KINETICS OF IRON(III) HYDROLYSIS AND PRECIPITATION IN AQUEOUS GLYCINE SOLUTIONS ASSESSED BY VOLTAMMETRY

The kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions were studied by cathodic voltammetry with a mercury drop electrode. The kinetics was controlled by changing ionic strength (I), pH and glycine concentration. Voltammetric measurements clearly showed formation and dissociation of a soluble Fe(III)-glycine complex, formation of iron(III) hydroxide and its precipitation. The rate constants of iron(III) hydroxide precipitation were assessed. The precipitation is first-order with respect to dissolved inorganic iron(III). The calculated rate constants of iron(III) precipitation varied from 0.18 x 10(-5) s(-1) (at 0.2 M total glycine, pH 7.30, I = 0.6 mol dm(-3)) to 2.22 x 10(-3) s(-1) (at 0.1 M total glycine, pH 7.30, I = 0.2 mol dm(-3)). At 0.5 M total glycine and I = 0.6 mol dm(-3), the iron(III) precipitation was not observed.