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 interlayer environment on the oxidative dissolution of intercalated hydroxy-Cr polymers. Seven montmorillonite clays with pure hydroxy-Cr interlayers and three with coprecipitated hydroxy-Cr and -Al interlayers were suspended in dilute NaOCI. The supernatant Cr concentrations of each were monitored over time. As the amount of Cr held by the pure Cr clays increased, the time required for complete interlayer dissolution decreased. Chromium(III) oxidation was consistent with a proton-catalyzed, second order reaction. Aluminum in the Al---Cr interlayers decreased, but did not stop, the Cr(III) oxidation rate by forming a barrier around the Al---Cr polymers. The slow but sustained oxidation of Cr(III) from the Al---Cr clays was due to diffusion of Cr through the polymers. Despite modest protection offered by Al, all intercalated Cr(III) was rapidly oxidized in the presence of OC1−.