Editorial for the Special Issue “Industrial Minerals Flotation—Fundamentals and Applications”

Industrial minerals are generally considered to be nonmetallic mineral resources [1]. Most industrial minerals, including limestone, clays, sand, gravel, diatomite, kaolin, bentonite, silica, barite, talc, and gypsum, are used in the construction industry and/or as additives, such as kaolinite in the production of paper [2,3,4,5,6,7]. The industrial minerals are valued for their physical and chemical properties, which make them useful for many industrial applications. In agriculture, industrial minerals such as potash and phosphate are essential fertilizer ingredients [8]. Bauxite is the primary source of aluminum ore and is also used to make ceramics, cement, and abrasives [9]. In the new energy sector, the industrial minerals also play an important supporting role. Graphite and manganese serve as electrodes in many lithium batteries [10,11]. Spodumene and various types of lithium clays are important sources of lithium for lithium-ion batteries [12]. Rare-earth resources are some of the most critical resources for many industries, including renewable energy and defense industries. As with many metallic mineral resources, concentration processes are needed to purify and enrich industrial minerals before further preparation and utilization. Flotation is a crucial process for the separation and concentration of industrial minerals from ores.

This Special Issue of Minerals, “Industrial Minerals Flotation—Fundamentals and Applications”, presents eight contributions that collectively advance our understanding of flotation chemistry and interfacial phenomena while also highlighting new technological developments and industrial applications.

1. Advances in Fundamental Understanding

Four papers in this collection provide new insights into mineral–reagent interactions, bubble dynamics, and interfacial phenomena which occur during the flotation process.

Zhu et al. (Contribution 1) studied the floatability of spodumene minerals of different colors (pink, white, and purple). The color variations are attributed to the presence of surface polyvalent metal ions, such as Fe³⁺ and Mn²⁺. Flotation experiments revealed distinct differences in the floatability of these colored spodumene samples. The authors further examined the adsorption and activation effects of calcium ions on spodumene of varying colors. Adsorption capacity measurements indicated that Ca²⁺ adsorption was higher on pink spodumene surfaces, which contain fewer polyvalent metal ions. Through experimental characterization and quantum chemical calculations, the study demonstrated how calcium species enhance collector adsorption and flotation performance, with significant implications for lithium resource processing.

Chen, Wang, and Zhang (Contribution 2) investigated the selective inhibition of fluorapatite by sulfuric acid during dolomite flotation. The effects of H₂SO₄ on the wettability and flotation selectivity of apatite and dolomite were evaluated using microflotation experiments and contact angle measurements. Molecular dynamics simulations (MDSs) revealed that H₂SO₄ interacts with Ca sites on both fluorapatite and dolomite surfaces, thereby hindering the interaction of NaOl (sodium oleate collector) with Ca²⁺ sites. However, SO₄²⁻ ions do not prevent oleate adsorption on Mg sites of dolomite surfaces. In this way, H₂SO₄ selectively depresses fluorapatite while allowing dolomite to float.

Gungoren et al. (Contribution 3) examined the synergistic effects of common aqueous ions on flotation performance in Pb–Zn sulfide ores. Using artificial process waters, they studied dynamic surface tension, bubble size distribution, foam stability, and bubble coalescence. The results showed that increasing ionic strength reduced bubble size and narrowed the size distribution, while also improving foam stability. High concentrations of potassium ethyl xanthate (KEX) were effective in reducing surface tension. The study demonstrated that aqueous ions significantly influence bubble properties and flotation efficiency, emphasizing the importance of water chemistry in flotation practice.

Complementing these studies, Liu et al. (Contribution 4) provided a comprehensive review on the interfacial regulation of apatite flotation. They discussed the surface characteristics of apatite and its main gangue minerals, emphasizing the challenges posed by fine-grained ores. The review summarized advances in collector and depressant design, their mechanisms of action, and the regulation of wettability at the mineral–water interface. It also covered particle–particle interactions and particle–bubble attachment phenomena. The authors concluded by outlining prospects for future research, including the development of innovative reagents and improved interfacial control strategies for phosphate beneficiation.

Together, these works advance the molecular- to process-scale understanding of flotation, offering a strong basis for designing more selective and efficient reagent systems.

2. Innovative Techniques and Applications

The remaining four contributions emphasize technological innovation and applied solutions.

Wang et al. (Contribution 5) explored the recovery of xenotime and florencite from silicate minerals using a combination of magnetic separation and flotation. Initial magnetic separation enriched the rare earth minerals, raising the concentrate grade to 14.29% with 94.48% recovery. Subsequent flotation further improved the concentrate grade to 51.26% at a recovery of 90.47%. This combined approach achieved high efficiency in separating xenotime and florencite from quartz and illite gangue, demonstrating strong potential for industrial applications in rare earth processing.

Valderrama et al. (Contribution 6) investigated copper recovery from smelting slags at the Hernán Videla Lira Smelter in Chile. Laboratory flotation tests optimized grinding, pH, reagent schemes, and flotation times, producing concentrates with copper grades up to 24.4% and recoveries above 70%. Industrial-scale trials demonstrated even higher separation efficiency, with rougher–cleaner circuits yielding copper grades of 27.9% and recoveries of 87.5% while processing 1344 tons per day. This study highlights the feasibility of flotation for slag treatment, offering both environmental benefits and contributions to the circular economy.

Zhang et al. (Contribution 7) reviewed recent advances in ultrasonic-assisted flotation. They analyzed the effects of ultrasound on slurry properties, flotation processes, and device development, as well as results from pilot-scale testing. Ultrasonic pretreatment was shown to improve concentrate recovery by around 10%. The review summarized four key aspects: optimization of ultrasonic parameters, synergistic effects with reagents, effects on different particle size fractions, and applications to new mineral systems. The authors also discussed future prospects, including integration of ultrasonic flotation with magnetic fields, big data, sensors, and automated process control technologies.

Finally, Wang, Cheng, and Ding (Contribution 8) reviewed recent advances in emulsion flotation for difficult-to-float coals. These coals, characterized by high hydrophilicity and fine particle size, present significant challenges for conventional collectors. Emulsions, with strong interfacial regulation properties, have emerged as effective collectors, improving charge regulation, hydrophobicity, and interfacial tension. The review summarized the influence of emulsion type and preparation method on flotation efficiency, while also outlining future directions such as precise control of emulsion structure, development of low-cost and eco-friendly reagents, and improved storage and transportation methods.

These studies underscore how flotation continues to adapt to new challenges, from processing low-grade resources to recovering value from waste and advancing cleaner energy technologies.

3. Future Directions

The contributions in this Special Issue highlight two complementary trends in industrial mineral flotation research: (1) fundamental investigations that deepen mechanistic understanding, and (2) innovative engineering approaches that translate this knowledge into industrial practice. Together, they demonstrate that flotation remains a dynamic field, essential not only for traditional ores but also for industrial minerals, critical minerals, waste reprocessing, and extended use of coal resources.

Looking forward, the integration of computational modeling, novel reagent chemistry, high efficiency separation devices, and advanced process technologies with sustainable and digitalized mineral processing will be central to further progress. The convergence of flotation science with modeling, big data analytics, and green chemistry also represents an important direction for future progress.

We thank all the authors for their valuable contributions, the reviewers for their thoughtful evaluations, and the editorial team of Minerals for their support. We anticipate that these contributions will serve as a valuable reference for researchers and practitioners, while also inspiring new directions in the science and engineering of flotation.