Effect of FeO on the formation of spinel phases and chromium distribution in the CaO-SiO2-MgO-Al2O3-Cr2O3 system

Synthetic slag samples of the CaO-SiO2-MgO-Al2O3-Cr2O3 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250 degrees C with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.Validerad; 2013; 20130411 (andbra

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented

Crystallization mechanism and properties of a blast furnace slag glass

The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between Tg (742°C) and the DSC crystallization peak (T = 1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt3Fe, detected by EDS and SAD-TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite. © 2000 Published by Elsevier Science B.V. All rights reserved.Vitreous Materials Laboratory Department of Materials Engineering Fed. University of São Carlos, C.P. 676, 13565-905 São Carlos, SPDepartment of Physics IGCE - UNESP, C.P. 178, 13500-970 Rio Claro, SPDepartment of Physics IGCE - UNESP, C.P. 178, 13500-970 Rio Claro, S

Glass sintering with concurrent crystallisation. Part 2. Nonisothermal sintering of jagged polydispersed particles

Relevance, literature review and objectives The preparation of porous and dense glass articles by sintering is a well established practice in both the laboratory and the industry. However, the development of advanced materials such as sintered glass ceramics, solgel derived glasses, amorphous and crystalline thin films and novel metallic alloys, have rekindled the need for a deeper understanding of viscous flow sintering parameters to control spontaneous crystallisation (which hinders sintering) and residual porosity in such materials. (1) A few models and a variety of experiments have been proposed and conducted on viscous flow sintering. The classical models of Frenkel and MackenzieShuttleworth for the isothermal densification of a porous body, composed of monodispersed glass particles or porous compacts having identical pores, successfully describe parts of the sintering process, e.g. Refs 2-5. In Part 1, In some situations however, depending on the relative rates of heating, sintering, and crystallisation, there may be an onset of these phenomena (or even completion) before the designed annealing temperature is reached. This is particularly true in the case of industrial processes in which large pieces and low heating rates are normally used. Thus it is important to understand and control the sintering and crystallisation process along the heating (and cooling) paths. To our knowledge very few attempts have been made to describe nonisothermal sintering kinetics of glass powders. In one of the earliest publications on the subject, Cutler (7) described the initial linear shrinkage (DL/L 0 <15%) of 25×25×4 mm compacts of 15-25 µm diameter soda-lime-silica glass spheres at heating rates of q=0·5-2·9 K/min, up to temperatures varying from 580 to 680°C. Although no corrections were made for particle size distribution and surface crystallisation his experimental data were described by the Frenkel equation. Fortuitously, perhaps, the complications caused by these factors and other experimental errors cancelled out. Nonisothermal sintering is further complicated by concurrent crystallisation as demonstrated by a fe