The Tertiary basin of Feres consists of sedimentary rocks, andesitic-rhyolitic volcanic rocks of K-rich calc-alkaline affinities, rocks with calc-alkaline and shoshonitic affinities and volcaniclastic fall and flow deposits. Volcanic and volcaniclastic rocks have variable concentrations of LIL elements (Ba, Sr, Rb, Th) and HFS elements (Zr, V) due to their mode of origin. The pyroclastic flows frequently show more or less intense devitrification, vapour-phase crystallization and, in some cases, evidence of fumarolic activity, as is indicated by the presence of scapolite. The volcanic and volcaniclastic rocks display various types of alteration including formation of zeolites (clinoptilolite, heulandite, mordenite, and laumontite) and smectite, as well as hydrothermal alteration (development of silicic, argillic, sericitic and propylitic zones) associated with polymetallic mineralization. The behaviour of chemical elements during alteration varies. Some are immobile and their distribution is controlled by the conditions prevailing during parent-rock formation and emplacement, but others, such as Ba and Sr, are mobile and selectively fractionate in zeolite extra-framework sites. The formation of zeolite from alteration of volcanic glass is accompanied by an increase in Mg and Al content, and a decrease in Si and Na content, whereas Ca is not affected by alteration. In certain pyroclastic flows, there is a significant difference in K-content between incipient glass and altered rock, due to K-feldspar formation during devitrification and vapour-phase crystallization.

Fluvial and aeolian sandstones of the Sergi Formation are the most important reservoirs of the Recôncavo Basin, Brazil. Optical and scanning electron microscopy, X-ray diffraction and infrared spectroscopy revealed the occurrence of dickite, a clay mineral indicative of deep burial conditions (T >100ºC), in the shallow Buracica (630–870 m) and Água Grande (1300–1530 m) oilfields. Vermicular dickite replaces K-feldspar and plagioclase grains, and fills intra- and inter-granular pores. Its vermicular habit is a product of pseudomorphic kaolinite transformation during burial. The presence of dickite is in accordance with the intensity of compaction, post-compactional quartz cementation and δ18O values of calcite cements (T up to 109ºC). These petrological features of deep burial, as well as apatite fission-track analyses, indicate that uplift and erosion of at least 1 km, and probably >1500 m, affected the central part of the Recôncavo Basin and possibly the entire region. This uplift has not been detected previously by conventional structural and stratigraphic models.

57Fe Mössbauer spectra of the Na+- and Ca2+-saturated forms of four ferruginous smectites,displaying a range of compositions, have been fitted with Voigtian profiles to represent (principally) two correlated distributions of isomer shifts and quadrupole splittings for the Fe3+ sites. Correlating the areas and hyperfine parameters of these distributions with simulations of the octahedral array of cations based on chemical analyses and infrared spectroscopy has enabled identification of the Fe3+ ions that contribute to the outer quadrupole doublet. The octahedral Fe3+ sites are characterized as having at least one Mg2+ nearest-cation neighbour and probably a cisconfiguration with respect to the OH– ions.

In this study, poly(methyl methacrylate-maleic anhydride) (P(MMA-MAh)) was synthesized in toluene from methyl methacrylate (MMA) and maleic anhydride (MAh) monomers via free radical polymerization, in the presence of 2,2′-Azo-bis-isobutyronitrile (AIBN), as initiator at 80ºC for 8 h. The molar ratio of monomers was found to be 1 MAh:8 MMA using hydrolysis and titration. The molecular weight of co-polymer was determined to be of the order of 104 (g/mol) by gel permeation chromatography. The co-polymer was characterized using Fourier transform infrared and nuclear magnetic resonance spectroscopy. Thermogravimetric analysis indicated the initial decomposition temperature was ~270ºC. Differential scanning calorimetry indicated that the glass transition temperature was near 126ºC.

Rectorite modified with benzyldimethyldodecylammonium chloride (OREC) was used as an additive to modify gel polymer electrolytes (GPEs) which consisted of P(MMA-MAh) used as a polymer matrix, propylene carbonate (PC) as a plasticizer and LiClO4 as the lithium ion source. X-ray diffraction analysis indicates that OREC can exfoliate well in GPEs when the amount of clay is suitable. The temperature dependence of the ionic conductivity of the resulting GPEs agreed well with the VTF (Vogel-Tamman-Fulcher) relation. OREC doses of 5 phr resulted in the greatest ionic conductivity. This OREC addition considerably improved the plasticized retention levels. As a consequence of OREC occupying the free volume space in the polymer matrix of GPEs, the bulk resistance of the GPEs was reduced and the glass transition temperature (Tg) increased.

The Lembo clay deposit occurs on orthogneiss, but it also comprises clays with litho-relicts of volcanic rocks. In this study, ten samples from two sites were investigated. The mineralogical compositions consisted of kaolinite + halloysite + illite + quartz + hematite + anatase ± rutile ± orthoclase ± sanidine ± magnetite ± maghemite ± goethite ± Ba-Al-Fe-phosphates ± carbonates ± sulphates. Kaolinite-halloysite and quartz are the prevailing minerals. Some volcanicderived clays contain Fe-rich kaolinite-halloysite (9.6–14.1 wt.% Fe2O3). The chemical compositions, colours and specific surface area (SSA) measurements reveal two groups of clays: one with a positive whiteness index (IB), small SSA and small Fe content, and the other showing a large SSA, negative IB and relatively large Fe contents. The compositions of the first group are close to those of clays from the Mayouom deposit (Cameroon), and from some European commercial kaolins used in ceramics. Relatively Fe-rich clay materials may conform to most formulations of earthen bricks. As a whole, the Lembo clay deposit comprises various compositions of kaolinitic clays, which may yield the opportunity for extensive application in ceramics.

The effects of cobalt ions on the precipitation of goethite in highly alkaline media were monitored using X-ray diffraction (XRD), Mössbauer, Fourier transform infrared (FTIR) and energy dispersive X-ray (EDS) spectroscopies and field emission scanning electron microscopy (FESEM) techniques. Tetramethylammonium hydroxide was used as a precipitating agent. The precipitates were collected after heating of the precipitation systems at 160ºC for 2 h. The XRD results showed the formation of goethite structure as a single phase up to r = 6.98 (where r = 100·[Co]/([Co]+[Fe])). Cobalt ferrite was found as an additional phase in the precipitates obtained at r = 9.09 and 13.04. Mössbauer spectroscopy showed the formation of solid solutions of α-(Fe,Co)OOH. The incorporation of cobalt ions into the goethite crystal structure was monitored by a decrease in the average hyperfine magnetic field (⟨Bhf⟩). The value ⟨Bhf⟩ decreased linearly up to r = 5.66, whereas a nonlinear dependence was obtained at r = 6.98 to 13.04. Infrared (IR) bands corresponding to the bending vibrations δOH and γOH were shifted from 892 to 903 cm–1 and from 797 to 800 cm–1, respectively, up to r = 6.98. Fourier transform infrared spectroscopy lacked the sensitivity to monitor the effects of cobalt ions, demonstrated by the Mössbauer analysis. Cobalt incorporation into the crystal structure of goethite induced a gradual elongation of α-(Fe,Co)OOH particles along the crystallographic c axis. The formation of α-(Fe,Co)OOH nanowires was shown at r ⩾6.98. These nanowires were ~700 nm long, whereas their diameter was ~15–20 nm. The majority of the cobalt ferrite particles were in the nanosize range, as observed by FE-SEM. On the basis of the Co/Fe ratio measured by EDS, it appears that the cobalt ferrite particles were not fully stoichiometric.

Namacotche gem-bearing pegmatites of Alto Ligonha pegmatite district are heterogeneous, strongly fractionated, and have large Li and Ta and extremely large Cs contents. Clay samples were collected in fracture infillings and dilation cavities with gemstones and were studied using X-ray diffraction (XRD), polarized light microscope, scanning electron microscopy-energy dispersive spectroscopy, high-resolution transmission electron microscopy and chemical analyses. The <2 μm fraction contains cookeite, illite, illite-smectite and suggested irregular mixed-layer cookeite-smectite, beidellite, montmorillonite, kaolinite and goethite.The XRD patterns of chlorite and their d values suggest the presence of ‘di-trioctahedral chlorite’ similar to cookeite-Ia polytype. Cookeite chemical analyses show that Li contents range from 0.82 to 1.08 atoms per half unit cell.

A close relationship has been established between occurrences of gemstones and clay minerals. Some important textures and crystal chemistry are discussed.The main gemstones related to the Namacotche Pegmatite are: morganite (pink cesian beryl), kunzite (spodumene) and elbaite tourmaline. As the mechanisms responsible for the gemstone formation take place at low temperature, the clay minerals paragenesis cookeite ± cookeite-smectite interstratification ± beidellite + montmorillonite ± illite-smectite interstratification, represents a late-stage secondary paragenesis, generated by hydrothermal alteration.

An investigation of bulk-rock and clay-fraction compositions of two sedimentary cores from southern Chile was performed to evaluate the record of temporal climatic changes during the late Quaternary (11 ky and 30 ky BP). The bulk mineralogy shows an abundance of feldspars, mica and quartz, with lesser chlorite, amphibole and pyroxene, and variable amounts of carbonates. The clay fraction consists of illite, chlorite and scarce smectite. Smectite shows platy morphology, an Al-Fe beidellite chemical composition, and is detrital. Smectite, together with biogenic carbonate, increases in levels diagnostic of warmer phases. Increases in smectite are attributed either to the beginning of chemical weathering, allowed by the glacial retreat, or to ice extension and sea-level variations. Warmer climates also favoured the increase of carbonate productivity. Levels diagnostic of colder phases show a large decrease in carbonate, small amounts of smectite and large amounts of chlorite and mica, as the abundance of glaciers reduced the productivity and prevented chemical weathering.

The effect of a Mg- and Al-containing layered double hydroxide (LDH), used as an additive or as a matrix, on the dissolution and solubility of two non-steroidal anti-inflammatory drugs (NSAIDs), namely, mefenamic and meclofenamic acids, is reported. The use of MgAl-LDH enhances the solubility of mefenamic acid at the three pH values tested, and the value is larger when the acid is intercalated as opposed to simply being mixed with the layered material. For pure mefenamic acid, the most unfavourable pH is 1.2, while for the physical mixture and the sample with the intercalated drug, the most unfavourable pH is 4.5, for which the minimum increase in the amount of dissolved acid is recorded. The (dissolution) release-rate for both drugs when they are intercalated between the layers is much slower than for the physical mixture or for the dissolution of the pure drug.

The clay-mineral fraction of samples from a bentonite deposit in the Zvolenská kotlina Basin (Slovakia), formed by the alteration of andesitic pyroclastics, was dominated by Fe-bearing montmorillonite of relatively low charge. The total Fe content of the samples ranged from 3.58 to 5.81 wt.% Fe. Variable-temperature Mössbauer spectroscopy revealed that structural Fe(III) in smectite accounts for 70–90% of the total Fe in the unfractionated samples. No structural Fe(II) was observed by Mössbauer spectroscopy, but a small amount was detected by wet chemical analysis. The remainder of the Fe is present in oxide and/or oxyhydroxide phases dominated by poorly ordered goethite and hematite. The hyperfine parameters of the Mössbauer spectra for the raw bentonite are consistent with structural Fe(III) in an aluminosilicate phase mixed with varying quantities of hematite, goethite and possibly maghemite. Except in the fine fraction of sample L28, the hematite failed to undergo the Morin transition, as shown by the negative values for quadrupole splitting at 298 K and 6 K.

Upper Cenomanian–Turonian clay mineral assemblages of sediments cropping out in the Western High Atlas basin are studied in four sections. Smectite and mixed-layer illite-smectite (I-S) have been identified as major constituents of the deposits. The composition of clay associations in black shales and associated sediments varies considerably according to age, but usually depends either on the general lithology, the abundance of organic matter, or the depth of burial. A distinct correlation is evident between clay mineral distribution and sea-level. Smectite and mixed-layer I-S with greater percentages of smectite layers increase in sediments deposited during transgressive periods, whereas they decrease progressively in the shallower facies deposited during regression in favour of illite and mixed-layer I-S with a greater percentage of illite. The vertical evolution and lateral distribution of clay assemblages and their relationships with sea-level as well as the palaeogeographic conditions prevailing during the Late Cenomanian–Turonian period (flattened topography and arid climate), indicate a detrital origin of the smectite minerals and a distribution pattern controlled by differential settling processes.

The transformation of schwertmannite to goethite was studied by ageing one synthetic and five natural schwertmannites in water at room temperature. Additionally, one synthetic and two natural schwertmannites were kept at variable pH (2, 4, 6 and 8). After one year, only the synthetic sample and one natural schwertmannite had transformed to goethite. However, the oxalate solubility of Fe and trace elements in all the samples decreased, whereas the total Fe/S ratios and specific surface areas of all samples increased. Arsenic and organic matter appeared to suppress the schwertmannite-to-goethite phase transformation. At pH 2, synthetic schwertmannite fully-transformed to goethite, but at pH 4–6 only minor transformation occurred. Depending on pH, many trace elements were released into solution during ageing of the natural schwertmannites. In general, Co, Mn, Zn and Si were released to solution, whereas As was enriched in the remaining iron oxide fraction. Al was dissolved at pH <4.

Dolerites from the Sierra de San Pedro (Betic Cordillera, southern Spain) develop three main types of microsystems during hydrothermal alteration: (1) centimetre-sized veins cross-cutting the dolerites; (2) microfractures in feldspar and diopside grains; and (3) alterations involving primary-igneous mafic phyllosilicate grains. The vein and microfracture sites developed alteration assemblages of randomly oriented smectites (saponite and beidellite) and halloysite. At these sites, the alteration mechanism was governed by complete dissolution of the parent material with subsequent crystallization of the products, with no parent-mineral crystallographic control. Pseudomorphed mafic phyllosilicate sites are characterized by oriented complex mineral assemblages made of chlorite, chlorite/smectite mixed layers, corrensite, saponite and relicts of biotite. These assemblages formed during the initial high-temperature stage of the hydrothermal process. In these microsites, the alteration sequence was controlled by the parent-mineral structure and chemistry, with products determined by structural relations with the parent phyllosilicate. Alteration of one phyllosilicate to the next most stable proceeds via interstratification of the parent and product phyllosilicates.

Weathered soil material derived from tectonically emplaced serpentinized ultrabasic intrusive rocks of southern Cameroon has received considerable attention from mining companies due to its extractable-metal (i.e. Ni, Co) potential. As these cations can be incorporated into Fe oxides, it was deemed appropriate to study the mineralogical assemblage of a highly weathered serpentinite soil profile from the area. This study focuses on the different Fe-oxide phases, which were investigated using 57Fe Mössbauer spectroscopy, showing goethite and hematite as the dominant Fe oxides throughout the weathering profile. These minerals, in association with gibbsite and kaolinite, indicate an advanced degree of weathering. The clay fraction of the ‘Lower Limonite’ layer, above the saprolite and at a depth of 7 m, is very rich in goethite, whereas hematite and magnetite are almost absent. Above this layer, the hematite content in the fine-earth and clay fractions increases upwards, while the goethite content remains constant. The significant substitution and change in the particle size of the goethite and the poor crystallinity of hematite, as indicated by the hyperfine parameters and XRD, suggest that the upper material evolved under different pedological conditions compared to the deeper layers. The mixed composition of the upper layers (above 7 m), which contain muscovite and a relatively chaotic distribution of trace elements, suggests ancient mica-schist capping and possibly different cycles of erosion and pedimentation.

The sedimentation characteristics of two commercial bentonites, Tixoton (organically treated) and Montigel-F (untreated), were investigated using a 3% w/v clay suspension at different concentrations (1, 3.5 and 10%) of NaCl and pH values (2, 7 and 12). Settling rates, floc diameters and sediment volumes were derived from changes in light transmittance using a Turbiscan Ma 2000 instrument.

Both bentonite suspensions were unstable (flocculated) in NaCl solutions. The settling rate increased with increasing concentration of NaCl and was directly related to floc diameter. The sediment volume reduced with increasing NaCl concentrations, a result of greater double layer compression caused by increased ionic strength. At comparable salt concentrations, the organically-treated bentonite (Tixoton) settled at a much slower rate and had a greater sedimentation volume. The suspensions of both organically-treated and untreated bentonites were stable (dispersed) above pH 7 and unstable in acidic conditions. The settling rate for Tixoton under acid conditions was much smaller than that for the Montigel-F. Differences in sedimentation characteristics between the two bentonite samples are probably due to the presence of an anionic polymer (carboxymethyl cellulose: CMC) in Tixoton.

The viscosity of the bentonite suspensions was also studied. The viscosity of the clay suspension is closely related to clay dispersivity in solution. The CMC was highly effective in increasing the viscosity of the bentonite suspensions, but only under neutral and alkaline conditions.

Kaolin deposits extending over an area of ~10 km2 in the western and southern parts of Limnos Island, northeast Aegean Sea, Greece, were studied. The kaolin deposits are alteration products of volcanic rocks, mainly trachytes, trachyandesites, andesites and dacites. Study of the collected samples was carried out using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive scanning electron microscopy (SEM-EDS), Fourier transform Raman spectroscopy (FT-Raman), Fourier transform infrared (FTIR) techniques and inductively-coupled plasma (ICP) bulk rock chemical analyses for major, trace and rare earth elements. The extensive alteration of the parent rocks resulted from the circulation of hydrothermal fluids through faults and fractures. The development of the various assemblages depends not only on the temperature and composition of the hydrothermal fluids but also on the distance of the rock from the fault or the channel of the ascending hydrothermal fluids.

Kaolinite, dickite, halloysite, illite, smectite and mixed-layer illite-smectite and jarosite were detected in the altered volcanic rocks forming locally various alteration zones. Smectite-rich zones and illite-rich zones are relatively infrequent. In the halloysite-rich zones, the kaolinization of feldspars is accomplished in four stages. The kaolinizaton of feldspars in the kaolinite-dickite-rich zones follows five discrete stages. In the less altered rocks, thin layers of kaolinite are formed on the surface of feldspars. With increasing kaolinization, kaolinite is developed on the surface of feldspars forming extended parallel booklets of newly formed kaolinite. In the third stage, feldspar crystals are partially altered to kaolinite booklets. As kaolinization advances, kaolinite becomes well formed and, in the most altered rocks, feldspars are partially or completely altered to dickite books, depending on the temperature of the hydrothermal fluids.

Over the past several decades, kaolin has been used intensively in the paper industry as a coating and filler material. These applications require kaolin of a high brightness grade, which depends heavily on the level of impurities (mainly Fe-bearing minerals such as Fe oxides and hydroxides) and may be improved by beneficiation processes involving grain-size classification, magnetic separation and chemical treatments. This investigation was carried out on five Brazilian kaolin samples of different geographical and geological origins. Granulometric, mineralogical, chemical and physical characterizations were performed on all samples before and after the beneficiation process.

Chemical compositions were determined by X-ray fluorescence and the most important crystalline phases were identified using X-ray diffraction. Kaolinite is the dominant mineralogical phase with minor amounts of muscovite and quartz. The nature of Fe impurities was investigated by electron spin resonance and 57Fe Mössbauer spectroscopy. For all studied kaolin samples, Fe ions (Fe3+ and Fe2+) are present in variable amounts, in the kaolinite structure and also in Fe oxides (magnetite, hematite and goethite). The beneficiation procedure aims to remove these Fe oxides and was found to be most efficient for the Mogi das Cruzes kaolin. The Seridó kaolin had the best whiteness index observed among the analysed samples.

This work examines possible new applications for common, clay-based formulations. We processed spray-dried grains of a common clay (ZA-4) and collected fines/rejects from the production of lightweight aggregates (LWA), which were used as filtration beds for removal of Pb2+ and Ni2+ from aqueous solutions. Experiments were performed at different contaminant concentrations and by testing several operational conditions. The removal performance of both tested materials is strongly dependent on the particle-size distribution of the batch, being better for beds made of smaller grain size, since packing density and specific contact area for removal are greater. In general, the efficiency for removal of Pb2+ was greater than for Ni2+. When compared with granular activated carbon, clay-based beds performed well. In particular, finer fractions of LWA show stable behaviour, without saturation after consecutive runs. Saturated beds can potentially be reused, in appropriate amounts, for production of new lightweight aggregates or common ceramic items (e.g. bricks), since retained contaminants will be fixed by firing in the clay matrix. Calcination of pressed pellets made of contaminated filter grains created consolidated ceramic components and sorbed metallic species became inert.

The Biga Peninsula of NW Turkey is host to six major halloysite deposits in the Go¨nen, Yenice and Balya districts. Mineralization took place in areas of Permian limestone blocks where the Triassic Karakaya Complex is in contact with early Miocene calc-alkaline volcanic rocks. Hypogene halloysite mineralization was controlled by the intersection of minor faults in the vicinity of clay deposits. During the Pleistocene, activity of the North Anatolian Fault (NAF) brought ascending geothermal solutions through the fault zones to the surface, which led to hydrothermal alteration and halloysite formation. N-MORB normalized element values for each halloysite deposit and the volcanic rocks suggest genetic links. Alunite and halloysite were formed in the Turplu area where upwelling hydrothermal waters contained major H2S and SO2 acids. Only halloysite mineralization occurred in outflow areas of the same fossil geothermal field.

Pyrite and alunite samples from the Turplu deposits have δ34S values of 0.6–1.8% and 4.8–7.9%, respectively, with values for gypsum of 3.1–3.5%. The δ34S values of pyrite suggest that local meteoric waters had partially mixed with the dominant fluid during the closure stage of fossil hydrothermal activities. The range of δD values of halloysite samples from Turplu is –58.4 to –68.6%. The δ18O values for halloysite are in the range 16.7–18.1%. All halloysite deposits in the study areas are either overlying or adjacent to limestone blocks, and these provide excellent drainage for the discharging geothermal waters. Subsurface drainage systems in the karstic environment and the SO2-bearing thermal waters indicate the importance of acidic waters and the continuous leaching of elements in forming relatively pure hydrated halloysite. A steam-heated dissolution-precipitation model is proposed for the occurrence of all halloysite and alunite deposits. Sulphur gases (H2S-SO2) of hypogene origin rose from deep in the fault zone to the surface where they encountered oxygenated groundwater at the water table. The occurrence of H2SO4 in this hydrothermal system enhanced the acidity of geothermal waters provoking advanced argillic alteration. Hypogene alunite deposits also have large P2O5 contents, suggesting a parent material with a magmatic origin deeper than the alkaline tuffs. Halloysite is a fast-forming metastable precursor to kaolinite.

The kaolinite from Albian sedimentary deposits (Escucha and Utrillas Formations) of the Iberian Range (Spain) have been investigated. This research has shown the presence of different types of kaolinites (detrital and diagenetic) along with micaceous phases in these deposits. Detrital kaolinites show anhedral morphology, low crystallinity and a degree of ordering as well as the presence of interstratified smectite layers. They constitute the matrix of the claystones and siltstones and were probably formed as a consequence of intense weathering processes in the source area during the warm period of the early Cretaceous. Diagenetic kaolinites have been recognized in the sandstones and siltstones, with kaolinite growing between ‘expanded’ mica flakes and vermiform and euhedral kaolinite forming the matrix. They have euhedral morphologies, high crystallinity and a high degree of ordering. They grew in situ as a response to incipient diagenesis by K-feldspar dissolution and/or organic acid-rich fluids derived from the maturation of organic matter in shales.