy-Na

    19. Effect of NaCl on Sedimentation of Kutch-Na

    20. Effect of NaCl on Swelling of Kutch-Na

    21. Density profiles: Sediment Wy-Na 5 g/l

    22. Density profiles: Sediment Wy-Na 5 g/l

    23. Density profiles: Sediment Wy-Na 2 g/l

    24. Density profiles: Sediment Mi-Na 4 g/l

    25. Charge differences among Wy, Mi and Ku

    26. Density profiles: Swelling Mi-Na 4 g/l

    27. Density profiles: Swelling Mi-Na 4 g/l

    28. Density profiles: Swelling Wy-Na 5 g/l

    29. Density profiles:Sediment Ku-Na 2 g/l

    30. Density profiles:Sediment Ku-Na 2 g/l

    31. Sedimentation using centrifuge

    32. Protocol for sample preparation clay fully dispersed in 5 ml de-ionized water 5 ml of NaCl solution of “double strength” added vials shaken not stirred rest 30 minutes (up to 90 min no difference) centrifugation turbidity measurements

    33. Results: Wy-Na 5g/litre

    34. Results

    35. Effect of pH In some cases adding more NaOH decreases pH in the suspension! Instantaneous increase but after time pH decreases NaOH has only marginal effect on the gel, slight tendency to weaken it, as seen from centrifugation, but does not prevent the formation.

    36. What is happening? Chemical analysis shows that the mineral dissolves and Al consumes OH and precipitates as Al(OH)3

    37. Future Titration using NaOH and chemical analysis. What requires to reach a point where the pH response is “normal”. Conclude the turbidity measurements and measure the profiles of all the samples.

    38. Summary Effects of calcium Small amount of Na in Ca montmorillonite lead to colloid formation Wyoming montmorillonite with Ca/Na ratios 100/0, 98/2, 95/5 gives no colloids (or very slowly). Do not show strong osmotic swelling. Wy-montmorillonite with Ca content = 60 % sediments as pure Na-montmorillonite. Clay fully exfoliated Wy-montmorillonite with Ca content = 60 % shows similar swelling behaviour asymptotically as pure Wy-Na. Wy-Ca/Na (80/20) sediment slightly faster. Larger particles? The effect of Ca seems stronger in Asha-montmorillonite, although the 80/20 mixture does not prevent colloid formation.

    39. Summary 2 NaCl effects Dispersions of Wy-Na with 2g and 5g clay/litre show phase separation at NaCl concentrations above 25 mM. House of card Dispersions of Asha-Na with 2g clay/litre show phase separation at NaCl concentrations above 5 mM! Wy-Na shows limited swelling in 25 mM NaCl. No colloids and clay unchanged after 70 days. Reduced Debye length. Un inhomogeneous force field can tear apart the gel phase formed in NaCl solution. With a centrifuge one can tune the angular frequency to find the strength of the gel Centrifugation demonstrates that the strength of the gel structure increases with NaCl concentration. Mi-Na forms gel at 10 mM Nacl i.e. in between Ku and Wy. Effect of charge distribution?

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