Abstract--Cu montmorillonite heated with or without potassium halide was studied by IR and ESR spectroscopy, supplemented by XRD measurements, microprobe and chemical analyses. It appears that on heating Cu montmorillonite, most of the Cu ions migrate into hexagonal cavities and eventually, when dehydroxylation occurs, into octahedral vacancies. Some Cu ions may penetrate into octahedral vacancies before dehydroxylation. In the presence of potassium halide, deprotonation facilitates penetration of Cu into octahedral vacancies. The presence within the layers of non-exchangeable Cu ions that are inaccessible to water does not necessarily cause the perturbation of OH bending vibrations conventionally attributed to migration of small cations into the structure. Such perturbation was only observed when the basal spacing was reduced to ~ 9.5,~.

Abstract--Two clay minerals, a dioctahedral, Na-montmorillonite from Wyoming and a trioctahedral, synthetic Na-laponite, were exchanged by cupric (Cu(II)) ions and subsequently heated at 100 ~ intervals up to 500 ~ The resulting materials were analyzed by chemical analysis, X-ray diffraction (XRD), cation exchange capacity (CEC) measurements, combined thermogravimetric and differential thermal analysis (TGA-DTA), infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). Montmorillonite exhibits a well-known Hoffmann-Klemen effect in that, when heated, cupric (Cu) ions migrate into the lacunae of the octahedral sheet, where they compensate the negative charge deficit of the clay layer. In the case of laponite, CEC measurements and spectroscopic measurements reveal that Cu ions migrate into the octahedral sheet where they replace Li and Mg ions. After heating at 200 ~ approximately half the interlayer Cu ions are exchanged. The exchange appears to be 1 Cu for 1 Li, resulting in a slight decrease of the negative charge of the layer. After heating at 300 ~ the remaining Cu ions are exchanged by either 1 Mg or 2 Li, which does not result in any further charge reduction. At 400 ~ some of the extracted Mg remigrates into the structure and exchanges some Li (1 Mg for 2 Li). The final product at 400 or 500 ~ is then a Li-laponite with Cu(II) in the octahedral sheet.

Abstract--X-ray photoelectron spectroscopy (XPS) has been used to characterize the bonding state of Cu 2 § Si 4+, A13 § and 02 ions in structural (octahedral and interlamellar) or adsorbed position in phyllosilicates. Five smectites, 5 kaolinites, and 1 chrysocolla with Cu(II) in known positions (octahedral, interlamellar, or surface adsorbed) have been investigated. Their spectra were compared with those of pure Cu metal and of pure Cu(I) and Cu(II) oxides.The line for Cu 2p3/2 (binding energy of 935.4 eV) and well-defined shake-up lines (binding energy of about 943 eV) observed after 1 hr of X-ray irradiation are characteristic of Cu(II) in phyllosilicate octahedral sites. But due to the photoreduction effect, they show Cu(I) oxidation states (Cu 2P3/2, binding energy of 933.2 eV and near absence of shake-up lines) for the phyllosilicates with adsorbed Cu or in interlamellar positions. The kinetics of photoreduction distinguishes octahedral from interlamellar positions, and the latter from a surface adsorbed position. The enlargement of the FWHM (full width at half maximum) of XPS lines has been used to describe crystallochemical parameters linked to local ordering around the probe cations. Crystallization produces decreasing O 1 s and Cu 2p (octahedral cation) line widths but has no effect on the Si 2p (tetrahedral cation) line width. The enlargement of FWHM for all ion lines of the lattice is linked to the nature (Cu > Mg > AI) and the number and amount of structural cations in the phyllosilicates.

ESR has been used to obtain information on the octahedral or interlamellar position of Cu(II) in natural smectites from Burkina Faso (West Africa). On the basis of 060 XRD reflections and chemical data, these smectites were found to be Al-rich and dioctahedral. After both Mehra & Jackson, and De Endredy deferrification treatments, the Cu contents remained high (4500 and 22000 p.p.m., respectively). The Cu(II) ESR spectra of these deferrated smectites were compared to those of two reference smectites for which the structural position of Cu(II) was precisely known. The interlayer Cu(II) signal was obtained on a Cu-saturated Camp Berteau montmorillonite, while the octahedral Cu(II) signal was obtained on a synthetic Cu-rich smectite. For this latter reference sample, EXAFS spectroscopy provided evidence that Cu was in six-fold coordination in the octahedral sheet only, and was not exchangeable. In agreement with the experiments by Clementz, Pinnavaia and Mortland, a shift in the g⊥ ESR signal was observed when the air-dried Cu-saturated Camp Berteau montmorillonite (g⊥ = 2·05) was soaked in water for 48 h (g⊥ = 2·13). A small shift in the opposite sense was observed for the synthetic Cu smectite (g⊥ = 2·05 for the air-dried sample, g⊥ = 2·02 for the water-soaked sample). For the two natural smectites a small shift similar to that for the synthetic Cu-smectite was observed. These results indicate that up to 10% of the Cu atoms substitute for Al-Mg-Fe atoms in the octahedral sheets of the smectites studied.

Abstract--In the copper deposit of Salobo 3A (Brazil), nontronite-like clay samples were found at the bottom of the weathering blanket. Samples were fractionated first by sedimentation and then by a HGMS method. From XRD data, it was found that the samples are essentially smectite with kaolinite in very small quantities. The average structural formula of the smectite, presented in the traditional manner, is:(Si3 ~gAlo 41)Olo(Fel.~Alo.39Mgo osTio.ol Cuo 02)(OH)2 (Cao. ~ 2Nao.o9 Ko.o, Cuo.o2) Chemical analyses show that the smectite samples contain a population of clay particles whose chemistry ranges between a nontronite end-member and an A1-Mg beidellite end-member.Spectroscopic studies by FTIR, M~ssbauer, and ESR show that the three major octahedral cations (A1, Fe, Mg) are present in each octahedral sheet of the smectite, forming a solid solution, and that the chemical trends of the smectite clay detected at a "macroscopic" scale (associated clay particles) can also be observed at the unit cell scale.