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The variable charge of dioctahedral smectites.

S Kaufhold1, R Dohrmann

  • 1BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany. s.kaufhold@bgr.de

Journal of Colloid and Interface Science
|October 20, 2012
PubMed
Summary
This summary is machine-generated.

This study quantifies the variable charge in smectites, finding it significantly impacts cation exchange capacity. Differences in variable charge are linked to smectite composition and surface properties.

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Area of Science:

  • Clay mineralogy
  • Geochemistry
  • Materials science

Background:

  • Smectites possess cation exchange capacity (CEC) from permanent structural charge and pH-dependent variable charge.
  • Variable charge, primarily from edge aluminol groups, is crucial but rarely quantified accurately.
  • Understanding variable charge is key for applications involving smectite clays.

Purpose of the Study:

  • To compare methods for measuring variable charge in dioctahedral smectites (e.g., montmorillonites).
  • To assess the variability of smectite charge across different geological deposits.
  • To identify factors contributing to differing variable charge values.

Main Methods:

  • Calculation of variable charge for a model montmorillonite particle.
  • Measurement using two copper-triethylenetetramine (Cu(trien)) based cation exchange capacity (CEC) methods.
  • Potentiometric titration to determine variable charge.

Main Results:

  • Calculated variable charge was ~10% of CEC for a model particle.
  • CEC-based methods yielded 2-14% (pH 4-6) and 10-30% (pH 4-9) variable charge.
  • Potentiometric titration indicated higher variable charge (15-35%).
  • All methods showed comparable trends in distinguishing materials with different variable charges.

Conclusions:

  • Variable charge significantly contributes to the overall CEC of smectites.
  • Smectite chemical composition (e.g., Mg content) and surface characteristics influence variable charge.
  • The tested methods are suitable for differentiating smectites based on their variable charge.