Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

Injection of CaCl2 and Na2SiO3 solutions into clay suspensions during electroosmosis often improves the cohesive strength of clays near the anode and cathode, whereas the cohesive strength of clays between the electrodes remains weak. Although the main improvement mechanism for the cohesive strength of clays near the cathode was demonstrated to be a pozzolanic reaction (formation of calcium silicate hydrate cement), the mechanism of improved cohesive strength near the anode is still not understood. The objective of the present study was to investigate the mechanism for the improvement of cohesive strength near the anode and, thus, make it possible to determine a way to enhance the range in improvement using kaolinite as the test clay. The test was performed by first injecting CaCl2 solution during electroosmosis until the optimum volume of CaCl2 was attained. This was followed by treatment with Na2SiO3 solution for different lengths of time. The results indicate that the anode region after treatment was acidic (pH = 4) because the electrolysis of water causes acidification near the anode. As Na2SiO3 solution was injected through the anode, the mechanism of cohesive strength improvement of the treated clay near the anode was attributed to the silicic acid polymerization effect provided by the Na2SiO3 solution. The silicic acid may link the clay particles together to form a gel network in a low pH environment. The clay gel network structure developed rigidity as the water content was reduced. In addition, as the volume of injected Na2SiO3 solution was increased, the cohesive strength near the anode also increased.

Dye molecular aggregation and other interactions on clay mineral surfaces cause phenomena such as methachromasy (change in color), fluorescence enhancement, or quenching, which represent significant changes in the spectral properties of the dye. These phenomena can be used to control the photophysical properties of hybrid systems based on cationic organic dyes. In the present study, the aggregation of two structurally similar cyanine dyes, 3,3’-diethyl-oxocyanine iodide (OxCy) and 3,3’-diethyl-2,2’-thiacyanine iodide (ThCy), in colloidal dispersions of three smectites (saponite, hectorite, and montmorillonite) was studied by absorption and fluorescence spectroscopy for a broad range of dye/smectite loadings. Spectral data were analysed by chemometric methods (principal component analysis, PCA, and multivariate curve resolution, MCR). Detailed analysis of the OxCy absorption spectra by the chemometric methods revealed the formation of two types of oblique aggregates exhibiting light absorption in both H- and J-bands. The existence of such similar aggregates, with similar splitting of excitation energies, appears to be related to the existence of two stable conformational isomers of this dye. On increasing the smectite CEC and dye/smectite loading, fluorescence quenching occurred. The ThCy dye exhibited a stronger tendency for molecular aggregation than OxCy. On increasing the smectite CEC, the formation of oblique aggregates with dominant H-bands also increased. On aging of the hybrid dispersions, equilibria of ThCy aggregates were shifted to the species with dominant J-bands. This behavior had a significant impact on the shape and intensity of the fluorescence emission of the hybrid dispersions. Using different smectites enables control of the dye aggregation and significant change to the photophysical properties of the hybrid systems. These systems can be used for the detailed study of the photophysical properties of cyanine dyes in various states. The colloidal systems with cyanine dyes can be used as precursors for the preparation of novel hybrid materials. In addition, the sensitive response of the photophysical properties of cyanine dyes to the clay mineral surface can be applied to the characterization of clay minerals.

The high-density siliciclastic minerals (e.g. zircon) in the coarse fractions (>44 mm, informally known as grit) of the mined Georgia kaolins are potential and significant sources of the rare-earth elements (REE). The abundances and provenance of the REE signature have not been studied extensively for the Georgia kaolins. The objective of the present study was, therefore, to define the contribution of these heavy minerals (e.g. zircon) to the REE inventory of the coarse fractions of Georgia kaolins. Heavy-mineral subfractions separated from the coarse fractions contained 1647 mg/kg REE from the Jeffersonville Member of the Lower Tertiary Huber Formation and 5012 mg/kg REE from the Buffalo Creek Kaolin Member of the Upper Cretaceous Galliard Formation, respectively. These heavy-mineral subfractions were enriched 10–100 times in the heavy rare-earth elements (HREE, Gd—Lu,), Hf, and Zr relative to the concentrations of these elements in Upper Continental Crust. The heavy-mineral subfractions comprised 5% of the coarse fractions (grit) of these two kaolin-producing formations. The heavy-mineral subfractions consisted of zircon, anatase, rutile, kaolinite, and minor amounts of muscovite, trace ilmenite, and staurolite. The large concentrations of REE were obtained by separating the dense heavy minerals from the coarse fraction (grit) obtained during the typical production of kaolin-group minerals (kaolinite) from kaolin ore. The amount of zircon (estimated from the 6–11 wt.% Zr) and the absence of monazite did not explain the high concentrations of REE in the heavy-mineral subfractions. The large amounts of REE could have resulted from the sorption of REE released during weathering reactions, or from the presence of small amounts (0.025 wt.%) each of monazite and xenotime in addition to the presence of zircon. This heavymineral subfraction represented a novel domestic resource of extractable REE, especially the HREE, of a grade as high as 0.50 wt.% total REE.

Chemical denudation and chemical weathering rates vary under climatic, bedrock, biotic, and topographic conditions. Constraints for landscape evolution models must consider changes in these factors on human and geologic time scales. Changes in nutrient dynamics, related to the storage and exchange of K+ in clay minerals as a response to land use change, can affect the rates of chemical weathering and denudation. Incorporation of these changes in landscape evolution models can add insight into how land use changes affect soil thickness and erodibility. In order to assess changes in soil clay mineralogy that result from land-use differences, the present study contrasts the clay mineral assemblages in three proximal sites that were managed differently over nearly the past two centuries where contemporary vegetation was dominated by old hardwood forest, old-field pine, and cultivated biomes. X-ray diffraction (XRD) of the oriented clay fraction using K-, Mg-, and Na-saturation treatments for the air-dried, ethylene glycol (Mg-EG and K-EG) solvated, and heated (100, 350, and 550°C) states were used to characterize the clay mineral assemblages. XRD patterns of degraded biotite (oxidized Fe and expelled charge-compensating interlayer K) exhibited coherent scattering characteristics similar to illite. XRD patterns of the Mg-EG samples were, therefore, accurately modeled using NEWMOD2® software by the use of mineral structure files for discrete illite, vermiculite, kaolinite, mixed-layer kaolinite-smectite, illite-vermiculite, kaolinite-illite, and hydroxy-interlayered vermiculite. The soil and upper saprolite profiles that formed on a Neoproterozoic gneiss in the Calhoun Experimental Forest in South Carolina, USA, revealed a depth-dependence for the deeply weathered kaolinitic to the shallowly weathered illitic/vermiculitic mineral assemblages that varied in the cultivated, pine, and hardwood sites, respectively. An analysis of archived samples that were collected over a five-decade growth period from the pine site suggests that the content of illite-like layers increased at the surface within 8 y. Historical management of the sites has resulted in different states of dynamic equilibrium, whereby deep rooting at the hardwood and pine sites promotes nutrient uplift of K from the weathering of orthoclase and micas. Differences in the denudation rates at the cultivated, pine, and hardwood sites through time were reflected by changes in the soil clay mineralogy. Specifically, an increased abundance of illite-like layers in the surface soils can serve as a reservoir of K+.

Toxic pollutants such as diclofenac (DCF) and cadmium(II) have been detected together in various water sources; these compounds have adverse effects on human health. The objective of the present study was to investigate the sorption of DCF and Cd(II) from aqueous solutions on an organobentonite. The organobentonite was synthesized by adsorbing the surfactant hexadecyltrimethylammonium (HDTMA) on bentonite; this was designated OBHDTMA. The sorption of DCF and Cd(II) on OBHDTMA and of Cd(II) on OBHDTMA saturated with DCF (OBHDTMA-DCF) were then studied. The bentonite, OBHDTMA, and OBHDTMA-DCF were characterized by X-ray diffraction, thermogravimetric analysis, and Fourier-transform infrared spectroscopy. The capacity of OBHDTMA for adsorbing DCF depended on the solution pH, ionic strength, and temperature. The effect of pH on the adsorption capacity of OBHDTMA was anomalous because, depending on the concentration of DCF at equilibrium, the adsorption capacity increased or decreased by raising the pH. The capacity of OBHDTMA was enhanced by increasing the temperature from 15 to 35°C and by reducing the ionic strength from 1 to 0.01 N. The dependence of the adsorption capacity on the operating conditions was explained by considering the interactions between the DCF in solution and the surface of OBHDTMA. The maximum sorption capacity of the OBHDTMA for DCF was 388 mg/g at T = 25°C and at pH = 7 and was comparable to those of carbon materials. The adsorption of DCF on OBHDTMA was scarcely reversible, but the desorption percentage increased with pH. The adsorption of DCF on OBHDTMA was due to partition and electrostatic attraction. More Cd(II) was adsorbed on OBHDTMA-DCF than on OBHDTMA and this was influenced by the loading of DCF on the OBHDTMA-DCF. The OBHDTMA-DCF may be used to remove Cd(II) from water solution.

The Boom Clay in northern Belgium has been studied intensively over recent decades as a potential host rock in the context of disposal of radioactive waste. One of the parameters of interest is the cation exchange capacity (CEC) as it is related to the sorption potential of radionuclides to the clay host rock. In the past, the CEC was determined using various methods on a limited number of samples, leading to significant variations. To constrain the CEC of the Boom Clay better, a sample set covering the entire stratigraphy was measured using the quick copper(II) triethylenetetramine method. Part of the sample set was also measured using the cobalt(III) hexamine method, as a quality control for the results of the former method. In addition, the exchangeable cation population of the Boom Clay was quantified systematically for the first time and these results were compared to the in situ pore-water chemistry, indicating a strong coupling between the pore-water composition and the exchangeable sites of clay minerals.

As a common mineral phase on Earth and Martian regolith, natural rutile was reported as a potential candidate for use as a Fenton catalyst in this study. The influences of Fe and V in various chemical states on the generation of reactive oxygen species (ROSs) and the catalytic activity of rutile were examined. A series of rutile samples with various surface and bulk states of Fe and V were obtained initially by hydrogen annealing of natural rutile at ~773–1173 K. X-ray diffraction, electron paramagnetic resonance spectra, and X-ray photoelectron spectroscopy demonstrated that the atomic fractions of Fe(III) and V(V) decreased sharply with increasing temperature, along with the accumulation of surface Fe(II) and bulk V(III). All as-prepared materials showed enhanced Fenton degradation efficiency on methylene blue (MB) compared with P25-TiO2, and the treated samples exhibited up to 3.5-fold improvement in efficiency at pH 3 compared to the untreated sample. The improved efficiency was attributed mainly to Fenton catalysis involving Fe(II) and V(III). The dissolved Fe2+ played a crucial role in the homogeneous Fenton reaction, while the bound V(III) favored adsorption primarily and may have facilitated heterogeneous Fenton reaction and the regeneration of Fe2+. The pH regulated the reaction mechanism among homogeneous (pH = 3) and heterogeneous (pH = 3.7) Fenton catalysis and physical adsorption (pH = 5, 6). The aim of the present study was to improve the understanding of the potential role of natural rutile with advanced oxidation functions in Earth systems and even on Mars, which also provide an inspiration for screening natural rutile and any other similar, Earth-abundant, low-cost minerals for environmental application.

Citrate is distributed widely in the Earth’s surface environments as a biological product released by microbes and plants. Citrate is also often used as a chelating agent for the selective dissolution of iron coatings and free iron oxides in soils. Adsorption experiments of Cs+ and IO3− before and after the complexation of citrate with the pseudoboehmite surface were conducted to evaluate the effects of citrate on the adsorption of these ions on the surface of pseudoboehmite. Additional adsorption experiments of Cs+ and IO3− after the decomposition of citrate adsorbed on the pseudoboehmite surface were also performed to confirm the recovery of the original surface properties. Citrate decomposition was carried out by means of 10% H2O2 treatments at 75°C and pH 5, 7, and 9. The results indicated that citrate complexation decreased remarkably the adsorption of both Cs+ and IO3− in the pH range 3–10, which was due to a decrease in the number of active charged sites available for adsorption of these ions. Decomposition of citrate adsorbed on the pseudoboehmite surface was found to be complete after three rounds of treatment with 10% H2O2 at 75°C and pH > 7. After the decomposition of citrate adsorbed on the pseudoboehmite surface, the adsorption of both Cs+ and IO3− was restored completely to the initial amounts before citrate complexation, and the inhibition effect of citrate on the adsorption of these ions disappeared under all pH conditions.

Because inorganic nanosheets, such as clay minerals, are anisotropic, the manipulation of nanosheet orientation is an important challenge in order to realize future functional materials. In the present study, a novel methodology for nanosheet manipulation using laser radiation pressure is proposed. When a linearly polarized laser beam was used to irradiate a niobate (Nb6O174-) nanosheet colloid, the nanosheet was trapped at the focal point so that the in-plane direction of the nanosheet was oriented parallel to the propagation direction of the incident laser beam so as to minimize the scattering force. In addition, the trapped nanosheet was aligned along the polarization direction of the linearly polarized laser beam.

The elimination of Pb2+ and recovery of lead metal during the treatment of industrial sewage is an important research topic. Montmorillonite (Mnt) is a promising material in this regard. The purpose of the present study was to improve the Pb2+ adsorption ability of Na-containing Mnt (Na-Mnt) by pillaring titania (anatase) into its interlayer spaces using a sol-gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ratio of Ti to Mnt affected the crystal phase of titania-pillared Na-Mnt (Ti-Mnt), and changed the interlayer spacing of the (001) plane of Ti-Mnt and the growth of anatase. The Pb2+-adsorption capabilities of Ti-Mnt were tested using an aqueous solution of lead nitrate as a wastewater model. The Ti-Mnt prepared adsorbed >99.99% of the Pb2+; leached and activated Ti-Mnt adsorbed >95.7% of the Pb2+, indicating that Ti-Mnt could be recycled effectively. Furthermore, the Pb2+-adsorption capability of Ti- Mnt was related to the interlayer spacing of Mnt, the distribution of anatase particles pillared in Mnt, and the specific surface area, especially with respect to the relationship between the anatase particles and the interlayer spacing of the (001) plane.

Selective sorption and/or fixation of cations with low hydration energies (e.g. K+, NH4+, Rb+, Cs+) by vermiculites is a well known phenomenon in soil science and it has been described by many investigators since the 1950s. Because most of the available studies deal with trioctahedral vermiculites, cation fixation in dioctahedral vermiculites is not as well understood as fixation by trioctahedral structures. The objective of the present study was to investigate the influence of NH4+ saturation on the structure of a natural dioctahedral vermiculite. Because no dioctahedral vermiculite standard reference material was available, two natural dioctahedral vermiculite-rich soil clay samples were used in the study. The clays were saturated with NH4+ using different protocols to simulate natural processes that likely take place in soils. The degree of NH4+ fixation by the dioctahedral vermiculite was evaluated using X-ray diffraction, elemental N analysis, and infrared spectroscopy. All the treatments that involved NH4+ saturation caused NH4+ fixation and irreversible collapse (i.e. contraction to ~10 Å) of at least a portion of the previously hydrated (vermiculitic) interlayers. Air drying of the NH4+-saturated samples greatly enhanced the degree of the collapse. The results indicated that the collapse of dioctahedral vermiculite leads to the formation of a NH4-illite-like phase that is likely to occur in some soils and sediments that are rich in organic matter. The formation of a NH4-illite-like phase by NHNH4+ fixation in vermiculitic interlayers needs to be taken into consideration in studies that deal with the clay mineralogy of sedimentary basins.

Zinc (Zn) is widely known as an essential trace element for fish and new ways to supply it to them are needed. Palygorskite (Pal) is a natural silicate clay mineral and the palygorskite structure contains nano-channels, which are filled with water and exchangeable ions. Zn-bearing palygorskites (Zn-Pal) prepared using ion exchange have attracted attention due to the durable antibacterial properties that limit pathogens and as a potential new Zn source for livestock. The present study was conducted to evaluate the effects of Zn-Pal supplementation on the growth performance, nutrient retention, meat quality, Zn accumulation, and intestinal Zn transporter protein gene expression in blunt snout bream Megalobrama amblycephala. The fish were fed a basal diet without an exogenous Zn source and the basal diet was supplemented with 125 mg/kg Zn as Zn sulfate (ZnSO4) or 35, 80, or 125 mg/kg Zn as Zn-Pal. Each diet was tested using three replicates for 7 weeks. The results showed that dietary Zn-Pal supplementation quadratically (P<0.05) increased growth performance, nutrient retention, total and Cu/Zn superoxide dismutase activity, Zn content in scales, and intestinal Zn transporter protein gene expression. The muscular cooking loss in blunt snout bream decreased with the optimum Zn-Pal Zn level of 35 mg/kg. Compared to the fish treated with ZnSO4, the fish supplemented with 35 mg/kg as Zn-Pal exhibited similar growth performance and nutrient retention (P>0.05), increased mRNA expression of the metal-response element-binding transcription factor-1 in the intestine (P<0.05), and decreased cooking loss of muscle (P<0.05).The results suggested that 35 mg/kg Zn supplementation as Zn-Pal could improve the growth performance and body composition, increase nutrient retention and tissue Zn concentrations, enhance the muscle water-holding capacity, and enhance antioxidant status in blunt snout bream. The Zn-Pal was more efficient and could be used as an alternative Zn source to ZnSO4 in the diet of blunt snout bream.

Numerous occurrences of asbestos minerals, notably chrysotile and tremolite, are to be found on fracture surfaces in thrust fault deformation zones of Cretaceous dunite-harzburgite and pyroxenite in the Çankırı and Ankara regions, central Anatolia, Turkey. Consequently, potential exists for the development of regional malignant mesothelioma. The means of serpentinization, such as reaction of seawater during accretion of the upper ophiolitic mantle crust in a subduction zone and/or following uplift of ophiolitic units and the influence of hydrothermal/meteoric fluids along fractures, were investigated. Cretaceous dunite-harzburgite and localized pyroxenite rocks are mainly composed of serpentinized olivine and pyroxene associated with opaque minerals and Fe-(oxyhydr)oxide phases. Smectite, chlorite, illite, kaolinite, hydromagnesite, goethite, quartz, and opal-CT are also present. Chrysotile and localized tremolite occur either as a mesh, a suboriented to oriented long-fiber bundle, or as fiber-filling millimetric micro-vein textures on relicts of olivine and pyroxene (enstatite, augite). The chrysotile and tremolite have non-pseudomorphic textures developed under high pressure and temperature. The textures suggest authigenic formation of chrysotile and tremolite via a dissolution and precipitation mechanism. Additionally, spherical structures of opal-CT and locally platy hydromagnesite crystals either enclose or are developed within chrysotile/tremolite fiber bundles. The leaching of MgO, Fe2O3, Al2O3, Ni, Cr, and Nb, an increase in the LREE/HREE ratio, and negative Eu anomalies in the dunite-harzburgite and pyroxenite, and asbestos samples suggest that the chrysotile and tremolite were derived from the serpentinization of olivine and pyroxene. The chrysotile and tremolite were developed along fractures by hydrothermal fluid alteration during accretion and/or following the uplift of ophiolitic units of the region under high pressure and temperature conditions. This interpretation is also supported by isotope data and the calculated formation temperature of 170–555°C for chrysotile and tremolite. The average structural formulae for chrysotile and tremolite are (NanK0.03)(Mg5.54Fe0.09Al0.05Ca0.01Mn0.001) (Si3.96Al0.03)O10(OH)8 and (Na0.17K0.07)(Ca1.59Mg0.19Mn0.002)(Mg4.72Fe0.28)(Si7.86Al0.1Fe0.06)O22(OH)2, respectively.

The present study presents a generalized procedure to accurately identify trioctahedral 1:1 layer silicates. The reciprocal space (RS) sections were obtained by the precession method by “unwarping” frames that were recorded using diffractometers with area detectors or from electron diffraction tomography (EDT) patterns. Distributions of subfamily reflections along the reciprocal lattice rows [21̄l]* / [11l]* / [1̄2l]* in (2hh̄lhex)* / (hhlhex)* / (h̄2hlhex)* RS planes were used to determine OD (Ordered — Disordered) subfamilies (Bailey’s groups A, B, C, D). The distributions along the [10l]* / [01l]* / [1̄1l]* rows in the (h0lhex)* / (0klhex)* / (h̄hlhex) RS planes allow determination of the polytypes. The use of traditional identification diagrams for the determination of OD subfamilies and polytypes was generalized in order to identify monoclinic and orthorhombic MDO (Maximum Degree of Order) polytypes. In these polytypes, the distribution of characteristic reflections along rows is different in RS sections that are perpendicular and diagonal to the symmetry plane of the polytype. The identification diagram of non-MDO polytype 6T2 is also presented. The method was applied to the identification of single crystals of cronstedtite that were synthesized during interactions of Fe metal with a natural claystone during experiments over a temperature range of 90-60°C. Conical and pyramidal crystals with a maximum size of a few micrometers were studied using electron diffraction tomography (EDT). The following polytypes were identified: 1M, 2M1, an apparently ninetuple polytype that was interpreted as triclinic 3A (group A), 1T (group C), and disordered crystals of group D. The 1M polytype was the most abundant. Some 1M crystals were twinned by reticular merohedry with a 120° rotation along the chex axis as the twin operation. The 2M1 occurred as isolated crystals as well as in mixed crystals. Intergrown 1T and 1M polytypes of the C and A group, respectively, were identified in one mixed crystal. The possible stacking sequence and the 3A polytype identification diagram was presented and discussed. Example RS sections of all polytypes were identified and demonstrated.

The electrical state of the interface between a kaolinite-dominated clay sample and aqueous electrolyte solutions was characterized using low-frequency conductance measurements. From these measurements, the ζ-potential and surface conductivity contributions from the diffuse and non-diffuse parts of the electrical double layer were obtained. The suspensions were studied as a function of volume fraction, electrolyte concentration, and electrolyte type (LiCl, NaCl, KCl, CsCl, CaCl2, SrCl2, and BaCl2). Interpretation in terms of the surface conductance revealed that a substantial part of the surface conductivity originates in the inner part of the double layer. Electrokinetic potentials and related diffuse double layer properties are highly dependent on the nature of monovalent counterions, whereas divalent counterions do not show such clear dependencies. Further presented was a simple way to estimate the order of magnitude of counterion mobilities in the inner part of the electrical double layer. All counterions were shown to have a substantial mobility in the inner part of the double layer. Finally, we suggest that the apparent ion-specific effects observed in the diffuse part of the double layer are at least in part related to the finite size of the counterions. Our findings are relevant to scenarios where fluid flow in porous media is accompanied by charged species transport, e.g., in electro-osmotic remediation, spectral-induced polarization, or permeability measurements.

The oil sands of western Canada represent the third largest hydrocarbon deposit in the world. Bitumen, a very heavy petroleum, is recovered from mined oil sands using warm water extraction followed by separation treatments to isolate the bitumen product. The high energy, water use, as well as tailings remediation challenges associated with the warm water extraction process raise major environmental concerns. Non-aqueous extraction using organic solvents at room temperature has been investigated extensively as an alternative to the warm water extraction process. The main challenge to the large-scale implementation of non-aqueous extraction is the retention of solvent in the tailings. The objective of this work was to present and validate a computational model for the interaction of solvents used in non-aqueous extraction with minerals, such as the abundant and adsorbent clay mineral kaolinite. The model system contained a periodically extended kaolinite platelet immersed in a solvent and all were treated at the atomic level using the 3D Reference Interaction Site Model with the Kovalenko-Hirata closure approximation (3D-RISM-KH) molecular theory of solvation. The solvent solvation free energy of interaction with kaolinite as well as site-specific adsorption energies and kinetic barriers for desorption were computed based on the solvent site density distribution functions. Moreover, the lateral and integrated density distributions were computed to analyze the organization of solvent at kaolinite surfaces. The integrated density distribution profiles were correlated with experimental adsorption isotherms. The results showed very strong adsorption of ethanol and weak adsorption of hydrocarbon solvents on kaolinite, which were in qualitative agreement with experimental solvent extraction reports. The model and these findings are valuable in understanding the mechanism of solvent retention in tailings after non-aqueous extraction and highlight the action of hydroxylated cosolvent additives to enhance extraction using nonpolar solvents.

Reflectance spectroscopy is a rapid, non-destructive technique capable of characterizing mineral and organic components within geologic materials at spatial scales that range from μm to km. The degree to which reflectance spectra can be used to provide quantitative information about organic compounds remains poorly understood, particularly for rocks with low organic content that are common in the Earth’s ancient rock record and that may be present on other planetary bodies, such as Mars. In the present study, reflectance spectra (0.35–25 μm) were acquired for a suite of Proterozoic shales and the kerogen was isolated to assess how spectral properties of aliphatic and aromatic C-H absorption bands can be used to predict organic matter abundance (total organic content, TOC, and H/C ratio). A number of spectral parameters were evaluated for organic absorption bands observed in the 3–4 μm wavelength region for comparison with independently measured TOC and H/C values. Ratios of the strengths of aliphatic to aromatic absorption bands were directly correlated to H/C values, but the reflectance spectra for pure kerogens with H/C < 0.2 lacked clear evidence for C-H absorption bands in this spectral region. Organic absorption bands are routinely observed for bulk rock powders with >1 wt.% TOC, but the detection limits of reflectance spectra for TOC may be <1 wt.% or as high as 10 wt.%. Organic detection limits for reflectance spectra are, thus, controlled by both TOC and H/C values, but these parameters can be predicted for clay-rich, kerogen-dominated samples for a range of values that are relevant to drill cores, outcrops, meteorites, and planetary surfaces.

Limonite is mainly derived from weathering of Fe sulfide, iron-bearing carbonate, or silicate minerals. The weathering of Fe sulfide or carbonate minerals to yield limonite from the Tongling mineralization cluster has been studied extensively. Knowledge of the mineralogical and geochemical characteristics of the limonite from weathering of Fe-bearing silicate minerals is still incomplete, however. To address this, black limonite containing ilvaite (a silicate mineral) found in Yeshan iron deposit, Tongling, China, was studied using mineralogical and chemical analysis. The mineralogical characteristics indicated that Mn goethite was present as nano-granular (<15 nm) or acicular (50–100 nm long, ~10 nm wide, i.e. high length/width ratio) crystals with low crystallinity. Groutite, ramsdellite, and pyrolusite were identified in the limonite as ~5 nm nanoparticles, and coated on the goethite surface. Amorphous Fe-Mn phases and silica were highly developed in the limonite studied. Ilvaite crystals showed idiomorphic granular morphology and were replaced by Fe-Mn oxides/hydroxides; pyrite was also present as inclusions within the ilvaite and the ilvaite structural formula calculated was Ca1.04(Fe1.57Mn0.31Mg0.04)(Fe1.09Al0.01)[Si1.95O]O(OH). According to the relatively high CuO and ZnO values and the low Al2O3 value in the black limonite, the negative correlations between (Fe2O3+MnO) and (CuO+ZnO+BaO), (Fe2O3+MnO) and Al2O3, high Mn and Si contents, and the characteristics of the textural relationships and compositions between the black limonite and ilvaite, a semi-enclosed environment with acidic to weakly alkaline conditions was deduced; ilvaite was found to be responsible for the formation and enrichment of limonite.