To enhance the catalytic activities of zeolites for the polycondensation reactions of humic precursors, Fe was loaded into a zeolite via an ion-exchange reaction and the resulting product was subjected to calcination at 773 K. Two types iron-loaded zeolites were prepared using one equivalent (Fe-Z-1) and 10-equivalents (Fe-Z-10) of Fe2+ to the cation-exchange capacity of a natural zeolite from Niki town (Hokkaido, Japan). X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) spectra showed that the Fe(II) that was originally loaded into the cation-exchange sites in the zeolite became oxidized to a Fe(III) ionic species during the preparation. The catalytic activities of each zeolite were evaluated, based on the degree of darkening for reaction mixtures containing catechol, glycine and glucose as model humic precursors. The catalytic activities of Fe-Z-1 and Fe-Z-10 were higher than that for an untreated zeolite, and increased with the amount of Fe in the zeolite.

Magnetite-rich waste from a niobium mine near Araxá, State of Minas Gerais, Brazil, was heated to 500°C and 1000°C under an O2 atmosphere. The original waste and its oxidized products were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), room-temperature 57Fe Mössbauer spectroscopy, thermogravimetric analysis (TG) and temperature-programmed reduction (TPR).

Semiquantitative analyses by EDS and quantitative chemical analyses showed the waste to be constituted primarily of Fe with minor amounts of Ti, Ba, Al, Si, Nb, Mn, S and P. Mössbauer and XRD showed the waste to consist predominantly of magnetite and hematite. The magnetite content decreases when the temperature increases due to its direct conversion to hematite. However, at 500°C only 10 wt.% of original magnetite was converted to hematite, confirming the high stability of this magnetite, which could still be detected at 1000°C. The TG profile shows no significant weight gain on heating, indicating a high stability of the magnetite. The TPR profiles show that the hematite in the waste is sintered after treatment at 1000°C and the reduction peaks are consequently shifted to higher temperatures. This high thermal stability is attributed to a moderate isomorphous replacement of Fe by other cations present in the Nb mining waste.

The mineral stability of two bentonites was studied in the presence of pyrite concentrate to simulate the possible reactions between the bentonite barrier used in a high-level nuclear waste (HLW) repository and host rock containing up to 5 wt.% of admixed pyrite. Smectite was the only bentonite mineral affected by pyrite treatment under the experimental conditions used. Bentonites reacted differently with pyrite due to the different nature of the smectites. The distinct crystal chemistry of the smectites controlled by the composition of the parent rocks influenced the smectite surface properties (cation exchange capacity and layer charge distribution) which resulted in a different response of the bentonites to pyrite treatment. A partial transformation of the original smectites into H-smectites represented the initial stage of smectite destabilization on acid attack. Rising non-equivalent isomorphous substitution in the octahedral sheets of the smectites enhanced smectite reactivity and thus the reaction between bentonite and pyrite, causing lower stability of the bentonite containing high-charge smectite.

We report a montmorillonite material with enhanced surface area but with very little alteration in cation exchange capacity (CEC) upon dealumination with para toluene sulphonic acid (p-TSA). The new material shows higher catalytic activity in comparison with mineral-acid-treated clay. Montmorillonite clay was treated with p-TSA for 10 minutes under microwave irradiation. The resulting clay was characterized by CEC, X-ray diffraction (XRD), BET analysis, Fourier transform infrared spectroscopy (FT-IR), temperature programmed desorption (TPD) of ammonia and cyclic voltametry (CV) techniques. XRD patterns show an unchanged structure of pristine matrix after the acid action. BET analysis revealed an increase in the surface area and pore volume on p-TSA treatment, indicating formation of voids in the octahedral layer which suggests dealumination. Nitrogen adsorption-desorption curves showed the creation of new micro porous regions, possibly in the octahedral sheets. In contrast to mineral acid treatment, p-TSA treated clay samples showed similar CEC which shows the absence of dissolution of isomorphously substituted Mg and Fe ions present in the octahedral layer. CV studies confirm the formation of an Al-p-TSA complex, suggesting dissolution of aluminium octahedral sheets. The complex subsequently hydrolyses, replacing interlayer cations with Al3+ ions. Similar treatment with mineral acid resulted in clay with enhanced surface area but with reduced CEC, evidently due to the removal of isomorphously substituted Fe and Mg. Further, the p-TSA treated clays showed relatively higher esterification activity under solvent-free microwave irradiation. The p-TSA treated clay retained its activity even after three subsequent runs and thus can be exploited for practical applications.

Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) with four pyridinium and carboxyl groups in the molecule was synthesized. The adsorption behaviour of TPyCP on the montmorillonite clay surface was examined in an aqueous colloidal solution. While the adsorption maximum λmax of TPyCP was 424 nm in water, it shifted to longer wavelengths on complex formation with clay. The λmax on the exfoliated clay surface was 450 nm, and that in the stacked clay sheets was 471 nm, respectively. Under alkaline conditions ([NaOH] = 2 × 10–4 M), the stacking behaviour of the clay was completely suppressed. It emerged that anionic parts in the porphyrin molecule can suppress the stacking of clay sheets. Judging from the quantitative analysis, the maximum adsorption amount of TPyCP was 100% vs. cation exchange capacity (CEC) of the clay. As the adsorption density of TPyCP increased, λmax shifted slightly to longer wavelengths due to the interactions between adjacent porphyrins. When the loading level of TPyCP was 200% vs. CEC, the stacking of TPyCP was indicated. The average stacking layer number was calculated to be 1.48. On the other hand, it is known that tetra cationic porphyrins without anionic parts do not form such stacking structures. Thus, it seems that zwitterionic porphyrin has the potential to form a three dimensional structure through electrostatic interactions between porphyrins on the clay surface.

We have examined the nature and origin of smectites in glaciomarine sediments of the AND-2A drill core (McMurdo Sound, Antarctica) by means of X-ray diffraction (XRD) analyses on the clay fraction, field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM) observations and SEM-EDS microanalyses on smectite particles. Relying on the smectite variation throughout the drill core it was possible to split the sequence into three units. Smectites throughout the core are either detrital or authigenic. Detrital smectites are close to montmorillonite-beidellite in composition while newly-formed smectites frequently have higher Fe-Mg contents and intermediate compositions between the saponite and nontronite field, with lower amounts in the montmorillonite-beidellite field. In the upper sedimentary sections (Unit I, and Unit II, 36-440 mbsf, 0.7-16.5 Ma) smectites are interpreted to be predominantly detrital, whereas in the lower portion of the core (Unit III, 440-1123.20 mbsf, 16.5-20.2 Ma) authigenic smectites are the most common feature. The predominance of mica, the abundance of chlorite, and the nature of smectites in the upper units indicate physical weathering under cold and dry climate, and a dominant provenance for the clay minerals from the Transantarctic Mountains. Smectites in the lower unit are considered mostly authigenic and they are most likely to be the result of early diagenetic processes, being formed from the alteration of volcanic material (glass, pyroxenes and feldspars) and/or through precipitation from fluids of a possible hydrothermal origin. Our survey attests to the importance of discriminating between a detrital and authigenic nature of smectites as the occurrence of authigenic clay minerals in ancient sedimentary successions might lead to incorrect palaeoclimatic interpretations, since they can be affected by diagenetic processes, thus obliterating the climatic signal.

Natural zeolitic tuff from Brus (Serbia) consisting mostly of clinoptilolite (about 90%) has been investigated for the reduction of the Mg concentration in spring water. The sorption capacity of the zeolite is relatively low (about 2.5 mg Mg g-1 for the initial concentration of 100 mg Mg dm-3). The zeolitic tuff removes Mg from water solutions by ion exchange, which has been demonstrated by energy dispersive X-ray analysis (EDS). The extent of ion exchange was influenced by the pH and the initial Mg concentration. Kinetic studies revealed that Lagergen's pseudo-second order model was followed. Intra-particle diffusion of Mg2+ influenced the ion exchange, but it is not the rate-limiting step. Rather than having to dispose of the Mg-loaded (waste) zeolite, a possible application was tested. Addition to a wastewater with a low concentration of Mg showed that it could successfully make up for the lack of Mg micronutrient and, accordingly, enabled the growth of phosphate-accumulating bacteria A. Junii, increasing the amount of phosphate removed from the wastewater.

The study assessed the effect of heating vermiculites on extractability of phosphorus, iron, zinc and manganese with respect to their potential agricultural use. Of these elements, phosphorus was from apatite and monazite that occur as accessory minerals in vermiculites. Vermiculites were heated at 15–800°C and digested by acetic acid for extracting phosphorus and diethylene triamine pentaacetic acid (DTPA) for extracting zinc, iron and manganese. Phosphorus in the extract was analysed by a flow injection method while zinc, iron and manganese were measured by atomic absorption spectrometry. The results showed that heating vermiculites to 400°C enhanced extractability of phosphorus from apatite and monazite to a level of 335 mg kg–1. Further heating to 800°C reduced extractable phosphorus to less than 75 mg kg–1. Maximum extractable zinc, iron and manganese found were 2.7, 19.1 and 22.9 mg kg–1, respectively, values that are beneficial and tolerable by most plants. Thus, it was concluded that heating vermiculites to ⩽ 400°C optimizes extractability of phosphorus from incorporated apatite and monazite and some essential plant micronutrients in vermiculites.

The use of clay materials as selective sorbents for different contaminants requires very efficient methods. A natural kaolinite was calcined to metakaolinite and than rehydrated at different temperatures to produce a highly porous sorbent. The kinetics of this process were measured, with subsequent IR characterization of the phases formed. The surface and pore distribution of new phases were also assigned. In addition, the kaolinite obtained was pre-treated with Fe3+ ions to improve its sorption affinity for anionic particles. The rehydrated kaolinite and its Fe-modification were used for the adsorption of toxic cations (Zn, Cd, Pb) and anions (As, Se). Adsorption capacities depending on the physical chemical properties of the initial solution (pH, concentration of toxic ions) and the surface properties of the sorbent (specific surface area, modification method) were investigated. The adsorption properties of the sorbents were defined by the Langmuir model.

The present occurrence is the only deposit among those found in Eskişehir province containing both sepiolite and palygorskite in economic amounts. To describe the geology, mineralogy and genetic relationships, two representative measured sections were examined by field work and XRD, XRF and SEM analyses. Sepiolite and palygorskite occur in a ∼40 m thick part of Pliocene sequence where saponite is also found. These minerals appear in ascending order as: palygorskite, saponite, saponite + palygorskite, sepiolite and sepiolite + palygorskite, frequently in association with dolomite. Chemical precipitation from the alkaline lake environment under semiarid or arid conditions was the main process resulting in sepiolite, palygorskite and saponite formation. Of these, saponite and palygorskite were formed when the lake water was rich-in Al and Fe. Changes in pH may have controlled whether saponite or palygorskite could be formed. Palygorskite was also developed by transformation from saponite during diagenesis.

The present study, which was carried out on a deep weathering profile of quartz diorite in the San'in district, Japan, along with two lateritic samples from India and Sri Lanka, provides convincing evidence supporting the dissolution and recrystallization mechanism for the halloysite-to-kaolinite transformation during weathering of crystalline rocks. In all the samples studied, tubular halloysite formed prior to kaolinite via the dissolution of feldspars and precipitation from solution. The crystal size distribution of tubular halloysite formed early was characterized by a lognormal curve having a positive asymmetry. When the activity of water decreased in the weathering profile, halloysite as well as goethite began to dehydrate, which acted as a trigger for dissolving halloysite. The heterogeneous nucleation of kaolinite took place on the edges and in the shrinkage pores of dehydrated halloysite tubes. The topotactic relationship of b*halloysite//b*kaolinite was kept between the substrate halloysite and the product kaolinite in the incipient growing stages of kaolinite. As a consequence, early formed halloysite transforms to kaolinite in a cannibalistic manner over a long period of time, owing to the intermittent supply of solution undersaturated with respect to halloysite in natural open systems.

There is interest in exploiting and developing natural resources, particularly deposits of natural clays. Senegal has several clay mineral deposits for which chemical and mineralogical compositions have been little studied. Some of these natural materials are nowadays used in pottery and ceramics. To extend applications, a better basic knowledge is required and, for this objective, the raw clay and separated <2 μm clay fraction from Keur Saër (Senegal) were subjected to chemical and mineralogical studies. Several techniques including X-ray diffraction (XRD), thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, cation exchange capacity (CEC) measurements and solid state nuclear magnetic resonance (NMR) have been used to characterize the material. It was found that the raw clay and the separated clay fraction consist of a mineral mixture in which kaolinite is the main component. 29Si and 27Al MAS-NMR spectra show the presence of silicon atoms linked to three other silicon atoms via an oxygen atom and six coordinated Al atoms. Significant increases in the specific surface area and cation exchange capacity were observed on purification, reaching a maximum of about 73.2 m2g–1 and 9.5 meq/100 g for the separated fine clay fraction while the values for the raw material were around 28.9 m2g–1 and 7.3 meq/100 g.

The radioactive contaminant plume in groundwater at the Karachai Lake site has been examined further. The source of pollution is the Karachai Lake which was used as a reservoir for liquid radioactive waste (LRW) from the Radiochemical Production Association “Mayak” (South Urals, Russia). Taking into account that colloid-facilitated transport of radionuclides can substantially increase the contaminant migration velocity, the composition and structure of colloid particles from the groundwater within the contaminant plume were studied. Sampling of groundwater was carried out in the observation well within the contaminant plume. Different fractions of colloid particles were extracted from the groundwater samples by sequential filtration through membranes with decreasing pore size. Chemical and mineralogical compositions of the colloid particles were determined by X-ray photoelectron spectroscopy in combination with ion etching of the particle surfaces. The host rocks were studied using characteristic samples from the surface outcrop nearest to the observation well. The analysis showed that the colloid particles consisted of an inorganic core with a discontinuous organic cover. The inorganic core was close in composition to the host rocks along the flow path with a predominance of layered hydrosilicates.

Although numerous models for the formation of glauconite have been presented, the precise process and micro-environment of glauconitization are still poorly constrained. We characterize the special micromilieu of glauconitization developed during early diagenesis and present a model for glauconite formation in fecal pellets.

Glauconitization at Oker (Central Germany) occurred predominantly in fecal pellets deposited in a shallow marine-lagoonal environment during the Kimmeridgian. Within the fecal pellets, rapid oxidation of organic matter provides the post-depositional, physicochemical conditions favourable for glauconitization. Replacements of matrix calcite, dissolution of detrital quartz, K-feldspar, and clay minerals, and Fe redox reactions were observed within the early micro-environment, followed by the precipitation of euhedral pyrite, matrix-replacive dolomite, and megaquartz accompanied by I-S formation as thin section analyses and SEM observations show. Carbonate geochemical compositions based on ICP-OES and stable oxygen and carbon isotope signatures demonstrate that glauconite formation started in a suboxic environment at a pH of 7–8 and a temperature of 22±3°C to 37±2°C at maximum.

TEM-EDX-SAED and XRD analyses on separated glauconite fecal pellets and on the <2 μm clay mineral fraction reveal the predominance of authigenic 1Md-glauconite, 1Md-glauconite-smectite, and 1Mdcis-vacant I-S, besides accessory detrital 2M1-illite and montmorillonite. Kinetic modelling of the glauconite (93–94% Fe-illite layers and 6–7% Fe-smectite layers, R3) and of I-S (66–68% Al-illite layers and 32–34% Al-smectite layers, R1) leads us to conclude that the I-S formed solely by slow burial diagenesis, whereas the glauconite formed close to the seafloor, suggesting significantly faster kinetics of the glauconitization reaction compared with smectite-illitization related to burial diagenesis. Thermodynamically, the substitution of octahedral Al3+ for Fe3+ and Mg2+ during the Fe-Mg-smectite to glauconite reaction via the formation of glauconite-smectite mixed-layered clay minerals may have resulted in a higher reaction rate for this low-temperature glauconitization process.

The mineralogical composition, microfabrics and geochemistry of a set of eight samples derived from a narrow area of NE Peloponnese (Greece), where engineering works are presently in progress, were investigated in this study. No important mineralogical differences were observed between the samples other than a variation in the proportions of the participating phases. Analyses reveal that these sediments consist mainly of carbonates (calcite, dolomite), quartz and feldspars (albite, orthoclase). Carbonate minerals exhibit a micritic texture and a high degree of cementation bonding. Phyllosilicates and clay minerals are also common, with smectite and mixed-layer smectite-chlorite being the prevailing phases, followed by chlorite and white mica (muscovite, illite). According to the physical properties measured on bulk samples, the samples were found to exhibit a low to medium expansion, low to intermediate plasticity, normal activity and brittle behaviour. The porosity does not exceed 46% and the organic matter ranges between 3.80 and 5.00%. The high degree of cementation, the dispersed appearance of clays, the small pores (<10 μm) and the common occurrence of smectite in a mixed-layer with chlorite are all favourable characteristics, positively influencing the sediment's stability for engineering constructions.

Different types of dioctahedral smectites (nontronite, beidellite, montmorillonite) were investigated by X-ray fluorescence analysis (XRF) and Fourier transmission infrared spectroscopy (FTIR). Starting with the chemical composition of the octahedral sheet, the occupancies within the octahedral sheet were adjusted by computer simulations to fit the occupancies derived from FTIR. For both cis-and trans-vacant smectites the AlAl and FeFe pairs are mainly randomly distributed but seem to be aligned along OH-bonded directions. Relative to the chemical composition, AlFe pairs are enriched in cis-vacant smectites and depleted in nontronites. This behaviour can be explained by the necessity to dehydrate and hydrolyse cations when they become incorporated into the structure during crystal growth. The first and second hydrolysis steps are necessary for incorporating cations in trans-vacant smectites, whereas only the first hydrolysis step is necessary for cis-vacant smectites. The corresponding difference in energy may explain why mostly cis-vacant smectites occur in low-temperature environments.

This study examines part of the thick palaeoweathering mantle that formed on the northern area of the Spanish Central System. The study of a compound profile indicates that despite weathering processes, the primary structure of the metamorphic rocks is preserved, and is only partially lost in some intervals of the upper part of the compound profile. Macro/micromorphology, mineralogy and geochemical changes within the profiles revealed two weathering paths. In the first path, Fe-chlorite weathered to chlorite-smectite mixed-layer/smectite/kaolinite+ iron oxides. In the second path, biotite and/or muscovite weathered to kaolinite + iron oxides. The profiles show a progressive decrease, from base to top, in mica and mixed-layers and an increase in smectite and kaolinite. Thus, the profiles only comprise the lower or intermediate zones of the weathering mantle. The weathering occurred under humid climates; the lower zones of the profiles were poorly drained, whereas the topmost zones were better drained and more oxidizing. The results obtained indicate that detailed mineralogical studies are very useful to reconstruct the characteristics of the weathering mantles, and as palaeogeographic and palaeoclimatic indicators.

Three types of AlFePILCs pillared clays have been prepared from Algerian clay precursors. They have been characterized and tested in the Baeyer–Villiger oxidation of cyclohexanone to caprolactone using benzaldehyde and oxygen as oxidant at room temperature. The structural and textural properties of the catalyst have been determined by X-ray diffraction, nitrogen adsorption-desorption isotherms and Mössbauer spectroscopy.

The different activities of the clays have been related to their Fe contents and accessible surface areas. The induction period observed before the reaction started has been attributed to the dissolution of a portion of the Fe3+ cations, mediated by either the perbenzoic acid intermediate or the benzoic acid co-product. The reaction was indeed catalysed by a few ppm of dissolved iron cations and the catalysis of the Baeyer–Villiger oxidation reaction should mechanistically be considered as homogeneous.

Electron paramagnetic resonance (EPR) spectra of different particle size fractions of four kaolins from diverse sources in North America, Europe and Asia have been investigated in order to characterize their paramagnetic properties and heterogeneity. There were major differences in the sources of the EPR signals from transition metals; V and Mn were structural, Fe was both structural and as associated oxides, and Cu was in the form of an adsorbed ion. The radiation-induced free radical signals commonly known as the A- and B-centres were observed in three of the deposits; however, in addition to the previously reported 27Al hyperfine structure associated with the B-centre, we also observed much smaller 27Al hyperfine structure on the g┴ feature of the A-centre. The other kaolin sample produced four free radical signals that have not previously been reported in kaolins. Each had substantial 1H hyperfine splitting; three are interpreted as corresponding to defect centres associated with Si-OH groups, and the other to a Si hole surrounded by protonated O atoms. The EPR spectra changed progressively with particle size, and measurements on the Asian specimens after grinding showed major differences in the Fe3+ signals from the same particle size fractions separated from the natural samples, thus supporting previous reports that grinding results in major structural changes in the minerals.