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Soil Science Society of America Journal Abstract -

Determining Completion of Excess Salt Removal from Clays: Method Comparisons


This article in SSSAJ

  1. Vol. 57 No. 3, p. 874-877
    Received: June 3, 1992

    * Corresponding author(s):
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  1. Eyasu J. Mekonnen,
  2. Edward A. Nater  and
  3. David A. Laird
  1. Soil Science Dep., 439 Borlaug Hall, Univ. of Minnesota, St Paul, MN 55108-6028
    USDA-ARS National Soil Tilth Lab., 2150 Pammel Drive, Ames, IA 50011



Three methods of determining the extent of excess salt removal during alcohol washing of clays were compared. Clays (<2 µm) separated from Wyoming bentonite, halloysite, and a Fargo soil (fine, montmorillonitic, frigid Vertic Haplaquoll) were saturated with 0.5 M CaCl2 or 1.0 M KCl. Excess salts were removed by eight consecutive washes with 95% ethanol. Vortex and ultrasonication mixing methods were also compared. After centrifugation, the supernatants were analyzed for excess salt by (i) the AgNO3-Cl test, and by measuring (ii) electrical conductivity, and (iii) elemental concentrations. Elemental concentration and conductivity measurements indicated that substantial amounts of excess Ca and K (approximately 5 to 10% of CEC) remained in the clays when the AgNO3-Cl test was first negative. Ultrasonication reduced the number of washings required to remove excess salt from clays when compared with vortex mixing. The results demonstrate that electrical conductivity is a rapid and reliable method of determining completion of excess salt removal.

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