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We investigated the chemical and mineralogical characteristics of a weathering profile of the Nui Nua serpentinized ultramafic-mafic massif (Thanh Hoa Province, Vietnam) using TEM-EDX, XRD, and FT-IR methods to understand the effects of monsoon climate conditions on weathering processes and clay minerals, especially transformation and neoformation of clay minerals. Clay minerals of this profile were characterized by a temporariness of serpentine clay minerals though chlorite seemed to be stable and increased from the bottom layer to the top layer. The nature of Fe changed rapidly from ferrous Fe (close to parent rocks) to ferric Fe and additionally it was incorporated into the octahedral sheet of dioctahedral smectite. Consequently, a Fe-rich smectite formed at the beginning of the weathering process and was detected as a dominant phase in the clay fraction of the profile. This phase was later transformed progressively to Al-rich smectite because of Fe-oxidation and corresponding Si-mitigation. Chemically, the contents of Fe and Mg reduced from the bottom layer to the top layer but Al developed vice versa. Magnetite in top layer was formed by bacterial activities. The transformations of clay minerals were controlled strongly by leaching conditions in the weathering system and by the effects of oxidation of Fe (Fe 2 + → Fe 3 + ) on clay minerals paragenesis.

Bentonites are suitable candidates as buffer and backfill materials in HLW-repositories. A target of this research is to define the mineralogical alteration of bentonite caused by its interaction with iron powder, which simulates the contact of bentonite with a steel container. Compacted MX80 bentonite and Friedland clay (raw density of 1.6 g/cm 3 ) were used as the initial materials for clay/iron interaction experiments (10 wt.% of iron) involving percolation with NaCl or Mg-rich IP21 solution. These experiments were conducted at 25 °C, 60 °C, and 90 °C and a suite of analytical techniques was applied to identify the mineralogical transformations. Smectite was the main phase and was fully expandable in all reaction products, though the octahedral and tetrahedral compositions were altered. “Illitization” was found as a main process of smectite alteration and was caused by the percolation component of these experiments. Smectitization occurred only when Fe-oxidation was considerable. The alteration of smectite was mainly driven by the high alkaline pH-value resulting from Fe-corrosion. Different interstratified phases like kaolinite–smectite–dioctahedral vermiculite, berthierine–saponite, chlorite–saponite–trioctahedral vermiculite, and cronstedtite–saponite–trioctahedral vermiculite interstratifications were identified as neo-formed phases which were formed in minor amounts. Cementation of particles by Fe- or Si-precipitation was assumed to reduce swelling pressure and permeability.

The Danish Tertiary Holmehus clay belongs to the series of illite-smectite mixed-layer clays in northern Europe and has a potential to serve as an effective engineered barrier for isolating hazardous waste. Mineralogical specification was made of the components illite/smectite mixed-layer and dioctahedral vermiculite/smectite mixed-layer structures. The lower content of expandable phase than of smectite- rich clays like MX-80 gives somewhat higher hydraulic conductivity and somewhat lower swelling pressure but both are deemed suitable for isolating canisters with high-level radioactive waste in deeprepositories for densities at water saturation of at least 1900 kg/m3. The lower swelling pressure, the potential of being chemically more stable, and the high buffer capacity by providing dissolved Si makes Holmehus clay a candidate for use in both deep and near-surface repositories. Validerad; 2015; Nivå 2; 20140310 (svek)

The stability of smectite-rich clay minerals is of interest because they could be candidates for engineered barriers for high-level radioactive waste repositories. This research characterized the chemical and mineralogical properties of the Nui Nua clay which forms from the weathering of the Nui Nua serpentinized ultramafic–mafic massif (Thanh Hoa Province, Viet Nam) using several methods (including Fourier transform infrared spectrometry and transmission electron microscopy). The Nui Nua clay, taken from Co Dinh and My Cai valleys, is composed of Fe-smectites as the main phase with minor phases of normal smectite, quartz, talc, chlorite, kaolinite, amphibole, antigorite, feldspars and magnetite. The Fe-smectites were characterized as mixed-layer minerals (including Fe-montmorillonitic as an end-member) composed of illitic or dioctahedral vermiculitic layers and Fe-rich smectitic layers. The proportion of the smectitic layer is approximately 80%; the interlayer sheet is dominated by Ca and Mg, while the octahedral sheet is dominated by Fe 3 + (not Al). The stability of the Nui Nua smectites was also investigated by a simulation in saturation of 1 M NaCl and deionized water under kinetic impaction. The average tetrahedral-Si content of the smectites increased or decreased depending on the “dynamic solution” or hydraulic regime. By chemical identification, the alteration of Fe-smectites is mainly increased by the smectitization process. This research suggests that the Nui Nua clay is a potential candidate for an engineered barrier because during the alteration process, neo-formation of a montmorillonitic layer occurs.

The Chengjiang and Guanshan fossil Lagerstatten of Yunnan represent key fossil deposits to understand and reconstruct early metazoan evolution. Despite extensive studies on the systematics of taxa from these Lagerstatten, the major mechanisms of exceptional soft-tissue preservation at these fossil Lagerstatten have remained controversial. The Chengjiang and Guanshan fossil Lagerstatten represent typical Burgess Shale-type deposits, influenced by late alteration and weathering that led to some major transformations in clay and iron minerals, as well as dissolution of dolomite and skeletal biominerals. The detailed geochemical screening of various fossil groups, such as brachiopods, priapulids, arthropods, and sponges, indicates a more complex preservational history than hitherto supposed. Besides oxidation processes during sub-recent/recent weathering, clay mineral formation and/or alteration, carbonization, phosphatization, and pyritization played key roles in the preservation of various metazoans. The Chengjiang fossil Lagerstatte is characterized by the existence of clay-dominated background beds (BGBs) and event beds (EBs). Fossil preservation varies considerably in the two different depositional settings, with soft-tissue preservation occurring preferentially in EBs, whereas skeletal accumulations are typical of BGBs. The samples were analyzed and classified into three groups with different degrees of alteration and fundamentally different chemistries. The specific clay mineral composition shows increasing chlorite and goethite, decreasing kaolinite, 2M1-mica, and dolomite, and a rise in the chemical alteration of mudstones. It also indicates slight variations between the primary types of beds (EB, BGB), hinting at variations in the source of clastics or the hydrochemical environment during the deposition of strata. Furthermore, the geochemical paleoredox proxy data indicate that dysoxic or anoxic conditions were not permanently present during the deposition of EBs and BGBs in the Chengjiang and Guanshan fossil Lagerstatten. We consider that rapid deposition in finest claystones had a greater influence on the preservation of highly volatile tissues than the presence of bottom-water anoxia, even though bottom-water anoxia and microbial sealing may further increase the probability of soft-tissue preservation. Using different geochemical proxies such as various redox indicators and iron speciation, statistics on framboid sizes, classical geological observation, and clay mineralogy, we show that iron mineral precipitation onto organic carcasses of the Chengjiang-type fossils is mostly confined to later diagenetic processes and thus is not crucial for the early fixation of easily decayable tissues in Burgess Shale-type faunas.

To investigate the potential of substituting non-natural agents in sunscreen, mixtures of some clays with Ganoderma pfeifferi extract were examined in regard to their protection abilities against ultraviolet (UV) radiation in the wavelength range 250–400 nm. Some mixtures showed remarkably high UV-protection potential in comparison with corresponding clay cream devoid of the fungal extract. Depending on interlayer charge of the dominant clay mineral contained in the clays, the interaction between the fungal extract and the clay mineral played a key role in the UV-protection ability of the mixtures. The optimal clay in the mixture with the G. pfeifferi extract for sunscreens was dominated by expandable clay minerals with low interlayer charge.

The potential of various clays including kaolin, smectite, mixed-layer series-dominated clay and mica-dominated clay to protect against ultraviolet (UV) radiation in the range 250–400 nm was examined. In order to understand the UV-protection abilities of the clays, properties of the clays were also characterized. The clays blocked UV radiation and bulk Fe2O3 content played a key role in the UV-protection properties, whereby the higher the bulk Fe2O3 content, the lower the UV-transmission level. However, UV-protection ability also depended on the expandability of the clay or the combination between clay mineral and mixed ointment.

A current semi-empirical model of conversion of smectite to illite implies that the process is associated with formation of quartz and chlorite and will not cause significant illitization in the hydrothermal period of a repository if the activation energy is of the commonly assumed magnitude and the temperature is lower than about 100 °C. The model is supported by several natural analogues and hydrothermal experiments in laboratories and field tests. In all the experiments, which were conducted under open chemical conditions, the confined clay was exposed to thermal gradients for at least 1 year. Most of the tests were small-scale and of “1D-type”, one being performed with strong gamma radiation, and the others with different porewater compositions. One was a Mock-up experiment simulating the KBS-3V concept on 50% scale, and one a full-scale KBS-3V field experiment at 400 m depth in granitic rock. They all showed that while smectite remained the major clay mineral a number of processes changed the physical properties in bulk, the most important changes being reduction of the expandability and increase of the hydraulic conductivity of the hottest part of the buffer. The latter is concluded to have been caused by contraction of clay aggregates that became permanent by precipitation of silica and iron compounds, the cementing agents emanating from dissolved accessory minerals as well as from montmorillonite. Fe-rich montmorillonite underwent particularly important dissolution.

The extremely long time in which clay surrounding canisters with radioactive waste must serve makes it necessary to consider long-term strain. It may have a sufficient shear strength for providing short-term stability but accumulated creep strain may well lead to failure if the microstructural coherence is lost. This can happen to non-expanding clays in which the number of “slip” units is more or less constant or reduced by bulk strain. For smectites, the risk of creep failure is believed to be insignificant because shearing of the originally dense clay aggregates break them up and produces an increasing number of slip units. This microstructural performance is described by a creep model based on stochastical mechanics, implying a spectrum of interparticle bond strengths that represent a first-order variation in barrier heights, and a second represented by the interaction of differently sized aggregates of discrete particles and a transient increase in the frequency of slip units. Low shear stresses cause strong attenuation of the creep rate, while for intermediate stresses the creep rate is of log time type. High shear stresses yield an increasing number of slip units that makes the clay perform as a purely viscous medium. Experiments made by the use of a new ring shear device support the theoretical creep model.

Heavy metal (HM) contaminations in the topsoil around handicraft villages with non-ferrous heavy metal recycling in the Red River Delta can impose serious threats to the subsoil as well as to the groundwater quality. This feature is very important for paddy soils due to relatively high leaching rates and the dissolution of Fe–Mn oxides under reducing conditions which can accelerate the amount of HM translocated to the subsoil and groundwater. The transport of Cu, Pb and Zn in paddy soils was simulated by numerical modeling of non-equilibrium solute transport with an adaptation of the Hydrus-1D model. For the simulation, a water layer on the soil surface was included, from which HM can infiltrate into the soil depending on the soil hydraulic properties. Sorption coefficients, obtained from batch experiments were used as input data for the simulations. Calculated leaching rates were compared with the binding forms of HM in the samples. The simulations show that leaching rates decrease in the order: Zn > Cu > Pb. This order is confirmed by the results of sequential extractions. Under constant flooded conditions at a water table of 20 cm, Cu, Pb and Zn were estimated to reach the soil depth of 1 m within 470, 495 and 370 days, respectively, emphasizing that reactive pollutants can reach groundwater in a relatively short time. A change of the water layer from 1 to 30 cm can accelerate the leaching rate of HM up to 36%. The hard pan layer was observed to induce a hysteresis in hydraulic conductivity and slow down the movement of HM. Uncertainties in modeling arise as several parameters in the simulation can be determined only with significant errors. However, Hydrus-1D is a suitable tool for simulation of the transport of HM in paddy soils.

In recent time search for suitable long-lasting “buffer clays” for isolating canisters with highly radioactive waste is going on in many countries. In Sweden and some other countries montmorillonite-rich clays are presently considered as primary candidates but other clays may do as well. The commonly expected major long-term alteration of buffer smectites is conversion to non-expandable forms like illite and chlorite, which reduces the swelling pressure of the buffer and thereby its tightness and self-sealing potential. This matter has been examined in a large-scale 2 year Mock-up test and small-scale hydrothermal tests using a Czech clay “RMN” rich in smectite and iron. The Mock-up test simulating the so called KBS-3V concept with a “canister” temperature of 95 °C showed that the Ca montmorillonite clay with 17% Fe lost more than half of its swelling pressure and became about 10 times more permeable than untreated clay. As expected from predictions based on chemical codes the smectite content remained nearly unchanged while significant loss of swelling ability and some slight loss in tightness took place. Both were ascribed to some dissolution of the smectite and precipitation of iron compounds that cemented partly dehydrated particle aggregates together.

The mineralogical and chemical changes of bentonites were studied under the boundary conditions of a repository in salt formations by means of a literature review, a natural analogue study, and laboratory experiments. In the natural analogue study the expandability of clays from deep boreholes in the East Slovakian Basin was found to be dependent not only on depth and temperature but also on the salinity of the pore waters. In laboratory experiments the fraction