HYDROXY-CHROMIUM SMECTITE - INFLUENCE OF CR ADDED

OH-Cr smectites were prepared with different mmol Cr/g smectite: 0.5, 1.5, 3.5, 5, 10 and 20 by treatment with hydroxy-chromium solution prepared at 60 degrees C and one day of hydrolysis with OH/Cr = 2. The samples were characterized by X-ray diffraction (XRD), differential thermal analyses (DTA) and N-2 adsorption-desorption isotherms. The d(001) spacings of OH-Cr-smectite were different according to Cr added/g smectite. Larger d(OO I) spacings: 1.95, 2.05 and 2.07 nm were obtained with 5, 10 and 20 mmol Cr per gram of sample. DTA diagrams of smectite treated with OH-Cr solution showed exothermic peak at 420 degrees C corresponding to Cr2O3 (confirmed by XRD). N-2 adsorption-desorption isotherms of smectite treated with different amounts of Cr preserved the same slit-shaped pores than original sample, but with different micropore volume. This behavior was maintained until treatment temperature of 380 degrees C. The specific area of smectite was increased from 36 to 175 m(2)/g after treatment with OH-Cr solution. The textural characteristics of OH-Cr smectite heated up to 420 degrees C were changed. The specific area decreased and mesopore volume was produced. The different Cr added modified the structural and textural behavior.