OXIDATIVE TREATMENT FOR THE PREVENTION OF CHROMIUM ACCUMULATION IN A POLYMERIC MATRIX

ABSTRACT

Chromium (III) species tend to accumulate in the organic matrix with carboxylic groups like weak acid ion exchanger resins. Using conventional acidic solutions, chromium (III) can be partially eluted in some circumstances, while an oxidative stripping using hydrogen peroxide in alkaline media seems to be useful. Previously, Cr(III)–H₂O₂ reaction has been studied in aqueous solutions (homogeneous system) at 20°C, testing for 0.5, 1.0 and 2.0?mM of Cr(III) as total metal concentration. The effect of hydroxide ion on the rate of oxidation was also examined. Chromate was continuously monitored using an FIA system. The general mechanism of the homogeneous reactions has been postulated and the main kinetic parameters of the reactions have been calculated. Ageing of chromium (III) solutions has an important effect on the experimental results. Metal elution from cationic resin is usually carried out by strong acids, but here chromium loaded onto a cation-exchange resin is completely stripped after oxidation to chromate ion. The reaction rate is mainly controlled by intraparticular diffusion of the anionic species through the cationic resin. Surprisingly, these are not rejected from the resin phase by the Donnan exclusion. This apparently anomalous behaviour has been explained in terms of the reaction mechanism.