Secondary surface layers form by replacement of almandine garnet during chemical weathering. This study tested the hypothesis that the kinetic role of almandine’s weathering products, and the consequent relationships of primary-mineral surface texture and specific assemblages of secondary minerals, both vary with the solid-solution-controlled variations in Fe and Al contents of the specific almandine experiencing weathering.

Surface layers are protective (PSL) when the volume of the products formed by replacement is greater than or equal to the volume of the reactants replaced. Under such circumstances, reaction kinetics at the interface between the garnet and the replacing mineral are transport controlled and either transport of solvents or other reactants to, or products from, the dissolving mineral is rate limiting. Beneath PSLs, almandine garnet surfaces are smooth, rounded, and featureless. Surface layers are unprotective (USL) when the volume of the products formed by replacement is less than the volume of the reactants replaced. Under such circumstances, reaction kinetics at the interface between the garnet and the replacing mineral are interface controlled and the detachment of ions or molecules from the mineral surface is rate limiting. Almandine garnet surfaces beneath USLs exhibit crystallographically oriented etch pits. However, contrary to expectations, etch pits occur on almandine garnet grains beneath some layers consisting of mineral assemblages consistent with PSLs.

Based on the Pilling-Bedworth criterion, surface layers are more likely to be protective over a broad range of reactant-mineral compositions when they contain goethite, kaolinite, and pyrolusite. However, this combination requires specific ranges of Fe and Al content of the natural reacting almandine garnet. To form a PSL of goethite and kaolinite, an almandine garnet must have a minimum Al stoichiometric coefficient of ~3.75 a.p.f.u., and a minimum Fe stoichiometric coefficient of ~2.7 a.p.f.u.

Product minerals also influence the mobility of the least-mobile major rock-forming elements. A PSL consisting of goethite, gibbsite, and kaolinite yields excess Al for export during almandine garnet weathering. As the quantity of kaolinite present in the PSL decreases, the amounts of Al available for export increases.

The delivery of plastic fines such as bentonite into loose saturated granular soil deposits is an effective method for mitigating the liquefaction phenomenon. While the bentonite should be injected into the deposits in the form of a concentrated suspension, such application is limited in practice because of the low mobility of the suspension. The initial mobility of the bentonite suspension should be managed in order to increase the penetration depth. On the other hand, the suspension needs to maintain its thixotropic nature to improve the resistance of the treated soils under cyclic loading over time. The objective of the present study was to investigate the dynamic rheological properties of the bentonite suspensions modified with an ionic additive, sodium pyrophosphate (SPP), to evaluate a possible application of the modified suspensions in mitigation of liquefaction. In the present study, the storage and loss modulus of SPP-modified bentonite suspensions were measured using a strain-sweep (oscillatory shear) technique. Bentonite suspensions with clay contents of 5, 7.5, 10, and 12 wt.% (by total weight of suspension) were tested at various SPP concentrations (0 to 4 wt.% by weight of dry bentonite). The time-dependent behavior of the suspensions was evaluated with a critical storage modulus at various resting times (0 to 480 h). The results showed that the initial critical storage modulus decreased significantly with increasing SPP concentrations, but the reduced critical storage modulus increased gradually with resting times. This initial reduction in critical storage modulus is attributed to a reduction of the inter-aggregated 3-D networks due to the presence of SPP; the amount of 3-D network formed in a suspension governs the critical storage modulus. With time, the networks are formed gradually, resulting in recovery of critical storage modulus. The normalized modulus was degraded more slowly in the modified suspensions than in the unmodified suspensions, which is a desirable property of the suspensions for mitigation of liquefaction.

Dioctahedral clays from an active continental geothermal system have been studied to assess their usefulness as proxies of paleo-hydrological and thermal conditions in the subsurface. Drill cuttings from Well WK244 in the Te Mihi area of the Wairakei Geothermal Field, New Zealand, were analyzed to determine the mineralogical, morphological, and isotopic characteristics of hydrothermal clays in these samples. Mixed-layer illite-dioctahedral smectite (I-S) and R0 chlorite-trioctahedral smectite are the main clay minerals, with I-S clays varying downward from R1 to R3 ordering and 50 to >90% illite over 160 m. The proportion of illite in I-S correlates positively with downhole temperature (r = 0.98) and I-S morphology changes from high aspect ratio ribbons, laths, and hairy fibers to pseudo-hexagonal plates with depth. Swelling clay percentages determined using the methylene blue method show a strong positive correlation with %S in I-S (r = 0.91), validating use of methylene blue as a rapid field tool for characterizing the smectite to illite transition in this active geothermal environment. The oxygen isotopic composition of I-S (dd18OI-S) decreases systematically with depth, and mostly reflects a progressive increase in subsurface temperature during clay formation. Estimates of water/rock ratios calculated using δ18OI-S values display stratigraphic variability that corresponds to variations in permeability. Oxygen isotopic measurements of I-S are a useful tool for understanding reservoir and permeability evolution in such geothermal systems and their related fossil analogs.

In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals (e.g. disseminated siderite, volcanic glass) and precipitation of others (e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water—rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower δ18O and δ2H values in cores located ≤ 10 m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower δ18O values during CSS, but a systematic shift in δ2H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam δ2H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-OB3 that contain hydroxy-interlayered smectite have lower δ2H values as a result of CSS.

A method to characterize and map both kaolinite and dickite polytypes in sandstone thin sections using infrared microspectroscopy (IRMS) was developed. Minerals identification using IRMS can be performed using the hydroxyl-stretching band of most clay minerals (3500–4000 cm−1) in spite of infrared (IR) interferences caused by the embedding resin and glass substratum. Emphasis was placed on determining the optimum analytical conditions for IR data acquisition. The best data-acquisition parameters for Fourier-transform infrared (FTIR) measurements (i.e. spectra quality as a function of beam size and the number of scans) were obtained from a series of single spectra. Then, spatial resolution was explored as a function of the IR beam size (from 50 μm × 50 μm to 15 μm × 15 μm) and the step-scan interval (i.e. the distance between two successive analysis points). The IRMS measurements were performed on thin sections of materials characterized previously using scanning electron microscopy (SEM) and chemical analysis. Using IRMS, locations on the thin sections containing nearly pure dickite or kaolinite polytypes were identified and mapped. Most spectra collected using IRMS represented kaolin mineral aggregates rather than individual crystals, however, and mixing of kaolin polytypes was common at the spatial resolution of the IR beam size used. The spatial resolution of the IRMS was comparable to optical petrography and made possible the identification of areas on the thin section for further ‘in situ’ investigation using other methods (e.g. microprobe, Laser Ablation Inductively Coupled Plasma Mass Spectrometry — LA-ICP-MS, etc.). Also, the use of blocky crystal morphology to identify dickite was questioned, as kaolinite with blocky habit was identified. Mineral mapping using IRMS seems particularly suited for investigating petrographic relationships between kaolinite and dickite in sandstone diagenesis, but could also be used for clay minerals in other rock types or soils.

A compositional gap between sepiolite and palygorskite has long been accepted even though they have similar structures, but recent studies found that such a gap does not exist and that the compositional series is continuous between them. If this is true, intergrowths between these two minerals should exist. The purpose of the present study was to demonstrate the existence of sepiolite-palygorskite intergrowths in all possible proportions, in order to establish the compositional links between ideal sepiolite and ideal palygorskite and to define the compositional limits of these two minerals. Sepiolite and palygorskite have similar structures but different chemical compositions: sepiolite is the most trioctahedral and magnesic extreme, while palygorskite is dioctahedral with Al and Mg in its octahedral sheet. The existence of all intermediate compositions between these two pure extremes has led to the definition of the intermediate minerals, Al-sepiolite and Mg-palygorskite, which can have similar chemical composition. The structural relations between the different minerals of the palygorskite—sepiolite series were studied here by powder X-ray diffraction (XRD), and continuous variation in the chemical composition is explained by the existence of intergrowths of sepiolite and palygorskite polysomes forming a continuous polysomatic series. The existence of intergrowths by mixtures of polysomes in modulated structures can be considered in the same way that the mixed-layer minerals in layered structures are considered. The continuous polysomatic series of sepiolite-palygorskite can be expressed by the general formula: [Si12Mg8O30(OH)4(OH2)4]y∙[Si8O20(Mg2Fe2)x(Mg2Al2)(1-x)(OH)2(OH2)4](1-y)·nH2O, where sepiolite and palygorskite are the end-members. They and xvalues can be calculated using a ternary plot with the oxide contents of the main octahedral cations (Al2O3, Fe2O3, and MgO). The proposed model, which is based on the intergrowth of sepiolite and palygorskite polysomes, explains both the variability in the chemical composition and the compositional limit for the identification of these minerals by X-ray diffraction.

The conventional cauliflower-like shape of magadiite imposes serious limitations on its applications in adsorption, catalysis, ion exchange, etc. To overcome this problem, a method to prepare it with plate-like structures was developed. This novel approach is based on an interface-controlled heterogeneous nucleation process. Zirconia grinding balls with diameters of 2.0 mm were dispersed in the starting solution to provide solid-liquid interfaces. Then the starting solution with a SiO2:NaOH:H2O molar ratio of 9:2:75 was subjected to hydrothermal treatment at 433 K for 96 h. The presence of the solid-liquid interface improved the crystallization yield and controlled the morphology and specific surface area of the crystals. With the zirconia balls, the yield and sizes of the plate-like magadiite were 52 wt.% and 1–3 μm, respectively. In the absence of zirconia balls, the yield was smaller (45 wt.%) and magadiite shaped like cauliflower was formed. The plate-like magadiite had a specific surface area of 66 m2 g−1 and a pore-size distribution between 4 and 5 nm, compared with a surface area of 28 m2 g−1 for the cauliflower-like magadiite. In addition, the plate-like magadiite was a more effective ion exchanger than the cauliflower-like magadiite with a cation exchange capacity of 64.5 mmol/100 g (compared to 53.8 mmol/100 g for the cauliflower-like form) and it had a faster sorption rate for calcium ions.

Bentonite is to be used as a sealing material for long-term storage of radioactive waste. During permafrost periods the buffer may freeze, causing the following: montmorillonite dehydration, ice formation, and pressure build-up that may fracture the surrounding rock. No previous study has been done on freezing of bentonite in saline water. Using small and wide angle X-ray scattering, the present study aimed to increase understanding of the combined impact of salt and temperature on the hydration (swelling) of Wyoming montmorillonite. The basal spacing of the Na-montmorillonite was very dependent on the water content, while this was not the case for the Ca-montmorillonite (after reaching 19 Å). The basal spacing of the free-swelling Na-montmorillonite (34–280 Å) was estimated successfully using simple calculations. During freezing of Na-montmorillonite in NaCl solution, both ice and hydrohalite formed (at -50 and -100ºC). At starting concentrations ≥ 1.5 M the basal spacing was not affected by freezing. During freezing of Ca-montmorillonite in CaCl2 solution, ice formed; antarcticite formed only sporadically. The basal spacing of the Ca-montmorillonite at high NaCl concentrations (>1 M) was greater at -50 and -100ºC (18 Å) than at 20ºC (16 Å). The opposite was observed at low concentrations. This change was attributed to small amounts of salts introduced into the montmorillonite interlayer, hence changing the interlayer water properties. The montmorillonite hydration was also temperature dependent; decreasing temperature increased the hydration (as long as no ice was formed) and increasing the temperature decreased the hydration. This was attributed to the temperature impact on the entropy of the hydration reaction. This observation was also reproduced in an experiment up to 90ºC. A small amount of salt in the groundwater was noted to reduce significantly the potential problem of ice formation in bentonite sealings.

Allophane and imogolite are common alteration products of volcanic materials. Natural and synthetic allophanes and imogolites were characterized in the present study in order to clarify the short-range order of these materials and to gain an understanding of their spectral properties. Spectral analyses included visible/near-infrared (VNIR), and infrared (IR) reflectance of particulate samples and thermal-infrared (TIR) emissivity spectra of particulate and pressed pellets. Spectral features were similar but not identical for allophane and imogolite. In the near-infrared (NIR) region, allophane spectra exhibited a doublet near 7265 and 7120 cm−1 (1.38 and 1.40 μm) due to OH2v, a broad band near 5220 cm−1 (1.92 μm) due to H2Ov+δ, and a band near 4560 cm−1 (2.19 μm) due to OHv+δ. Reflectance spectra of imogolite in this region included a doublet near 7295 and 7190 cm−1 (1.37 and 1.39 μm) due to OH2v, a broad band near 5200 cm−1 (1.92 μm) due to H2Ov+δ, and a band near 4565 cm−1 (2.19 μm) due to OHv+δ. A strong broad band was also observed near 3200–3700 cm−1 (~2.8–3.1 μm) which is a composite of OHv, H2Ov, and H2O2δ vibrations. Visible/near-infrared spectra were also collected under two relative humidity (RH) conditions. High-RH conditions resulted in increasing band strength for the H2O combination modes near 6900–6930 cm−1 (1.45 μm) and 5170–5180 cm−1 (1.93 μm) in the allophane and imogolite spectra due to increased abundances of adsorbed H2O molecules. Variation in adsorbed H2O content caused an apparent shift in the bands near 1.4 and 1.9 μm. A doublet H2Oδ vibration was observed at 1600–1670 cm−1 (~6.0–6.2 μm) and a band due to OH bending for O3SiOH was observed at ~1350–1485 cm−1 (~6.7–7.4 μm). The Si-O-Al stretching vibrations occurred near 1030 and 940 cm−1 (~9.7 and 10.6 μm) for allophane and near 1010 and 930 cm−1 (~9.9 and 10.7 μm) for imogolite. OH out-of-plane bending modes occurred near 610 cm−1 (16.4 μm) for allophane and at 595 cm−1 (16.8 μm) for imogolite. Features due to Si-O-Al bending vibrations were observed at 545, 420, and 335 cm−1 (~18, 24, and 30 μm) for allophane and at 495, 415, and 335 cm−1 (~20, 24, and 30 μm) for imogolite. The emissivity spectra were obtained from pressed pellets of the samples, which greatly enhanced the spectral contrast of the TIR absorptions. Predicted NIR bands were calculated from the mid-IR fundamental stretching and bending vibrations and compared with the measured NIR values. Controlled-RH X-ray diffraction (XRD) experiments were also performed in order to investigate changes in the mineral structure with changing RH conditions. Both allophane and imogolite exhibited decreasing low-angle XRD intensity with increasing RH, which was probably a result of interactions between H2O molecules and the curved allophane and imogolite structures.

The structure of trimethylsulfoxonium-exchanged vermiculite has been examined to compare it with other onium-exchanged structures, such as tetramethylammonium- and tetramethylphosphonium-exchanged vermiculite. The three organic cations are tetrahedral in shape, but trimethylsulfoxonium [(CH3)3SO+] has an oxygen atom replacing a methyl group at one apex. This study describes the effect this substitution and the larger S atom have on the site location in the interlayer and the effect on the vermiculite 2:1 layer. These clay minerals may be commercially useful as adsorbents.

Na-exchanged crystals of vermiculite from Santa Olalla, Spain, were intercalated with trimethylsulfoxonium [Me3SO+ = (CH3)3SO+] molecules by refluxing in an aqueous 0.25 M trimethylsulfoxonium iodide solution at 80°C for 14 days. The resulting Me3SO+-exchanged vermiculite crystals were studied by single-crystal, X-ray diffraction methods and by computer modeling (density functional theory). Cell parameters are a = 5.349(2), b = 9.270(3), c = 13.825(8) Å, and β = 97.40(4)°, the space group is C2/m, and the polytype is 1M. Refinement results (R = 0.073, wR = 0.080) show that in the average structure of C2/m, the S atoms of the Me3SO+ molecules form two partially occupied planes [2.066(2) Å from each basal oxygen plane] between the 2:1 layers, and the S atoms show considerable positional disorder. The O atom of the Me3SO+ molecule occurs in the central plane of the interlayer, as far away from each 2:1 layer as possible. In projection down the c* axis, the Me3SO+ molecule resides within the center of the silicate rings from each adjacent 2:1 layer. In the ideal (static) model of the Me3SO+-exchanged vermiculite structure, the Me3SO+ molecule is oriented such that two methyl groups point toward charge-deficient bridging oxygen atoms of the basal plane; thus, the organic pillars charge compensate the bridging oxygen atoms of the 2:1 layer that are charge deficient. In projection, the oxygen atom of the Me3SO+ molecule projects over a tetrahedron containing Si. Computer modeling showed that if H2O is not included in the model, the Me3SO+ molecule (S and O atoms) is in the center of the interlayer, but with the addition of randomly placed H2O, two partially occupied planes similar to the X-ray derived model are formed.

Chlorite is a layered silicate mineral group of importance in geology, agriculture, and in the processing of mineral resources. A more detailed analysis of the surface charge of chlorite minerals is important in order to improve our fundamental understanding of such particle structures and their behavior in suspension. In this study, the anisotropic surface charging of chlorite has been established using Atomic Force Microscopy surface-force measurements with a silicon nitride tip. The surface-charge densities and surface potentials at the chlorite basal-plane surfaces and edge surface were obtained by fitting force curves with the Derjaguin-Landau-Verwey-Overbeek theoretical model. The results show that at pH 5.6, 8.0, and 9.0 the chlorite mica-like face is negatively charged with the isoelectric point (IEP) less than pH 5.6. In contrast, the chlorite brucite-like face is positively charged in this pH range and the IEP is greater than pH 9.0. The surface charging of the chlorite edge surface was found to be pH-dependent with the IEP occurring at pH 8.5, which is slightly greater than the edge surfaces of talc and muscovite due to the larger content of magnesium hydroxide at the chlorite edge surface. Findings from the present research are expected to provide a fundamental foundation for the analysis of industrial requirements, e.g. collector adsorption, slime coating, and particle interactions in the area of mineral-processing technology.

The intercalating growth of new silicate layers or metal hydroxide layers in the interlayer space of other clay minerals is known from various mixed-layer clay minerals such as illite-smectite (I-S), chlorite-vermiculite, and mica-vermiculite. In a recent study, the present authors proposed that smectite-group minerals can be synthesized from solution as new 2:1 silicate layers within the low-charge interlayers of rectorite. That study showed how oxalate catalyzes the crystallization of saponite from a silicate gel at low temperatures (60ºC) and ambient pressure. As an extension of this work the aim of the present study was to test the claim that new 2:1 silicate layers can be synthesized as new intercalating layers in the low-charge interlayers of rectorite and whether oxalate could promote such an intercalation synthesis. Two experiments were conducted at 60ºC and atmospheric pressure. First, disodium oxalate solution was added to a suspension of rectorite in order to investigate the effects that oxalate anions have on the structure of rectorite. In a second experiment, silicate gel of saponitic composition (calculated interlayer charge -0.33 eq/O10(OH)2) was mixed with a suspension of rectorite and incubated in disodium oxalate solution. The synthesis products were extracted after 3 months and analyzed by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The treatment of ultrathin sections with octadecylammonium (nC =18) cations revealed the presence of 2:1 layer silicates with different interlayer charges that grew from the silicate gel. The oxalate-promoted nucleation of saponite and talc crystallites on the rectorite led to the alteration and ultimately to the destruction of the rectorite structure. The change was documented in HRTEM lattice-fringe images. The crystallization of new 2:1 layer silicates also occurred within the expandable interlayers of rectorite but not as new 2:1 silicate layers parallel to the previous 2:1 silicate layers. Instead, they grew independently of any orientation predetermined by the rectorite crystal substrate and their crystallization was responsible for the destruction of the rectorite structure.

The production and industrial use of asbestos cement and other asbestos-containing materials have been restricted in most countries because of the potential detrimental effects on human health and the environment. Chrysotile is the most common form of asbestos and investigations into how to recycle this serpentine phyllosilicate mineral have attracted extensive attention. Chrysotile asbestos tailings can be transformed thermally, at high temperature, by in situ carbothermal reduction (CR). The CR method aims to maximize use of the chrysotile available and uses high temperatures and carbon to change the mineral form and structure of the chrysotile asbestos tailings. When chrysotile asbestos is employed as the raw material and coke (carbon) powder is used as the reducing agent for CR transformation, stable, high-temperature composites consisting of forsterite, stishovite, and silicon carbide are formed. Forsterite (Mg2SiO4) was the most abundant crystalline phase formed in samples heat treated below 1500ºC. At 1600ºC, forsterite was exhausted through decomposition and β-SiC formed by reduction of stishovite. A larger proportion of β-SiC was generated as the carbon content was increased. This research revealed that both temperature and carbon addition play key roles in the transformation of chrysotile asbestos tailings.

Authigenic analcimes were observed in different amounts in Miocene units in central Anatolia, Turkey. Two types of analcime occurrences were defined: (1) as continuous but inhomogeneous concentrations varying from 3 to 75 wt.% in lacustrine sedimentary rocks; and (2) as low concentrations (between 3 and 20%) and discontinuous components in the tuffs and claystones intercalated with tuff. The type 2 analcimes have been investigated by many researchers while the origin and properties of the sedimentary analcimes, which are widespread in different parts of Turkey, have not been clarified. The present study focused on the genesis and the mineralogical and geochemical properties of both types of analcime. The analcimes were investigated using X-ray diffraction, optical microscopy, scanning electron microscopy, and chemical analytical methods. In the first type, other than volcaniclastic material, analcime is the only zeolite mineral. The first type of analcime was associated mainly with montmorillonite, dolomite, and feldspar and sometimes with calcite, and rarely with illite and kaolinite. The second type of analcime was found as an accessory mineral accompanied by montmorillonite, feldspar, and heulandite/clinoptilolite, and more rarely by erionite, kaolinite, and mica. The pyroclastic rocks are chemically classified into two subgroups, dacitic and andesitic rocks, with an intermediate to high silica content and a high percentage of alkali cations. Analcime in the pyroclastics intercalated with clay layers commonly replaced early-formed zeolites, such as clinoptilolite or volcanic materials. The first type of analcime was not formed from precursor zeolites and had a different origin than the second type. Type 1 analcime contains larger amounts of Si (34.19 to 34.68 Si per unit cell) and less Al and Na than in theoretical analcime. The theoretical structural formula of analcime is Na16(Al16Si32O96)H2O. The strongly decomposing feldspar and clay minerals (in particular montmorillonite and partially illite) of the older formations and the dissolution of halite and also soda minerals, e.g. thenardite and glauberite, allow the authigenic formation of type 1 analcime, dolomite, K-feldspar, and montmorillonite in a saline and highly alkaline environment such as the marginal part of Lake Tuzgölü. Type 2 analcime may have been precipitated directly from solution, pyroclastic material, or precursor zeolite minerals in saline and alkaline lake water.

The present study investigated the use of local and affordable clinoptilolite for the removal of persistent dyes from water. To improve its adsorption capacity, Na-clinoptilolite was modified chemically with two N-terminated siloxanes (molar mass: 2600 and 11000 g/mol) and used to adsorb the dye phenol red. The results of Fourier-transform infrared spectroscopy (FTIR) showed that N-terminated siloxanes were grafted successfully onto clinoptilolite. Examination by X-ray diffraction and scanning electron microscopy supported the suggestion of modifications observed by FTIR. The modified clinoptilolite showed improved adsorption properties for phenol red: up to 0.32 mg of phenol red were removed per g of clinoptilolite modified with N-terminated siloxanes from water, while HCl-treated clinoptilolite removed only 0.15 mg after 4 h. Langmuir and Freundlich models were used to obtain isotherm parameters. Results (with R2 > 0.84) from pseudo-first and pseudo-second order equations suggested that adsorption could have involved chemisorption and physisorption, probably because of the mineral-organic nature of the materials prepared.

Desorption processes of low-molecular-weight compounds from the surface of smectites into the gas phase determine a number of processes, e.g. those involved in drug delivery and the release of herbicides. The desorption has not been investigated thoroughly and is not well understood. The present study was undertaken in order to understand better the factors influencing these desorption mechanisms. Starting with a very pure standard (Na+-rich) montmorillonite (Kunipia-F), which was exchanged against cations with different hydration properties (Ca2+, Li+, phenyltrimethylammonium, hexyltrimethyl-ammonium), the experiments explored the rate of desorption of volatiles with different chemical functionalities (water, ethanol, ethyl acetate, and toluene). The desorption was monitored by thermogravimetry and differential scanning calorimetry under isothermal conditions, and by ramping the temperature at a constant rate. The experiments were compared with numerical calculations based on finite-element methods and with analytical models. These data point to a two-step mechanism where the desorption follows the curve of the equilibrium desorption isotherms of those molecules on the montmorillonite. The bulk-like volatiles (i.e. volatiles with release kinetics close to that of the bulk liquids) were desorbed in a first step. With a decrease in the degree of coverage of the volatile on the montmorillonite, the desorption was increasingly dominated by the strength of interaction between the volatile and the interlayer cations of the montmorillonite.

A major problem with polymeric membranes is low hydrophilicity and consequently a tendency to fouling. Preparing composite membranes is one way to improve the properties and performance of the neat membrane. In the present study, the effects of coagulation-bath temperature (CBT) and the hydrophilic nanoclay concentration of montmorillonite (MMT) on the morphology and performance of asymmetric cellulose acetate butyrate (CAB) membranes were investigated. The membranes were prepared via phase inversion induced by immersion precipitation in a water-coagulation bath. The morphology of the membranes prepared was studied by scanning electron microscopy (SEM). The permeation performance of the membranes prepared was studied by experiments using pure water and bovine serum albumin (BSA) solutions as feeds. The results showed that the membrane thickness and pure water flux (PWF) were increased by adding up to 2 wt.% MMT nanoclay to the casting solution. These two parameters decreased with further addition of MMT, however. In addition, the results obtained in the case of filtration of BSA solution indicated that the addition of MMT in the casting solution increased permeate flux and reduced BSA rejection slightly. Furthermore, increasing the MMT nanoclay concentration in the casting solution increased pure water flux recovery and consequently decreased the fouling. Decreasing the CBT in the presence of MMT during membrane preparation resulted in the formation of a more porous structure and consequently increased the flux and simultaneously decreased the BSA rejection.

The environmental conditions and reaction paths of shallow-water glauconitization (<500 m water depth, ~15°C) close to the sediment-seawater interface are generally considered to be well understood. In contrast, the key factors controlling deep-sea glauconite formation are still poorly constrained. In the present study, green grains formed in the recent deep-sea environment of the ODP Site 959, Ivory Coast-Ghana Marginal Ridge, (~2100 m water depth, 3-6°C) were investigated by X-ray diffraction and electron microscopic methods in order to determine the rate and mechanism of glauconitization.

Green clay authigenesis at Hole 959C occurred mainly in the tests of calcareous foraminifera which provided post-depositional conditions ideal for glauconitization. Within this organic-rich microenvironment, Fe-smectite developed <10 ky after deposition of the sediments by precipitation from precursor gels containing Fe, Mg, Al, and silica. This gel formation was supported by microbial activity and cation supply from the interstitial solution by diffusion. At a later stage of early marine diagenesis (900 ky), the Fe-smectites reacted to form mixed-layer glauconite-smectite. Further down (~2500 ky), almost pure glauconite with no compositional gaps between the Fe-smectite and glauconite end members formed. This burial-related Fe-smectite-to-glauconite reaction indicates that the glauconitization process was controlled mainly by the chemistry of the interstitial solutions. The composition of the interstitial solution depends heavily on micro-environmental changes related to early diagenetic oxidation of biodegradable (marine) organic matter, microbial sulfate reduction, silicate mineral alteration, carbonate dissolution, and Fe redox reactions. The availability of Fe is suggested as the probable limiting factor for glauconitization, explaining the various states of green-grain maturity within the samples, and this cation may be the most important rate-determining element.

The rate of glauconite formation at ODP Site 959 is given by %GlSed = 22.6·log(ageSed) + 1.6 (R2 = 0.97) where %GlSed is the state of glauconitization in the sediment and ageSed is the sediment age (in ky). This glauconitization rate depends mainly on continuous cation supply (in particular Fe) and is about five times less than that in shallow-shelf regions, suggesting significantly slower reaction at the lower temperature of deep-sea environments.