The chemical and the mineralogical composition of a group of pumiceous tuffs associated with recent salic volcanic episodes from Tenerife (Canary Islands) have been studied. The investigation focused on the two main types of pyroclastic deposits of the zone: ash-flows and ash-falls. The samples can be classified chemically as trachytic and phonolitic rocks with an intermediate silica content and a high percentage of alkali cations (Na+ and K+). The mineralogical composition, determined by X-ray diffraction, scanning electron microscopy, and optical microscopy, shows the occurrence of zeolites (mainly phillipsite, with lesser chabazite and analcime), associated with the parent glass. K-feldspar (sanidine) and calcite are accessory minerals. Zeolites are significantly more abundant in the ash-flow deposits. Zeolite formation by hydrothermal weathering in closed-system conditions varies according to the nature and the origin of the pyroclastic deposits. Tenerife phillipsites differ from typical diagenetic, lacustrine, and deep-sea phillipsites, both in chemical and mineralogical features. Alkali cations exceed divalent cations in the unit-cell that, assuming a monoclinic symmetry, has the following parameters: a = 8.46–10.55 Å, b = 14.21–14.40 Å, c = 7.80–8.70 Å, and β = 105°–110°.

While soils formed in tephra are typically dominated by poorly crystalline clay minerals, the occurrence of smectite in E horizons of podzolized soils (Spodosols) has been well-documented. We have observed a well-crystallized smectite mineral dominating the clay fraction of E horizons in tephra-derived soils of northern Idaho. This study was initiated to examine properties and distribution of this mineral along a developmental sequence of high-elevation, forested Spodosols formed in 6800-yr-old Mazama tephra. Three soils exhibiting strong, moderate, and weak E horizon development were sampled along an elevational and climatic gradient. The smectite mineral was identified as beidellite based on expansion and layer charge characteristics. Heated, Li-saturated samples from the most strongly developed E horizon exhibited relatively complete expansion to 1.8 nm with glycerol solvation and mean layer charge was calculated to be 0.44 molc/formula unit using sorption characteristics of alkylammonium ions. Apparent crystallinity and relative abundance of the beidellite in clay fractions decrease with decreasing E horizon development. The more poorly crystalline beidellite is associated with a non-expansive 1.4-nm mineral with considerable Al-hydroxy interlayering. Beidellite was not detected in underlying glacial drift or in a thin layer of 200-yr-old ash that mantles these soils, suggesting it is not inherited from these materials. Rather, our results indicate that beidellite forms in these soils in an environment characterized by low pH and a large flux of organic metal-complexing agents.

The sedimentary series from Academician Ridge, Lake Baikal, eastern Siberia, was examined using cation exchange capacity (CEC) to estimate the amount of expandable clay minerals (ECM) and high-temperature X-ray diffraction (HT-XRD) to determine their basic classification. The comparison of the magnetic susceptibility (MS) at sub-millennial resolution and the δl8O record of a reference Atlantic core (ODP 980) was used to create an age model. The most closely studied part of the series covered the major part of the last glacial cycle (120–20 ky BP). The HT-XRD analysis is based on monitoring the course of ECM dehydration with 5°C steps between 25 and 250°C and enabled us to improve the discrimination between ECM, chlorite and micas. The CEC obtained at millennial resolution showed that the neoformation of ECM in warmer periods of the last interglacial was either insignificant or fully compensated by their dissolution or dilution. The CEC record was correlated with the main climatic stages in the period studied. Both MS and CEC records reflected the environmental changes at about millennial resolution, including climatic instabilities between 117 and 73 ky BP (late MIS5).

The nature of organo-phosphate and carboxylate bonding in aqueous suspensions of noncrystalline alumina, boehmite, and gibbsite has been studied using the anionic nitroxide spin probes 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl and 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxyl dihydrogen phosphate. Analysis of the electron spin resonance (ESR) spectra of these molecules revealed that adsorption of both molecules occurred rapidly on the high surface area alumina and boehmite, whereas only the organophosphate adsorbed on gibbsite. A loss in rotational motion of the molecules accompanied adsorption, with the greater degree of motional restriction observed for the carboxylate attributed to steric restrictions to rotation about the surface-bound C-COO− bond axis. The ease of displacement of adsorbed carboxylate from surface binding sites by weakly adsorbing anions (Cl−, ClO4−) compared to organophosphate suggests that the carboxylate adsorbed by ligand exchange of a single surface OH, whereas the organophosphate probably formed a bidentate bond. The carboxylate bound on noncrystalline alumina showed evidence of nonspecific electrostatic adsorption in addition to ligand exchange of surface OH. This weak bonding was indicated by a moderate loss in rotational motion and ease of exchangeability.

Experimental alteration of obsidian with HCl solution was performed to elucidate dissolution mechanism and formation process of clay minerals in acid solution. Reactions were carried out using 0.1, 0.5, and 4.0 g of obsidian to 100 ml of 0.01 N HCl solution at 150° and 200°C for 1 to 60 days. The reaction products were examined by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and energy dispersive X-ray analysis. The surface composition of obsidian before and after alteration was investigated by X-ray photoelectron spectroscopy (XPS). TEM showed that boehmite precipitated at early stage and spherical kaolinite appeared subsequently by 200°C reactions. However, spherical halloysite occurred predominantly with small amounts of allophane, boehmite, and kaolinite by 150°C reaction in which formation process of the halloysite from allophane passing through an intermediate phase of small size rounded aggregate that consists of fine particles of allophane was observed. A boehmite exhibiting hexagonal platy habit with higher degree of crystallinity was formed by 200°C reaction as a stable phase in solution containing lower Si concentration at which the solution composition coincides with the stability field of boehmite on activity diagram for the system Na2O-Al2O3-SiO2-H2O. The fibrous boehmite having lower crystallinity appeared with increasing Si concentration, considered as a metastable phase in the stability field of kaolinite. XPS indicated that dissolution of obsidian in acid solution proceeded initially by cation exchange between Na ions and hydronium ions in solution and subsequently by preferential release of Al ions relative to Si from the Na depleted surface.

The adsorption of the herbicides quinmerac 7-chloro-3-methylquinoline-8-carboxylic acid (QMe) and quinclorac 3,7-dichloroquinoline-8-carboxylic acid (QCl) on homoionic Fe3+-, Al3+-, Cu2+-, Ca2+-, K+- and Na+-exchanged montmorillonite was studied in aqueous solution. Adsorption data were fitted to the logarithmic form of the Freundlich equation. Ca- and Na-exchanged montmorillonites were ineffective in the adsorption of QMe. On the other hand, the QMe adsorption on Fe-exchanged montmorillonite was rapid and the equilibrium was attained after 15 min. An H-type isotherm was observed for the QMe adsorption on Fe-clay, indicating a high affinity of the solute for the sorption sites and almost complete adsorption from dilute solution. On the other hand, the adsorption isotherm of QMe on Al- and K-clay was of the S-type. This shape suggests that the solvent molecules may compete for the sorption sites. A Fourier transform infrared (FTIR) study suggested that the adsorption mechanism of QMe on Fe-, Al- and K-clay involves the protonation of QMe molecule due to the acidic water surrounding the saturating cations. The greater acidity of Fe-clay compared with Al- and K-clay explains both the lower QMe adsorption observed on Al and K systems and the lack of adsorption on Na and Ca systems. In contrast, the formation of a Cu complex permitted QMe to be adsorbed to a large extent to Cu-clay as shown by FTIR analysis. The QCl was adsorbed only by Fe-clay and the adsorption isotherm of QCl on Fe clay was of the S-type. This finding is consistent with the lower basic character of the QCl molecule nitrogen. In fact, the replacement of the electron-releasing methyl group in QMe with an electron-withdrawing Cl atom to form QCl makes the nitrogen lone-pair electrons of the quinoline ring unavailable for either protonation or complexation.

The response of two swelling clays (SWy-1 and SAz-1) and of one non-swelling clay (KGa-1) and of a series of mixtures of these clays to different electrolyte concentrations was examined using clay-modified electrode techniques. A non-interacting probe ion, Fe(CN)63−, was monitored via reduction for its arrival at a Pt electrode coated with thin films of the clay mixtures. The three clays had both different temporal responses and different equilibrium currents. For SWy-1 the currents were developed over time and were dependent upon the electrolyte of the bathing solution, which was consistent with X-ray diffraction data literature for the interlayer dimension. Similar behavior was found for SAz-1, but for KGa-1, currents were instantaneous and were independent of the bathing electrolyte. This suggests that the pores controlling the probe ion transport were between particle or pinhole in nature. When mixtures of the clays were examined, it was found that KGa-1 caused defects within the structures of the mixed clay films. The SWy-1 mixture was not as affected by these disruptions as was the SAz-1 mixture.

Testing shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).

Although the specific outcrop from which the original kaolin at Kauling (Gaoling) Mine, China, was collected cannot now be relocated, samples were collected and studied from the mine tunnel, country rock, and pegmatite which constitute the sources of kaolin in this region. The kaolin is a residual product of weathering. Where the parent rock was a granite the clay is a mixture of platy and elongate kaolin-group minerals, whereas from the pegmatite portion of the parent rock it is halloysite(10Â) with elongate morphology. These mineral identifications are based on X-ray powder diffractograms, scanning electron micrographs, differential thermograms, and an infrared spectrum hitherto not documented for material from this area.

Although the Kauling locality is the region for which kaolin is named, the mineral kaolinite is a defined species without a specific type locality. The 11th century Chinese locality was not mentioned in the two classic research papers defining kaolinite. The data on the Chinese kaolin, therefore, cannot be used directly to provide criteria for sharply differentiating the otherwise vague boundary between the minerals kaolinite and halloysite(7Å). Pertinent questions on these kaolin-group mineral relationships are brought into clearer focus.

The performance of bentonite barriers for high level radioactive waste (HLRW) disposal is currently being tested in various real-and up-scale disposal tests. One of the disposal tests, the ABM test (ABM = alternative buffer material), was conducted by SKB (Svensk Kärnbränslehantering) as a mediumscale experiment at the Äspö hard rock laboratory in Sweden. The present study deals with the second parcel (ABM-II), which was retrieved after 6.5 years with 2.5 years of water saturation and 3–4 years of heating up to 141°C. Nine different bentonites and two marine clays were tested to investigate the performance. The aim of the study was to provide a detailed characterization of the mineralogical and chemical changes that took place in ABM-II, compare the findings with ABM-I (the first of the six test parcels), and try to draw some general conclusions concerning the use of bentonites in such geotechnical barriers. The ABM-II test parcel revealed a set of reactions that a HLRW bentonite might undergo. The most prominent reaction was the rather complete exchange of cations, which was discussed in a second part to this publication (II — cation exchange; Dohrmann and Kaufhold, 2017). The corrosion of the Fe in metal canisters was observed, but no discrete corrosion product was identified. At the interface of bentonite and the metal canister, the formation of smectite-type trioctahedral clay minerals was observed. In contrast to the ABM-I test, anhydrite was present in many of the bentonite blocks of the ABM-II test. In most concepts used for HLRW disposal in crystalline rocks, a temperature below 100°C at the canister surface was applied to avoid boiling. In the ABM-II test, boiling of water was possibly observed. Throughout the experiment, a pressure/water loss was recorded in the upper part of the geotechnical barrier and water was added to maintain pressure in the bentonite. As a result of evaporation, NaCl crusts might have formed and the barrier was partly disintegrated. These results demonstrated that a reasonable assumption is that no boiling of water occurs in disposal concepts in which a pressure loss can occur.

The smectic clays from Cabo de Gata region, Almeria, Spain, are composed mainly of montmorillonite, but they contain appreciable quantities of fibrous clay minerals, some of which are of the palygorskite type. However, there also is a mineral that has properties intermediate between those of palygorskite and sepiolite. Its structure seems to be a random intergrowth of both.

Mössbauer spectra were obtained for five Ca-exchanged nontronites and one Ca-exchanged vermiculite as the 2-layer hydrates following dehydration at 200°C. Exchange of the samples with Ca2+ and subsequent dehydration resulted in the appearance of a shoulder at about −0.50 mm/s in the Mössbauer spectra of some of the samples. The appearance of these shoulders necessitated the inclusion of doublets with Mössbauer parameters corresponding to tetrahedrally-coordinated Fe3+ (IVFe3+) in the model used to fit the Mössbauer spectra. That the IVFe3+ sites detected in these samples were those in the nontronite structure was confirmed using samples whose IVFe3+ contents have been previously determined from chemical analysis. It appears that this sample preparation method allowed IVFe3+ contents to be determined to within 40%. On this basis, the IVFe3+ content appeared to be unrelated to the total Fe content for the samples studied.

The effects of NaOAc removal of carbonates, H2O2 removal of organic materials, and sodium citrate-bicarbonate-dithionite (SCBD) removal of iron oxides upon the X-ray powder diffraction (XRD) characteristics of clay minerals present within weathered volcanic ash deposits were examined. All pretreatments of samples derived from the Ae and Bhf horizons containing volcanic ash resulted in dramatic increases in XRD peak intensities, while the treatment of IIC-horizon samples resulted in subdued XRD peak intensities. Also, the chemical treatments produced an apparent increase in the amount of expandable clay minerals within the Ae horizon, due probably to the hydrolysis and removal of interlayer Al3+ when H2O2 and SCBD were used. Hence, poorly ordered and pedogenically modified vermiculite or vermiculite/montmorillonite interstratifications became “weathered” by H+ attack and Al3+ removal in a manner similar to the natural processes which take place in the acid and eluvial A horizon. In addition, possible XRD peak modification due to the dilution of crystalline clay concentrations by amorphous clay-size material appeared to be subordinate to the laboratory-induced chemical alteration of the weathered clay minerals.

The substitution in layered double hydroxide-like phases (LDH) of composition $\begin{array}{cc}{\left({\text{Co}}_{1-y}^{2+}{\text{Cu}}_y^{2+}\right)}_2{\text{Al}}^{3+}{\left(\text{OH}\right)}_6{\text{Cl}}^{-}\cdot n{\text{H}}_{\text{2}}\text{O}& \left(0⩽y⩽1\right)\end{array}$ was studied by X-ray diffraction and X-ray absorption spectroscopy. It was found that the lamellar character is maintained over the entire range of the substitution. The local order for the composition {Co2Al} is typical of brucite-like sheets, whereas segregation into small domains may explain the results obtained when the percentage of Cu atoms is increased. The {Cu2Al} end-member material presents a local order around the Cu atoms closely related to the botallackite structure as present in basic layered Cu salts, with the presence of two distinct Cu-Cu distances.

Halloysite nanotubes (HNTs) are hollow clay nanotubes in the nanometer size range, made up of double-layered aluminum silicate mineral layers. HNTs represent an extremely versatile, safe, and biocompatible nanomaterial, used in a wide range of applications in biomedicine and nanomedicine. For example, they are used as transporters for the controlled release of drugs or genes, in tissue engineering, in the isolation of stem cells and cancer cells, and in bioimaging. Consequently, the assessment of the biocompatibility of HNTs has acquired considerable importance. In recent years, HNT composites have attracted attention due to their improved biocompatibility, compared to HNTs, suggesting potential for applications in tissue engineering or as vehicles for drugs or genes. In this review, recent advances in the application of HNTs and HNT composites in biomedicine are discussed to provide a valuable guide to scientists in the design and development of viable, functional bio-devices for biomedical applications.

Selective-dissolution techniques by ammonium oxalate (OX), dithionite-citrate-bicarbonate (DCB), and dithionite-ethylenediaminetetraacetic acid (D-EDTA), and X-ray diffraction and Mössbauer spectroscopy were used to identify and characterize iron oxides and oxyhydroxides in the <2-mm, <50-μm, and <2-μm size fractions of a Mollisol from Bahia Bianca, Argentina. Iron compounds are present at low concentrations in mixtures with quartz, Na-rich feldspar, illite, interstratified illite-montmorillonite, and traces of kaolinite. Total Fe and Al content increases as soil particle size decreases, from 4.3 and 13.3 wt. % in the <2-mm size fraction to 8.5 and 22.8 wt. % in the clay fraction (<2 μm), respectively. No more than 25–30% of the total Fe is associated with the crystalline and the amorphous Fe oxides. Weakly ferromagnetic hematite and goethite were identified in the different fractions. These phases have small particle sizes and/or low crystallinity. They may also have Al for Fe substitutions. Crystalline magnetite or maghemite is rare. These Fe-rich phases are probably coating coarser particles.

The efficiency of Fe removal is highest for the D-EDTA treatment and least efficient for the OX method, for all fractions. The opposite is true for Al removal. Poorly crystalline hematite and goethite, which are soluble in oxalate, are only present in the coarser fractions. Poorly crystalline and crystalline hematite and goethite, which are soluble in DCB and EDTA, are present in coarser fractions, but do not occur in the clay fraction. DCB treatment probably dissolves Al in the 2:1 type phyllosilicates occurring in this soil, whereas D-EDTA dissolves Fe in the hydroxy interlayers of the smectite minerals or in the silicate phases.

The main objective of factorial design is to construct an empirical model to understand complex phenomena such as a purification process up to a given level of accuracy. The present study aimed to investigate the adsorption of Neutral Red dye (NR) from an aqueous solution onto sepiolite using 24 full factorial design. The combined effect of initial dye concentration, adsorbent dosage, pH, and particle size on adsorption of the dye was studied. The results were analyzed statistically using the student’s t-test, analysis of variance (ANOVA), and an F-test to define important experimental factors and their relative levels of importance. A regression model which may be used to estimate the removal efficiency of NR without performing any experiments was suggested. The coefficient of determination (R2 = 0.9938) indicated that <1% only of the total variations remain unexplained by the regression model. The experimental factors selected were determined to influence the adsorption process, but their relative importance varied according to the following sequence: pH > adsorbent dosage > particle size > initial concentration. The magnitude of the effects measured in this work can be used as a guide for how to adapt the adsorption process for different process conditions. The results also indicated that natural sepiolite is a suitable adsorbent for NR.