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Quantitative Determination of Vermiculite in Soils
Author(s) -
Alexiades C. A.,
Jackson M. L.
Publication year - 1965
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1965.03615995002900050016x
Subject(s) - vermiculite , kaolinite , cation exchange capacity , clay minerals , chemistry , halloysite , potassium , feldspar , mineralogy , soil water , muscovite , montmorillonite , mica , chlorite , quartz , dissolution , geology , soil science , geochemistry , paleontology , organic chemistry
A chemical method based on potassium fixation was developed for quantitative determination of vermiculite in soils. The cation‐exchange capacity (CEC) of a sample is determined by washing with CaCl 2 and replacement of Ca with MgCl 2 . The sample is then washed with KCl, heated to 110C overnight to dehydrate and collapse the layers of vermiculite and to fix K. The K remaining exchangeable is determined by NH 4 Cl washings. The difference between these two CEC values gives the interlayer charge of vermiculite. A number of vermiculite standards and soil samples of widely different clay mineral compositions give remarkably near 100% totals when the vermiculite content is based on the average value of interlayer charge of 154 meq/100 g of vermiculite and when the other minerals present are appropriately determined (mica by K 2 O, chlorite by ignition loss, montmorillonite by CEC measured by non‐fixed K, quartz and feldspar by Na 2 S 2 O 7 fusion, allophane, kaolinite, and halloysite by selective dissolution in NaOH). The total CEC of vermiculite is 159 meq/100 g when the allocated external surface charge of 5 meq is included.