Guixia Fan

Quartz and feldspar are used in a range of industrial applications owing to their distinct physicochemical properties. However, their selective separation remains challenging because of the similar bulk and surface physicochemical properties. Froth flotation has become the principal approach for quartz–feldspar separation, whereas conventional hydrofluoric acid-based processes are increasingly restricted by their toxicity, corrosivity, and environmental impacts. This review critically summarized the development of quartz–feldspar flotation from traditional HF systems to fluoride-free acidic processes and emerging fluoride- and acid-free technologies. Particular attention was given to the flotation behavior and adsorption mechanisms of cationic, anionic, and mixed cationic/anionic collectors under different pH conditions. The roles of surface charge, active sites, electrostatic interactions, hydrogen bonding, chemisorption, and synergistic adsorption in governing flotation selectivity were systematically discussed. Recent advances emphasized reduced reliance on HF and molecular-level regulation of mineral interfaces. However, laboratory selectivity does not by itself establish industrial applicability. This review also evaluated constraints imposed by fine particles, slimes, impurities, dissolved ions, recycled process water, and incomplete liberation, and identifies priorities for pilot- and plant-scale validation of promising fluoride-free and acid-free systems.

The middle trough of spirals serves simultaneously as a buffer zone for variations in hydrodynamic parameters and as a region where mineral particles of different densities are prone to mixing, exerting a profound influence on particle-separation effect. This study employed a multi-fluid volume of fluid (VOF) model incorporating the Bagnold effect to simulate the ilmenite–chlorite slurry flow in a custom-designed Φ400 mm short-travel spiral concentrator with three turns. This study systematically investigated the influence of the transverse inclination angle of the middle trough (ranging from 3.5° to 9.5°) on separation indicators, flow film morphology, secondary circulation characteristics, and particle force dynamics. The results indicate that employing a lower transverse inclination angle is more conducive to improving the technical separation indicators for ilmenite and chlorite. When using enrichment ratio and separation efficiency as criteria, the optimal inclination angles range from 3.5° to 5° and 3.5° to 6.5°, respectively. Meanwhile the separation efficiency and its sensitivity to the middle trough transverse inclination angle vary remarkably with different feeding sizes. Feeding of 112 μm ilmenite and 19 μm chlorite yields the premium separation performance and is minimally affected by the middle trough transverse inclination angle. Conversely, as the ilmenite particle size decreases or the chlorite particle size increases, the separation indicators decline but become significantly regulated by the middle trough transverse inclination angle, exhibiting a desirable angle range of 3.5–6.5°. Hydrodynamic parameter analyses indicate that a moderate flow film depth, continuous secondary circulation morphology and stabilizing inner circulation in the middle trough can be obtained at a middle trough transverse inclination angle scope of 3.5–6.5°. Once the inclination angle exceeds 6.5°, a distinct ridge forms in the flow film of the middle trough, and extensive disruptions occur in the outward circulation, which subsequently impedes the outward transport of low-density particles along with the fluid. At a middle trough transverse inclination angle scope of 3.5–6.5°, the Bagnold force exerted on the ilmenite particles in the middle trough remains low during the initial stage of flow field evolution, which favors their retention in the lower fluid layer to become the concentrate product. Concurrently, the chlorite particles near the inner region experience a higher Bagnold force, which facilitates their suspension into the upper outer circulation, thereby amplifying the kinematic differences between the chlorite and ilmenite particles. This study demonstrates that fluid dynamic parameters and the force characteristics of mineral particles can effectively characterize the separation process of mineral particles in spirals.

As a rare metal element, niobium is widely used in steel, electronics, aerospace and many other fields. Eschynite is one of the most important niobium-bearing minerals in Bayan Obo niobium ores. Investigating the beneficiation process and associated reagents is of great significance for improving niobium resource utilization. In this study, mixed ore with eschynite as the main niobium-bearing mineral was used as the research object. Under the condition that the Nb₂O₅ grade of the feed ore was 0.37%, a niobium concentrate with an Nb₂O₅ grade of 5.250% was obtained through one rougher stage and four cleaner stages, followed by magnetic separation. The content of eschynite in the niobium concentrate increased from 0.76% in the run-of-mine ore to 26.32%, with an enrichment ratio of 34.63 times, and the proportion of eschynite in all niobium-bearing minerals rose from 50.67% to 86.10%. Experimental results show that the combined flotation–magnetic separation process can realize the efficient concentration of niobium minerals dominated by eschynite, providing a technical reference for the subsequent development and utilization of eschynite-type niobium ore resources.

Efficient and selective separation of gallium (Ga(III)) from alkaline industrial waste streams remains a significant challenge due to the coexistence of chemically similar ions such as Al(III) and V(V). In this study, a novel ion-imprinted chitosan-based adsorbent (CS/(H-CGCS)-Ga-IIP) was synthesized via a hybrid cross-linking strategy using glutaraldehyde and siloxane-modified chitosan. The optimized material exhibited a high adsorption capacity of 106.31 mg·g⁻¹ for Ga(III) at pH 9, with fast adsorption kinetics reaching equilibrium within 60 min. Adsorption behavior followed the pseudo-second-order kinetic and Langmuir isotherm models, and thermodynamic analysis indicated a spontaneous and endothermic process. In simulated Bayer mother liquor systems, the material demonstrated outstanding selectivity and a distribution coefficient ratio k_d-Ga/k_d-Al = 146.9, highlighting its strong discrimination ability toward Ga(III). Mechanistic insights from SEM-EDS, FTIR, and XPS analyses revealed that Ga(III) adsorption occurs via electrostatic interaction, ligand coordination, and structural stabilization by the siloxane network. The material maintained good adsorption performance over three regeneration cycles, indicating potential for reuse. These findings suggest that CS/(H-CGCS)-Ga-IIP is a promising candidate for the sustainable recovery of gallium from complex alkaline waste streams such as Bayer process residues.

The structural memory effect is normally considered one of the most important properties of LDHs. However, certain anions can have adverse effects on it. In this study, three types of CLDHs (Mg2Al1-CLDH, Mg2Al0.5Fe0.5-CLDH, Mg2Fe1-CLDH) were obtained and used to observe their regeneration behaviors in the presence of sulfate, silicate, and phosphate, respectively, at initial pH values of 10 and 13. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTG), scanning electron microscope (SEM), and N2 adsorption–desorption isotherm (BET). The results suggested that silicate and phosphate have significant impacts on the regeneration of CLDHs, while sulfate does not. Specifically, phosphate and silicate reacted with MgO to generate magnesium silicate and magnesium phosphate dibasic, which were covered on the surface of particles and hindered the hydroxylation of metal oxides. However, a higher pH can suppress the formation of new substances and promote the regeneration of LDHs. Moreover, the CLDHs with high specific surface area had a stronger anti-interference performance regarding the effects of phosphate and silicate.

This systematic study was conducted on the separation of yttrium (Y) and erbium (Er) from a chloride medium using a mixed extractant system composed of [N1444][P507] and TRPO (trialkylphosphine oxide) in kerosene. This investigation focused on the effects of various extractants, extraction systems, the initial acidity of the aqueous phase, and the phase contact time on the extraction efficiencies of Y and Er. This study showed that using the combination of [N1444][P507] and TRPO notably increased the extraction performance and enhanced the separation factor between Y and Er, outperforming the individual use of P507 or [N1444][P507] under identical conditions. The extraction efficiencies for Y and Er reached 88.4% and 93.3%, respectively, with a separation factor (Er/Y) of 1.84, highlighting the system’s effectiveness in selectively isolating rare earth elements. Optimal stripping conditions were obtained using 0.1 mol/L of HCl, resulting in a successful recovery of 93.1% of Y³⁺ and 78.9% of Er³⁺ from the organic phase. The extraction mechanism involved both ion exchange and ion association. The enthalpy changes (ΔH) associated with the extraction of Y³⁺ (−2.5 kJ·mol⁻¹) and Er³⁺ (4.6 KJ·mol⁻¹) demonstrate that the extraction processes are exothermic, reflecting the thermodynamic differences between the two ions.

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.