Halloysite is a 1:1 dioctahedral clay mineral that has been studied widely for applications in nanotechnology and as a mineral exploration guide for recognizing regolith-hosted heavy rare earth element (HREE) deposits. In Brazil, pegmatites from the state of Rio de Janeiro have been catalogued, but their potential to host halloysite deposits has never been studied. After a mineral exploration programme, one pegmatite with considerable halloysite contents and economic potential was discovered. This study reports the mineralogical and chemical characterization of the halloysite of this pegmatite and evaluates the possibility of clay-adsorbed HREE deposits, like that in the Zudong (China) regolith-hosted HREE deposit. Seven samples were collected in horizontal channels. Bulk samples and clay fractions (<2 μm) were analysed by quantitative mineral analysis (X-ray diffraction/Rietveld method), chemical analysis (major elements by X-ray fluorescence and Y, U, Th and rare earth elements by inductively coupled plasma mass spectrometry), scanning electron microscopy, Fourier-transform infrared spectroscopy, particle-size analysis, nitrogen physisorption and cation-exchange capacity. Mixed polygonal/cylindrical halloysite-7Å in concentrations between 6.3 and 35.4 wt.% in bulk samples and between 58.0 and 89.8 wt.% in the clay fractions were identified in the pegmatite. The clay fractions presented an average chemical composition of 45.46 wt.% SiO2, 36.10 wt.% Al2O3, 14.62 wt.% loss on ignition and 1.04 wt.% Fe2O3, as well as technological properties close to those observed in world-class halloysite deposits such as Dragon Mine (USA) and Matauri Bay (New Zealand). The clay minerals did not present significant HREE contents.

Two novel adsorbents – montmorillonite (Mnt)-hyamine and Mnt-hyamine-sodium dodecyl sulfate (SDS) – were synthesized using Mnt nanoparticles. The modified Mnt and Mnt nanoparticles were used for the removal of crystal violet from water, and they were characterized using various techniques. The effects of pH, time, temperature, adsorbent dosage and initial dye concentration on the dye-removal efficiency were investigated using response surface methodology. The optimum conditions for maximum dye removal were obtained. The optimum conditions for crystal violet adsorption on Mnt-hyamine, Mnt-hyamine-SDS and Mnt nanoparticles are temperatures 25.00°C, 29.97°C and 27.28°C; pH values 9.00, 10.41 and 9.40; adsorbent dosages 1.00, 1.15 and 1.06 g L–1; and initial dye concentrations 30.00, 98.74 and 99.44 mg L–1, respectively. The adsorbent dosage is the most critical variable for dye removal. Temkin and Langmuir are the best isotherms for studying adsorption equilibria. In the kinetic study, the fractal-like integrated kinetic Langmuir model was the most appropriate model, and the thermodynamic parameters were also determined. The synthesized adsorbents could be easily separated from solution. The Mnt-hyamine-SDS adsorbent has a high adsorption capacity (690.69 mg g–1) for the removal of crystal violet.

NaY zeolite was synthesized from kaolin/dimethyl sulfoxide (DMSO) intercalation composites using an in situ crystallization technique. The effects of the intercalation ratios and the amounts of the kaolin/DMSO intercalation composite on the synthesis of an NaY zeolite molecular sieve were studied. The samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, differential thermal analysis, N2 adsorption–desorption and scanning electron microscopy. In the in situ synthesis system, when the kaolin/DMSO intercalation composite was added, pure NaY zeolite was formed. By increasing the amount of kaolin/DMSO intercalation composite added, the crystallinity of the samples increased, and after reaching the maximum amount of kaolin/DMSO intercalation composite added, the crystallinity decreased with further increases of the amount of kaolin/DMSO intercalation composite added. To higher intercalation ratio, the crystallinity can be greatly improved at the lower addition content. At an intercalation ratio of 84%, the added amount of kaolin/DMSO intercalation composite was 2.5% and the crystallinity of the NaY zeolite molecular sieve reached a maximum value of 45%. At intercalation ratios of 55% and 22%, the amount of kaolin/DMSO intercalation composite added was 15% and the crystallinities of the NaY zeolite molecular sieves were 44% and 47%, respectively. The NaY zeolite has good thermal stability and a particle diameter of ~0.5 μm. The Brunauer–Emmett–Teller (BET) specific surface area and pore volume of the sample were 519 m2 g–1 and 0.355 cm3 g–1, respectively.

A hybrid fluorescent pigment composed of fluorescent yellow X-10GFF (FY-10G) and palygorskite (PLG) was prepared by semi-dry grinding. The effects of the physically adsorbed water content and grinding time on the environmental stability of FY-10G/PLG hybrid fluorescent pigments in terms of acid, ethanol and ultraviolet irradiation are discussed in detail. The incorporated FY-10 G molecules are mainly trapped on the external surface and the groove of PLG. Due to the host–guest interaction between PAL and FY-10G, the emission spectrum of the FY-10G/PLG hybrids shifts to a greater wavelength compared with that of FY-10G, but the physically adsorbed water content and grinding time have no effect on the position of the emission spectrum except for its intensity. A larger, physically adsorbed water content and appropriate grinding time may effectively prevent the aggregation and breakage of the bundles of PLG and facilitate FY-10 G molecules to enter into the groove of PAL. This increases the environmental stability of the as-prepared hybrid pigments.

Microcapsules are successfully used in various applications such as self-healing, drug delivery and military camouflage. The shells of the microcapsules based on the traditional surfactant-stabilized emulsion template method are often single organic materials. The surfactants generally have insufficient stability against demulsification during preparation of the microcapsules. In the present study, kaolinite was used as an emulsifier for stabilizing Pickering emulsions and subsequently as an enhancer for forming microcapsules. Kaolinite-armoured polyurea microcapsules were fabricated based on the interfacial polymerization of isophorone diisocyanate at the oil–water interfaces of kaolinite-stabilized Pickering emulsions. The prepared microcapsules with core–shell structure were spherical and exhibited good dispersibility in anhydrous ethanol. The shell thickness (~0.5–1.0 μm) and diameter (~20.0–160.0 μm) of kaolinite-armoured polyurea microcapsules may be tailored by varying the dosages of isophorone diisocyanate and kaolinite and the emulsifying speed of the high-shear homogenizer. Hence, the encapsulation and release performance of microcapsules may be controlled. The kaolinite particles were embedded and armoured in a polyurea matrix. The formed kaolinite-embedded and -armoured polyurea structures might prolong the release of the encapsulated lipophilic Sudan Red (III) from 20 to 45 h. The microcapsules have controllable encapsulation and release characteristics for lipophilic compounds and are cost effective, making them suitable pesticides.

This work presents the results of the physical characterization of palygorskite and its adsorptive behaviour for three solvatochromic dyes (Nile blue chloride (NBC), methylene blue (MTB) and dithizone (DTZ)). Adsorption isotherms were used to determine the maximum adsorption of the solvatochromic dyes on the palygorskite. The characterization of palygorskite was carried out via mineralogical and chemical analysis with X-ray diffraction, X-ray fluorescence, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy, surface-charge measurement (ζ-potential), thermogravimetric analysis, textural analysis and cation-exchange capacity analysis. The material consists of palygorskite and quartz and its chemistry is dominated by SiO2, MgO and Fe2O3. The specific surface area and cation-exchange capacity of the palygorskite are 142 m2 g–1 and 41 cmol(+) kg–1, respectively. The SEM and TEM analyses showed a fibrous structure with fibres 20–100 nm long. The thermogravimetric analysis showed three endothermic events at 57.3°C, 171.8°C and 439.6°C. The adsorption capacities of the palygorskite for NBC (basic pH), MTB (basic pH) and DTZ (neutral pH) were 0.082, 0.013 and 0.102 g g–1, respectively. The adsorptions of NBC and MTB were fitted with the Langmuir isotherm model and the adsorption of DTZ was fitted with the Sips model.

Nitrate contamination of surface waters and groundwater is one of the main problems associated with agricultural activities worldwide, and there is an urgent need to develop effective materials and processes to remove efficiently excess nitrate from aquatic environments. Bittern is a seawater resource that contains large amounts of Mg2+ and Ca2+, and its utilization has received much recent attention. In this study, an Fe-type layered double hydroxide (Fe-LDH) product was prepared from bittern with the addition of an inexpensive agent (FeCl3) for nitrate removal. The greatest nitrate removal was obtained for synthesis conditions of pH 8.5–9.5 at 50°C for 0.5 h. The equilibrium adsorption capacity of the product for nitrate was measured and fitted with the Langmuir and Freundlich isotherm models. The experimental data better fit the Langmuir model than the Freundlich model. The calculated maximum adsorption capacity for nitrate was 0.40 mmol g–1, which was greater than those of other reported nitrate adsorbents. The product removed nitrate ions from a highly saline solution. The order of interference of anion species for nitrate removal was CO32– > SO42– > Br– > NO2– > Cl– > F–. The pH of the solution and removal of nitrate increased with increasing solution temperature because of ion exchange between the Cl– in Fe-LDH and the NO3– in the solution. Nitrate ions were repeatedly adsorbed and desorbed. The prepared Fe-LDH is expected to be a new inorganic anion exchanger for the removal and recovery of nitrate ions from aquatic environments.

Steam jet milling was applied for the first time to ultra-fine grind the filter cake (moisture content 23.80%) produced by a kaolin concentrator. The material was dehydrated and dried simultaneously during grinding, and the final ground sample met the moisture content requirement for powder products of <2%. The particle size of the ground kaolin samples decreased and the particle-size distribution was more concentrated, indicating that the steam jet milling was more effective for kaolin processing than the conventional dry grinding process. In addition, steam jet milling can improve the whiteness and decrease the crystal order of the samples, thus improving the kaolin properties in follow-up applications.