Adsorbed Cr(III) on Chlorite, Illite, and Kaolinite: An X-Ray Photoelectron Spectroscopic Study

The adsorption of Cr(III) was studied at pH 1, 2, 3, 4, 6, 8, and 10 on chlorite and kaolinite and at pH 1, 2, 3, and 6 on illite. The amount of chromium adsorbed on chlorite varied from 3.1 × 10–5 mole/ g at pH 1 to 16.6 × 10–5 mole/g at pH 4, and on illite from 4.9 × 10–5 mole/g to 9.2 × 10–5 mole/g at pH 1 and 3, respectively. Kaolinite adsorbed 3.7 × 10–5 mole Cr/g at pH 1, 2, and 3 and 5.5 × 10–5 mole Cr/g at pH 4. Measurements of the Cr 2p core-level binding energies indicate that chromium is probably adsorbed as a Cr(III) aqua ion at pH values below 4. The binding energies for the Cr 2p level for samples prepared above pH 4 compare favorably with the value determined for chromium hydroxide and lead to the conclusion that the chromium species present at pH 6, 8, and 10 is chromium hydroxide.