Layered Clay Minerals in Cancer Therapy: Recent Progress and Prospects.

Cancer is one of the deadliest diseases, and current treatment regimens suffer from limited efficacy, nonspecific toxicity, and chemoresistance. With the advantages of good biocompatibility, large specific surface area, excellent cation exchange capacity, and easy availability, clay minerals have been receiving ever-increasing interests in cancer treatment. They can act as carriers to reduce the toxic side effects of chemotherapeutic drugs, and some of their own properties can kill cancer cells, etc. Compared with other morphologies clays, layered clay minerals (LCM) have attracted more and more attention due to adjustable interlayer spacing, easier ion exchange, and stronger adsorption capacity. In this review, the structure, classification, physicochemical properties, and functionalization methods of LCM are summarized. The state-of-the-art progress of LCM in antitumor therapy is systematically described, with emphasis on the application of montmorillonite, kaolinite, and vermiculite. Furthermore, the property-function relationships of LCM are comprehensively illustrated to reveal the design principles of clay-based antitumor systems. Finally, foreseeable challenges and outlook in this field are discussed.

Chitosan-kaolinite clay composite as durable coating material for slow release NPK fertilizer.

Durable chitosan-based coating material used as a barrier for slow-release fertilizers in the agricultural soil. This approach decreases the intense usage of fertilizer and works on their accessibility for the plants' necessities. In present paper, the proposed coating material was prepared on the basis of chitosan-kaolinite composite (CS-Gl-K). Fourier transform infrared spectroscopy analysis (FTIR), Scanning Electron Microscopy (SEM), thermogravimetric analysis (ATG), XRD, swelling degree and biodegradability studies were used to analyze the influence of the kaolinite clay incorporation in chitosan film properties. The characterization of the chitosan composites has been thoroughly studied. The NPK mineral fertilizer was coated according to the dip-immersing process of chitosan-kaolinite composites. Slow-release efficiency was evaluated by determining the rate of phosphorus release from the covered granules into water and soil. Moreover, phosphorus release from coated NPK/CS-Gl-K granules was generally delayed contrasted with NPK/uncoated. In addition, the biodegradation investigation of the composite material (CS-Gl-K) in soil was affirmed its durability. The proposed coating material has good slow-release properties, low cost and is environmentally friendly. The FTIR, ATG and XRD spectra revealed a good intercalation between the kaolinite-clay pores and chitosan chains.

Development of Polyvinyl Alcohol/Kaolin Sponges Stimulated by Marjoram as Hemostatic, Antibacterial, and Antioxidant Dressings for Wound Healing Promotion.

The predominant impediments to cutaneous wound regeneration are hemorrhage and bacterial infections that lead to extensive inflammation with lethal impact. We thus developed a series of composite sponges based on polyvinyl alcohol (PVA) inspired by marjoram essential oil and kaolin (PVA/marjoram/kaolin), adopting a freeze-thaw method to treat irregular wounds by thwarting lethal bleeding and microbial infections. Microstructure analyses manifested three-dimensional interconnected porous structures for PVA/marjoram/kaolin. Additionally, upon increasing marjoram and kaolin concentrations, the pore diameters of the sponges significantly increased, recording a maximum of 34 ± 5.8 µm for PVA-M0.5-K0.1. Moreover, the porosity and degradation properties of PVA/marjoram/kaolin sponges were markedly enhanced compared with the PVA sponge with high swelling capacity. Furthermore, the PVA/marjoram/kaolin sponges exerted exceptional antibacterial performance against Escherichia coli and Bacillus cereus, along with remarkable antioxidant properties. Moreover, PVA/marjoram/kaolin sponges demonstrated significant thrombogenicity, developing high thrombus mass and hemocompatibility, in addition to their remarkable safety toward fibroblast cells. Notably, this is the first study to our knowledge investigating the effectiveness of marjoram in a polymeric carrier for prospective functioning as a wound dressing. Collectively, the findings suggest the prospective usage of the PVA-M0.5-K0.1 sponge in wound healing for hemorrhage and bacterial infection control.

Effects of ethanol, activated carbon, and activated kaolin on perilla seed oil: Volatile organic compounds, physicochemical characteristics, and fatty acid composition.

Perilla seed oil (PSO) has a special aromatic odor, which is unpleasant to the personal preferences of some consumers. To this end, this article evaluated the differences in volatile organic compounds (VOCs), physicochemical characteristics, and fatty acid composition of PSO treated with ethanol (PSO-EA), activated carbon (PSO-AC), and activated kaolin (PSO-AK). The results showed that in the PSO, PSO-EA, PSO-AC, and PSO-AK samples, the content of linolenic acid, oleic acid, and linoleic acid hardly changed. Among the physicochemical characteristics of the four samples, the color difference between PSO and PSO-EA was greater than the color difference between PSO and PSO-AC, PSO-AK. The three treatment methods had the greatest impact on the PSO peroxide value but had little effect on other indicators. Gas chromatography-ion mobility spectrum results identified 28 known volatiles, of which aldehydes, alkenals, alcohols, ketones, and esters were the main groups. Fingerprint analysis found that PSO had an aromatic odor, which includes 1-hexanol, hexanal, and 2-pentylfuran; the removal effect of ethanol on VOCs in PSO was better than that of activated carbon and activated kaolin. The difference between the four oil samples was found from the strength of the VOCs' signals in a two-dimensional map. From the principal components analysis and the "nearest neighbor" fingerprint analysis, it was found that PSO is generally quite different from PSO-EA, PSO-AC, and PSO-AK, while in the "nearest neighbor" fingerprint analysis, PSO-AC and PSO-AK are similar in general. In short, PSO will have better applications in the food field. PRACTICAL APPLICATION: Treatment of PSO with ethanol, activated carbon, and activated kaolin is conducive to the comprehensive utilization of edible resources. In this work, ethanol, activated carbon, and activated kaolin were used to remove VOCs in PSO, and PSO-EA, PSO-AC, and PSO-AK were obtained. The perilla seed oil after these three treatment methods was tested for VOCs, physicochemical characteristics, and fatty acid composition. They can meet the needs of more consumers without affecting the fatty acid composition in the PSO, and have broad development prospects.

Toxicity, mutagenicity and trace metal constituent of Termitomyces schimperi (Pat.) R. Heim (Lyophyllaceae) and kaolin, a recipe used traditionally in cancer management in Cote d'Ivoire.

ETHNOPHARMACOLOGICAL RELEVANCE: Some local communities in Cote d'Ivoire use the mushroom Termitomyces schimperi combined with kaolin (TSK) to manage various cancers in patients. However, there is a paucity of data on toxicity, mutagenicity and trace metal constituent of TSK. AIM OF THE STUDY: We sought to investigate the acute and sub-chronic toxicities, mutagenic potential, and trace metal constituents of TSK. MATERIALS AND METHODS: To assess acute toxicity, single doses (1000, 3000 and 5000 mg/kg) of aqueous extract of TSK were administrated per os to Sprague Dawley (SD) rats on Day 1. The rats were then monitored for 13 consecutive days. Sub-chronic toxicity was evaluated by daily administration of 200 and 500 mg/kg of the extract per os for 90 consecutive days. SD rats used as control received distilled water. Signs of toxicity, changes in body weight and mortality were monitored. After the aforementioned monitoring processes, rats were sacrificed and blood collected for full blood count and biochemistry analysis. Animal organs were also collected for histopathological examination. The mutagenic potential of the aqueous extract of TSK (10000 µg/mL) on TA98 Salmonella typhimurium was estimated. Additionally, energy-dispersive X-ray fluorescence (ED-XRF) method was employed to determine trace metal constituents of TSK. RESULTS: Single-dose administration of 5000 mg/kg of TSK did not cause any death in the SD rats; thus, LD50 was above 5000 mg/kg. Administration of 1000 and 3000 mg/kg of the aqueous extract of TSK did not cause any significant change in behaviour and body weight of SD rats during the 14-day monitoring period. However, the mean corpuscular volume and the mean corpuscular haemoglobin concentration increased significantly (p < 0.01) among rats administered 1000 and 3000 mg/kg of TSK. There was a significant increase (p < 0.0001) in alanine transaminase levels in rats administered 1000 and 3000 mg/kg of TSK extract compared with control. Conversely, there was a significant decrease (p=0.0122) in serum creatine level among rats administered 1000 and 3000 mg/kg of TSK extract compared with control. After 14 days, there were minimal changes with isolated organs of TSK-treated and control rats. Furthermore, 90-day treatment with extract of TSK caused no significant change in parameters assessed. TSK induced frameshift gene mutation in S. typhimurium before (p < 0.05) and after metabolic activation (p < 0.001). Elemental analysis of TSK revealed the presence of toxic (aluminium) or potentially toxic (silver, rabidium, titanium and zirconium) elements. CONCLUSIONS: The aqueous extract of TSK showed no toxicity (acute and sub-chronic) at doses tested. These findings are consistent with the absence of heavy metals (i.e., cadmium) and potentially toxic elements (i.e., uranium) in TSK samples analysed. TSK showed some level of mutagenic potential. Further mutagenic and chronic toxicity studies on TSK are required.

Properties of hydric and biodegradability of cassava starch-based bioplastics reinforced with thermally modified kaolin.

In this study, hydric and biodegradability properties of cassava starch-based bioplastics reinforced with crude kaolin or treated kaolinitic clay at 700 °C called metakaolin were investigated using water adsorption and microbiological tests. Non-reinforced bioplastics (BP) and those containing 5 wt.% crude kaolin (BPKB) or metakaolin (BPMKB) were manufactured using the casting/evaporation method. Results obtained showed a decrease in the solubility and in the water diffusion and permeability of clay-reinforced bioplastics with respect to the ones without reinforcement. This improvement of the hydric properties has been attributed to the reduction in the free volumes existing between the starch macromolecules due to their interactions with clay platelets. These interactions might favor a more homogeneous and compact microstructure. The biodegradability of the clay reinforced bioplastics was significantly improved due to the bacterial proliferation. The thermal treatment of kaolinitic clay further improved the hydric and biodegradability properties of starch-based bioplastics.

Kaolinite group minerals: Applications in cancer diagnosis and treatment.

The clay minerals are characterized as important minerals due to their specific properties. One of the most important groups of the clay minerals is the kaolinite's group minerals due to their morphology, availability and range of potential applications. Halloysite and kaolinite are investigated here for their pharmaceutical applications and especially for their potential in cancer treatment. This review study is focusing on the potential applications of the kaolinite's group minerals in cancer diagnosis and monitoring, cancer treatment, the avoidance of metastasis, and the relief of cancer pains. Anticancer drug-loaded formulations based on these minerals show high potential for the treatment of various types of cancer as they have been shown to exhibit high anticancer activity in cancer cell lines and cancer animal models, high biocompatibility, low side effects, and high drug bioavailability.

Using a novel polysaccharide BM2 produced by Bacillus megaterium strain PL8 as an efficient bioflocculant for wastewater treatment.

In this study, the purification and characterization of a novel polysaccharide-based bioflocculant BM2 produced by a bacterium Bacillus megaterium strain PL8 with self-flocculating property were investigated. The results showed that BM2 was an acidic polysaccharide composed of Gal, GalUA, Glc, GlcUA and Man at a molar ratio of 45.1: 33.8:9.3:9.2:2.4, respectively. The molecular weight of BM2 was 4.55 × 106 Da. BM2 had high flocculation efficiencies across a wide pH ranged from 4 to 11 and a wide temperature ranged from 20 to 100 °C towards kaolin clay. BM2 was a cation-independent bioflocculant which could achieve high flocculation activity without the addition of other cations. Adsorption bridging was the main mechanism in the flocculation process of BM2 towards kaolin clay. The BM2 also displayed a high removal efficiency in terms of Congo red (88.14%) and Pb2+ ions (82.64%). These results suggested that BM2 had a great potential as an efficient bioflocculant candidate in wastewater treatment.

The interweaving roles of mineral and microbiome in shaping the antibacterial activity of archaeological medicinal clays.

ETHNOPHARMACOLOGICAL RELEVANCE: Medicinal Earths (MEs), natural aluminosilicate-based substances (largely kaolinite and montmorillonite), have been part of the European pharmacopoeia for well over two millennia; they were used generically as antidotes to 'poison'. AIM OF THE STUDY: To test the antibacterial activity of three Lemnian and three Silesian Earths, medicinal earths in the collection of the Pharmacy Museum of the University of Basel, dating to 16th-18th century and following the methodology outlined in the graphical abstract. To compare them with natural clays of the same composition (reference clays) and synthetic clays (natural clays spiked with elements such as B, Al, Ti and Fe); to assess the parameters which drive antibacterial activity, when present, in each group of samples. MATERIALS AND METHODS: a total of 31 samples are investigated chemically (ICP-MS), mineralogically (both bulk (XRD) and at the nano-sized level (TEM-EDAX)); their organic load (bacterial and fungal) is DNA-sequenced; their bioactivity (MIC60) is tested against Gram-positive, S. aureus and Gram-negative, P. aeruginosa. RESULTS: Reference smectites and kaolinites show no antibacterial activity against the above pathogens. However, the same clays when spiked with B or Al (but not with Ti or Fe) do show antibacterial activity. Of the six MEs, only two are antibacterial against both pathogens. Following DNA sequencing of the bioactive MEs, we show the presence within of a fungal component, Talaromyces sp, a fungus of the family of Trichocomaceae (order Eurotiales), historically associated with Penicillium. Talaromyces is a known producer of the exometabolite bioxanthracene B, and in an earlier publication we have already identified a closely related member of the bioxanthracene group, in association with one of the LE samples examined here. By linking fungus to its exometabolite we suggest that this fungal load may be the key parameter driving antibacterial activity of the MEs. CONCLUSIONS: Antibacterial activity in kaolinite and smectite clays can arise either from spiking natural clays with elements like B and Al, or from an organic (fungal) load found only within some archaeological earths. It cannot be assumed, a priori, that this organic load was acquired randomly and as a result of long-term storage in museum collections. This is because, at least in the case of medicinal Lemnian Earth, there is historical evidence to suggest that the addition of a fungal component may have been deliberate.

Nutrient Reduction of Dairy Manure Through Solid-Liquid Separation with Flocculation and Subsequent Microalgal Treatment.

High concentrations of dairy operations in Southern Idaho have brought up big challenges for proper manure management to alleviate the eutrophication stress. In order to explore more technologies confronting the high nutrient load in dairy manure, a sequential process combining enhanced solid-liquid separation through flocculation-centrifuge and the subsequent microalgal growth in the liquid part was studied in this study. Solid-liquid separation by flocculation-centrifuge process, using a natural flocculant chitosan and a flocculation aid kaolin, was optimized through response surface methodology (RSM) technique using central composite design (CCD) method. Under the optimal flocculation-centrifuge pretreatment, i.e., the maximal total suspended solid (turbidity) removal group, turbidity, COD, TKN, and TP have been removed by 92.7%, 72.6%, 58.7%, and 43.0%, respectively. Applying 2-fold dilution, the supernatant from this treatment was further used for microalgae Chlorella vulgaris cultivation. COD, TKN, and TP were further reduced by 82.2%, 90.1%, and 83.4%, respectively. Turbidity was largely removed from the original dairy manure, providing a relatively clear solution that became suitable for photo-mixotrophic culture of microalgae.

Attachment of cerium oxide nanoparticles of different surface charges to kaolinite: Molecular and atomic mechanisms.

Sustainable applications of nanotechnology in agriculture require insights into the interactions between engineered nanoparticles (ENPs) and clay minerals, a key component in soil that governs the soil properties and functions. This study investigated the charge-dependent interactions of cerium oxide nanoparticles (CeO2NPs) with kaolinite at atomic level with several complementary surface characterization techniques. High resolution transmission electron microscope (HRTEM) and atomic force microscope (AFM) images showed strong attachment of positively charged and neutral CeO2NPs to the surface of kaolinite while the negatively charged CeO2NPs demonstrated low affinity to the surface of kaolinite, indicating strong electrostatic interactions between CeO2NPs and kaolinite surface. Attached CeO2NPs on kaolinite surface displayed charge-dependent aggregation, with neutral CeO2NPs showing the most substantial aggregation on kaolinite surface. The variation in hydrodynamic size and surface charge of kaolinite with the charge on CeO2NPs was observed. The attachment of CeO2NPs also changed the surface charge density distribution on the surface of kaolinite, converting a relatively homogenously charged basal plane into a heterogeneously charged plate. The change on kaolinite surface charge density may markedly affect the interactions of clay minerals with surrounding macro- and micro-nutrients in soil pore water and affect their bioavailability to plants.

Adhesion mediated transport of bacterial pathogens in saturated sands coated by phyllosilicates and Al-oxides.

The current knowledge of bacterial migration is mainly derived from work using bare or Fe-coated quartz sands as porous media. However, mineral coatings on quartz by phyllosilicates and Al-oxides prevail in natural soils, and their effect on bacterial transport remains unknown. Herein, we systematically explored the transport of two bacterial pathogens (Escherichia coli and Staphylococcus aureus) through saturated bare quartz and those coated by kaolinite (KaoQuartz), montmorillonite (MontQuartz) or Al-oxides (AlQuartz) under various solution ionic strength (IS) and pH levels. Elevating IS or decreasing pH discouraged bacterial mobility in all cases, with one exception for the migration of S. aureus through AlQuartz at various IS levels. E. coli showed a higher mobility than S. aureus in all cases. All the three coatings, especially the Al-oxides inhibited bacterial transport through quartz. Overall, the two phyllosilicates-coated sands showed transport behaviors (mobility trends with IS, pH, and cell type) similar to those for the bare quartz which could be explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Nevertheless, for transport within AlQuartz, there were deviations between the observations and the DLVO predictions, probably because of the existence of non-DLVO forces such as hydrophobic and chemical interactions. More importantly, the bacterial retention was found to correlate well with the adhesion regardless of the solution condition and the bacteria and media type, thereby revealing a central role of adhesion in mediating migration through mineral-coated sands. These findings highlight the significance of mineral coating and adhesion in pathogen dissemination in natural soils.

Towards Green Titration: Batchwise Titration with Reusable Solid Sorbed Indicators.

We propose the creation of reusable indicator-sorbed-solids, using anion-exchange resins or kaolin as supports, with the aim to reduce chemical use towards green analytical chemistry. Indicators (phenolphthalein, thymol blue and butterfly pea flower extract as a natural indicator) sorbed on a solid support, were employed in acid-base titration, in both homogenous aqueous and heterogenous aqueous organic phases. Applications of the developed techniques to some real samples, such as vinegar, colored fruit juice and vegetable oil, have been demonstrated.

Gliding arc plasma pre-treatment of kaolin in spatial post-discharge mode for removal of Reactive Red 2 dye from aqueous solution.

This study investigates the ability of spatial post-discharge mode functionalized kaolin to remove textile dye Reactive Red 2 from aqueous solution compared to that of the raw kaolinite. To fulfill the aim, the removal conditions, including plasma exposure time, processed mode (direct and post-discharge), pH of the aqueous dye solution, initial dye concentration and adsorbent dosage, were investigated. The changes that occur on clay surfaces before and after gliding arc plasma treatment were followed by Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen physisorption. The point of zero charge and the changes of the textural properties after gliding arc plasma treatment were also examined. The experimental data were analyzed using pseudo-first-order, pseudo-second-order and empirical Elovich models. The diffusion phenomenon was also studied. The results obtained indicate that spatial post-discharge pre-treatment of kaolin deeply influences the functional groups of some of its minerals as well as the morphology and texture of its particles. Consequently, at room temperature (∼30 °C), the maximum adsorption capacities of natural raw kaolin clay were tripled after treatment with gliding arc plasma in spatial post-discharge mode and were almost doubled after the direct treatment mode.

Uranium (VI) transport in saturated heterogeneous media: Influence of kaolinite and humic acid.

Natural aquifers typically exhibit a variety of structural heterogeneities. However, the effect of mineral colloids and natural organic matter on the transport behavior of uranium (U) in saturated heterogeneous media are not totally understood. In this study, heterogeneous column experiments were conducted, and the constructed columns contained a fast-flow domain (FFD) and a slow-flow domain (SFD). The effect of kaolinite, humic acid (HA), and kaolinite/HA mixture on U(VI) retention and release in saturated heterogeneous media was examined. Media heterogeneity significantly influenced U fate and transport behavior in saturated subsurface environment. The presence of kaolinite, HA, and kaolinite/HA enhanced the mobility of U in heterogeneous media, and the mobility of U was the highest in the presence of kaolinite/HA and the lowest in the presence of kaolinite. In the presence of kaolinite, there was no difference in the amount of U released from the FFD and SFD. However, in the presence of HA and kaolinite/HA, a higher amount of U was released from the FFD. The findings in this study showed that medium structure and mineral colloids, as well as natural organic matter in the aqueous phase had significant effects on U transport and fate in subsurface environment.

Kaolinite in pharmaceutics and biomedicine.

Kaolinite Al2Si2O5(OH)4 is an abundant and inexpensive geomaterial regarded as one of the most common clay minerals in the earth's crust and the most widespread phase among the other kaolin polymorphs (halloysite, dickite and nacrite). Structurally, it is a hydrous aluminum phyllosilicate member belonging to the dioctahedral 1:1 kaolin mineral group. The particle size of the pseudohexagonal kaolinite platelets is normally <2µm (if compared to a human red blood cell of a typical diameter 6.2-8.2µm or to a virus particle of about 50nm diameter). The kaolinite platelets, either stacked together with a common booklet-like shape in a highly ordered structure (well crystallized) or disordered structure (poorly crystallized), consist of layers considered as a strong dipole of hydrophobic siloxane surface dominated by negative charges, and the other hydrophilic aluminol surface carries positive charges. Kaolinite has been used in many pharmaceutical applications as excipient or active ingredient, because it exhibits excellent physical, chemical and surface physicochemical properties. In addition to their classical pharmaceutical uses, kaolinite and its derivatives have been recently considered as a promising material in many biomedical innovation areas such as drug, protein and gene delivery based on the high interaction capacities with organic and biochemical molecules, bioadhesion and cellular uptake. Pharmaceutical kaolin grades are considerably demanded for usage as excipient in formulations of solid and semi-solid dosage forms. The most important functionalities of kaolin used as excipient are reported as diluent, binder, disintegrant, pelletizing and granulating, amorphizing, particle film coating, emulsifying and suspending agent. Because of its uninjured bioactivity, kaolinite has been also used as active agent for treatment of some common diseases. It can be topically administered as hemostatic agent, dermatological protector, anti-inflammatory agent and in pelotherapy, or orally as gastrointestinal protector, and antibacterial, antiviral, detoxification or antidiarrheal agent. With these premises, the future of kaolinite in health-care uses is strongly interesting, especially in the development of pharmaceutical and cosmetic industries. In biomedicinal investigations, it can be considered as a promising natural geomaterial for designing new derivatives that can contribute in the trials of discovering new therapeutic systems and treatment pathways of global challenge diseases such as cancer, viruses, antibiotic resistant bacteria, alzheimer, chronic skeletomuscular and geriatric diseases.

Imaging of Jurassic fossils from the Talbragar Fish Bed using fluorescence, photoluminescence, and elemental and mineralogical mapping.

The Talbragar Fish Bed is one of Australia's most important Jurassic deposits for freshwater fishes, land plants and aquatic and terrestrial insects. The site has yielded many well preserved fossils, which has led to the formal description of numerous new species and higher taxa. The excellent preservation of many fossils has allowed detailed anatomical studies, e.g. of the early teleost fish Cavenderichthys talbragarensis (Woodward, 1895). Here we report on the fluorescent characteristics and mineral composition of a range of Talbragar fossils. Most specimens fluoresce under ultraviolet, blue and green light. Elemental and mineralogical analyses revealed that the Talbragar fossils consist predominantly of quartz (SiO2), a mineral that is likely to account for the observed fluorescence, with trace kaolinite (Al2Si2O5(OH)4) in some of the fish fossils. Rock matrices are predominantly composed of quartz and goethite (FeO(OH)). Closer inspection of a plant leaf (Pentoxylon australicum White, 1981) establishes fluorescence as a useful tool for the visualisation of anatomical details that are difficult to see under normal light conditions.

Effects of ammonium on uranium partitioning and kaolinite mineral dissolution.

Ammonia gas injection is a promising technique for the remediation of uranium within the vadose zone. It can be used to manipulate the pH of a system and cause co-precipitation processes that are expected to remove uranium from the aqueous phase and decrease leaching from the solid phase. The work presented in this paper explores the effects of ammonium and sodium hydroxide on the partitioning of uranium and dissolution of the kaolinite mineral in simplified synthetic groundwaters using equilibrium batch sorption and sequential extraction experiments. It shows that there is a significant increase in uranium removal in systems with divalent cations present in the aqueous phase but not in sodium chloride synthetic groundwaters. Further, the initial conditions of the aqueous phase do not affect the dissolution of kaolinite. However, the type of base treatment does have an effect on mineral dissolution.

[Effect of Zirconium Modified Kaolin-Based Cap on Migration and Transformation of Phosphorus Between Sediment and Overlying Water].

In this study, microcosm incubation experiments were conducted to investigate the effect of zirconium modified kaolin (ZrMK)-based cap on the migration and transformation of phosphorus (P) between sediments collected from a heavily polluted river and overlying waters under anaerobic conditions. The results showed that a large amount of P was released from the sediments into the overlying water column under anaerobic conditions, and the overwhelming majority of P in the overlying water existed in the form of phosphate. The flux of P from the anaerobic sediments was slightly reduced by the kaolin-based cap, while significantly reduced by the ZrMK-based cap. Sequential extraction of P from the kaolin-based cap at the end of incubation experiments suggested that 29% of P adsorbed by kaolin existed as the bicarbonate-dithionite extracted P (BD-P), and 63% of adsorbed P existed as the residual P (Res-P). Sequential extraction of P from the ZrMK-based cap at the end of incubation experiments suggested that 90% of P adsorbed by ZrMK existed as the NaOH extractable P (NaOH-P) and Res-P, which were unlikely to be released under anaerobic conditions. Compared with no capping, sediments capping with ZrMK did not promote BD-P release from the sediments under anaerobic conditions, but promoted the formation of NaOH-P in the sediments. X-ray photoelectron spectroscopy (XPS) and solid state ³¹P nuclear magnetic resonance (NMR) analyses of ZrMK-based caps before and after sediment incubation experiments indicated that the adsorption of P by the ZrMK-based caps followed the ligand exchange and inner-sphere complexing mechanism. Results of this work indicate that ZrMK is a promising active capping material for controlling P release from sediments in heavily polluted rivers.

Study of uranium(VI) and radium(II) sorption at trace level on kaolinite using a multisite ion exchange model.

Uranium and the long-lived decay product radium-226 are abundantly present in mine wastes produced during uranium extraction activities. In the case of release to the surrounding environment, these radionuclides are at trace level compared to groundwater solutes, and the presence, content and properties of clay minerals in the host environment influence the extent of radionuclide sorption and, in turn, migration. Since clays are known to have the distinctive property of retaining ions, the aim of this work was to study the sorption of trace U(VI) and Ra(II) on a common phyllosilicate mineral, kaolinite, in the presence of excess K, a common groundwater cation, in order to obtain a thermodynamic database that describes the ion exchange equilibria occurring at the mineral-solution interface. Following a detailed experimental protocol using chemical and radiochemical analytical techniques, batch experiments over a wide pH range (from 2 to 11) and fixed concentration (ca. 10(-9) M), and additional adsorption isotherms at two different solution pH (6.2 and 10.4) over a concentration range (10(-10) to 10(-4) M) were carried out to measure the distribution coefficient (Kd) of U(VI) and Ra(II) sorption on kaolinite. The experimental sorption data was processed according to a general multisite sorbent/multispecies sorbate ion exchange model, which allowed deducing the charge of adsorbed species and the stoichiometry of the associated adsorption equilibria on kaolinite's surface sites. Aqueous speciation calculations predicted Ra(II) as Ra(2+) over the working pH range, and its adsorption curves and isotherms were explained using three sorption sites. Adsorption of U(VI) occurred on four sorption sites and was governed by its solution speciation, with positively charged hydroxylated (UO2(2+) and UO2(OH)(+)) and silicate (UO2(H3SiO4)(+)) species being adsorbed between pH 2 and 6, whereas its negatively charged forms (UO2(OH)3(-) and UO2(OH)4(2-)) dominated U(VI) sorption at pH > 7. Nonlinear fitting of the experimental data using the ion exchange model provided the associated equilibrium constants as corrected selectivity coefficients.