Synthetic aluminous hematites and goethites have been examined by Fourier-transform infrared spectroscopy. For aluminous hematites prepared at 950°C a linear relationship exists between Al content and the location of the band near 470 cm−1, up to 10 mole % Al substitution which is shown to be the solubility limit. The spectra of aluminous goethites prepared in two different ways are qualitatively similar to each other, but differ as to the relationship between the position of the band near 900 cm−1 and the Al content. The spectra of the two series of hematites produced by calcining the goethites at 590°C also show a strong dependence of band position and intensity on the goethite preparative method.

57Fe Mössbauer spectra have been used to interpret the effects of different cleaning processes on the iron mineralogy of a Weipa, Australia, kaolin. A magnetically separated fraction contained 28% of its iron as hematite likely of secondary origin. An initial centrifugal size separation was shown to give an improved final product, and oxalic acid was found to be more efficient at removing Fe from the kaolinite surface than dithionite bleach. The Mössbauer spectra clearly show that beneficiation steps which give a substantial increase in kaolin brightness result in only minor changes in the clay iron mineralogy. Similar results were also obtained for two commercially available kaolins.

Mineralogical weathering sequences in sediments overlying lignite beds were investigated in a core (27 m deep) from Calvert, Robertson County, northeast Texas. Weathering trends were evaluated based on the properties and relative distributions of both the expandable and non-expandable minerals. The sulfide minerals in these sediments are the most susceptible to weathering and were only observed in the unaltered (reduced) zone below 7 m. Oxidation of the sulfides has resulted in the formation of jarosite and gypsum in the upper 7 m of the core (oxidized zone). The oxidized zone is further characterized by reddish brown colors (high chroma), a greater quantity of dithionite-extractable iron, and absence of chlorite. Although the major clay minerals in these sediments (smectite, kaolinite, mica) are largely detrital, weathering has resulted in an increase in the content of kaolinite and a decrease in the content of mica towards the surface. The mica appears to have altered to a high-charge smectite characterized by basal spacings of 32 Â after intercalation with octadecylammonium cations. The high-charge smectite is most abundant in the soil horizons at the top of the core and gradually decreases with depth. A low-charge smectite is the most abundant species in the un weathered parent sediments and increases with depth. Key Words—Lignite, Oxidation, Reclamation, Smectite, Soil, Weathering.

Measurements of the differential heats of K-Ca exchange are used to show that 6 groups of sites (ranging from −13.8 to −5.1 kJ/eq and with as many as 4 in any one sample) exist in kaolins that range from 0 to 15% in their 2:1 phyllosillicate content. These heat values, coupled with entropies of exchange, suggest that 0.1−10% vermiculitic, micaceous, and smectitic layers are present, presumably interstratified with kaolinitic layers which are assumed to have no permanent charge. Changes in the activity coefficients of adsorbed K with K saturation confirm these conclusions qualitatively. Thus, fK values at x ↑ 0 correlate inversely (r2 = 0.655) with the content of vermiculite + partially expanding micas, and x values at maximum fK indicate the content of vermiculite + nonexpanding mica + partially expanding micas (r2 = 0.732).

Electron spin resonance (ESR) spectra of Cu2+-hexadecylpyridinium (HDP) montmorillonites were investigated as a function of HDP+ content and the hydration state of Cu2+ at relative humidities of p/p0 = 0.52-8 × 10-7 at 298°K. The symmetry of the Cu2+ ESR spectra and the intensity of the ESR signal increased upon dehydration of the complex. The HDP+ cation caused an increase in the hydration state of Cu2+ at a given p/p0 and an increase in the covalency of the Cu-O bond.

Clay minerals and zeolites, candidate backfill minerals for nuclear waste repositories, were treated with saturated NaCl brine and Mg-rich (Mg-Ca-Na-K) brine at 200°C and 300°C for 4 weeks under a confining pressure of 30 MPa. The Al concentrations released in NaCl brine were lower than those in Mg-rich brine at both temperatures indicating that the Mg-rich brine is more acidic than the NaCl brine under these hydrothermal conditions. The Si concentrations in both brines were low because of the relatively acidic conditions developed during the hydrothermal treatment. As determined by X-ray powder diffraction or by specific Cs and Sr sorption measurements, no alteration could be detected in clay minerals treated with NaCl brine at 200°C. Among the zeolites tested, only phillipsite and erionite altered to analcime in NaCl brine at 200°C. Zeolites and most of the clay minerals tested did not alter in the Mg-rich brine treated at 200°C. Vermiculite altered to randomly interstratified vermiculite/K-vermiculite (mica-like) by selective K uptake from the Mg-rich brine.

At 300°C, the clay minerals did not greatly alter, whereas the zeolites altered to analcime and/or albite in the presence of the NaCl brine. In the Mg-rich brine, Al-rich montmorillonite from Wyoming did not alter, whereas Al-poor montmorillonite from Texas altered to randomly interstratified montmorillonite/ illite at 300°C. Vermiculite collapsed to form K-vermiculite (~ 10.2 Å) by the selective uptake of K from the Mg-rich brine at 300°C. Most of the zeolites altered to smectites in the Mg-rich brine at 300°C because of the acidic conditions generated by the hydrolysis of Mg. The selective Cs-sorption Kd decreased from 11,700 for untreated phillipsite to 240 and 15 for the hydrothermally produced analcime/albite mixtures from the phillipsite at 200° and 300°C, respectively, in NaCl brine. These results suggest that montmorillonites and mordenites are relatively more resistant than vermiculite or other zeolites at elevated temperatures and pressures in concentrated hydrothermal brines expected in a salt repository.

A hydrated alumino-phosphate mineral was identified in thin, kaolinitic clay beds of the Cretaceous Dakota Group and the overlying Mowry Shale in the Dakota hogback west of Denver, Colorado. It occurs as 1–3-μm size euhedral crystals and makes up as much as 15% of the rock. Sr is by far the dominent divalent cation present, ranging from 9.4 to 13.1%, confirming the X-ray powder diffraction identification of this mineral as goyazite, the Sr member of the plumbogummite group. The characteristic pseudo-cubic, rhombohedral morphology of this mineral is plainly visible in scanning electron micrographs. On the basis of its euhedral morphology and its occurrence in volcanic ash-derived kaolin beds, the goyazite probably formed during early diagenesis, before or during the alteration of the ash, and before much compaction of the beds.

Ion-exchange isotherms between hydrotalcite-like compounds (HT) of the NO3-, Cl-, and SO4- forms and F−, Cl− Br−, I−, OH−, SO42−, CO32−, and Naphthol Yellow S (NYS2−) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition. The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH− > F− > Cl− > Br− > NO3− > I−, those for divalent anions are in the sequence CO32− > NYS2− > SO42−. The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity. The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction.

Two kerolite and one garnierite samples were subjected to progressive heat treatments prior to their examination by infrared spectroscopy (IR) in the 1200-600-cm−1 and 3800-3000-cm−1 regions. The heat treatment of the garnierite (a mixture of nepouite and pimelite) selectively dehydroxylated the nepouite thus allowing an examination to be made of the OH-vibration bands due to the pimelite. Both the relative intensities of the 710-670-cm−1 doublet and of the different OH-stretching bands indicated the Ni content of this pimelite to be about 70%. The heat treatments did not modify the 1200-600-cm−1 region of the spectra of kerolites but caused a noticeable sharpening in the OH-stretching region. The relative intensities of the structural OH-stretching bands of dehydrated kerolites showed that they differ from Ni-talcs of similar composition in the distribution of Ni and Mg in the octahedral sites. These cations are randomly distributed in Ni-talc but are mainly segregated into Mg and Ni domains in kerolite. Changes in sharpness, intensity, and position of the structural OH-stretching bands of the kerolites as temperature increases and dehydration progresses are similar to those undergone by Mg- or Li-saturated trioctahedral smectites. Also thermal analysis curves of these minerals show similarities with those of Mg- and Ni-saturated smectites, and suggest that in kerolites too, the hydration water is associated with interlayer (though non-exchangeable) Ni and/or Mg cations.