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This article in SSSAJ

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


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doi:10.2136/sssaj1993.03615995005700030039x

Determining Completion of Excess Salt Removal from Clays: Method Comparisons

  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

Abstract

Abstract

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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