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Determination of the cation exchange capacity of clays with copper complexes revisited

¹ Institute of Inorganic Chemistry, University of Kiel, D-24098 Kiel, Germany, and ² CRMD-CNRS-Université d’Orléans, 1b, rue de la Férollerie, F-45071 Orléans Cedex 02, France

^* E-mail: h.mittag{at}email.uni-kiel.de

(Received 15 June 2004; revised 9 September 2004)

The determination of the cation exchange capacity (CEC) of clays by exchange with the cationic copper complexes [Cu(en)₂]²⁺ and [Cu(trien)]²⁺ is revisited. The procedures reported by Bergaya & Vayer (1997) and Meier & Kahr (1999) are modified slightly. The concentration of the copper complexes in the equilibrium solutions is measured by spectral photometry. Correct CEC values of the [Cu(en)₂]²⁺ exchange are only obtained when a buffer (‘tris’, tris (hydroxymethyl) aminomethane, pH = 8) is added to the equilibrium solution after separation of the clay, because the molar extinction coefficient of this complex depends on the pH of the solution. A standard procedure is recommended as a reference method. In most cases, tris addition is not needed for the determination with [Cu(trien)]²⁺ cations. Nevertheless, tris addition is recommended in the standard procedure. Determination of CEC for 40 samples (kaolins, ‘common clays’, bentonites, montmorillonites and beidellite) shows a good agreement between measurements using [Cu(en)₂]²⁺ and [Cu(trien)]²⁺ cations and with results by the ammonium acetate method.

KEYWORDS: ammonium acetate method, bentonites, CEC, competitive adsorption, copper complexes

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