SORPTIVE CAPACITY OF MONTMORILLONITE FOR HYDROXY-CR POLYMERS AND THE MODE OF CR COMPLEXATION

Separate montmorillonite suspensions were treated with CrCl3 to give seven Cr(III) concentrations. Each suspension was then titrated with 0.1 N NaOH to give a NaOH/Cr3+ molar ratio of 2.5. Montmorillonite was an effective sorbent for hydroxy-Cr species up to 1200 cmol(+)/kg; above that concentration, sorption continued, though less efficiently. However, N-2-BET specific surfaces and cation exchange capacity measurements indicated that the montmorillonite could sorb significantly more than 1200 cmol(+)/kg. There was virtually no exchangeable Cr in any of the clays, suggesting that this element was covalently bonded to the siloxane surface. Infrared spectroscopy revealed a vibration at 1015-1020 cm(-1) in the Cr clays which was not present in the control. This new absorption band was attributed to an attenuation of the Si-O a(1)(1) vibration caused by inner-sphere complexation of the interlayer Cr with the siloxane oxygen. Because Cr was strongly held and efficiently sorbed, montmorillonite was shown to be an effective sorbent for hydroxy-Cr polymers.