Abstract--The adsorption of Ni(II) and Cu(II) on to the clay minerMs kaolinite, chlorite, and illite has been investigated. The quantity of Ni(II) at pH 6 and Cu(II) at pH 5 adsorbed has been found to vary in the manner chlorite > illite > kaolinite. Examination of the mode of bonding of the metal ions to the clay minerals using X-ray photoelectron spectroscopy (XPS) has been carried out. Comparison of the binding energies for metal ions in octahedral sites in selected minerals (reference minerals) and in simple nickel and copper containing compounds with values for Ni(II) and Cu(II) adsorbed on chlorite indicate that nickel(II) is probably bound as the aquo ion while copper(II) may be adsorbed as Cu(OH) § INTRODUCTION

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The adsorption of Cr(III) was studied at pH 1, 2, 3, 4, 6, 8, and 10 on chlorite and kaolinite and at pH l, 2, 3, and 6 on illite. The amount of chromium adsorbed on chlorite varied from 3.1 • l0 -5 mole/ g at pH 1 to 16.6 • 10 -3 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 l0 is chromium hydroxide.

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