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

Abstract

Abstract 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.