Bentonite clay is used all around the world as an additive in drilling fluids. However, impurities present in this material can compromise the compatibility of the clay-fluid system. The present study aimed to analyze the effects of the purification of bentonite samples from new deposits in the state of Paraíba, Brazil, in order to make them usable in water-based drilling fluids. The samples were first purified by centrifugation, and their characteristics were determined using the following techniques: laser granulometry, X-ray diffraction, chemical analysis, cation exchange capacity, thermogravimetric analysis, and differential thermal analysis. After these determinations, the polycationic clay samples were made sodic through the addition of sodium carbonate (Na2CO3) in the proportion of 125 meq/100 g of dry clay. The rheological and filtration properties (apparent viscosity, plastic viscosity, and filtrate volume) were then tested. The results showed that the purification process was efficient for removing accessory minerals such as quartz, iron, and carbonates. With regard to rheological and filtration properties, the results following centrifugation showed that the material can be suitable for use in water-based drilling fluids.

Currently, the removal of contaminants such as wastewater dye has become an essential task. In view of this, improving the performance of the adsorbents in order to improve the adsorption technique and reduce the total cost of the adsorption process is of great interest to the industrial sector. This study investigated the adsorption process of natural and purified bentonite clay adsorbents, using rhodamine B in an aqueous media. Rhodamine B is very toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment. These clays were used both in the natural form and after purification by centrifuge. All adsorbents were characterized. The kinetics and equilibrium isotherms were studied. In equilibrium, the Freundlich isotherm model was the best fit to the experimental data. In kinetics study, the data were best fit by the pseudo-second order model. The purified clays efficiently removed the rhodamine B.

Controlled-release fertilizers are interesting alternatives to current commercial chemical fertilizers, which present a higher nutrient release rate, and can negatively impact the ecosystem. In this work, two urea controlled-release fertilizer types were manufactured from carnauba wax (CW), commercial granulated urea (U), and natural and sodium bentonite (Bent-R and Bent-Na, respectively). In the first type, the mechanochemical method produced fertilizers in bars, from a mixture containing different proportions of U, Bent-R, and Bent-Na. In the second type, the dip-coating method was used to coat urea bars with coatings containing different proportions of the Bent-R, Bent-Na, and CW. The cumulative urea release was evaluated over the 30-day incubation period, through soil columns tests and UV/visible spectroscopy. Overall, both fertilizers developed in this work presented lower cumulative urea release than standard fertilizers. On the other hand, the new fertilizers produced from the dip-coating method, provided cumulative urea release lower than that obtained by the mechanochemical method. In summary, carnauba wax and bentonite (raw and sodium modified) are promising materials for developing new urea controlled-release fertilizers. Furthermore, both carnauba wax and bentonite are non-toxic, biodegradable, relatively inexpensive, and created from materials that are easily purchased in Brazil, indicating that the new fertilizers developed in this work have the potential to be produced on a large scale.