Abstract In the last decades, clays have been used in sectors such as health and cosmetics. This requires products that are increasingly pure and present homogeneous properties, hardly found in natural clays. The use of synthetic clays can be a solution. For this, it is necessary to explore techniques for their production. The main focus of this study was to synthesize a smectite clay in a simple, fast and economic way at low temperature and pressure, called static and dynamic methods. To regulate the pH of the reaction and bring it closer to the ideal synthesis conditions, two different acids were used: nitric acid (the most widely used in the literature) and hydrochloric acid (more accessible and cheaper). The results showed characteristics of uniform crystalline material with a porous structure similar to that of the smectite group. Small particle sizes of approximately 100 nm were observed by scanning electron microscopy. Stevensite clay was obtained by both synthesis methods using two different acids; the static method with hydrochloric acid stood out. The greater practicality in its development provides a more viable option for large-scale industrial production.

Abstract Atrazine’s adsorptive capabilities make the use of clays practical and effective. Three types of organophilic clays modified by cationic surfactants with the ability of one of these clays to adsorb atrazine in an aqueous medium are discussed in this work. The modification in clays was done with the surfactants cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and dodecyltrimethylammonium chloride. The X-ray diffraction data indicated different lamellar expansions for the three organophilic clays obtained when compared to in natura clay, proving the presence of quaternary ammonium salts in the interlamellar space. There was also a decrease in the specific surface area showing less accessibility to the lamellar spaces due to the presence of surfactants. The thermogravimetric analysis showed a negative variation profile in all the clays. The adsorption test showed a better capacity for atrazine adsorption in the organophilic clay of 64% when compared with 36% of in natura clay, and it followed the Freundlich isotherm model.

Argila do grupo das esmectitas foi obtida com êxito em baixa temperatura de processamento por via hidrotérmica utilizando como precursores metassilicato de sódio, nitrato de zinco e uréia. Durante a etapa de síntese a composição molar da mistura reacional e a temperatura permaneceram constantes, variando-se o tempo de reação. As amostras sintetizadas foram caracterizadas por difração de raios X, microscopia eletrônica de varredura, espectroscopia de refletância difusa no infravermelho com transformada de Fourier, análise térmica diferencial e gravimétrica, análise de adsorção gasosa de nitrogênio pelo método BET e capacidade de troca de cátions. Os resultados evidenciam que com a metodologia empregada obtêm-se Zn-estevensita apresentando uma área superficial total na faixa de 171,6 a 203,4 m²/g e boa cristalinidade; sendo esta a única fase presente no produto sintetizado após reação estática a 90 ºC por um período de 44 a 138 h, indicando ser o aumento no tempo de síntese um parâmetro importante para o processo de cristalização da argila.

Clay of the smectite group was successfully obtained at a low temperature hydrothermal processing using sodium metasilicate, zinc nitrate and urea as precursor materials. During the synthesis step, the molar composition of the mixture and the temperature remained constant varying the reaction time. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance Fourier Transform infrared spectroscopy, differential thermal analysis and thermogravimetry, cation exchange capacity (CEC) and BET surface area measurements. The results show that in the methodology utilized is obtained Zn-stevensite with specific surface area of 171.6-203.4 m²/g and good crystallinity as present single phase in the reaction product after static synthesis at 90 ºC for 44 to 138 h, indicating that, the increased synthesis time is an important parameter for crystallization process of the clay.

Materiais zeolíticos foram sintetizados utilizando como fonte principal de silício e alumínio um rejeito industrial gerado durante o beneficiamento do caulim para cobertura de papel; o material de partida e as fases formadas como produtos de reação foram caracterizados por difração de raios X, microscopia eletrônica de varredura e espectroscopia de refletância difusa no infravermelho com transformada de Fourier. O processo de síntese ocorreu em condições hidrotermais através de autoclavagem estática e os efeitos tempo-temperatura, assim como também as relações Si/Al e Na/Al foram considerados. Os resultados mostram que na metodologia desenvolvida com o rejeito de caulim, inicialmente calcinado a 700 ºC por 2 h, submetido em seguida à reação em meio alcalino a 90 ºC por 48 h na presença de uma fonte adicional de sílica foi obtida zeólita do tipo faujasita com boa cristalinidade como fase predominante no produto de síntese.

Zeolitic materials were synthesized using as main source of silicon and aluminum an industrial waste generated during the processing of kaolin for paper coating, the starting material and formed phases as reaction products were characterized by XRD, SEM and DRIFT. The synthesis process occurred in hydrothermal conditions and the effects, time-temperature, as well as the relations Si/Al and Na/Al were considered. The results show that in the methodology developed from kaolin waste, initially calcined at 700 ºC for 2 h, subjected then reaction in alkaline medium at 90 ºC for 48 h in presence of additional silica was obtained faujasite-type zeolite with good crystallinity as phase predominant in the synthesis product.

Estudou-se a preparação de argilas organofílicas com o sal cloreto hexadeciltrimetilamônio (HDTMA-Cl) a diferentes concentrações. As amostras sem e com tratamento com o sal HDTMA-Cl foram caracterizadas por difração de raios X, análise térmica diferencial, análise termogravimétrica, microscopia eletrônica de varredura e espectroscopia de raios X por energia dispersiva. Ensaios de difração de raios X mostraram que a distância basal da argila " Chocolate" antes da modificação era 14,8 e após tratamento com o sal HDTMA-Cl (0,8 meq/g) é 19,1 e com o sal HDTMA-Cl (1,0 meq/g) 17,8 . O processo de intercalação não causou modificações substanciais na morfologia das partículas da argila " Chocolate" .

The preparation of organophilic clays using the salt hexadecyltrimethyl ammonium chloride (HDTMA-Cl) at different concentrations was studied. The samples before and after treatment with HDTMA-Cl salt were characterized by X-ray diffraction, differential thermal analysis, thermogravimetric analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy. X-ray diffraction analysis show that the basal spacing of the clay " Chocolate" before the modification was 14.8 and after treatment with the HDTMA-Cl salt (0,8 meq/g) 19.1 and with HDTMA-CL (1,0 meq/g) 17.8 . The intercalation process did not cause substantial modifications in the morphology of particles of the " Chocolate" clay.

O principal objetivo deste trabalho é caracterizar argilas esmectíticas "Chocolate" de Boa-Vista, PB, tanto na sua forma natural quanto tratada quimicamente, visando sua aplicação em catálise. As argilas foram caracterizadas por fluorescência de raios X, difração de raios X e espectrofotometria de absorção óptica na região do infravermelho. Os resultados mostraram que o tratamento ácido alterou a estrutura da montmorilonita. A reação de isomerização do meta-xileno, para o material ativado, mostrou que a argila ácida foi mais ativa que a natural.

The main objective of this paper is to characterize the chocolate smectite clays of Boa-Vista, PB, Brazil, in their natural form, and after chemical treatment, for their application in catalysis. The experimental methods were: X-ray fluorescence, X-ray diffraction and infrared spectroscopy. The results show that the acid treatment altered the montimorillonite structure. The obtained reaction (isomerization of m-xylene) for the treated material showed that treated clays were more active than the natural ones.