Abstract
AbstractA 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 CaCl2 and replacement of Ca with MgCl2. 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 NH4Cl 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 K2O, chlorite by ignition loss, montmorillonite by CEC measured by non‐fixed K, quartz and feldspar by Na2S2O7 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.
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