The effect of heat treatment on the adsorptive capacity of a Brazilian palygorskite to remove the dyes crystal violet (CV) and congo red (CR) was investigated. The natural palygorskite was calcined at different temperatures (300, 500 and 700 °C) for 4 h. Changes in the palygorskite structure were evaluated using X-ray diffraction, X-ray fluorescence, thermogravimetric and differential thermal analysis, N₂ adsorption/desorption and Fourier transform infrared spectroscopy. The adsorption efficiency of CV and CR was investigated through the effect of initial concentration, contact time, temperature, pH and dosage of adsorbent. The calcination increased the adsorption capacity of palygorskite, and the greatest adsorption capacity of CV and CR dyes occurred in the sample calcined at 700 °C (Pal-700T). The natural and calcined samples at 300 and 500 °C followed the Freundlich isothermal model, while the Pal-700T followed the Langmuir isothermal model. Adsorption kinetics results were well described by the Elovich model. Pal-700T showed better adsorption performance at basic pH, with removal greater than 98%, for both dyes. Pal-700T proved to be a great candidate for removing cationic and anionic dyes present in water.

The effect of acid treatment on the adsorptive capacity of a Brazilian palygorskite to remove the crystal violet (CV) and congo red (CR) dyes was investigated. The raw palygorskite was acid-treated by different HCl solutions (2, 4, and 6 mol/L). The modifications on the palygorskite structure were investigated using X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, N₂ adsorption/desorption, and thermogravimetric and differential thermal analysis. The efficiency of CV and CR adsorption was investigated, and the effect of the initial concentration, contact time, pH, and adsorbent amount was analyzed. The results revealed that CV adsorption in the acid-treated palygorskite was higher than that of the raw material. A Langmuir isotherm model was observed for the adsorption behavior of CV, while a Freundlich isotherm model was verified for the CR adsorption. A pseudo-second-order model was observed for the adsorption kinetics of both dyes. The higher CV adsorption capacity was observed at basic pH, higher than 97%, and the higher CR removal was observed at acidic pH, higher than 50%. The adsorption parameters of enthalpy (ΔH), entropy (ΔS), and Gibbs energy (ΔG) were evaluated. The adsorption process of the CV and CR dyes on the raw and acid-treated Brazilian palygorskite was predominantly endothermic and occurred spontaneously. The studied raw palygorskite has a mild-adsorption capacity to remove anionic dyes, while acid-treated samples effectively remove cationic dyes.

This work presents the successful production of highly porous 3D nanofibrous hybrid scaffolds of polylactic acid (PLA)/polyethylene glycol (PEG) blends with the incorporation of calcium phosphate (CaP) bioceramics by a facile two-step process using the solution blow spinning (SBS) technique. CaP nanofibers were obtained at two calcium/phosphorus (Ca/P) ratios, 1.67 and 1.1, by SBS and calcination at 1000 °C. They were incorporated in PLA/PEG blends by SBS at 10 and 20 wt% to form 3D hybrid cotton-wool-like scaffolds. Morphological analysis showed that the fibrous scaffolds obtained had a randomly interconnected and highly porous structure. Also, the mean fiber diameter ranged from 408 ± 141 nm to 893 ± 496 nm. Apatite deposited considerably within 14 days in a simulated body fluid (SBF) test for hybrid scaffolds containing a mix of hydroxyapatite (HAp) and tri-calcium phosphate-β (β-TCP) phases. The scaffolds with 20 wt% CaP and a Ca/P ration of 1.1 showed better in vitro bioactivity to induce calcium mineralization for bone regeneration. Cellular tests evidenced that the developed scaffolds can support the osteogenic differentiation and proliferation of pre-osteoblastic MC3T3-E1 cells into mature osteoblasts. The results showed that the developed 3D scaffolds have potential applications for bone tissue engineering.

Perlite waste materials with different particle sizes were evaluated as potential candidates for removing the malachite green (MG) and Congo red (CR) dyes from contaminated water. Two types of waste, referred to as coarse (CP) and fine (FP), with particle sizes of 0.075 mm, 0.045 mm, and 0.037 mm, were used. The samples were characterized using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, and N₂ adsorption/desorption. The adsorption efficiency of MG and CR was investigated by varying the parameters of pH, contact time, and initial concentration. The reduction in particle size significantly influenced the removal of the CR dye, leading to an increase in the adsorption rate of 23.9% and 45.5% for CP and FP, respectively. Conversely, the adsorption of the MG dye on the residues was not affected by different particle sizes. CP and FP exhibited a removal rate exceeding 70% for both dyes. The adsorption of MG and CR on the wastes was well-described by the Sips isotherm model. The results of adsorption kinetics were best fit by the Elovich model. Perlite waste materials have demonstrated significant potential for the adsorptive remove of cationic and anionic dyes from aqueous solutions.

In this work, kaolin processing waste (KW) and columbite–tantalite waste (CTW) from mining activities were used to manufacture sustainable self-supporting ceramic membranes using the freeze-casting technique. The wastes were characterized, and formulations using only wastes were developed. Gelatin was used in the freeze-casting as a processing aid to avoid dendritic or lamellar pores. The membranes were sintered at different temperatures (1100 °C, 1200 °C and 1300 °C) and analyzed by X-ray diffraction, scanning electron microscopy, flexural strength measurement, and mercury porosimetry. The flux through the membranes was measured using a gravity-driven dead-end filtration system. The membranes containing 80% KW and 20% CTW sintered at 1200 °C showed high porosity (59%), a water permeate flux of 126.5 L/hm², and a mechanical strength of 1.5 MPa. Filtration tests demonstrated effective turbidity removal (>99%) for synthetic water consisting of tap water and bentonite, reaching 0.1 NTU. The use of mining waste has shown considerable promise for the development of sustainable and affordable membranes for water treatment applications.