In the absence of the necessary valley topography, karst depressions are sometimes used to construct conventional impoundments in order to contain tailings. Leakage is a primary concern for such impoundments. The purpose of the current study was to determine the characteristics and barrier performance of laterite mantling karst depressions, using, as an example, the Wujiwatang (WJWT) tailings impoundment, located in the Gejiu mining area, southwestern China. The geotechnical-hydrogeological properties, geochemistry, mineral compositions, and particle shapes of the laterite were investigated by geotechnical techniques, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the laterite contained poorly sorted particles that covered a wide spectrum of grain sizes (<5 mm to <50 nm), and was unexpectedly categorized as silty clay or silt with a high liquid limit. The continuous gradation and small D90 value helped the laterite achieve saturated hydraulic conductivities in the range of <10–6 cm/s required for impoundment liners. The laterite beneath the tailings impoundment was finer-grained and had a lower permeability than that of the laterite on the depression walls within the same depression. Geochemically and mineralogically, the laterite was classified as true laterite and its major mineralogical constituents were gibbsite and goethite with chlorite occurring in trace amounts. The laterite was dominated by subspherolitic–spherolitic cohesionless grains (concretions) made up of Al, Fe, Ti, and Mn oxides and hydroxides. The laterite did not have plasticity indices in the clay range. Fortunately, slopewash prior to tailings containment selectively transported the finer oxide concretions to the depression floor, creating a natural low-permeability barrier for the WJWT tailings impoundment. This is undoubtedly important for the planning and design of future karst depression-type tailings impoundments around the world.

Palygorskite-rich mudstone interbedded with gypsum occurs in the Neogene Baiyanghe Formation in the Yangtaiwatan basin, northwest China, but the genesis of palygorskite in the mudstone is unclear. The objective of the present study was to clarify the manner by which the palygorskite evolved by analyzing the mineralogical and geochemical characteristics of the mudstone. The mineralogical composition of bulk-rock mudstone consisted of clay minerals, quartz, feldspar, dolomite, calcite, and gypsum. Palygorskite is dominant in the clay fraction together with illite and accessory chlorite and kaolinite. The interwoven rod-like palygorskite aggregates and delicate palygorskite particles indicated an authigenic origin. The bulk rock of palygorskite-rich mudstone was rich in the trace elements Cs, U, B, Li, Sb, Bi, and As, which, together with REE, all showed very positive correlation with major element oxides Al2O3, Fe2O3, MgO, K2O, and TiO2 of the mudstone, indicating that the REE and trace elements occurred mainly in the clay minerals. The detrital illite, chlorite, and kaolinite were the main original host of the REE and enriched trace elements. Statistical analyses showed that the authigenic palygorskite had strong affinity to such elements compared to the detrital clay minerals. In addition, the chondrite-normalized REE of the bulk mudstone showed essentially the same pattern irrespective of the proportions of detrital illite, kaolinite, chlorite, and authigenic palygorskite present in the samples. Thus, the conclusion reached was that palygorskite was generated from the dissolution of detrital clay minerals. The REE and enriched trace elements in authigenic palygorskite were inherited from the detrital clay minerals.

X-ray powder diffraction (XRPD) is found consistently to be the most accurate analytical technique for quantitative analysis of clay-bearing mixtures based on results from round-robin competitions such as the Reynolds Cup (RC). A range of computationally intensive approaches can be used to quantify phase concentrations from XRPD data, of which the ‘full-pattern summation of prior measured standards’ (FPS) has proven accurate and parsimonious. Despite its proven utility, the approach often requires time-consuming selection of appropriate pure reference patterns to use for a given sample. As such, applying FPS to large and mineralogically diverse datasets is challenging. In the present work, the accuracy of an automated FPS algorithm implemented within the powdR package for the R Language and Environment for Statistical Computing was tested on a set of 27 samples from nine RC contests. The samples represent challenging and diverse clay-bearing mixtures with known concentrations, with the added advantage of allowing the accuracy of the algorithm to be compared with results submitted to previous contests. When supplied with a library of 201 reference patterns representing a comprehensive range of phases that may be encountered in natural clay-bearing mixtures, the algorithm selected appropriate phases and achieved a mean absolute bias of 0.57% for non-clay minerals (n = 275), 2.37% for clay minerals (n = 120), and 4.43% for amorphous phases (n = 14). This accuracy would be sufficient for top-3 placings in all nine RC contests held to date (RC1 = 2nd, RC2 = 2nd, RC3 = 1st; RC4 = 2nd; RC5 = 1st; RC6 = 3rd; RC7 = 3rd; RC8 = 1st; RC9 = 2nd). The comparatively low values of absolute bias in combination with the competitive placings in all RC contests tested is particularly promising for the future of automated quantitative phase analyses by XRPD.

Knowledge of clay mineralogy is essential for understanding the source areas and weathering environments of fluvial sediments, particularly in large reservoirs facing serious problems with sediment deposition, such as the Three Gorges Reservoir (TGR) in east-central China. The purpose of the present study was to identify the sediment provenances and weathering regimes contributing to the sediment load in the TGR by determining the clay-mineral and geochemical compositions of surface sediments during various seasons. X-ray diffractometry and scanning electron microscopy (SEM) were used to identify the clay minerals. The results showed that illite was the dominant mineral, followed in order by kaolinite, chlorite, and montmorillonite. From a mineralogical perspective, distal sources were the main contributors to the TGR sediments, and regional sources (surrounding tributaries) also contributed much during the three seasons, while proximal sources (hillslope soils) supplied sediment in the flood season but not in the other two seasons. The geochemical and hydrological data generally supported the mineralogical results. In the flood season, the chemical indices of the TGR sediments were >0.4, showing that the sediments contained Al-rich illite minerals and experienced intense hydrolysis. In the other two seasons the TGR sediments were enriched in Fe- and Mg-rich illite minerals, resulting from strong physical weathering. Furthermore, precipitation, rather than air temperature or latitude, was the factor that controlled weathering intensity. These findings provide deep insights into the sediment cycle and chemical weathering in this large reservoir basin.

Gray-black kaolinitic claystones of industrial value are abundant in Upper Carboniferous–Lower Permian coal-bearing strata of the Datong Coalfield of northern China. The main types are tonsteins and cryptocrystalline kaolinitic claystones, distinguished by the thinness and greater crystallinity of kaolinite in the former and by the presence of detrital illite and authigenic pyrite in the latter. In order to determine the formation history of these two types of kaolinitic claystone, the petrological, mineralogical, and geochemical characteristics of borehole samples from the Upper Carboniferous Taiyuan Formation which comprises siliciclastics and coal seams deposited in a coastal environment, were analyzed. In addition to kaolinite, the claystones contain subordinate illite, quartz, pyrite, anatase, feldspar, siderite, and calcite. The tonsteins and cryptocrystalline kaolinitic claystones have different sources, as shown by petrographic data, elemental ratios, and chondrite-normalized rare earth element (REE) patterns. The volcanic origin of the tonsteins is revealed by an abundance of volcanic quartz and vitric fragments as well as Al2O3/TiO2, Zr/Hf, and Nb/Ta ratios consistent with a felsic igneous source. Their REE fraction was derived from feldspars or micas of the parent rocks, and the fraction decreased with alteration of these minerals to kaolinite. The sedimentary origin of the cryptocrystalline kaolinitic claystones is revealed by an abundance of detrital quartz and illite grains derived from either granite or sedimentary upper crust, and by the total REE contents (ΣREE) and (La/Yb)N values which are consistent with granitic material. Their depositional environment was in a transitional (coastal) setting (as shown by intermediate Sr/Ba ratios) hosting an open acidic hydrologic system (as shown by high chemical index of alteration (CIA) values indicative of intensive chemical weathering) that was suboxic to anoxic (as shown by high U/Th ratios and trace-metal enrichment factors). The present chemistry of these claystones was thus controlled by a combination of parent rock type and diagenetic alteration.

Halloysite nanotubes (HNTs) have attracted much attention as delivery carriers for various drugs, but the loading of one such drug, quercetin, on HNTs has been investigated only rarely and usually involved cyclic vacuum pumping. The main objective of the present study was to develop a novel carrier system based on HNTs for quercetin delivery without a vacuum process and to investigate the effect of chemical modification of HNTs on the loading and release of quercetin. For this purpose, comparative studies of five chemical modification reagents (sodium lauroamphoacetate, cocoamidopropyl betaine, 1-hydroxyethyl 2-nonyl imidazoline betaine, triethanolamine, and dipicolinic acid) functionalized on HNTs were investigated for quercetin loading and in vitro release. Characterization of raw halloysite, modified halloysite, and quercetin-loaded halloysite were done by X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The results indicated that chemical modification could improve the interactions between HNTs and quercetin. After chemical modification, quercetin was anchored to both the inner and outer surfaces of HNTs by electrostatic attraction, hydrogen bonding, and van der Waals forces. Sodium lauroamphoacetate-modified HNTs were given the highest loading of 1.96 wt.% among the five reagents. Cocamidopropyl betaine-modified HNTs exhibited the best sustained-release profile with only 29.07% for initial burst release and 480 h of consecutive release. Carboxyl groups of the modification reagent improved the loading capacity of quercetin. Amide groups prolonged drug release due to the strong affinity between amine and phenolic hydroxyl groups of quercetin. The release of quercetin from the cocamidopropyl betaine-modified HNTs fitted a first-order kinetics model well. The present study suggested that cocamidopropyl betaine-modified HNTs offer promise as vehicles for delivery of quercetin and for extending the application of quercetin.

Bentonite is used as a catalyst in the removal of olefins from aromatic compounds and the present study was designed to investigate how its performance might be improved by various treatments. Bentonite from Semnan mine, Iran, was used in the study following initial characterization. In order to investigate the effect of acid and thermal treatments on the removal of olefins from aromatic compounds, bentonite samples were modified using HNO3 at different concentrations (0.15, 0.3, 0.5, 0.7, 1, and 2 M) and were also at temperatures between 100 and 340°C for 3 h. To examine the catalytic activity of bentonite-based catalysts, the samples were evaluated after running batch and continuous experiments. The optimum catalyst was characterized using thermo-programmed desorption (TPD) of NH3 to examine the acidic sites. Scanning Electron Microscopy (SEM) images, nitrogen adsorption-desorption isotherms (BET analysis), and X-ray diffraction (XRD) patterns were used to study the structural changes of the bentonite produced by the acid and thermal activation. The removal of olefins by the catalysts in batch and continuous systems revealed that the sample modified with 0.3 M Nitric acid at 150°C had superior catalytic activity, with olefin conversion remaining at >50% for up to 20 h. Nitrogen adsorption-desorption isotherms showed that acid treatment can produce a mesoporous structure. On the other hand, the TPD analysis indicated that during weak acid treatment, some cations, such as Al3+ and Fe3+, were leached from octahedral sheets and the interlayers of the clay mineral resulting in weak acid sites being generated. Finally, a novel method was proposed and tested for measuring the Bromine Index (BI) using potentiometric titration.

Water is essential for humans, animals, and plants; pollutants, usually derived from anthropogenic activities, can have a serious effect on its quality. Heavy metals are significant pollutants and are often highly toxic to living organisms, even at very low concentrations. Among the numerous removal techniques proposed, adsorption onto suitable adsorbent materials is considered to be one of the most promising. The objective of the current study was to determine the effectiveness of halloysite nanotubes (HNT) functionalized with organic amino or thiol groups as adsorbent materials to decontaminate polluted waters, using the removal of Hg2+ ions, one of the most dangerous heavy metals, as the test case. The effects of pH, ionic strength (I), and temperature of the metal ion solution on the adsorption ability and affinity of both materials were evaluated. To this end, adsorption experiments were carried out with no ionic medium and in NaNO3 and NaCl at I = 0.1 mol L−1, in the pH range 3–5 and in the temperature range 283.15–313.15 K. Kinetic and thermodynamic aspects of adsorption were considered by measuring the metal ion concentrations in aqueous solution. Various equations were used to fit experimental data, and the results obtained were explained on the basis of both the adsorbent’s characterization and the Hg2+ speciation under the given experimental conditions. Thiol and amino groups enhanced the adsorption capability of halloysite for Hg2+ ions in the pH range 3–5. The pH, the ionic medium, and the ionic strength of aqueous solution all play an important role in the adsorption process. A physical adsorption mechanism enhanced by ion exchange is proposed for both functionalized materials.

The hydrolysis of sodium borohydride (NaBH4) is a promising reaction with a possible practical application as a means of generating hydrogen. The efficiency of hydrogen production can be enhanced significantly by use of a catalyst during the reaction. Cobalt borides show significant catalytic activity, but unsupported CoB particles aggregate easily and are difficult to separate from the reaction medium for re-use. The objectives of the present study were to use halloysite (Hly) as a support material to increase the catalytic activity and reusability of a Co metal-based system and to investigate the binary effect of metal loading and reaction parameters on the hydrolysis of NaBH4. Catalysts were prepared by wet impregnation and chemical reduction. The surface morphology and structural properties of the prepared catalysts were characterized using N2 adsorption-desorption and the Brunauer-Emmet-Teller (BET) method, field emission scanning electron microscopy (FE-SEM), with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS). Response surface methodology (RSM) was used to optimize metal loading and reaction conditions for the hydrogen-generation rate. Optimum reaction conditions were determined (using Design Expert 7.0 software) as 5.01 wt.% Co loading using a Co-B/Hly-supported catalyst, 0.44 M NaBH4, 10.66 mg catalyst, and at a reaction temperature of 39.96°C. The maximum hydrogen generation rate was 33,854 mL min−1 gCo−1 under these conditions.

The poor environmental stability of natural anthocyanin hinders its usefulness in various functional applications. The objectives of the present study were to enhance the environmental stability of anthocyanin extracted from Lycium ruthenicum by mixing it with montmorillonite to form an organic/inorganic hybrid pigment, and then to synthesize allochroic biodegradable composite films by incorporating the hybrid pigment into sodium alginate and test them for potential applications in food testing and packaging. The results of X-ray diffraction, Fourier-transform infrared spectroscopy, and use of the Brunauer–Emmett–Teller method and zeta potential demonstrated that anthocyanin was both adsorbed on the surface and intercalated into the interlayer of montmorillonite via host–guest interaction, and the hybrid pigments obtained allowed good, reversible, acid/base behavior after exposure to HCl and NH3 atmospheres. The composite films containing hybrid pigments had good mechanical properties due to the uniform dispersion of the pigments in a sodium alginate substrate and the formation of hydrogen bonds between them. Interestingly, the composite films also exhibited reversible acidichromism. The as-prepared hybrid pigments in composite films could, therefore, serve simultaneously as a reinforced material and as a smart coloring agent for a polymer substrate.