Editorial for Special Issue “Advances in Flotation of Copper, Lead and Zinc Minerals”

Copper, lead, and zinc metals are fundamental pillars of modern industry, yet their extraction faces increasing hurdles. Froth flotation, the dominant concentration technology, relies on exploiting subtle differences in surface properties. However, the depletion of high-grade ores compels the industry to tackle more complex, lower-grade, and often oxidized or finely disseminated mineral resources. Concurrently, the drive for sustainability necessitates more selective and efficient flotation processes with minimized environmental footprints. This convergence of challenges demands continuous innovation in flotation science and technology specific to copper, lead, and zinc minerals. This Special Issue, “Advances in Flotation of Copper, Lead, and Zinc Minerals,” aims to consolidate recent progress, presenting research that spans from fundamental mechanisms to practical process optimization for these vital non-ferrous metals.

The contributions gathered herein reflect the multifaceted nature of current research in Cu-Pb-Zn flotation. A significant focus remains on the development and mechanistic understanding of novel flotation reagents designed to enhance selectivity in difficult separations. Addressing the classic challenge of separating smithsonite from calcite, Wang et al. [1] demonstrate the efficacy of the chelating agent cupferron, meticulously elucidating its selective adsorption mechanism through comprehensive surface analyses (FTIR, zeta potential, and XPS). The broader potential of chelating agents, not only as collectors but also as activators or depressants in zinc oxide systems, is systematically reviewed by Song et al. [2], offering a valuable guide for future reagent design.

Moving beyond single reagents, the synergistic potential of collector mixtures is explored. Li et al. [3] present an optimized open-circuit strategy for zinc oxide ore beneficiation using a ternary collector system (DDA + NaIX + ADD). Their work underscores how combined collectors can enhance hydrophobicity and improve flotation kinetics compared to single or binary systems, supported by detailed adsorption studies. Similarly, Wang et al. [4], while focusing on the reverse flotation of hematite, investigate the interaction of mixed anionic/cationic collectors (DTAC/Tall oil) on quartz. Understanding such interactions on quartz, a ubiquitous gangue mineral often associated with Cu-Pb-Zn ores, provides transferable insights into managing gangue behavior in base metal flotation circuits.

The selective depression of undesired minerals is equally crucial. Two studies by Zeng et al. [5,6] introduce novel depressants for the selective separation of galena from chalcopyrite. The first employs PMA–EDTC, a functionalized macromolecular depressant, demonstrating its selective chemisorption on galena via its –N–(C=S)–S– group through FTIR, XPS, and DFT studies. The second investigates thioureidoacetic acid (TA), a small-molecule depressant with dual functional groups (C=S, C=O), again using a multi-technique approach including DFT with a COHP analysis to reveal strong, dual-point chemisorption (Pb–S, Pb–O bonds) on galena, establishing a compelling case for molecular orbital engineering in depressant design.

Fundamental parameters governing flotation response are also critically examined. The pervasive influence of pulp chemistry, specifically the role of various metal ions (Cu²⁺, Pb²⁺, Fe²⁺/Fe³⁺, Ca²⁺, Mg²⁺, etc.), is comprehensively reviewed by Wei et al. [7]. They detail the diverse sources of these ions and their complex activation or depression mechanisms on different Cu, Pb, and Zn minerals, highlighting the necessity of considering ionic interactions in process control. Process conditions like pH are universally critical; Wang et al. [8] investigate the specific inhibiting mechanism of high pH on molybdenite flotation, using experimental and DFT methods to differentiate the response of its distinct basal and edge surfaces (MS001 vs. MS100). While focused on molybdenite, the study provides fundamental insights into how pH and consequent surface hydroxylation can differentially affect anisotropic mineral surfaces—a concept relevant to layered or variably terminated base metal sulfides as well.

Furthermore, the physical aspects of flotation hydrodynamics, particularly bubble size, are essential for optimizing particle capture, especially with emerging coarse particle flotation technologies. Gahona et al. [9] characterize bubble size distribution within a HydroFloat^® fluidized-bed cell, comparing tap water and seawater systems with different frothers. Their findings offer valuable data on bubble behavior in this specific equipment under varying water qualities, directly relevant to applying such technologies efficiently in Cu-Pb-Zn circuits, particularly those operating in regions facing water scarcity or processing coarser feeds.

Finally, bridging fundamental understanding with practical application, Yu et al. [10] present a detailed study integrating process mineralogy (XRF, XRD, and EPMA) with flotation optimization for a challenging low-grade oxidized lead–zinc ore from the Lanping mine. This work exemplifies the crucial link between thoroughly characterizing the ore’s specific mineralogical features—composition, liberation, and intergrowths—and developing a tailored, effective flotation flowsheet, ultimately employing mixed depressants and specialized collectors to achieve separation.

In summary, this Special Issue encapsulates key advancements in the flotation of copper, lead, and zinc minerals. The collective works span the molecular design and mechanistic elucidation of novel, selective collectors and depressants; comprehensive reviews of fundamental factors like chelating agents and metal ion chemistry; investigations into process hydrodynamics; and ore-specific treatment strategies guided by process mineralogy. The sophisticated integration of advanced analytical techniques (XPS, FTIR, ToF-SIMS, and EPMA) and computational methods (DFT and MD) is evident throughout, providing deeper insights into complex interfacial phenomena. While significant progress has been demonstrated, the translation to robust industrial practice—considering economic factors, reagent synthesis scalability, environmental profiles, and adaptation to diverse ore types and process waters—remains the critical next step. We trust this collection will serve as a valuable resource and stimulus for continued innovation in the sustainable processing of copper, lead, and zinc resources.