Portland cement production is among the most energy-intensive industrial processes worldwide and is responsible for approximately 7%–8% of global anthropogenic CO₂ emissions (Zhang et al., 2021; Khalil and AbouZeid, 2025; Zong et al., 2025). This substantial environmental burden is primarily associated with the high temperatures required for clinker formation (Abdul et al., 2025), typically in the range of 1450 °C–1500 °C, to ensure sufficient development of tricalcium silicate (C₃S, alite) (Ouzia and Scrivener, 2019), the principal phase governing early-age strength of cement (Martin et al., 2024). In response to increasing regulatory pressure and global decarbonization targets, reducing the clinkering temperature has emerged as a key strategy for lowering thermal energy demand, fuel consumption, and process-related CO₂ emissions in the cement industry (Han et al., 2026; Zapata and Bosch, 2009; Hafiz et al., 2020; Qian et al., 2016; Li et al., 2022; Wang et al., 2024; Igami et al., 2025). Within this framework, the use of mineralizers has attracted significant attention as an effective and industrially feasible approach to enhance clinker burnability (Song et al., 2026). Mineralizers facilitate clinker formation by increasing raw-meal reactivity, promoting early liquid-phase formation, and accelerating phase transformations under reduced thermal input (Lin et al., 2025; Amare et al., 2025). Among the various mineralizing agents investigated, calcium fluoride (CaF₂) has been widely reported as an effective mineralizer for lowering clinkering temperature while maintaining or improving clinker quality (Dahhou et al., 2021) It should be noted that reported reductions in clinkering temperature are highly system-dependent and vary with raw-meal composition, co-dopants, and the criteria used to define clinker formation. In this context, previous studies have shown that CaF₂-containing systems can exhibit apparent temperature reductions on the order of ∼100 °C in ordinary Portland cement and up to ∼100 °C–300 °C in belite-rich compositions, reflecting combined compositional and process-related effects rather than the isolated action of CaF₂ alone.

The pronounced mineralizing effect of CaF₂ arises from several interconnected mechanisms operating at both lattice and melt scales. At the lattice level, fluoride ions (F⁻) substitute for non-bridging oxygen sites within the C₃S crystal structure, leading to the formation of calcium vacancies and an increased concentration of lattice defects (Da et al., 2022a). These defects enhance ionic mobility and lower the activation energy for cation diffusion, thereby facilitating the solid-state transformation of dicalcium silicate (C₂S) into C₃S at reduced temperatures (Guan et al., 2025; Yang et al., 2024; Li et al., 2024). At the melt level, CaF₂ lowers the liquidus temperature and reduces melt viscosity, enabling earlier formation of a fluid phase that enhances mass transport and accelerates the incorporation of CaO into silicate phases (Tao et al., 2025; Hu et al., 2025; Guo et al., 2025). In addition, CaF₂ promotes the formation and stabilization of high-symmetry alite polymorphs, such as monoclinic and rhombohedral C₃S, which preferentially crystallize under lower thermal conditions and exhibit superior burnability compared to low-symmetry counterparts.

In recent years, the relevance of CaF₂ mineralization has been further strengthened by advances in waste valorization. Industrial sludges generated from semiconductor processing, photovoltaic manufacturing, and metal pickling frequently contain high proportions of CaF₂, typically ranging from 40 to 60 wt% (Banshchikov et al., 2023; Wu et al., 2024; Zhang et al., 2025; Thakur et al., 2026; Shtan’ko et al., 2020). Experimental and industrial studies have demonstrated that waste-derived CaF₂ retains mineralizing performance comparable to that of natural fluorite, while simultaneously enabling the immobilization of fluorine and heavy metals within clinker mineral phases.

This dual functionality supports circular-economy strategies by reducing reliance on virgin raw materials and providing a safe pathway for the co-processing of fluoride-bearing industrial wastes. Despite these advantages, the application of CaF₂ requires careful optimization. Excessive fluorine content may result in the formation of insoluble CaF₂-rich surface layers on clinker minerals, potentially inhibiting early hydration. Most studies report an optimal CaF₂ dosage in the range of 1–3 wt%, depending on raw-meal composition and coexisting oxides (Wang et al., 2021; Kulikov et al., 2024). Moreover, the presence of metal oxides such as TiO₂, ZnO, and CuO can either enhance or suppress the mineralizing effect of CaF₂ through synergistic or competitive interactions, underscoring the need for a mechanistic understanding of multi-component systems.

Accordingly, this mini review critically synthesizes recent advances in understanding the role of CaF₂ in reducing the clinkering temperature of Portland cement. Special attention is given to distinguishing between kinetic accessibility and thermodynamic considerations in reported CaF₂-assisted mineralization mechanisms. Emphasis is placed on lattice-level defect chemistry, melt-phase behavior, alite polymorph stabilization, and synergistic effects arising from co-doping with metal oxides and waste-derived additives. The objective is to provide both a mechanistic framework and practical insights to support the industrial implementation of CaF₂-based mineralization strategies for low-temperature, energy-efficient, and low-carbon cement production.

Beyond its individual mineralizing effect, CaF₂ exhibits pronounced synergistic behavior when combined with selected metal oxides, resulting in further reductions in clinkering temperature and enhanced clinker reactivity. These co-doping systems operate through complementary mechanisms, in which CaF₂ primarily modifies lattice defect chemistry and melt-phase properties, while metal oxides influence cation mobility, intermediate phase formation, and polymorph stability. The synergistic effect of CaF₂ and TiO₂ has been widely reported in both laboratory and industrial clinker systems. Da et al. (2021a) demonstrated that TiO₂ promotes early formation of reactive aluminate and silicate intermediates and accelerates CaCO₃ decomposition, thereby lowering the overall sintering temperature. When combined with CaF₂, these effects are significantly intensified due to the simultaneous reduction in melt viscosity and enhancement of lattice-level diffusion. The dual action of TiO₂-induced lattice distortion and CaF₂-driven melt formation widens the effective formation window of alite, enabling clinker formation at temperatures below 1300 °C.

Copper oxide also exhibits strong synergy with CaF₂. Laonamsai et al. (2025) reported that CuO enhances CaO mobility and promotes the early formation of intermediate phases, while CaF₂ facilitates melt formation and stabilizes alite at reduced temperatures. X-ray photoelectron spectroscopy analysis revealed that fluorine predominantly substitutes for oxygen in silicate lattices, whereas Cu²⁺ preferentially substitutes for Fe³⁺ in ferrite phases. This coupled anion cation substitution induces simultaneous lattice distortion in both silicate and interstitial phases, markedly accelerating alite nucleation. As a result, substantial C₃S formation was achieved at temperatures as low as 1250 °C, which are insufficient for meaningful alite development in conventional systems.

Zinc oxide represents another effective co-dopant in CaF₂-based mineralization strategies. Da et al. (2025) demonstrated that ZnO and CaF₂ co-doping generates dual lattice defects through the concurrent substitution of Zn²⁺ into silicate phases and F⁻ into oxygen sites. This defect coupling significantly enhances phase transformation kinetics and promotes stabilization of the rhombohedral C₃S polymorph, as confirmed by characteristic X-ray diffraction peak shifts. In addition to improved burnability, ZnO–CaF₂ systems exhibit exceptionally low free-lime contents and efficient incorporation of zinc into clinker minerals, offering advantages for both clinker quality and heavy-metal immobilization.

Synergistic mineralization effects are particularly prominent in waste-derived CaF₂ systems, which inherently contain multiple co-dopants. Xu et al. (2025) reported that fluorite tailings containing CaF₂, iron oxides, and clay minerals produced strong multi-component mineralization effects, resulting in enhanced early- and long-term strength development despite compositional variability. Similarly, Da et al. (2022b) observed that fluorine-containing industrial sludges rich in CaF₂, MgF₂, and metal oxides generated cooperative lattice melt effects. Microstructural analysis revealed preferential fluorine enrichment at silicate grain boundaries, while Zn, Cu, and Ni were distributed across both silicate and interstitial phases, supporting a multi-scale synergy mechanism.

Collectively, these findings demonstrate that CaF₂-based co-doping systems operate through coordinated lattice-level, melt-phase, and polymorph-stabilization mechanisms. The presence of complementary metal oxides amplifies the mineralizing efficiency of CaF₂, enabling reliable low-temperature clinker formation across a wide range of raw-meal compositions. Such synergistic behavior is particularly advantageous for industrial applications involving waste-derived mineralizers, where compositional variability necessitates robust and adaptable mineralization strategies.

The practical significance of CaF₂-based mineralization extends well beyond laboratory-scale studies and demonstrates strong potential for industrial implementation. Reducing the clinkering temperature through CaF₂ addition offers multiple operational advantages for cement manufacturing. Holban et al. (2015) reported that a reduction of 100 °C in kiln temperature can decrease thermal energy consumption by approximately 7%–12%, resulting in lower fuel costs and extended service life of refractory linings. Owing to its ability to promote early liquid-phase formation, CaF₂ also enables a reduction in residence time within the sintering zone without compromising clinker phase development, as demonstrated by Da et al. (2021b). This characteristic makes CaF₂-compatible mineralization strategies suitable for both wet and dry kiln technologies currently employed in commercial cement plants. Waste-derived mineralizers are of particular interest from a circular-economy perspective. Mend et al. (2025) demonstrated that fluorine-containing industrial sludge rich in CaF₂ and MgF₂ retains mineralizing performance comparable to that of natural fluorite and can partially replace virgin mineral resources. Similarly, Zhao et al. (2025) reported that low-temperature calcination of fluorine-rich sludge produces reactive fluoride phases that improve melt fluidity and facilitate the immobilization of hazardous elements during clinker formation. The ability of CaF₂ to incorporate heavy metals into silicate and aluminate clinker phases provides a significant environmental advantage, particularly for the co-processing of wastes containing fluorine, zinc, and copper.

Xu et al. (2025) showed that fluorite tailings containing CaF₂, iron oxides, and clay minerals, when used as co-dopants in high-silica clinker systems, enhance mechanical strength while ensuring stable incorporation of fluorine into clinker phases. These findings suggest that industrial by-products containing CaF₂, ZnO, Fe oxides, or Cu-bearing compounds should be regarded not as contaminants but as synergistic mineralizers. Da et al. (2022a) further emphasized that fluorine-containing sludge exhibits multi-component fluxing effects, enabling reliable reductions in clinkering temperature even under variable raw-meal compositions a critical requirement for industrial-scale applications. When applied at optimized dosages of 1–3 wt%, CaF₂-based mineralization consistently improves clinker burnability, reduces free-lime content, lowers CO₂ emissions, and enhances the immobilization of trace metals within clinker minerals. Consequently, CaF₂-based mineralization represents a practical, resource-efficient, and environmentally beneficial strategy for achieving low-temperature, energy-efficient, and low-carbon cement production.

Despite growing evidence supporting CaF₂-based mineralization, several unresolved issues remain that limit predictive control and large-scale industrial implementation. The key knowledge gaps and corresponding research priorities are summarized in Table 2. A major limitation lies in the lack of quantitative separation between lattice-level defect formation and melt-phase enhancement under realistic clinkering conditions. Addressing this issue will require in-situ high-temperature techniques, such as synchrotron X-ray diffraction and real-time phase tracking, to directly observe defect evolution and phase transformations. Additional challenges arise in multi-component systems derived from industrial wastes, where interactions among CaF₂, metal oxides, and melt structure remain insufficiently understood.

Predictive thermodynamic frameworks combining CALPHAD-based modeling with molecular dynamics simulations are needed to reliably describe eutectic behavior, phase equilibria, and fluxing efficiency in such complex systems. Hydration performance represents another critical uncertainty. Excessive fluorine may lead to the formation of CaF₂-rich surface layers that delay early hydration, yet composition-specific threshold levels remain poorly defined. Long-term hydration studies incorporating pore-solution chemistry and surface-spectroscopic analysis are therefore required to establish safe operational windows. Finally, environmental and process-control considerations including fluorine volatility, long-term leaching stability of immobilized metals, and variability in waste-derived feedstocks require systematic investigation. Comprehensive emission monitoring accelerated leaching tests, and adaptive process-control strategies will be essential to ensure environmentally compliant and robust low-temperature clinker production.

Calcium fluoride (CaF₂) is one of the most effective mineralizers for reducing the clinkering temperature of Portland cement and represents a practical pathway toward low-carbon cement production. This mini review highlights that the mineralizing action of CaF₂ arises from the combined effects of fluoride-induced lattice defect formation, melt-phase modification, and stabilization of high-symmetry alite polymorphs. Fluoride substitution in the C₃S lattice generates calcium vacancies that enhance ionic mobility and lower the activation energy for the C₂S-to-C₃S transformation, while simultaneous reductions in liquidus temperature and melt viscosity promote early liquid-phase formation and accelerated clinker reactions. Together, these mechanisms enable efficient clinker formation at temperatures 50 °C–300 °C below conventional conditions.

The mineralizing efficiency of CaF₂ is further amplified through synergistic interactions with metal oxides such as TiO₂, CuO, and ZnO, which enhance lattice distortion, melt fluidity, and polymorph stability. Importantly, CaF₂ derived from industrial waste streams exhibits mineralizing performance comparable to that of natural fluorite, while facilitating the immobilization of fluorine and heavy metals within clinker phases. When applied at optimized dosages of 1–3 wt%, CaF₂-based mineralization consistently reduces energy consumption and CO₂ emissions while improving clinker burnability and process robustness. Overall, CaF₂-based mineralization offers a viable, resource-efficient, and environmentally beneficial strategy for low-temperature clinker production. Continued advances in mechanistic understanding, thermodynamic modeling, and process control will further support its industrial implementation in next-generation sustainable cement manufacturing.