Froth flotation has been widely used in upgrading iron ores. Iron ore flotation can be performed in two technical routes: direct flotation of iron oxides and reverse flotation of gangue minerals with depression of iron oxides. Nowadays, reverse flotation is the most commonly used route in iron ore flotation. This review is focused on the reverse flotation of iron ores, consisting of reverse cationic flotation and reverse anionic flotation. It covers different types of collecting agents used in reverse iron ore flotation, the surface characteristics of minerals commonly present in iron ores (e.g., iron oxides, quartz, alumina-bearing minerals, phosphorus-bearing minerals, iron-bearing carbonates, and iron-bearing silicates), and the adsorption mechanisms of the collecting agents at the mineral surface. The implications of collecting agent–mineral interactions for improving iron ore flotation are discussed.

Nanobubbles (NBs) have been extensively utilized in mineral flotation, acting as secondary collectors to improve flotation efficiency. However, the fundamental interaction mechanisms between NBs and flotation collector remain unclear. In this study, NBs generated through hydrodynamic cavitation were introduced into the flotation of microfine ilmenite. With octyl hydroxamic acid (OHA) as the flotation collector, the effects of NBs on the flotation of microfine ilmenite were systematically investigated using a series of techniques. The results show that NBs not only improve the flotation recovery and flotation rate of microfine ilmenite, but also significantly lower OHA consumption while maintaining comparable recovery to the flotation without NBs. The measurements of the apparent size of ilmenite particles, contact angle, and the three-phase contact line between carrier bubbles and ilmenite surface indicate that NBs enhance the interaction between carrier bubbles and ilmenite particles during the flotation process. Furthermore, atomic force microscope imaging in different solutions confirms the adsorption of OHA-loaded NBs on the ilmenite surface. Most importantly, quartz crystal microbalance with dissipation monitoring results reveal that the presence of NBs leads to a reduction in OHA adsorption mass but an increase in adsorption rate at the ilmenite interface.

This study presents an innovative approach to utilize coal gasification coarse slag (CGCS) for efficient and low-cost gallium extraction. Using a one-step acid leaching process, mesoporous silica with a surface area of 258 m²/g and a pore volume of 0.15 cm³/g was synthesized. The properties of CGCS before and after acid leaching were characterized through SEM, FTIR, XRD, and BET analyses, with optimal conditions identified for maximizing specific surface area and generating saturated silanol groups. The prepared mesoporous silica demonstrated a 99% Ga(III) adsorption efficiency. Adsorption conditions were optimized, and adsorption kinetics, isotherms, and competitive adsorption behaviors were evaluated. Competitive adsorption with vanadium suggests potential application in Ga(III) extraction from vanadium-rich waste solutions. Furthermore, the recyclability of both the acid and adsorbent was explored, with the adsorbent maintaining over 85% adsorption efficiency after five cycles. The adsorption mechanism was further elucidated through SEM-EDS, XPS, and FTIR analyses. This work not only advances resource recovery from industrial waste but also offers a sustainable method for gallium extraction with industrial applications.

Shenmu-Fugu coal liquefaction residue (SFCLR) was ultrasonically extracted with methanol, ethanol, and isopropanol, respectively. Abundant of condensed arenes (CAs) were identified in the extracts using gas chromatography/mass spectrometer (GC/MS) by quantitative analysis, besides some alkanes and heteroatom-containing compounds. The most dominant CAs is benzo[ghi]perylene with its yield of 71.77 mg/g in isopropanol extract based on GC/MS analysis. Series of alkanoates were identified in the extracts from SFCLR with high yields. Interestingly, methyl alkanoates were identified in each of the three extracts, while ethyl and isopropyl alkanoates were only identified in the ethanol and isopropanol extracts, respectively. Accordingly, we presume that transesterification of methyl alkanoates with ethanol or isopropanol occurs during the ultrasonication-assisted solvent extraction.