RESUMO

Nd-Pr-Fe-B sintered magnets are considered important for emerging technologies. They are fundamental to the energy matrix transition, such as electric and hybrid vehicles and wind turbines. The production of these magnets generates tons of residues in the machining process step. Since China dominates the rare-earth (RE) market, leading to supply shortages, processing wastes are a promising alternative for recycling or reusing RE materials. Due to the amount generated and the chemical composition, containing up to 30 wt % of critical rare-earth elements, the studies of RE magnets are expanding in the current circular economy scenario. In this work, Nd-Pr-Fe-B machining wastes from two different machining processes (diamond cutting and grinding) were characterized by X-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometer with first-order-reversal-curves, scanning electron microscopy, X-ray fluorescence, elemental analysis, and X-ray photoelectron spectroscopy. The results showed that the degradation of the phases in both wastes is relatively strong. The phases of the magnets are decomposed into oxides, hydroxides, and hydrated oxides such as Nd(OH)3, ferrihydrite, and metallic iron. In addition, the machining process provokes a change in the iron vicinity of the Nd2Fe14B phase. The presence of impurities and the wide dispersion of particle sizes resulted in low magnetic properties and affected the magnetization behavior of the machining waste. Using different characterization techniques, it was found that the oxides formed during the machining processes are located on the surfaces of the particles, while the center consists of a nondegraded Nd2Fe14B phase. It was also found that the Nd-Pr-Fe-B wastes have similarities, indicating that it is possible to mix wastes from different machining processes before recycling. The complete characterization of the Nd-Pr-Fe-B machining residues indicated that different reuse and recycling strategies can be evaluated to improve the efficiency of reusing these machining wastes as secondary sources.

RESUMO

The identification of sources that produce particulate atmospheric matter (PM) can be of paramount importance for the reduction of air pollution and the development of environmental policies. In order to identify the environmental impact resulting from industrial metallurgical activities in the Metropolitan Region of Vitória, ES, Brazil, it was investigated the contribution to PM that result from industrial activities and from local natural sources. For this purpose, analytical techniques were used to identify the apportionment of sources that contribute to the formation of insoluble settled dust collected at two points near the city of Vitória. Samples of soil, iron ore, limestone, coal, iron ore pellets, sinter, coke, slag, environmental samples of settled dust, and samples representative of the actual flows of materials used in an integrated steel mill were analyzed. Physicochemical characterizations, based on X-ray diffraction and 57Fe Mössbauer spectroscopy of ferruginous compounds found in sources and receptor samples, revealed the presence of highly crystallized hematite and low crystallized hematite. The latter is primarily found in soil samples, while well-crystallized hematite is found in natural samples from iron ores or after thermo-chemical processes applied during the industrial transformation of raw materials, as it happens during the production of pellets. Ferrous crystallographic forms α-FeOOH and Fe5HO8·4H2O, observed in environmental and soil samples, were also found in samples from industrial sources. Source apportionment of carbon based on the IMPROVE_A protocol for thermal/optical carbon analysis showed the participation of the elementary carbon fractions, separating contributions originated from coke and coal sources in the environmental samples. These results allowed a significant reduction of collinearity between source profiles in the application of the chemical mass balance receptor model "EPA-CMB8.2" receptor model. Consequently, it was possible to distinguish sources that process mainly ferrous and carbonaceous materials, identifying the contribution of different sources to the settled dust collected.

Assuntos

RESUMO

Samples of soil, iron ore, and airborne particulate matter (size <10 µm) were analyzed with the main goal of investigating the differentiating physicochemical properties of their ferruginous compounds. These data were used to identify whether the sources of airborne particulate matter in the metropolitan area of Belo Horizonte, Minas Gerais, Brazil, are either from natural origin, as, for instance, re-suspension of particles from soil, or due to anthropogenic activities, meaning that it would be originated from the many iron ore minings surrounding the metropolitan area. Numerical simulations were used to model the atmospheric dispersion of the airborne particulate matter emitted by iron mining located at the Iron Quadrangle geodomain, Minas Gerais. Results from these numerical simulations supported identifying the sites with the highest concentrations of airborne particulate matter in the metropolitan area. Samples of these suspended materials were collected at the selected sites by using high-volume air samplers. The physicochemical features of the solid materials were assessed by X-ray fluorescence, X-ray diffraction, magnetometry, and 57Fe Mössbauer spectroscopy. The soil materials were found to be rich in quartz, aluminum, organic matter, and low contents of iron, mainly as low crystalline iron oxides. The samples of the iron ores, on the other hand, contain high concentration of iron, dominantly as relatively pure and crystalline hematite (α-Fe2O3). The samples of the airborne particulate matter are rich in iron, mainly as hematite, but contained also quartz, aluminum, and calcium. Mössbauer spectroscopy was used to evaluate the hyperfine structure of 57Fe of the hematite both from the iron ore and the soil samples. The structural characteristics of the hematite of these particulate materials were further explored. The direct influence of the iron ore mining on the composition of the airborne particulate matter was clearly evidenced based on the trace ability of hematite to its source of emission. Even the atmospheric air on regions relatively far away from the mining activities is also significantly influenced.

Assuntos