Dyes are toxic and considered to be extremely hazardous to natural environments. Hence, adsorbents to remove dyes from contaminated water are needed. To develop adsorbents with a high adsorption capacity for different dyes, easy separation, and low cost, a novel dye adsorbent was prepared by activating fly ash with NaOH. The adsorbent morphology, structure, and specific surface area were characterized using scanning electron microscopy, X-ray powder diffraction, and surface area measurements using N2 adsorption-desorption. The adsorption abilities of the synthesized adsorbents were examined based on methylene blue and acid fuchsin adsorption from water. The capabilities of the adsorbents as a function of adsorbent use, dye type, dye concentration, time, and pH were investigated and compared. The results for methylene blue and acid fuchsin adsorption were modeled using pseudo-second order kinetics and the Langmuir adsorption isotherm, respectively. These modified adsorbents synthesized from fly ash may provide a promising solution to purify dye-contaminated waste water with the advantages of high efficiency and low cost.

Bentonite is considered as an ideal buffer/backfill material for preparing an engineering barrier for high-level radioactive waste (HLW) disposal. During initial sample preparation, the tendency of wet bentonite powder to gather into large agglomerates and the water to be spread unevenly in the traditional water content adjustment process decreases the homogeneity of compacted bentonite. The main purpose of this study was to solve this problem by applying a new wetting method, which mixes ice powder with bentonite powder (the ice-bentonite mixing method). This new method was used to adjust the water distribution in Gaomiaozi County, China (GMZ) bentonite powder and was compared to the traditional spray method. The screening method was used to separate macro-agglomerates (≥ 0.25 mm) from the water and bentonite mixture. The properties, the content of the various size agglomerates in loose mixtures, and the heterogeneity defects observed in compacted bentonite were compared. An index (P) was defined to quantitatively evaluate the water distribution in a loose bentonite/water mixture. Macro-agglomerates in loose mixtures produced heterogeneities in water content, density, and shrinkage. By using the ice-bentonite mixing method, fewer macro-agglomerates were formed and a homogeneous distribution of water was produced in the compacted bentonite. A homogeneous water distribution had the tendency to decrease the number of shrinkage cracks after the drying process and to maintain high mechanical strength in the compacted bentonite. Although the production of ice powder was laborious, the ice-bentonite mixing method has workability advantages: (i) a high mixing efficiency, (ii) a low mass loss rate, and (iii) a small deviation between measured water content and target water content. The low thawing efficiency of ice-bentonite mixtures can be solved by using a microwave-assisted thawing method. This research can improve the sample preparation method used to produce compacted buffer/backfill materials for HLW disposal.

Purification processes performed on natural clays to select specific clay minerals are complex and expensive and can lead to over-exploitation of some deposits. The present study aimed to examine physicochemical (mineralogy, morphology, size, surface charge, chemical composition, cation exchange capacity [CEC], and pH) and hydration (swelling, wettability, water sorption, and rheological behavior) properties of three native clays from Italian deposits for potential pharmaceutical and cosmetic uses due to the presence of phyllosilicate minerals. Particular emphasis was placed on energy dispersive X-ray (EDX) microanalysis coupled with the ‘cesium method’ to assay clay elemental composition and CEC. One bentonite of volcanic origin (BNT) and two kaolins, one of hydrothermal origin (K-H) and another of lacustrine-fluvial origin (K-L), were evaluated in comparison with a commercial, purified bentonite. The CEC assay revealed the complete substitution of exchangeable cations (Na+ and Ca2+) by Cs+ in BNT samples and CEC values consistent with those of typical smectites (100.64 ± 7.33 meq/100 g). For kaolins, partial substitution of Na+ cations occurred only in the K-L samples because of the interstratified mineral component which has small CEC values (11.13 ± 5.46 meq/100 g for the K-H sample and 14.75 ± 6.58 meq/100 g for the K-L sample). The degree of isomorphous substitution of Al3+ by Mg2+ affected the hydration properties of BNT in terms of swelling, water sorption, and rheology, whereas both of the poorly expandable kaolins exhibited significant water-adsorption properties. The EDX microanalysis has proved to be of considerable interest in terms of providing more information about clay properties in comparison with other commonly used methods and to identify the role played by both chemical and mineralogical composition of natural clays for their appropriate use in pharmaceutical and cosmetic fields.

Polycarboxylate superplasticizer (PCE) is a widely used water-reducing agent that can reduce significantly the water demand of concrete, which reduces the porosity and enhances the strength and durability of the concrete. (The PCE consists of a single backbone with many long PEO side chains.) Generally, aggregate occupies >70 wt.% of concrete; clay minerals are ubiquitous in nature and are difficult to avoid in mined aggregates. Clay minerals in aggregate often render the PCE ineffective and give rise to rapid loss of the fluidity of the concrete; this phenomenon is referred to as ‘poor clay tolerance of PCE.’ Though the poor clay tolerance of PCE is known widely, the relationship between the clay tolerance and the molecular structure of the PCE, in particular the effect of the side-chain structures, on clay tolerance is not understood completely. The objective of the present study was to determine the effect of different grafting densities of polyethylene oxide (PEO) side chains on the clay tolerance of PCE. The raw materials included mainly PCE, which was synthesized using acrylic acid and isopentenol polyoxyethylene ether, and a natural montmorillonite (Mnt), one of the most common clay minerals. The loss of fluidity of the cement paste was tested to assess the clay tolerance; total organic carbon was used to measure the amount of PCE adsorbed; X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis were used to investigate the microstructure of the intercalated Mnt. The results showed that preventing the superficially adsorbed PCE from being intercalated into Mnt was of great importance in terms of the improvement in clay tolerance of PCE, which increased with greater grafting density of PEO in the side chain of the PCE. The results also suggested the possibility that polymers which intercalate preferentially into the Mnt could improve significantly the clay tolerance of the PCE system.

In some real and up-scale tests using high-level radioactive waste (HLRW), Mg accumulation was observed in smectites at the contact of heated Fe or Cu metal tubes. It is important to understand why Mg accumulated in order to model the long term performance of bentonites in HLRW systems. In some of these tests, an increased number of trioctahedral domains was measured in the smectites using X-ray diffraction (XRD) and infrared spectroscopy (IR). The trioctahedral domains either formed by the dissolution/precipitation of smectites or by the addition of Mg through a solid-state reaction similar to the Hofmann-Klemen effect. The Hofmann-Klemen effect is used in the Greene-Kelly test to distinguish montmorillonites from beidellites. Many studies have been carried out about Li-uptake by smectites, but Mg was rarely taken into account. The present study was, therefore, undertaken to compare the interactions of different bentonites with Li and Mg under various conditions. A significant CEC decrease was found for Li- and Mg-saturated bentonite samples after heating at 250°C under dry conditions. The extent of this CEC reduction depended on the octahedral to tetrahedral charge ratio and was smaller for Mg-saturated samples than Li-saturated samples. This finding proved that it is much more difficult for Mg to enter octahedral vacancies than Li, which probably can be explained by the larger hydration energy and/or slightly larger radius of Mg. The relationship between CEC reduction and the octahedral/tetrahedral charge ratio of both Li- and Mg-saturated samples, however, suggests a similar process. The Mg that can reside at the bottom of the pseudohexagonal holes would not explain this relationship. The important result with respect to understanding HLRW bentonite performance, on the other hand, is that Mg fixation only occurs under dry conditions and that Mg fixation acts as a sink for Mg and, hence, leads Mg to diffuse towards the heated metal surface.

The influence of anionic dispersing agents, such as sodium poly(acrylic acid), sodium hexametaphosphate, and sodium silicate on the dissolution of crude kaolin was examined by measuring the dissolved metals produced in the absence and presence of dispersing agents. For this purpose, the rheological and structural changes caused by the dissolution of kaolin metal constituents were studied in batch mode using several parameters, namely, solids (wt.%), pH, contact time (aging), and dispersing agent dose. A noteworthy increase in kaolin dissolution was caused by the presence of dispersing agents, particularly poly(acrylic acid) and sodium hexametaphosphate. These agents produced conspicuously large amounts of dissolved Al in comparison to the other experimental treatments. Little dissolved Si was measured under similar conditions in distilled water, but the amount of Si released using dispersing agents was nearly double that observed in distilled water only. Excess dispersing agents interacted with kaolin and dissolved accessory elements in the kaolin (i.e. Fe, Ca, Mg) and thus released enough Fe to form a stable Fe—dispersant complex. The present study showed that this phenomenon also contributed to a significant increase in the release of dissolved Al and Si through complexation.

The aim of the present study was to discriminate between distinct types of clay units by applying multivariate statistical techniques, which have seldom been applied to the exploitation of ceramic clays. At the outcrop scale, texturally similar argillaceous or clayey layers of different ceramic types cannot be effectively distinguished, which can result in the misuse and loss of raw materials. Representative samples of clayey raw materials from central Portugal Cenozoic deposits with potential use in the manufacture of structural clay products were first assessed for granulometric, mineralogical, chemical, and technological properties. Based on those properties and the use of multivariate statistical techniques, i.e., factor analysis (FA) and cluster analysis (CA), a novel statistical approach that combined all these variable properties was produced. This approach made it possible to distinguish the ceramic suitability and perceive which parameters most influence that suitability. The use of R-mode FA made it feasible to differentiate and group samples based on the most influential variables: the contents of Al2O3, Fe, illite, quartz, feldspars, and K2O. The use of R-mode CA substantiated the FA results in the identification of influential variables, such as Al2O3, Fe, and illite. The use of Q-mode CA established two main clusters: clayey-silt samples and sandy and/or feldspathic samples, the clayey-silt samples encompassed three sub-clusters. These three sub-clusters match ceramic types with different suitabilities and relate sample stratigraphic setting to the encompassing stratigraphic units. Diagrams that relate the grain size, the content of different oxides, the content of different minerals, and the plasticity to the ceramic suitability illustrate the CA groupings. An adequate blend of sand and clay for red stoneware (bricks and tiles) manufacture was indicated as a major requirement for most raw materials of the clayey-silt cluster. Raw materials represented by the sandy and/or feldspathic cluster can either be used to blend with materials that lack sand or to blend with excessively plastic samples.