Direct determination of the NaF/AlF3 molar ratio by Raman spectroscopy in NaF-AlF3-CaF2 melts at 1000 °C.
For the last 40 years, Raman spectroscopy has been very useful in investigating the structure of corrosive molten salts, such as the cryolite-based melts widely used as electrolyte in the Hall-Heroult process. Even if this process remains the most economically efficient for metallic aluminum electro-production, it suffers from a high energy loss, which is dependent on the melt composition. Therefore, controlling the chemical composition of the electrolyte is essential. The present paper proposes to apply Raman spectroscopy for the direct determination of the NaF-AlF3 molar ratio in NaF-AlF3-CaF2-based melts. Despite the experimental difficulties, a calibration curve based on equilibria taking place in the melt has been developed and the procedure has been successfully compared to industrial samples of known compositions. The possible exportation of the laboratory scale procedure to an industrial environment application for the control of the Hall-Heroult process is finally discussed.
Concentration Mechanisms of Rare Earth Element-Nb-Zr-Be Mineralization in the Baerzhe Deposit, Northeast China: Insights from Textural and Chemical Features of Amphibole and Rare Metal Minerals

 The Early Cretaceous Baerzhe deposit in Inner Mongolia, Northeast China, hosts a world-class resource of rare earth elements (REEs), niobium, zirconium, and beryllium. In contrast to previous interpretations of the deposit as a multiphase, miaskitic alkaline granite, our observations of the relationships of various rock phases, the textural features and chemical evolution of amphibole, and the distribution of primary and secondary mineral assemblages suggest that the igneous phases evolved from a hypersolvus porphyritic granite, through a variably altered transsolvus granite, both of which are miaskitic, to a strongly altered, agpaitic, transsolvus granite that contained primary elpidite. All of these phases share a common igneous lineage. The Baerzhe deposit is characterized by five stages of rare metal mineralization, starting with the magmatic crystallization of elpidite (stage I). Elpidite was subsequently hydrothermally replaced by zircon and quartz to form pseudomorphs in stage II. Stage II is also characterized by Na metasomatism (albite and aegirine alteration of alkali feldspar and amphibole, respectively) and by snowball quartz that contains inclusions of albite, aegirine, and zircon. Sodium metasomatism, Zr mineralization, and snowball quartz are restricted to the agpaitic rocks. REEs, Nb, and Be occur as a variety of minerals that are disseminated through all the altered rocks and were precipitated in three sequential stages (stages III-V), with the formation of heavy REE-dominant phases generally preceding light REE-dominant phases. Moderate to pervasive hematization, which altered much of the transsolvus miaskitic granite and all the agpaitic granite, initiated late in stage II and accompanied most of the REE-Nb-Be mineralization in stage III. The stage-III mineralization, represented by hingganite-(Y), hingganite-(Ce), aeschynite-(Y), and columbite-(Fe), developed in two substages, with hingganite-(Y) preceding hingganite-(Ce); these REE-Nb-Be minerals are mainly contained in quartz-rich pseudomorphs (REE-Nb-Be–rich pseudomorphs) but also occur as partial replacement of earlier minerals. Stages IV and V represent a transition from F-absent assemblages that are characterized by euxenite-group minerals and monazite-(Ce) in stage IV-A, to light REE and F-rich minerals: bastnäsite-(Ce) in stage IV-B and fluocerite-(Ce) and synchysite-(Ce) in stage V. The low REE, Nb, and Be concentrations in amphibole and the fact that REE-Nb-Be assemblages never contain zircon as a constituent preclude leaching of preexisting amphibole or zirconosilicates as significant sources of REEs, Nb, or Be. Rather, these elements may have inherently been present in magmatic-hydrothermal fluids or have been leached from crystallized fluoride melts.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.