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Rare-earth separations enhanced by magnetic field
No full textThe separation of rare earth (RE) elements is a challenge from their discovery to the present day, due to the chemical and physical similarities as a group. The intrinsic properties of REs are basic for separation mechanisms. Due to the large difference in magnetic moment, a new method of selected crystallization enhanced by magnetic field was developed to separate REs efficiently, at room temperature and pressure without complex equipment. An experimental proof of concept is provided for the binary systems RE2(SO4)3-Lu2(SO4)3 (RE = Gd, Nd, Tb, Dy or Ho). This magnetic separation process increases the separation factors of Gd(III)/Lu(III) from their mixture by 39% in kinetics, but similar in or near thermodynamic equilibrium without magnetic field. The beta RE/Lu (RE = Gd, Nd, Tb, Dy or Ho) were promoted by 17%-47% with permanent magnet, increasing with raising of the applied magnetic field strength. A process based on magnetic moment difference is a potential alternative method for rare-earth separations, with low energy consumption and high efficiency in the presence of an external magnetic field
An innovation technology for recovering silver and valuable metals from hazardous zinc leaching residue through direct reduction
No full textZinc leaching residue (ZLR) is a hazardous solid waste with complex phase composition, comprising high content of valuable metals, and sulfur. The extraction of silver is the key to harmless utilization of ZLR. In this paper, a short-flowsheet comprehensive recycling valuable metals method by direct reduction was proposed. During reduction, lead and zinc compounds were reduced to metallic state, which were volatilized and recovered in gas phase. Moreover, metallic iron in reduction product was recovered by magnetic separation. Silver was enriched in FeS phase, and it was beneficiated by flotation with hydrophobic FeS as carrier. Under the optimized conditions, silver concentrate with silver content and recovery of 601.43 g/t and 83.41 %, respectively; iron powder with iron content of 96.39 %; and lead and zinc volatilization rate of 78.65 % and 97.64 %, respectively, were obtained. Toxicity characteristic leaching procedure (TCLP) results indicated that tailings were harmless. The mechanisms were subsequently investigated by combining thermodynamics analyses and systematic characterizations. Especially, a one-step containing two-stage capture silver mechanism was ascertained in reduction with sulfur: formation of silver-lead alloys, and encapsulation of silver-lead alloys by FeS phase to decrease symbiotic relationship between valuable metals and slag. This entire recycling process can provide ideas for harmless recovering precious metals from hazardous waste
A novel method to synthesize pure-phase Si2N2O powders in a fluidized bed reactor
No full textSi2N2O ceramic, an emerging functional and structural material, has a wide range of applications. However, the preparation of pure-phase Si2N2O powder remains challenging due to the mass transfer resistance and unde-sirable side reactions in the conventional methods. Herein, a novel molecular approach combined with the decomposition process has been developed to synthesize pure-phase Si2N2O powders. The hydrated Si(NH)2 precursors were synthesized through the chemical vapor deposition (CVD) of SiCl4, NH3, and humidified N2 in a fluidized bed reactor (FBR) in two steps. Then, the hydrated Si(NH)2 precursors were decomposed into amor-phous and subsequently transformed into crystalline powders under different temperatures and time. It was found that the molar ratio of N/O of the hydrolyzed Si(NH)2 can be controlled by N2 ventilation time and played an important role in synthesizing high pure Si2N2O powder. When it varied from 2.5:1 to 2:1, pure-phase Si2N2O powder was obtained after heat treatment at 1300-1500 degrees C, which features a big tolerance for N/O ratios. This newly developed method offered a chance for the preparation of high-quality Si2N2O powder with high efficiency and low cost
Abundant Oxygen Vacancies Induced by the Mechanochemical Process Boost the Low-Temperature Catalytic Performance of MnO2 in NH3-SCR
No full textManganese oxides (MnOx) have attracted particular attention in the selective catalytic reduction of NOx with NH3 (NH3-SCR) because of their excellent low-temperature activity. Herein, we prepared a highly efficient MnO2 (MnO2-M) catalyst through a facile ball milling-assisted redox strategy. MnO2-M shows a 90% NOx conversion in a wide operating temperature window of 75-200 degrees C under a gas hourly space velocity of 40,000 h(-1), which is much more active than the MnO2 catalyst prepared by the redox method without the ball-milling process. Moreover, MnO2-M exhibits better H2O and SO2 resistance. The enhanced catalytic properties of MnO2-M originated from the high surface area, abundant oxygen vacancies, more acid sites, and higher Mn4+ content induced by the ball-milling process. In situ DRIFTS studies probed the reaction intermediates, and the SCR reaction was deduced to proceed via the typical Eley-Rideal mechanism. This work provides a facile method to enhance the catalytic performance of Mn-based catalysts for low-temperature denitrification and deep insights into the NH3-SCR reaction process
Ionic liquids enhance the electrocatalysis of lignin model compounds towards generating valuable aromatic molecules
No full textThe valuable exploitation of lignin depends mainly on the conversion strategy of lignin, of which the conversion of lignin into valuable aromatic molecules is a critical approach. In this study, three lignin model compounds, veratrylglycerol-b-guaiacyl ether (VG), 4-phenoxyphenol (PP), 4-ethoxyphenol (EP), are comparatively degraded by electrochemical oxidation in an aprotic ionic liquid (IL), [Bmim][OTf], and two protic ILs, [PrSO3Hmim][OTf] and [BSO3Hmim][HSO4]. The protic ILs are more favorable for the degradation of lignin-derived substrates compared to aprotic ILs. Oxygen reduction reaction (ORR) in the O2 atmosphere generates reactive oxygen species (ROSs) that play an indirect oxidation effect on substrates, which is stronger for the protic ILs. In addition, the different types of ILs allow modulating the distribution of degradation products. Combined with the identification of products and CV curves, the microscopic mechanisms of the degradation process for lignin model compounds are further elucidated. (c) 2022 Published by Elsevier B.V