The evaluation of the thermodynamic properties and the phase diagrams for the binary BaO-SiO₂ and SrO-SiO₂ systems is carried out using a structural model for silicate melts and glasses. This thermodynamic model is based on the assumption that an addition of metal oxides to silica results in the depolymerization of the silicon-oxygen network, with a characteristic free energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for the above binary systems have been analysed and represented with a small number of parameters. The resulting equations represent the thermodynamic and phase diagram data for the alkaline-earth oxide-silica systems within error limits for most of the experimental data. In particular, the measured limiting liquidus slope, at X _{SiO 2} = 1, is well reproduced.

Japan's largest platform for academic e-journals: J-STAGE is a full text database for reviewed academic papers published by Japanese societies

Two hydrothermal techniques under microwave irradiation were used to synthesize γ-MnO₂ from 90°C to 150°C in 10−30 min. The first technique is based on reducing KMnO₄ with MnSO₄, and the second one involves liquid-phase oxidation between MnSO₄ and (NH₄)₂S₂O₈. The structures and morphologies of the samples were analyzed using X-ray diffraction, scanning electron microscopy, and N₂ physisorption measurements. The electrochemical properties were evaluated through cyclic voltammetry and electrochemical impedance spectroscopy. The γ-MnO₂ materials obtained by the first technique mainly exhibited nanorods with diameters of 40–60 nm, and the samples obtained by the second technique showed flower-like microspheres with diameters of 1−2 µm; each flower was composed of nanosheets with a thickness of 10−20 nm. The processing time directly depends on the size of the nanorods. The sample synthesized by the first technique at 150°C and 10 min has the highest specific surface area of up to 59.08 m² g⁻¹ and mean pore diameter of 34.11 nm. Furthermore, this sample exhibits a near-rectangular cyclic voltammetry curves and high specific capacitance of 331.3 F g⁻¹ in 0.1 M Na₂SO₄ solution at 5 mV s⁻¹ scan rate. Graphic abstract

This work focuses on the recovery of lead and silver from jarosite waste by a three-stage process: drying, roasting and reduction at 100 °C, 700 °C and 1400 °C, respectively. A flux mixture with 48 mass% CaO and 52% SiO₂ was used for the reduction stage. A gas consisting of 70 vol% CO and 30 vol% CO₂ was used as a reducing agent. To select the temperatures and the amount of flux and reducing agent, a characterization of the jarosite waste was carried out using thermogravimetry and high-temperature X-ray diffraction, as well as a thermodynamic study of the effects of the process parameters. The lead-rich metallic and slag phases were characterized by chemical analysis, SEM-EDS and XRD. In addition, the jarosite residue and the final slag were leached with an aqueous acetic acid solution to estimate their chemical stability. The results show a recovery of over 95% of the lead and silver and the formation of an environmentally friendly residual slag.