Author
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Laird, David |
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Submitted to: Methods of Soil Analysis
Publication Type: Book / Chapter Publication Acceptance Date: 5/11/2006 Publication Date: 2/18/2008 Citation: Laird, D.A. Analysis of Layer Charge, Cation and Anion Exchange Capacities, and Synthesis of Reduced Charge Clays. 2008. In: Ulery, A., Drees, R. editors. Methods of Soil Analysis, Part 5, Mineralogical Methods. Madison, WI. SSSA Book Serv. 5. SSSA. p. 485-508. Interpretive Summary: Electrical charge of clay surfaces is one of the most important properties of soils. Surface charge has a big effect on how clay minerals behave in both environmental and industrial settings. This chapter describes several analytical methods for measuring surface charge properties of clays. The advantages and disadvantages of each method are discussed along with the appropriate conditions where a particular method should be used. The chapter thus serves as a guide for scientists to select an appropriate analytical method for their project. This work will be of primary importance to soil scientists and geologists who study clay mineralogy and engineers who seek to develop industrial processes involving clay minerals. Technical Abstract: Surface charge is one of the most important properties of clay minerals. Surface charge is used in classification of 2:1 phyllosilicates and has a strong influence on properties of clays such as hydration, swelling, cation exchange, and reactions with organic molecules. In this chapter, analytical methods for determining layer charge, cation exchange capacity (CEC), anion exchange capacity (AEC) and for preparation of reduced charge clays are described. The structural formula method is the standard method for determining layer charge of 2:1 phyllosilicates. However, the structural formula method can only be used with nearly pure samples of 2:1 phyllosilicates and, therefore, cannot be used with most natural samples. The alkylammonium method of determining layer charge can be used with mixed mineralogy samples. The alkyammonium method gives a value of layer charge only for the smectite or vermiculite phase in mixed samples. Three different methods of determining CEC are described. The sodium acetate method should be used with samples containing carbonates. The magnesium-ammonium method is designed for neutral or slightly acidic samples that are dominated by permanent charge clays. And, the compulsive exchange method is designed for clay samples dominated by variable charge minerals. The magnesium-ammonium and compulsive exchange methods can also be used to determine AEC. A procedure for preparing reduced charge clays is also described. Reduced charge clays have proven valuable in many layer charge studies as they provide a means of isolating the layer charge effect. |
