Cation exchange capacity methodology II: A modified silver–thiourea method

• Published in: Applied clay science Vol. 34; no. 1; pp. 38 - 46
• Main Author: Dohrmann, R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01-10-2006; Amsterdam Elsevier Science; New York, NY
• Subjects: Ammonium acetate method; Barium chloride method; CEC; Earth sciences; Earth, ocean, space; Exact sciences and technology; Excess adsorption; Exchangeable cations; Mineralogy; Modified silver–thiourea method; Silicates; CEC; Barium chloride method; Modified silver–thiourea method; Excess adsorption; Exchangeable cations; Ammonium acetate method; chlorides; adsorption; cations; strength; cation exchange capacity; ammonium; barium; halides; acetate; precipitation; solid solution; instability; sheet silicates; silicates; clay minerals; silver; sulfides; Modified silver-thiourea method
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2006.02.009

The silver–thiourea method for the determination of the cation exchange capacity (CEC) has been critically examined. The chemical instability of the exchange solution used causes silver sulphide precipitation on the walls of tubes resulting in a loss of the index cation. This produces misinterpretation and yields usually in an overestimation of the CEC. Furthermore, when expandable clay minerals are investigated excess adsorption occurs leading to unreliable CEC results dependent on solution/solid ratio and ionic strength of the exchange solution. A modified silver–thiourea method is proposed, which uses a chemically more stable exchange solution, eliminating silver sulphide precipitation and substantially lowering excess adsorption, which is abolished by additional washings. The results are comparable to the ammonium acetate method.