[en] Short communication

[en] Full text: Rare earth permanent magnets are of great importance for cutting-edge technologies, such as: energy generation, electronic information, home appliances, medical treatment, aerospace, among others. The magnets based on Nd-Fe-B stand out, mainly due to their high value of energy product (BH)max, which grants to the miniaturization of technologies in which as higher (BH)max value is, smaller the magnet volume required. In recent years, there has been a growing demand and, consequently, an increase in magnets production and waste generation. One of the challenges in the production of rare earth-based permanent magnets is the recycling of their waste, due to the various challenges inherent to reprocessing techniques. Among all residues, machining sludge residue stands out for being obtained in the mandatory machining step in the production process of sintered magnets based on Nd-Fe-B. The recycling and reuse of machining sludge residues is still a challenge for the magnet industry, due to the lack of knowledge about the characteristics of the residues, such as their structural properties, the level of degradation, which makes it difficult to develop efficient recycling processes. In order to contribute to this research gap, this work aimed to determine the structural characteristics of the machining residue of sintered Nd-Fe-B magnets to enable the evaluation of its use in different recycling technologies. For this purpose, machining sludge residues of sintered Nd-Fe-B magnets and the magnet used for the generation of residues were characterized by Mössbauer spectroscopy, X-ray diffraction and Rietveld refinement method. Mössbauer spectroscopy enabled alpha-iron phases quantification and diffraction patterns contributed to phase quantification analyses, lattice parameters and crystallite size evaluation. By analyzing the Mössbauer spectrum it was possible to determine that the cutting process without the use of a cutting fluid was more aggressive and resulted in higher phase degradation. In another hand, the diffraction patterns analysis showed that the cutting fluid did not affect the parameters of the Nd-Fe-B phase in the machining residue, but it causes a reduction in the crystallite size. (author)

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[en] Zinc hexacyanoferrate (ZnHCF) is a Prussian Blue analog and can be intercalated by both monovalent and divalent ions. ZnHCF/multi-walled carbon nanotube (MWCNT) film could be used as a cathode for zinc ions battery. Carbon nanotubes improved significantly the electrochemical performance of the electrode. It is described the preparation of ZnHCF/MWCNT films by the interfacial method with cyclohexane/water mixture as solvent. The crystal structure, morphology, and microstructure of the as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, Mossbaüer, Raman spectroscopy, and infrared spectroscopy. Results revealed that the MWCNTs extend the electrochemical properties of the ZnHCF and influence the structure and morphology of the hexacyanoferrate particles. If tested as cathode material for zinc ion batteries, the nanocomposite film exhibits a capacity of 25.81 mA h g^-1, which is much higher than those obtained for a ZnHCF single-component film (3.28 mA h g^-1). The physical characteristics and properties that allow good reversibility to a high potential difference, achieved with the ZnHCF/MWCNT film, suggest new developments in the manufacture of translucent, flexible and light energy storage devices, which can be used as a lower-cost, safer and environmentally friendly alternative to the currently existing technologies. (author)

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[en] In this work, iron ore tailing (IOT) was used for the production of two different materials: sodium silicate and geopolymers. Initially, reactions of IOT with NaOH were carried out by hydrothermal reaction in autoclave at 200 °C (1:1.5 and 1:2.5 SiO₂:NaOH molar ratio) and reaction times of 4 and 8 h. X-ray fluorescence by dispersive energy (XRF), X-ray diffraction (XRD), Mössbauer spectroscopy, scanning electron microscopy (SEM-EDS) and titrations showed that IOT:NaOH ratios of 1:2.5 and reaction time 8 h completely dissolved the quartz from the IOT, obtaining a solid fraction consisting mainly of hematite and an aqueous phase of sodium silicate, which showed contents of ca. 23% SiO₂ and 19% Na₂O. This sodium silicate obtained was then combined with IOT (25 and 50 wt.%) to produce geopolimeric material with excellent physicochemical properties, fast curing time and very good compressive strength results, which ranged from 41 to 58 MPa and many potential applications. (author)

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