Cation exchange capacity methodology I: An efficient model for the detection of incorrect cation exchange capacity and exchangeable cation results

In this study a model is proposed enabling the detection of incorrect cation exchange capacity (CEC) and exchangeable cation values. Numerous CEC and exchangeable cation analyses of clayey sediments, soils and bentonites were performed using triethanolamine-buffered barium chloride, ammonium acetate, silver thiourea and other exchange techniques. As long as these naturally clayey materials only contain adsorbents like clay minerals, organic substances and a group of mainly detrital minerals like quartz, feldspar and mica, results obtained with most procedures are correct. Problems arise when materials contain secondary phases like soluble Ca-carbonates and -sulphates. During the CEC-experiments, these phases interact with the exchange solution. According to expectations, results of exchangeable calcium values are incorrect but CEC is also affected [Deller, B., 1981. Determination of exchangeable acidity, carbonate ions and change of buffer in triethanolamine-buffered solutions percolated through soil samples containing carbonates. Commun. Soil Sci. Plant Analysis 12, 161-177.]. Using the proposed Carbonate and Sulphate Field Model (CSF model) an evaluation of the accuracy of results is possible. (c) 2006 Elsevier B.V. All rights reserved.