OXIDATIVE DISSOLUTION OF HYDROXY-CR INTERLAYERS FROM MONTMORILLONITE

Expandable layer silicates can sorb considerable amounts of hydrolyzed Cr(III). This study was conducted to determine the effect of the inte rlayer environment on the oxidative dissolution of intercalated hydrox y-Cr polymers, Seven montmorillonite clays with pure hydroxy-Cr interl ayers and three with coprecipitated hydroxy-Cr and -Al interlayers wer e suspended in dilute NaOCl, The supernatant Cr concentrations of each were monitored over time. As the amount of Cr held by the pure Cr cla ys increased, the time required for complete interlayer dissolution de creased, Chromium(III) oxidation was consistent with a proton-catalyze d, second order reaction. Aluminum in the Al-Cr interlayers decreased, but did not stop, the Cr(III) oxidation rate by forming a barrier aro und the Al-Cr polymers, The slow but sustained oxidation of Cr(III) fr om the AI-Cr clays was due to diffusion of Cr through the polymers, De spite modest protection offered by Al, all intercalated Cr(III) was ra pidly oxidized in the presence of OCl-. (C) 1997 Elsevier Science Ltd.