Alkaline sulfur-containing lixiviants, including thiosulfate, polysulfides, and alkaline sulfide solutions, stand out as a promising class of alternatives to cyanide because of their low toxicity, high efficiency, and strong adaptability. In this paper, we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents. After a brief introduction to the preparation method, the transformation process of various sulfur-containing species in alkaline solutions was discussed. Thereafter, some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects, including thermodynamics analysis, electrochemical dissolution, and leaching kinetics. Moreover, recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well. Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems. Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction, particularly for refractory gold ores containing copper and carbonaceous matter.

We investigated whether the vertical roller mill can be efficiently used in the beneficiation of low-grade magnesite and whether it can improve upon the separation indices achieved by the ball mill. We conducted experiments involving the reverse flotation and positive flotation of low-grade magnesite to determine the optimum process parameters, and then performed closed-circuit beneficiation experiments using the vertical roller mill and ball mill. The results show that the optimum process parameters for the vertical roller mill are as follows: a grinding fineness of 81.6wt% of particles less than 0.074 mm, a dodecyl amine (DDA) dosage in magnesite reverse flotation of 100 g·t⁻¹, and dosages of Na₂CO₃, (NaPO₃)₆, and NaOL in the positive flotation section of 1000, 100, and 1000 g·t⁻¹, respectively. Compared with the ball mill, the use of the vertical roller mill in the beneficiation of low-grade magnesite resulted in a 1.28% increase in the concentrate grade of MgO and a 5.88% increase in the recovery of MgO. The results of our causation mechanism analysis show that a higher specific surface area and greater surface roughness are the main reasons for the better flotation performance of particles ground by the vertical roller mill in the beneficiation of low-grade magnesite.

A new process for preparing high-purity iron (HPI) was proposed, and it was investigated by laboratory experiments and pilot tests. The results show that under conditions of a reduced temperature of 1075°C, reduced time of 5 h, and CaO content of 2.5wt%, a DRI with a metallization rate of 96.5% was obtained through coal-based direct reduction of ultra-high-grade iron concentrate. Then, an HPI with a Fe purity of 99.95% and C, Si, Mn, and P contents as low as 0.0008wt%, 0.0006wt%, 0.0014wt%, and 0.0015wt%, respectively, was prepared by smelting separation of the DRI using a smelting temperature of 1625°C, smelting time of 45 min, and CaO content of 9.3wt%. The product of the pilot test with a scale of 0.01 Mt/a had a lower impurity content than the Chinese industry standard. An HPI with a Fe purity of 99.98wt% can be produced through the direct reduction‒smelting separation of ultra-high-grade iron concentrate at relatively low cost. The proposed process shows a promising prospect for application in the future.

Carbonated decomposition of hydrogarnet is one of the vital reactions of the calcification–carbonation method, which is designed to dispose of low-grade bauxite and Bayer red mud and is a novel eco-friendly method. In this study, the effect of the silica saturation coefficient (x) on the carbonation of hydrogarnet was investigated from the kinetic perspective. The results indicated that the carbonation of hydrogarnets with different x values (x = 0.27, 0.36, 0.70, and 0.73) underwent two stages with significantly different rates, and the kinetic mechanisms of the two stages can be described by the kinetic functions R3 and D3. The apparent activation energies at Stages 1 and 2 were 41.96–81.64 and 14.80–34.84 kJ/mol, respectively. Moreover, the corresponding limiting steps of the two stages were interfacial chemical reaction and diffusion.

The mechanical properties and wear resistance of the ultrafine bainitic steel austempered at various temperatures were investigated. Scanning electron microscopy (SEM) and X-ray diffraction were used to analyze the microstructure. The worn surfaces were observed via laser scanning confocal microscopy and SEM. Results indicated that, under low austempering temperatures, the mechanical properties differed, and the wear resistance remained basically unchanged. The tensile strength of the samples was above 1800 MPa, but only one sample austempered at 230°C had an elongation of more than 10%. The weight loss of samples was approximately linear with the cycles of wear and nonlinear with the loads. The samples showed little difference in wear resistance at different isothermal temperatures, whereas the thickness of their deformed layers varied greatly. The results are related to the initial hardness of the sample and the stability of the retained austenite. Meanwhile, the experimental results showed that the effect of austempering temperature on the wear resistance of ultrafine bainitic steel can be neglected under low applied loads and low austempering temperature.

The effect of carbonation on the chloride resistance of low-carbon steel and two Cr-bearing alloy steels in simulated concrete pore solutions was investigated. The chloride threshold values of steels were determined on the basis of corrosion potential (E_corr) and polarization resistance (R_p). Moreover, the chloride-induced corrosion behavior of steels was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry, cathodic potentiodynamic polarization, and scanning electron microscopy/energy dispersive X-ray spectroscopy measurements. Alloy steels have higher chloride resistance than low-carbon steel in carbonated and non-carbonated concrete pore solutions. The chloride resistance of alloy steels improves with increasing Cr content. In addition, the chloride resistance of all steels is negatively affected by the carbonation of concrete pore solution, especially for alloy steel with high Cr content in the presence of high chloride content.

The effect of graphene oxide (GO) and reduced graphene oxide (RGO) nanosheets on the microstructure and mechanical properties of welded joints of mild steel was evaluated by flux-cored arc welding. GO was synthesized by the Hummer’s method and was reduced under hydrothermal conditions at a pressure of 1.1 MPa at 180°C for 12 h. 1, 3, and 10 mg/mL paste fillers were used in GO and RGO, and applied to the weld notch. The results clearly showed that by increasing the concentration of RGO up to 10 mg/mL, the tensile strength and hardness of the weld metal were improved by approximately 20.5% and 38.4%, respectively, because the coarse grains were changed into fine domains. The domain of the nanosheets cluster was 19.85 × 10⁻⁹ m. Specifically, the RGO nanosheets contributed to modifying the mechanical properties of the welded steel, likely due to dislocation pinning.

Li-ion batteries (LIBs) have demonstrated great promise in electric vehicles and hybrid electric vehicles. However, commercial graphite materials, the current predominant anodes in LIBs, have a low theoretical capacity of only 372 mAh·g⁻¹, which cannot meet the ever-increasing demand of LIBs for high energy density. Nanoscale Si is considered an ideal form of Si for the fabrication of LIB anodes as Si–C composites. Synthesis of nanoscale Si in a facile, cost-effective way, however, still poses a great challenge. In this work, nanoscale Si was prepared by a controlled magnesiothermic reaction using diatomite as the Si source. It was found that the nanoscale Si prepared under optimized conditions (800°C, 10 h) can deliver a high initial specific capacity (3053 mAh·g⁻¹ on discharge, 2519 mAh·g⁻¹ on charge) with a high first coulombic efficiency (82.5%). When using sand-milled diatomite as a precursor, the obtained nanoscale Si exhibited a well-dispersed morphology and had a higher first coulombic efficiency (85.6%). The Si–C (Si : graphite = 1:7 in weight) composite using Si from the sand-milled diatomite demonstrated a high specific capacity (over 700 mAh·g⁻¹ at 100 mA·g⁻¹), good rate capability (587 mAh·g⁻¹ at 500 mA·g⁻¹), and a long cycle life (480 mAh·g⁻¹ after 200 cycles at 500 mA·g⁻¹). This work gives a facile method to synthesize nanoscale Si with both high capacity and high first coulombic efficiency.

Ni–48.5at%Ti thin films were irradiated in the austenite phase by different energy-level protons at a dose rate of 1.85 × 10¹² p/(cm²·s), and the total dose was 2.0 × 10¹⁶ p/cm². The microstructures of the thin films before and after irradiation were evaluated by transmission electron microscopy (TEM) and grazing-incidence X-ray diffraction (GIXRD), which showed that the volume fraction of Ti₃Ni₄ phase elevated with proton energy level. The influence of proton irradiation on the transformation behavior of the TiNi thin films was investigated by differential scanning calorimetry (DSC). Compared with the unirradiation film, the reverse transformation start temperatures (A_s) decreased by about 3°C after 120 keV proton-irradiation. The proton irradiation also had a significant effect on the mechanical properties of the TiNi thin films. After 120 keV energy proton-irradiation, the fracture strength increased by 8.44%, and the critical stress increased by 21.1%. In addition, the nanoindenter measurement image showed that the hardness of the thin films increased with the increase of proton-irradiation energy. This may be due to the defects caused by irradiation, which strengthen the matrix.

The aim of this study is to evaluate the effect of various molar ratios of glycine to chromium salt (Gly : Cr) and different current densities on the corrosion and wear behaviors of Cr(III) electroplated coatings. The morphology and thickness of the coatings were investigated by scanning electron microscopy. The wear properties of the coatings were studied using pin on disk and hardness tests, while corrosion behavior of the coatings was identified using linear polarization, small amplitude cyclic voltammetry, and electrochemical impedance spectroscopy methods. By increasing the glycine concentration, a structure with low crack density was obtained. In all molar ratios, maximum thickness and current efficiency was observed at a current density of 150 mA·cm⁻². All the electrochemical methods had a consistent result, and maximum corrosion resistance of approximately 16000 Ω·cm² was obtained in the case of Gly : Cr = 3:1 and current density of 200 mA·cm⁻².

The present study aimed to investigate the durability and microstructure evolution of road base materials (RBM) prepared from red mud and flue gas desulfurization fly ash. The durability testing showed that the strength of RBM with the blast furnace slag addition of 1wt%, 3wt% and 5wt% reached 3.81, 4.87, and 5.84 MPa after 5 freezing–thawing (F–T) cycles and reached 5.21, 5.75, and 6.98 MPa after 20 weting–drying (W–D) cycles, respectively. The results also indicated that hydration products were continuously formed even during W–D and F–T exposures, resulting in an increase of the strength and durability of RBM. The observed increase of macropores (>1 μm) after F–T and W–D exposures suggested that the mechanism of RBM deterioration is pore enlargement due to cracks that develop inside their matrix. Moreover, the F–T exposure showed a greater negative effect on the durability of RBM compared to the W–D exposure. The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement, which indicates that these wastes are suitable for use as a natural material replacement in road base construction.