Refractory sulphidic ore with gold captured in pyrite has motivated researchers to find efficient means to break down pyrite to make gold accessible and, ultimately, improve gold extraction. Thus, the dissolution of pyrite was investigated to understand the mechanism and find the corresponding kinetics in a nitric acid solution. To carry this out, the temperature (25 to 85 °C), nitric acid concentration (1 to 4 M), the particle size of pyrite from 53 to 212 µm, and different stirring speeds were examined to observe their effect on pyrite dissolution. An increase in temperature and nitric acid concentration were influential parameters to obtaining a substantial improvement in pyrite dissolution (95% Fe extraction achieved). The new shrinking core equation (1/3ln (1 − X) + [(1 − X)^−1/3 − 1)]) = kt) fit the measured rates of dissolution well. Thus, the mixed–controlled kinetics model describing the interfacial transfer and diffusion governed the reaction kinetics of pyrite. The activation energies (E_a) were 145.2 kJ/mol at 25–45 °C and 44.3 kJ/mol at higher temperatures (55–85 °C). A semiempirical expression describing the reaction of pyrite dissolution under the conditions studied was proposed: 1/3ln(1 − X) + [(1 − X)^−1/3 − 1)] = 88.3 [HNO₃]^2.6 r₀^−1.3 e^−44280/RT t. The solid residue was analysed using SEM, XRD, and Raman spectrometry, which all identified sulphur formation as the pyrite dissolved. Interestingly, two sulphur species, i.e., S₈ and S₆, formed during the dissolution process, which were detected using XRD Rietveld refinement.

P2-type Na_0.67Mg_0.28Mn_0.72O₂ based cathode materials for sodium-ion batteries were prepared using combustion synthesis. The effect of microwave irradiation and fluorination was investigated with the aim to improve the electrochemical performance. Four samples were considered: samples were prepared by the combustion method (NaMgMnO-a) and then either microwave-irradiated or fluorinated (NaMgMnO-ma and NaMgMnO-af, respectively) or both microwave-irradiated and fluorinated (NaMgMnO-maf). The powder XRD analyses showed that pure single phase P2-type powders were successfully prepared. SEM analyses revealed an impact of microwave irradiation and fluorination on the morphology of the materials, suggesting a change in the electrochemical performance. The galvanostatic charge-discharge studies revealed that both microwave irradiation and fluorination improved the capacity and cycle performance. The electrochemical data (from first discharge capacity to coulombic efficiency, capacity retention, cyclability and impedance) show that microwave- and fluorine-treated samples performed better. The key finding clearly shows the impact of microwave irradiation and fluorination processes in suppressing the P2-O2 phase transformation process and the Mn³⁺-induced Jahn-Teller distortion effect.

Efforts to lower the operating temperature of solid oxide fuel cells include producing electrolytes that are sufficiently conductive and stable below 600 °C. Doped ceria is one such electrolyte being considered. During this study, codoped ceria powders (Ce_0.8Sm_0.2-xM_xO_2-δ, M = Bi³⁺, Zn²⁺ and x = 0, 0.05, 0.1, 0.15, 0.2) were prepared via coprecipitation by the addition of sodium carbonate and annealed at 800 and 1200 °C, respectively. Poor solubility of the codopants in the ceria was observed for samples annealed at 800 °C, resulting in a mixed-phase product including stable phases of the oxides of these codopants. A second-stage partial incorporation of these codopants into the ceria lattice was observed when the annealing temperature was increased to 1200 °C, with both codopants forming cubic-type phases of their respective oxides. Materials were characterized using X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), as well as scanning electron microscopy (SEM) for structural and morphological investigations. The oxide ion conductivity was evaluated using electrochemical impedance spectroscopy between 550 and 750 °C. Fuel cell performance tests of selected samples (annealed at 1200 °C) showed remarkable improvement in peak power densities when the test temperature was increased from 500 to 600 °C (∼720 mW/cm² for Ce_0.8Sm_0.15Bi_0.05O_2-δ and ∼1230 mW/cm² for Ce_0.8Sm_0.15Zn_0.05O_2-δ), indicating possible contribution from the distinct cubic-type oxide phases of the codopants in performance enhancement.