Effects of ethylene glycol saturation protocols on XRD patterns; a critical review and discussion

• Published in: Clays and clay minerals Vol. 53; no. 6; pp. 631 - 638
• Main Authors: Mosser-Ruck, Régine, Devineau, Karine, Charpentier, Delphine, Cathelineau, Michel
• Format: Journal Article
• Language: English
• Published: Boulder, CO Clay Minerals Society 01.12.2005; The Clay Minerals Society
• Subjects: chemical properties; chlorite; chlorite group; clay mineralogy; clay minerals; complexing; Earth sciences; Earth, ocean, space; effects; ethylene glycol; Ethylene Glycol Solvation; Exact sciences and technology; experimental studies; geochemistry; High-Charge Smectite; illite; K Saturation; Mg Saturation; Mineralogy; mixed-layer minerals; rock, sediment, soil; saturation; sed rocks, sediments; Sedimentary petrology; sheet silicates; Silicates; smectite; Vermiculite; experimental studies; illite; vermiculite; potassium; Ethylene Glycol Solvation; unit cell; X-ray diffraction; critical review; chlorite; magnesium; expansion; smectite; saturation; K Saturation; High-charge Smectite; Mg Saturation; transformations; clay minerals; sheet silicates; silicates
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/CCMN.2005.0530609

Study of the transformation of smectite to illite, chlorite or vermiculite via interstratified clay minerals needs precise qualitative and quantitative determinations of the different layers in the mixed-layer clays and is generally based on X-ray diffraction (XRD) patterns after specific treatments of the clay samples. Saturation with K or Mg followed by ethylene glycol (EG) solvation are classical methods used to identify high-charge smectite and vermiculite. These procedures have been applied to two experimental clays, one composed of smectite layers and the second, a mixture of vermiculite and smectite layers. Different methods of glycolation (EG vapor or liquid EG) produce significant differences in the XRD patterns. Comparison with literature data indicates that K-saturated, high-charge smectite (∼0.8<total charge<1/unit-cell) and Mg-vermiculite (whatever its charge) do not expand in ethylene glycol vapor (d values ∼14-15 Å). Expansion to 17 Å in liquid ethylene glycol occurs for Mg-vermiculite with a total charge of <∼1.2/unit-cell and for K-saturated, high-charge smectite, when the tetrahedral charge is <∼0.7/unit-cell. This study shows that: (1) glycolation procedures need to be standardized; (2) the use of saturation protocols using both liquid ethylene glycol and ethylene glycol vapor yields useful additional information about the distribution of charges in clay minerals.