Critical-zone reactions involve inorganic and biogenic colloids in a cation-rich environment. The present research defines the rates and structure of purified Mg-montmorillonite aggregates formed in the presence of monovalent (K+) and divalent (Ca2+, Mg 2+) cations using light-extinction measurements. Time evolution of turbidity was employed to determine early-stage aggregation rates. Turbidity spectra were used to measure the fractal dimension at later stages. The power law dependence of the stability ratios on cation concentration was found to vary with the reciprocal of the valence rather than the predicted reciprocal of valence-squared, indicating that the platelet structure may be a factor influencing aggregation rates. The critical coagulation concentrations (CCC) (3 mM for CaCl2, 4 mM for MgCl2, and 70 mM for KCl) were obtained from the stability ratios. At a later time and above a minimal cation concentration, turbidity reached a quasi-stable state, indicating the formation of large aggregates. Under this condition, an approximate turbidity forward-scattering correction factor was applied and the fractal dimension was determined from the extinction spectra. For the divalent cations, the fractal dimensions were 1.65 ± 0.3 for Ca2+ and 1.75 ± 0.3 for Mg2+ and independent of cation concentrations above the CCC. For the monovalent cation, the fractal dimension increased with K+ concentration from 1.35 to 1.95, indicating a transition to a face-to-face geometry from either an edge-to-edge or edge-to-face orientation.

The aim of the present study was to synthesize a photocatalyst on the basis of TiO2 with kaolin as the support material. Properties such as layered structure and a suitable particle size of kaolin could be beneficial in the production of a high-quality and relatively cheap photocatalyst on an industrial scale. Homogeneous hydrolysis with urea as a precipitation agent and kaolin as support material was used to obtain a kaolin surface covered with TiO2. Samples were characterized by means of X-ray powder diffraction, infrared and Raman spectroscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller surface area, and Barrett-Joyner-Halenda porosity determination. Photocatalytic activity was assessed by a Reactive Black 5 azo dye discoloration in a water suspension and by acetone decomposition on a thin layer of sample in a gas phase. The characterization confirmed that the well crystallized TiO2 was distributed effectively over the whole surface of a kaolin substrate, and photocatalytic tests revealed that the active surface layer of titania particles on kaolin performed well, suggesting that kaolin acts as a suitable support.

The present study investigated the anisotropy in the orientation of particles in synthetic swelling clay media prepared from the sedimentation of particle-sized fractions of vermiculite. The different size fractions (<0.1, 0.1–0.2, 1–2, and 10–20 μm) were chosen because they represent the wide range of particle sizes of swelling clay minerals encountered in natural environments. Small-angle neutron scattering (SANS) and neutron diffraction measurements allowed the characteristic scattering/diffraction features to be derived and the quantitative information about the particle orientation distributions along two directions with respect to the sedimentation plane to be extracted. The results obtained confirmed that the increase in particle size was associated with the development of a random orientation for the particles, whereas the hydration state had a negligible impact on the organization of the porous media. For finer vermiculite particles, the rocking curves demonstrated an anisotropy of the systems that is similar to those reported previously on natural montmorillonite minerals. This result suggests that the location of the layer charge has little or no impact on the anisotropy features of particle orientation. For the coarsest fraction (10–20 μm), quantitative information about the particle orientation revealed that the relative proportion of the isotropic contribution represents up to 85% of the material. The anisotropy in the 2D SANS patterns revealed a pore-network anisotropy that was consistent with the particle size.

In the present study, the gradual layer-charge reduction of two Li-saturated smectites, SAz-1 from Arizona, USA, and FEO-G from Troodos, Cyprus, with octahedral charge of 0.54 electrons per half unit cell (e/huc) and 0.39 e/huc, respectively, was monitored by X-ray diffraction of K-saturated, ethylene glycol-solvated samples, by thermogravimetry-differential thermogravimetry, and by mid- and near-Fourier transform infrared spectroscopy after heating at 80–300ºC. With increasing heating temperature, the layer charge and cation exchange capacity (CEC) of both smectites decreased gradually due to Li fixation. At temperatures >200ºC, ~25% residual CEC was observed, suggesting incomplete Li fixation due to kinetic constraints. Dehydration of the original Li-smectites occurred in two steps, one peaking at ~100ºC and another at 175–180ºC. The latter decreased upon progressive Li fixation and vanished from smectites treated above ~125ºC. Dehydroxylation occurred at 635–640ºC in both smectites and was not affected by Li fixation. The second derivative analysis of the infrared spectra showed that Li fixation was manifested in both smectites by the growth of two new sharp OH-stretching fundamentals at ~3640 and 3670 cm−1 and their overtones at ~7115 and 7170 cm−1. The new bands constitute pairs of fixed energy and relative intensity which grow simultaneously at the expense of the broad OH-stretching and overtone features of the original smectites. Based on this result, Li fixation is suggested to be accompanied by the simultaneous formation of two distinct trioctahedral-like structural OH species, which is compatible with Li+ occupying trans-octahedral vacancies in both smectites.

Geological disposal is the preferred option for the final storage of high-level nuclear waste and spent nuclear fuel in most countries. The selected host rock may be different in individual national programs for radioactive-waste management and the engineered barrier systems that protect and isolate the waste may also differ, but almost all programs are considering an engineered barrier. Clay is used as a buffer that surrounds and protects the individual waste packages and/or as tunnel seal that seals off the disposal galleries from the shafts leading to the surface.

Bentonite and bentonite/sand mixtures are selected primarily because of their low hydraulic permeability in a saturated state. This ensures that diffusion will be the dominant transport mechanism in the barrier. Another key advantage is the swelling pressure, which ensures a self-sealing ability and closes gaps in the installed barrier and the excavation-damaged zone around the emplacement tunnels. Bentonite is a natural geological material that has been stable over timescales of millions of years and this is important as the barriers need to retain their properties for up to 106 y.

In order to be able to license a final repository for high-level radioactive waste, a solid understanding of how the barriers evolve with time is needed. This understanding is based on scientific knowledge about the processes and boundary conditions acting on the barriers in the repository. These are often divided into thermal, hydraulic, mechanical, and (bio)chemical processes. Examples of areas that need to be evaluated are the evolution of temperature in the repository during the early stage due to the decay heat in the waste, re-saturation of the bentonite blocks installed, build-up of swelling pressure on the containers and the surrounding rock, and degradation of the montmorillonite component in the bentonite. Another important area of development is the engineering aspects: how can the barriers be manufactured, subjected to quality control, and installed?

Geological disposal programs for radioactive waste have generated a large body of information on the safety-relevant properties of clays used as engineered barriers. The major relevant findings of the past 35 y are reviewed here.

The cooling of steel containers in radioactive-waste storage was simulated in a step-by-step experiment from 90 to 40ºC. Among newly formed clay minerals observed in run products, cronstedtite was identified by a number of analytical techniques (powder X-ray diffraction, transmission electron microscopy, and scanning electron microscopy). Cronstedtite has not previously been recognized to be so abundant and so well crystallized in an iron—clay interaction experiment. The supersaturation of experimental solutions with respect to cronstedtite was due to the availability of Fe and Si in solution, as a result of the dissolution of iron metal powder, quartz, and minor amounts of other silicates. Cronstedtite crystals are characterized by various morphologies: pyramidal (truncated or not) with a triangular base and conical with a rounded or hexagonal cross-section. The pyramidal crystals occur more frequently and their polytypes (2M1, 1M, 3T) were identified by selected area electron diffraction patterns and by automated diffraction tomography. Cronstedtite is stable within the 90-60ºC temperature range. At temperatures of ⩽ 50ºC, the cronstedite crystals showed evidence of alteration.

Dioctahedral vermiculite commonly occurs in soils and fresh sediments, but has not been reported in sedimentary rocks. Little is known of the evolution of this mineral during diagenesis. According to the available literature, dioctahedral vermiculite is likely to exhibit strong potential for selective sorption and fixation of K+ involving interlayer dehydration and collapse. he objective of the present study was to investigate the influence of K+ saturation and seawater treatments on the structure o dioctahedral vermiculite. Due to the fact that no dioctahedral vermiculite standard reference material was available, a natural sample of soil clay containing dioctahedral vermiculite was used in the study. The clay was saturated with K+ using different protocols simulating natural processes taking place in soils and marine environments. The solid products of the experiments were analyzed for potassium content using flame photometry. The effect of the treatments used on the structure of dioctahedral vermiculite was studied using X-ray diffraction (XRD). The percentages of the collapsed interlayers were estimated by modeling the XRD patterns based on a whole-pattern multi-specimen modeling technique. All the treatments involving K+ saturation caused K+ fixation and irreversible collapse (i.e. contraction to 10 Å) of at least a portion of the hydrated (vermiculitic) interlayers. Air drying of the K+-saturated samples greatly enhanced the degree of the collapse. The results obtained gave no clear answer as to whether time had had a significant effect on the degree to which irreversible collapse occurred. Selective sorption of K+ from artificial seawater was observed. These results clearly indicate that collapse of dioctahedral vermiculite is likely to occur in soils during weathering and in sediments during early diagenesis. Both processes need to be taken into consideration in sedimentary basin studies.

Geologic mapping and crystal-chemical analysis of Middle-Upper Miocene volcanics in the Sandıklı-Afyonkarahisar region of Turkey, coupled with published zeolite analyses has revealed that western Turkey hosts unique zeolitic mineral assemblages with distinct paragenetic sequences. The present investigation focused on pyroclastic deposits, including low to intermediate potassic trachytic/trachyandesitic tuffs (LPT) and high potassic tephriphonolitic, tephritic, and trachybasaltic tuffs (HPT), each of which contains various styles of zeolites. Optical petrography, X-ray powder diffraction, and chemical analyses have revealed varying degrees of lithification, probably related to differences in initial emplacement temperature, depositional mechanism and thickness, chilling rate, and extent of mafic composition. Zeolitization was further influenced by meteoric flushing in a hydrologically open system. Chabazite in the LPT from the Selçik area occurs extensively as coatings and infillings of pores. Phillipsite in the HPT found in the Ballık, Küfeke, and Ömerkuyu areas dominates the assemblage and is accompanied by chabazite and minor amounts of analcime. Analcime was probably generated by alteration of leucite which is found as a pyrogene mineral. Alkali zeolites or Ca-bearing zeolites formed as a consequence of the addition of Ca and/or the removal of Na (i.e. dissolution of analcime). The paragenetic sequence may be described as: analcime/phillipsite → chabazite → calcite. The characterization of these assemblages may lead to better exploitation strategies for natural zeolitic resources in the region.

Iron oxides, typical constituents of many soils, represent a natural immobilization mechanism for toxic elements. Most iron oxides are formed during the transformation of poorly crystalline ferrihydrite to more crystalline iron phases. The present study examined the impact of well known contaminants, such as P(V), As(V), and Sb(V), on the ferrihydrite transformation and investigated the transformation products with a set of bulk and nano-resolution methods. Irrespective of the pH, P(V) and As(V) favor the formation of hematite (α-Fe2O3) over goethite (α-FeOOH) and retard these transformations at high concentrations. Sb(V), on the other hand, favors the formation of goethite, feroxyhyte (d’-FeOOH), and tripuhyite (FeSbO4) depending on pH and Sb(V) concentration. The elemental composition of the transformation products analyzed by inductively coupled plasma optical emission spectroscopy show high loadings of Sb(V) with molar Sb:Fe ratios of 0.12, whereas the molar P:Fe and As:Fe ratios do not exceed 0.03 and 0.06, respectively. The structural similarity of feroxyhyte and hematite was resolved by detailed electron diffraction studies, and feroxyhyte was positively identified in a number of the samples examined. These results indicate that, compared to P(V) and As(V), Sb(V) can be incorporated into the structure of certain iron oxides through Fe(III)-Sb(V) substitution, coupled with other substitutions. However, the outcome of the ferrihydrite transformation (hematite, goethite, feroxyhyte, or tripuhyite) depends on the Sb(V) concentration, pH, and temperature.

Halloysite is used for targeted delivery of drugs and other biomolecules. Renewed interest in examination by X-ray diffraction (XRD) to predict the size of particles that can be loaded onto the nanotubes has resulted. Anhydrous halloysite consists of spiraled tubules the length and diameter of which can be determined by measurement using an electron microscope. In spite of ample evidence regarding the spiral structure of halloysite, current programs to evaluate the structure of halloysite nanotubes consider it to be a hollow tube or a cylinder which prevents accurate prediction of its structure and leads to misinformation about the sizes of materials that can be loaded onto the nanotubes. The overall objective of the current study was to derive equations to estimate the structure of halloysite nanotubes which take into consideration its spiral structure. The study of Fourier transform either by electron diffraction or XRD led to the measurement of the spiral thickness and the nature of the spiral. Calculations of the nanotube dimensions may determine the ability of these carriers to allow the mechanical delivery of certain drugs. Here the structure of hydrated halloysite (hollow cylindrical tubes with a doughnut-like cross-section) and anhydrous halloysite (spiraled or helical structure) are described as previously reported in the literature. The Fourier transform of the spiraled structure was selected based on three different kinds of spirals: the Archimedean spiral, the Power spiral, and the Logarithmic spiral. Programs used to define the crystal structure of materials and to calculate the Fourier transform need to take the spiral structure into consideration.

Several detailed studies have been done on the characterization of organoclays and the type of structures developed when they interact with alkylammonium molecules. Few published contributions exist, however, on the distribution of surfactant within the organoclays and the mechanism by which they are intercalated. Also, although X-ray photoelectron spectroscopy (XPS) is a suitable technique for the study of the surface characteristics of organoclays, very few such XPS studies have been carried out. With the aim of contributing to a better understanding of the intercalation process, a series of organoclays was synthesized using a montmorillonite and the cationic surfactant hexadecyltrimethylammonium bromide (HDTMABr), with an increasing surfactant load of between 0.2 and 4.0 times the cation exchange capacity of the starting clay. By means of XPS, zeta potential, and thermal analysis techniques, distinguishing the strongly interacting fraction from the weakly interacting fraction of the adsorbed surfactant molecules was possible. Adsorption isotherms of each of these processes were constructed and then adjusted using the Langmuir and Dubinin-Radusquevich adsorption models. Three types of interaction between the surfactant and the clay were identified and described qualitatively and quantitatively. Two of these interactions, strong and weak, involved the hexadecyltrimethylammonium cation (HDTMA+). The third was a weak interaction involving the ion pair HDTMA+Br−. The results of this study may be useful for the comprehensive design of organoclays with specific physicochemical properties according to the application for which they are destined.

Creating an environmentally friendly precursor to form a kaolinite intercalation compound is important for promoting the applications of nanohybrid kaolinite in electrochemical sensors, low- or zero-toxicity drug carriers, and clay-polymer nanocompounds. In the present study, a stable hydrated kaolinite pre-cursor with d001= 0.84 nm was prepared successfully by heating the transition phase, the as-prepared kaolinite-hydrazine intercalate, at temperatures between 40 and 70ºC. The structure of the hydrated kaolinite was characterized by X-ray diffraction and infrared spectroscopy. The morphology was examined using scanning electron microscopy. The results showed that the hydrated hydrazine of the transition phase was easy to decompose to hydrazines and water molecules in the interlayer at 40-70ºC. Hydrazine molecules de-intercalated gradually, and water molecules remained in the ditrigonal holes of the silicate layer with sufficient stability, finally forming the stable 0.84 nm hydrated kaolinite in the system with a success rate of 80–90%. The 0.84 nm hydrated kaolinite may become an excellent precursor for the preparation of other kaolinite intercalates. A degree of intercalation of ~100% was obtained for the kaolinite-ethylene glycol intercalate, and a degree of intercalation of ~80% was obtained for the kaolinite-glycine intercalate from the 0.84 nm hydrated kaolinite precursor.

The Upper Silurian–Lower Devonian section of the Dniester gorge in Podolia and samples from boreholes located S and N of this area were studied in order to reconstruct the thermal history of Lower Paleozoic sedimentary rocks in the Dniester segment of the Peri-Tornquist margin of the East European Craton which is the most eastern part of a major shale-gas target in Europe. X-ray diffraction data for illite-smectite from shales and carbonates indicate very advanced diagenesis and maximum paleotemperatures of ~200ºC, higher than interpreted from the ‘conodont alteration index’ (CAI) data. Diagenesis of the Devonian section is slightly less advanced than that of the underlying Silurian section, indicating that it is a regional feature and the result of burial. The regional distribution of the diagenetic grade based on illite matches well with the pattern established from the CAI data. K-Ar dating of illite-smectite from Silurian bentonites and shales gave a consistent set of dates ranging from 390 to 312 Ma. To explain such advanced levels of diagenesis and such K-Ar dates, the extension of the Carboniferous foreland basin (which today is only preserved to the NW of L’viv) toward the SE on the craton margin has to be assumed. The diagenetic zonation pattern of the Carboniferous coals supports this hypothesis. The Carboniferous cover may have been either sedimentary or partially tectonic (Variscan intracratonic duplexes) in origin and the thickness, necessary for the observed level of diagenesis, may have been reduced by an elevated heat flow along the major tectonic zone at the edge of the craton (TESZ). The presence of such cover is confirmed by completely reset Cretaceous apatite fission track (AFT) ages of the Silurian bentonites. The AFT dates also imply a Tertiary heating event in the area.

The 10 Å clay mineral present in the dolomitic part of the profile (Silurian), both in bentonites and in other rocks, is aluminoceladonite or intermediate between illite and aluminoceladonite, while in the Devonian shale section only illite was documented. Chlorite is also common in the studied rocks and is at least partially authigenic. It is non-expandable in the samples from boreholes, while often expandable to variable extents in the samples from outcrops, which also contain goethite. Such variation in chlorite is attributed to contemporary weathering.

The high fission yield and long half life of cesium and strontium make them the two most high-risk products from nuclear fission, so their separation from radioactive wastes is an important step in mitigating their harmful effects. Clinoptilolite, because of its thermal stability, high radiation resistance, and selectivity, was considered as the adsorbent for this purpose. In order to then separate the adsorbent-adsorbate complex from aqueous solution, the clinoptilolite was prepared as a magnetized composite with nanomagnetite. This magnetically modified zeolite enabled the efficient and quick separation of the adsorbent from solution using magnetic separation. The ability of this composite to remove Cs+ and Sr2+ from aqueous solutions was assessed and characterized using X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, differential thermogravimetric analysis, and vibrating-sample magnetometry. Variables such as initial ion concentration, pH, contact time, and temperature in the sorption process were studied and optimized. The maximum adsorption capacities of the composite were 188.7 and 36.63 mg g-1 for Cs+ and Sr2+, respectively. Investigation of the kinetics revealed that the adsorption process onto the composite was quicker than in the case of the zeolite alone. The equilibrium data were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The mean free energy of sorption (E) for both ions was in the range 8–16 kJ mol-1, confirming that an ion-exchange mechanism had occurred. Positive ΔH° and negative ΔG° values were indicative of the endothermic and spontaneous nature of the removal of Cs+ and Sr2+. The saturation magnetization of the composite was measured (17.46 Am2/kg), implying fast magnetic separation of the sample after adsorption. The results obtained revealed that the natural Iranian zeolite nanomagnetite composite was a good ion exchanger in the removal of Cs+ and Sr2+.

Pedogenic smectite from a young (Holocene) tropical soil was reacted in Al-rich solution at 150ºC for a range of reaction times (3 to 120 days) in orderto study mechanisms and rates associated with the transformation of smectite to kaolinite via interstratified kaolinite-smectite (K-S). As has been observed in tropical soils, the overall reaction rate is logarithmic, with rapid initial transformation of smectite to K-S with ~50% smectite layers, followed by progressively slower transformation of intermediate K-S to kaolinite-rich K-S and eventually Fe-kaolinite. Sub-micron hexagonal non-Fe-bearing kaolinite forms in the final stage (after 120 days) as a minor mineral in an assemblage dominated by Fe-kaolinite. The pedogenic smectite used as starting material consisted of two end-members, Fe-beidellite and Al-smectite, enabling comparison of reaction pathways. Fe-beidellite transforms to K-S or Fe-kaolinite within 3 days, whereas Al-smectite transforms much more slowly, appearing to reach a maximum rate in intermediate stages. This difference is probably due to hydrolysis of relatively weak Mg-O and Fe-O bonds (relative to Al-O bonds) in Fe-beidellite octahedral sheets, which drives rapid reaction, whereas the driving force behind transformation of Al-smectite is more likely to be related to stripping of tetrahedral sheets which reaches its maximum rate at intermediate stages. Multiple analytical approaches have indicated that Al is rapidly fixed from solution into smectite interlayers within K-S, and that K-S and Fe-kaolinite inherit octahedral Fe and Mg from precursor smectite; as the reaction progresses, octahedral sheets become progressively more Al-rich and Fe and Mg are lost to solution. These results demonstrate that: (1) early-formed pedogenic smectite in tropical soils is expected to transform to kaolinite via interstratified K-S; (2) K-S has a strong potential to sequester plant-toxic Al in tropical soil; and (3) the presence in tropical soils of Fe-kaolinites with relatively large cation exchange capacities may be related to inheritance of octahedral sheets from precursor smectite and K-S.

In order to extend the application of magadiite to optical fields (rather than the usual focus on adsorption, catalysis, ion exchange, etc.), a magadiite-CdS (Mag-CdS) composite was synthesized from Na-magadiite by ion exchange. Various techniques were used to characterize the composite. X-ray diffraction results indicated that the Mag-CdS composite retained the host magadiite structure in spite of decrease in the intensity of the X-ray diffraction peak of the host magadiite. The analytical results confirmed the formation of the Mag-CdS composite, along with the modification of the optical properties of CdS by the host magadiite.

The increasing levels of industrial wastewater released to the environment present a serious threat to human health, living resources, and ecological systems. Fe-modified zeolites were developed and tested for removal of Cu2+ and Zn2+ from contaminated water. The surfaces of the naturally occurring zeolite, clinoptilolite, were modified with Fe(III) oxyhydroxides using three different methods, denoted I, II, and III (FeCli1, FeCli2, and FeNaCli1, respectively). The oxyhydroxides were prepared in Method I using 0.1 M FeCl3·6H2O in an acetate buffer (pH = 3.6); in Method II, using 10ai] FeCl3·6H2O solution in 0.1 M KOH (pH = 10); and Method III was the same as Method I except the clinoptilolite was pretreated with NaCl. Newly synthesized materials from these three methods were then tested for their ability to enhance the sorption capacity for Cu and Zn compared to the natural sample (Cli). Powder X-ray diffraction measurements and the chemical composition of these modified samples confirmed that clinoptilolite maintained its structure while amorphous Fe3+ species were synthesized. The specific surface area (BET method) of both the natural and modified clinoptilolite increased by 2 and 7.5 times for Methods I and II, respectively. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that CaO was formed during Method I (FeClii). Throughout the adsorption process, the hydrolysis of CaO and the release of OH− caused the precipitation of Cu and Zn hydroxide, which made the determination of the sorption capacity of FeClii impossible. This phenomenon was avoided in Method III (FeNaClii) because of the absence of exchangeable Ca2+. The adsorption experiments with Method II resulted in double-enchanced adsoprtion capacity. Laboratory batch experiments revealed that the sorption capacities increased in the following order: Cli < FeCli2 < FeNaCli1, for Cu: 0.121 mmol/g < 0.251 mmol/g < 0.403 mmol/g and for Zn: 0.128 mmol/g < 0.234 mmol/g < 0.381 mmol/g.

Syntheses of Fe-, Co-, and Ni-containing Mg-Al-layered double hydroxides (LDHs) are described here because Fe, Co, and Ni represent the major constituents in steel containers used for storing spent nuclear fuel. Much evidence exists for the formation of LDHs during the corrosion of such containers under repository-relevant conditions. Because of their anion-exchange properties, LDHs can be considered as materials with the potential to retain and immobilize anionic radionuclides. Evaluation of the thermodynamic properties of LDHs is essential for reliable prediction of their behavior (solubility, anion exchange properties) in geochemical environments. The impact on the thermodynamic properties of the isostructural incorporation of divalent cations into the LDH was the main focus of the present study.

Mg-Al-Cl-LDH and the Fe-, Co-, and Ni-doped LDHs were synthesized by the co-precipitation method and then characterized (using powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), and thermogravimetric analyses (TGA)).

The PXRD and EXAFS analyses indicated that all synthesized samples were pure LDHs where Co, Ni, and Fe were incorporated isostructurally. The EXAFS and XANES results demonstrated that Ni and Co were incorporated as divalent cations and Fe as a trivalent cation. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis. The first estimates of the molar Gibbs free energies for Fe-, Co-, and Ni-containing LDHs at 70ºC were provided. The calculated Gibbs free energy of the pure Mg-Al-LDH (-3629 kJ/mol) was slightly less than those for Fe-, Co-, and Ni-containing compositions (-3612±50, -3604±50, -3593±50kJ/mol).

The early and sensitive detection of microbial contamination of kaolinite slurries is needed for timely treatment to prevent spoilage. The sensitivity, reproducibility, and time required by current methods, such as the dip-slide method, do not meet this challenge. A more sensitive, reproducible, and efficient method is required. The objective of the present study was to develop and validate such a method. The new method is based on the measured growth kinetics of indigenous kaolinite-slurry microorganisms. The microorganisms from kaolinite slurries with different contamination levels were eluted and quantified as colony-forming units (CFUs). Known quantities of E. coli (ATCC 11775) were inoculated into sterilized kaolinite slurries to relate kaolinite-slurry CFUs to true microbial concentrations. The inoculated slurries were subsequently incubated, re-extracted, and microbial concentrations quantified. The ratio of the known inoculated E. coli concentration to the measured concentration was expressed as the recovery efficiency coefficient. Indigenous microbial communities were serially diluted, incubated, and the growth kinetics measured and related to CFUs. Using the new method, greater optical densities (OD) and visible microbial growth were measured for greater dilutions of kaolinite slurries with large microbial-cell concentrations. Growth conditions were optimized to maximize the correlation between contamination level, microbial growth kinetics, and OD value. A Standard Bacterial Unit (SBU) scale with five levels of microbial contamination was designed for kaolinite slurries using the experimental results. The SBU scale was validated using a blind test of 50 unknown slurry samples with various contamination levels provided by the Imerys Company. The validation tests revealed that the new method using the SBU scale was more time efficient, sensitive, and reproducible than the dip-slide method.

Bentonite-bonded molding sand is one of the most common mold materials used in metal casting. The high casting temperatures cause dehydration and alteration of the molding sand, thereby degrading its reusability. Neutron radiography and neutron diffraction were applied to study these processes by using pure bentonite-quartz-water mixtures in simulation casting experiments. The aim of the experiments was to compare the dehydration behavior of raw and recycled mold material in order to assess possible causes of the limited reusability of molding sands in industrial application. Neutron radiography provided quantitative data for the local water concentrations within the mold material as a function of time and temperature. Dehydration zones, condensation zones, and areas of pristine hydrated molding sand could be established clearly. The kinematics of the zones was quantified. Within four cycles of de- and rehydration, no significant differences in water kinematics were detected. The data, therefore, suggest that the industrial handling (molding-sand additives and the presence of metal melt) may have greater effects on molding-sand reusability than the intrinsic properties of the pure bentonite–quartz–water system.