Utilization of Natural Mineral Materials in Environmental Remediation: Processes and Applications

Abstract

The discharge of wastewater containing persistent organic pollutants presents significant ecological and health challenges due to their toxicity and resilience. Recent advances in advanced oxidation processes (AOPs) and other remediation mechanisms, notably utilizing natural mineral materials (NMMs), offer promising solutions to these challenges. NMMs, with their cost-effectiveness, accessibility, eco-friendly nature, non-toxicity, and unique structural properties, have shown significant promise in environmental remediation and could effectively replace conventional catalysts in related applications. These minerals enable the activation of oxidants, generating reactive oxygen species crucial for the degradation of pollutants. This article reviews the mechanisms of NMMs in various AOPs, including photocatalysis, Fenton-like reactions, and persulfate-activation-based processes, and discusses the potential of these materials in enhancing pollutant degradation efficiency, with a focus on the activation of persulfates and the photo-induced redox processes. The synergy between photocatalytic properties and catalytic activation provided by NMMs offers a robust approach to managing water pollution without the drawbacks of secondary waste production, thus supporting sustainable remediation efforts.

1. Introduction

The uncontrolled release of wastewater has become a pressing issue for ecosystems and public health, primarily due to its adverse impacts on water quality and the availability of potable water. The presence of organic pollutants, which are both resilient and toxic, further complicates efforts in environmental remediation [1]. Recent advancements have introduced various methods to address these environmental contaminants, such as absorption, membrane separation, biodegradation, and especially advanced oxidation processes (AOPs) [2]. These AOPs are highly regarded for their capacity to efficiently degrade or mineralize harmful organics via reactive oxygen species (ROS), such as hydroxyl (•OH; redox potential: 2.8 V vs. NHE), sulfate ($\mathrm{S}{\mathrm{O}}_4^{•-}$, 2.5–3.1 V), and superoxide radicals (•O₂⁻). Furthermore, AOPs can generate ROS through activation processes involving peroxymonosulfate, persulfate, and hydrogen peroxide, catalyzed by ultrasound [3], microwave radiation [4], thermal methods [5], and ultraviolet radiation [6]. AOPs can efficiently degrade recalcitrant organic pollutants and broad-spectrum treatment capabilities in environmental applications, leveraging highly reactive oxidative radicals to enable rapid mineralization. Additionally, their mild reaction conditions and versatile applicability across diverse systems allow for the effective treatment of complex environmental matrices while minimizing toxic byproduct formation, demonstrating strong environmental compatibility and a promising potential for practical use.

Natural mineral materials (NMMs) and their synthesized derivatives have garnered significant attention in advanced oxidation processes (AOPs) due to their cost-effectiveness, abundance, non-toxicity, and physicochemical stability. Geological data reveal significant global reserves of key transition metals: iron (164.3 billion tons proven, 582.8 billion tons estimated), manganese (2.034 billion tons proven, 8.073 billion tons estimated), and copper (821.63 million tons proven, 1.92 billion tons estimated) [7]. Enriched with transition metals, these materials function as efficient heterogeneous catalysts for peroxide activation, effectively degrading organic pollutants with minimal metal ion leaching [8]. Certain minerals—such as hematite [9], sphalerite [10], and anatase [11,12]—also demonstrate intrinsic photocatalytic properties, enabling contaminant removal under light irradiation. However, the long-term stability of these catalysts under the conditions of a fluctuating pH and coexisting anions remains insufficiently explored, and the mechanisms behind metal leaching during repeated catalytic cycles warrant a more in-depth investigation.

This review examines the potential of NMMs in various AOPs—including photocatalysis, Fenton reactions [13], Fenton-like processes [14], and persulfate activation [15]—focusing on their capacity to generate reactive species for decomposing persistent organic pollutants. It summarizes recent progress in employing mineral-based photocatalysts for water decontamination, highlighting how mineral composition and structure influence photocatalytic performance. The discussion also addresses current research gaps, stresses the sustainability and ecological safety of these materials, and proposes directions for future development.

2. Mechanism of Environmental Purification Driven by NMMs

2.1. Photocatalytic Redox Reaction

There are abundant natural semiconductor minerals in the key zones of the Earth’s surface; notably, many kinds of metal oxide minerals and metal sulfide minerals exhibit typical semiconductor characteristics. Research has demonstrated that various oxides and sulfides in natural metallic minerals—such as hematite (Fe₂O₃), anatase (TiO₂), pyrite (FeS₂), sphalerite (ZnS), and greenockite (CdS)—exhibit photocatalytic activity.

Table 1. Photocatalytic characteristic parameters of NMMS.

Mineral Materials	Band Gap Eg/eV	Wavelength/nm
Hematite (Fe2O3)	2.20	565
Goethite (FeOOH)	2.60	478
Anatase (TiO2)	3.20	388
Pyrolusite (MnO2)	0.25	4972
Ilmenite (FeTiO3)	2.80	444
Pyrite (FeS2)	0.95	1309
Alabandite (MnS)	3.00	414
Molybdenite (MoS)	1.17	1062
Greenokite (CdS)	2.40	518
Chalcopyrite (CuFeS2)	0.35	3552

summarizes the characteristic parameters, including band gap energy and maximal wavelength, of representative metal oxide and sulfide semiconductor minerals. These findings reveal the critical conditions for generating photoinduced charge carriers in such minerals, providing a significant theoretical foundation for the study of photocatalytic mineral materials [16,17].

Under light irradiation, the electrons in the valance band of semiconductor minerals will transition to the conduction band, and thus a hole will remain in the valance band. Then, the oxidative holes and reductive electrons will trigger a series of redox reactions. These reactions can influence the transformation of environmental pollutants and trigger the environmental purification process, such as the oxidative degradation of organic pollutants and the reduction in high-valance-state toxic metals. In fact, oxygen and water often participate in photocatalytic reactions and induce the production of various reactive oxygen species (ROS), such as •OH, •O₂⁻, and H₂O₂ (

Table 2. Production mechanism of reactive oxygen species in the photocatalytic process.

Reaction	E (V) vs. NHE (pH = 0)
H2O + h+ → OH + H+	2.38
2H2O + 2h+ → H2O2 + 2H+	1.763
H2O2 + h+ → •O2− + 2H+	1.72
O2 + e− → •O2−	−0.33
O2 + H2O + e− → H2O2 + OH−	−0.134
H2O2 + e− → •OH + OH−	0.93

). The photo-generated holes and produced ROS are responsible for the degradation of pollutants via oxidation, while the photo-generated electrons are responsible for the reduction in high-valance-state toxic metals, such as Cr(VI).

The photocatalytic redox efficiency of a semiconductor is mainly determined by the light response range and the separation efficiency of the photo-generated electron–holes. Generally, ion doping and substitution phenomena will inevitably occur in naturally formed semiconductor minerals due to the complex actual environment, while impurity ions play a positive role in widening the light response range and promoting the separation of the photo-generated electron–holes of semiconductor minerals. This facilitates the photocatalytic redox process for environmental purification.

2.2. Fenton-like Process and Persulfate-Based Advanced Oxidation Process

Fenton reactions have found widespread application in environmental remediation due to their effective oxidative capabilities [18]. These reactions primarily rely on the generation of highly ROS, such as •OH, to facilitate the degradation of organic pollutants, the reduction and transformation of heavy metals, and the inactivation of microorganisms. In the classic Fenton process, Fe²⁺ reacts with hydrogen peroxide (H₂O₂) to produce •OH, with the reaction being sustained by the iron redox cycle. Specifically, Fe²⁺ reacts with H₂O₂ to generate •OH and Fe³⁺ (Equation (1)), and the resulting Fe³⁺ can be reduced back to Fe²⁺ (Equation (2)), thus maintaining the reaction cycle. This process allows the Fenton reaction to efficiently degrade a wide range of organic pollutants [19,20,21,22]. However, the practical application of the Fenton reaction is limited by its narrow effective pH range (pH > 3) and the generation of excessive iron hydroxide sludge [23]. Notably, transition metal catalysts are not limited to iron-based systems. Recent studies indicate that the Cu(I)/Cu(II) redox couple exhibits faster electron transfer kinetics compared to the Fe(II)/Fe(III) counterpart, facilitating efficient •OH generation under near-neutral pH conditions—the catalytic cycle of copper-based Fenton-like reactions, as described in Equations (3) and (4) [24]. Moreover, copper-based materials demonstrate excellent catalytic activity within a pH range of 3 to 7, addressing a key limitation of traditional iron-based Fenton systems [25]. The Cu⁺/H₂O₂ system, with a reaction rate constant k of 1 × 10⁴ M⁻¹s⁻¹, significantly outperforms the Fe²⁺/H₂O₂ system (k = 63–76 M⁻¹s⁻¹), highlighting the considerable potential of copper-based materials in Fenton-like reactions [26].

$$\mathrm{F}{\mathrm{e}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{F}{\mathrm{e}}^{3+}+•\mathrm{O}\mathrm{H}+{\mathrm{O}\mathrm{H}}^{-}$$

(1)

$$\mathrm{F}{\mathrm{e}}^{3+}+{\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{F}{\mathrm{e}}^{2+}+•\mathrm{H}{\mathrm{O}}_2+{\mathrm{H}}^{+}$$

(2)

$${\mathrm{C}\mathrm{u}}^{+}+{\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{C}\mathrm{u}}^{2+}+•\mathrm{O}\mathrm{H}+{\mathrm{O}\mathrm{H}}^{-}$$

(3)

$${\mathrm{C}\mathrm{u}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{C}\mathrm{u}}^{+}+•\mathrm{H}{\mathrm{O}}_2+{\mathrm{H}}^{+}$$

(4)

To mitigate the drawbacks of homogeneous Fenton reactions, heterogeneous catalysts have been developed to activate H₂O₂ without iron sludge formation while extending the operational pH range [27]. Concurrently, persulfates (PDS) and peroxymonosulfates (PMS) have emerged as alternative oxidants for wastewater treatment. Although persulfates can directly degrade pollutants, their slow reactivity necessitates activation to generate sulfate radicals (SO₄^•−) or •OH [28]. Activation methods include thermal energy, which cleaves the O-O bond in persulfate to produce SO₄•⁻ (Equations (5) and (6)) [29], and ultrasound (US), where cavitation-induced localized heating and pressure collapse persulfate molecules into radicals (Equation (7)) [30]. Transition metal ions (Fe²⁺, Co²⁺) further activate persulfates via redox reactions, generating SO₄•⁻ (Equations (8) and (9)) [31,32]. These radicals degrade pollutants into intermediates, ultimately mineralizing them into harmless products like CO₂ and H₂O (Equations (10) and (11)) [33]. Beyond persulfates, transition metals also activate peroxides such as peracetic acid (PAA). Iron-mediated systems drive PAA activation: (1) Fe²⁺ transfers electrons to PAA, yielding acetoxy radicals (CH₃C(O)O•, E_h⁰= 1.60 V Equation (12)) [34]; and (2) Fe²⁺ induces the homolytic cleavage of PAA to produce •OH (Equation (13)) [35]. Such multi-path radical generation underscores the versatility of transition metal catalysts in advanced oxidation processes, enabling efficient pollutant degradation across diverse aquatic environments.

$$\mathrm{H}\mathrm{S}{\mathrm{O}}_5^{-}\stackrel{\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{t}}{\to }\mathrm{S}{\mathrm{O}}_4^{•-}+•\mathrm{O}\mathrm{H}$$

(5)

$${\mathrm{S}}_2{\mathrm{O}}_8^{2-}\stackrel{\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{t}}{\to }2\mathrm{S}{\mathrm{O}}_4^{•-}$$

(6)

$$\mathrm{H}\mathrm{S}{\mathrm{O}}_5^{-}\stackrel{\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{c}}{\to }\mathrm{S}{\mathrm{O}}_4^{•-}+•\mathrm{O}\mathrm{H}$$

(7)

$$\mathrm{H}\mathrm{S}{\mathrm{O}}_5^{-}+{\mathrm{M}}^{\mathrm{n}+}\to \mathrm{S}{\mathrm{O}}_4^{•-}+{\mathrm{M}}^{\mathrm{n}+1}+\mathrm{O}{\mathrm{H}}^{-}$$

(8)

$${\mathrm{S}}_2{\mathrm{O}}_8^{2-}+{\mathrm{M}}^{\mathrm{n}+}\to \mathrm{S}{\mathrm{O}}_4^{•-}+{\mathrm{M}}^{\mathrm{n}+1}+\mathrm{S}{\mathrm{O}}_4^{2-}$$

(9)

$$\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{t}\mathrm{s}+\mathrm{S}{\mathrm{O}}_4^{•-}\to \mathrm{d}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{d}\mathrm{e}\mathrm{d} \mathrm{p}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{s}$$

(10)

$$\mathrm{degraded} \mathrm{products}+\mathrm{S}{\mathrm{O}}_4^{•-}\to \mathrm{C}{\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}$$

(11)

$$\mathrm{F}{\mathrm{e}}^{2+}+\mathrm{C}{\mathrm{H}}_3\mathrm{C}\left(\mathrm{O}\right)\mathrm{OOH}\to \mathrm{F}{\mathrm{e}}^{3+}+\mathrm{C}{\mathrm{H}}_3\mathrm{C}\left(\mathrm{O}\right)\mathrm{O}•+\mathrm{O}{\mathrm{H}}^{-}$$

(12)

$$\mathrm{F}{\mathrm{e}}^{2+}+\mathrm{C}{\mathrm{H}}_3\mathrm{C}\left(\mathrm{O}\right)\mathrm{OOH}\to \mathrm{F}{\mathrm{e}}^{3+}+\mathrm{C}{\mathrm{H}}_3\mathrm{C}\left(\mathrm{O}\right){\mathrm{O}}^{-}+•\mathrm{O}\mathrm{H}$$

(13)

2.3. Photocatalytic-Based Persulfate Activation

Traditional persulfate activation methods, though effective, are often constrained by operational parameters such as temperature and pH, resulting in high costs and limited practical efficiency [36]. Light activation addresses these limitations by reducing the energy barrier for persulfate decomposition while providing supplementary energy, thereby enhancing the generation of reactive radicals (SO₄•⁻ and •OH) critical for pollutant degradation (Equations (14)–(20)) [37]. Semiconductor photocatalysts optimize this process by improving electron transfer kinetics to boost radical production. Concurrently, redox-active natural mineral materials (NMMs), including Fe-, Cu-, and Mn-based minerals, demonstrate versatile activation capabilities under both illuminated and dark conditions. Their large specific surface areas enhance persulfate adsorption, enabling localized decomposition and sustained radical generation through surface-bound metal redox cycling [38]. The synergy between photocatalytic and mineral-mediated activation broadens the environmental adaptability of persulfate systems, offering a robust and efficient strategy for pollutant remediation.

$$\mathrm{Photocatalyst}+\mathrm{h}\mathsf{\nu }\to {\mathrm{e}}^{-}+{\mathrm{h}}^{+}$$

(14)

$${\mathrm{e}}^{-}+\mathrm{H}\mathrm{S}{\mathrm{O}}_5^{-}\to \mathrm{S}{\mathrm{O}}_4^{•-}+\mathrm{O}{\mathrm{H}}^{-}$$

(15)

$${\mathrm{h}}^{+}+{\mathrm{H}}_2\mathrm{O}\to •\mathrm{O}\mathrm{H}+{\mathrm{H}}^{+}$$

(16)

$${\mathrm{e}}^{-}+{\mathrm{O}}_2\to •{\mathrm{O}}_2^{-}$$

(17)

$$\mathrm{F}{\mathrm{e}}^{3+}+{\mathrm{e}}^{-}\to \mathrm{F}{\mathrm{e}}^{2+}$$

(18)

$$\mathrm{F}{\mathrm{e}}^{2+}+\mathrm{H}\mathrm{S}{\mathrm{O}}_5^{-}\to \mathrm{F}{\mathrm{e}}^{3+}+\mathrm{S}{\mathrm{O}}_4^{•-}+\mathrm{O}{\mathrm{H}}^{-}$$

(19)

$$\mathrm{S}{\mathrm{O}}_4^{•-}/{\mathrm{h}}^{+}/•{\mathrm{O}}_2^{-}/•\mathrm{OH}+\mathrm{Pollutants}\to \mathrm{degraded} \mathrm{products}$$

(20)

2.4. Other Remediation Mechanisms

NMMs exhibit versatile remediation mechanisms beyond conventional photocatalytic and oxidative pathways. In ozonation systems, transition metal sites on mineral surfaces catalyze O₃ decomposition via redox cycling, generating •OH and •O₂⁻ radicals, while synergistically adsorbing pollutants to enhance degradation efficiency [39]. Piezocatalysis leverages piezoelectric materials that generate charges under mechanical vibration (energy conversion efficiency up to 78%). These charges drive electrochemical redox reactions to produce reactive species, enabling efficient degradation of organic pollutants in dye wastewater. The mechanism integrates the piezoelectric effect with charge transfer in solution, directly converting mechanical energy into reactive intermediates for catalytic processes [40]. For reductive remediation, sulfide-rich minerals or structural Fe²⁺ drive contaminant detoxification through direct electron transfer or aqueous electron (e⁻_aq) generation, achieving critical pathways such as dehalogenation (C-Cl bond cleavage) and Cr(VI) reduction [41]. Notably, minerals can orchestrate oxidation–reduction synergy by simultaneously activating oxidants and reductants, enabling parallel organic pollutant degradation and heavy metal immobilization. This multifunctionality hinges on the spatiotemporal control of reactive species diffusion and interfacial partitioning, positioning natural minerals as adaptive, eco-compatible solutions for complex co-contamination scenarios.

3. NMMs for Sustainable Pollutants Degradation

3.1. Metal Oxide Materials

3.1.1. Iron Oxide Minerals

Iron (Fe) is the most abundant and widely distributed transition metal element in the Earth’s crust and exists in the form of stable iron oxides and hydroxides, such as hematite, goethite, and magnetite. The outstanding oxidation–reduction and photochemical activities of iron oxides (hydroxides) have a non-negligible impact and regulatory effect on environmental pollutants [42].

Hematite (hexagonal system) is one of the most common iron oxide minerals found in strongly weathered soils, such as red soil and brick red soil, because its stable mineral structure, which is widely distributed in the sediments and surface soil, is 70% iron. This mineral has attracted significant attention due to its abundant occurrence, economic potential, non-toxic nature, and exceptional reactivity to visible light. Its narrow band gap, ranging from 2.0 to 2.2 eV, allows it to absorb visible-light wavelengths up to 600 nm, thereby promoting chemical reactions through the generation of photoinduced charge carriers [43,44]. Hematite shows great potential in environmental remediation due to its advantages, such as high specific surface area, fast electron transport, and high redox activity. Many studies have reported on the treatment of heavy metal and organic pollutants by hematite. Liu et al. investigated the effect of hematite on the fate and transport of Cr under sunlight irradiation, with the reaction mechanism illustrated in Figure 1a [45]. It was found that hematite can induce the photocatalytic redox of Cr, thus enhancing the immobilization of Cr, and the acidic condition is more conducive to the immobilization of Cr. The photocatalytic oxidation of Mn²⁺ by hematite was also reported, where the oxidized Mn²⁺(aq) will further form tunneled Mn (III/IV) oxides, thus remediating Mn²⁺(aq)-contaminated water [46]. Oxalate, which widely exists in the environment, has been proven to be a favorable factor for the photocatalytic performance of hematite. A solar/hematite/oxalate system was constructed to drive roxarsone degradation and induce the simultaneous As(V) immobilization. It was found that within 6 h, 85.1% of roxarsone can be converted to inorganic As(V) by the oxidation effect of •OH produced in the solar/hematite/oxalate system, and the reaction mechanism is shown in Figure 1b. The production process of •OH can be attributed to the following steps: Firstly, oxalate chelated with Fe(III) on the surface of hematite to form Fe(III)-oxalate. Then, Fe(III)-oxalate could be reduced to Fe(II)-oxalate under light irradiation, while •CO₂⁻ with reducibility was produced simultaneously. The produced •CO₂⁻ could further induce the activation of oxygen molecules; thus, the ROS, including •OH, could be produced with the assistance of Fe(II) [47]. Moreover, the similar oxalate/hematite can also induce the degradation of dissolved organic matter by the oxidative ROS produced under light irradiation (Figure 1c) [48].

As an iron-rich mineral, hematite can also serve as a catalyst for the activation of oxidants in the advanced oxidation process. Liu et al. modified natural hematite using a reducing agent (NaBH₄), and this modified hematite was applied to the activation of peracetic acid for the efficient degradation of cefazolin. The high content of Fe(II) in the modified hematite mainly contributed to the activation of peracetic acid, where the O₂, CH₃C(O)OO•, and •OH produced in this process were identified as the activated species for cefazolin degradation [49]. Additionally, the photo-Fenton process using natural hematite and siderite as heterogeneous catalysts has also been reported, and it exhibited an outstanding effect in 4-chlorophenol removal [50].

Goethite (α-FeOOH) is also a commonly distributed natural iron hydroxide mineral with a similar structure to gibbsite, of which the anions are arranged in a hexagonal, close-packed structure. Goethite is a thermodynamically stable mineral, making it the termination phase of the transformation process of many iron oxides. The abundant structure of hydroxyl groups and surface function groups endow goethite with good surface adsorption performance and reactivity; thus, it can influence the transformation and fate of many environmental contaminants. Another paper reported the synergistic promotion effect of goethite and humic acid on the photodegradation of bifenthrin under light irradiation. The improved photocatalytic activity of goethite for bifenthrin degradation can be attributed to its extended light adsorption and improved electron–hole separation induced by humic acid, as shown in Figure 2. In this system, both the oxidative species, •OH and ¹O₂, and reducing species, such as hydrogen atoms (H•), contributed to the degradation of bifenthrin [51]. The element substitution phenomenon often occurs in goethite, and Al, Mn, Cr, and Ni can replace the lattice Fe in goethite, which can change the band structure of goethite and further influence its photocatalytic performance. In a typical example, the influence of Mn doping on the band structure has been investigated by both theoretical calculation and experimental confirmation. It was reported that Mn-substitution could cause the reduction in the band gap of goethite when the Mn-substitution is lower than 3–4 mol%. Accordingly, the photocatalytic performance of goethite for methylene blue degradation increased due to its improved response [52].

In addition to hematite and goethite, other iron oxides (hydroxides) such as magnetite, ferrihydrite, ilmenite, and lepidocrocite were also investigated for their environmental remediation effect [53]. Wang et al. reported a natural-magnetite-based PMS activation system, where hydroxylamine was introduced into this system to synergistically enhance its degradation effect toward organic pollutants. The results showed that the degradation efficiency of rhodamine B (rhB) was increased by 61.82% after the addition of hydroxylamine, which was caused by the promotion effect of hydroxylamine on Fe²⁺/Fe³⁺ conversion in the magnetite/peroxymonosulfate system [54]. Compared to the monometallic Fe, the cooperation of multiple transition metal elements in natural minerals was confirmed to be a favorable factor for Fe(III)/Fe(II) circulation and ROS generation in sulfate-radical-advanced oxidation processes. The natural Ti- and V-enriched magnetite was applied as the catalyst in the UV-assisted PMS activation system, which achieved a 100% degradation efficiency of BPS within 20 min. It was suggested that the photo-generated electron–holes of TiO₂ and the subsequent electron transfer by V(III)/V(IV)/V(V) redox cycles had effectively accelerated the Fe(III)/Fe(II) circulation [55]. Similarly, the other bimetallic natural mineral–ilmenite showed excellent bacterial inactivation performance in the persulfate-mediated catalytic and photocatalytic system [56]. Ferrihydrite is a widely studied natural iron oxide with the characteristics of low crystallinity and nanoscale particle size, showing high reactivity with environmental pollutants. In addition to the well-known good adsorption performance of ferrihydrite, its semiconductor properties have also been noticed. Wang et al. clarified the effective photocatalytic reduction in U(VI) by ferrihydrite under both anaerobic and aerobic conditions [57]. These catalysts have two critical advantages: (1) sustained oxidant activation via surface-bound Fe³⁺/Fe²⁺ redox cycles, which effectively minimizes iron ion leaching and prevents hydroxide precipitation and (2) broad pH tolerance, allowing them to maintain a high catalytic activity from acidic to neutral conditions. Their structural integrity ensures exceptional reusability, with most systems retaining their efficiency after multiple cycles. This synergy of stability, pH adaptability, and recyclability positions heterogeneous Fenton catalysts as sustainable alternatives to conventional homogeneous systems.

3.1.2. Titanium Oxide Mineral

Titanium dioxide occurs in phase structure forms of anatase, rutile, and brookite, which are typical semiconductor minerals. Among them, rutile is the most stable structure thermodynamically, making it the most frequently occurring titanium dioxide mineral in nature. Some trace impurity ions, such as V and Fe, can sometimes be doped into the structure of natural rutile, which will affect its band structure and photocatalytic performance. Li et al. determined the band gap of natural rutile (2.7 eV) using synchrotron-based O K-edge X-ray absorption and emission spectra, finding it to be narrower than that of synthetic rutile (3.0 eV), where the doping V and Fe ions were considered the main leading factor for the narrowed band gap of rutile from the DFT calculation results. This narrow band gap endows rutile with visible-light response properties, which can more efficiently drive photocatalytic redox in the Earth’s surface environment; the energy band and structure of natural rutile are shown in Figure 3a,b [58]. The photocatalytic performance of V-doping natural rutile for the degradation of organic pollutants, such as methyl orange and halohydrocarbons, was examined. It was found that the natural rutile bearing V⁵⁺ and Fe³⁺ substitution exhibited good methyl orange degradation performance with the presence of H₂O₂ under visible-light irradiation, and 60.59% of methyl orange was removed within 1 h, which is comparable to the commercial nano-TiO₂ (P25). The increased light absorption and promoted electron–hole separation efficiency induced by the electron trapping effect of high-valance metal ions (V⁵⁺ and Fe³⁺) were both reasonable for the good photocatalytic performance of natural rutile. Lu et al. conducted heating, quenching, and electron irradiation treatments of natural rutile to change its surface characteristics. Quenching improved the exposure of adsorbed water and V on the surface of rutile, leading to its high photoactivity for halohydrocarbon degradation (trichloroethylene and tetrachloroethylene). In addition to photocatalytic activity, ion substitution can also influence the Fenton catalytic activity of natural rutile. Rutile with different levels of V and Fe doping was obtained by the hydrogen annealing of natural rutile, thus elucidating the influence of doping ions on the Fenton catalytic activity of rutile. Hydrogen annealing led to the formation of surface Fe(II) and bulk V(III) in rutile, benefiting the Fenton catalytic reaction and organic pollutant degradation [59].

Outside of engineering applications, the photocatalytic effect of titanium dioxide also drives the oxidation and transformation process of many substances in the natural environment, such as the fixation of NOx, the oxidation of Mn²⁺, and manganese oxide formation [60]. Nitrogen oxides (NO_x = NO + NO₂) in the atmosphere are considered a threat to human health, and the photocatalytic oxidation of NOx to nitrate (NO₃⁻) is an efficient way to reduce NOx pollution. It was reported that the small amount (≤5%) of titanium dioxide (anatase and rutile) naturally occurring in soils could lead to NOx fixation by oxidizing NOx to NO₃⁻ under light irradiation. It provides an abiotic renoxification route for N-fixation and NOx pollution alleviation with the leading role of titanium dioxide in soils, and the mechanism of the redox reaction of manganese (Mn) is very important for environmental evolution. Jung et al. found that the TiO₂ minerals could catalyze the rapid oxidation of Mn²⁺ (aq) in a neutral environment under light irradiation, and the reaction rate was even higher than those of the reported biotic/abiotic processes. This finding provided new insight into the formation of manganese oxide minerals in the natural environment. Moreover, the main minerals in the red sediment from the Danxia landform was determined to be iron oxide (hematite) and titanium oxide (anatase). It was confirmed that the combination of anatase and hematite played a significant role in the photocatalytic reaction, where the photocurrent produced by hematite was improved 23-fold at 0.8 V (vs. Ag/AgCl) after coupling with anatase; the reaction process is shown in Figure 3c [61].

Figure 3. Schematic diagram for the structure of natural rutile: (a) band gap and (b) cell [58], Copyright © 2018, Elsevier; (c) reaction mechanism of titanium dioxide-catalyzed dissolution of Mn²⁺ and formation of tunnel-structured manganese oxide [61], Copyright © 2018, MDPI.

Figure 3. Schematic diagram for the structure of natural rutile: (a) band gap and (b) cell [58], Copyright © 2018, Elsevier; (c) reaction mechanism of titanium dioxide-catalyzed dissolution of Mn²⁺ and formation of tunnel-structured manganese oxide [61], Copyright © 2018, MDPI.

3.1.3. Manganese Oxide Mineral

Manganese oxides, naturally abundant and diverse, serve as crucial environmental mineral materials due to their structural versatility and redox properties. The Mn in the manganese oxides generally exists in the form of Mn²⁺, Mn³⁺, and Mn⁴⁺; they can undergo mutual transformation under specific conditions; and the variable valance states of Mn endow manganese oxides with outstanding redox activity. Their crystal structures originate from the arrangement of [MnO₆] octahedral units, which interconnect via shared edges or corners to form chain-like frameworks. These chains further assemble into porous architectures with rectangular or square channels, enhancing their environmental purification performance through heavy metal adsorption and organic pollutant degradation [62]. Birnessite, a prominent manganese oxide, effectively oxidizes contaminants such as Co(II), Cr(III), V(IV), Pu(IV), and Se(IV) to higher oxidation states [63,64,65,66]. Li et al. demonstrated that the birnessite-mediated chemical oxidation of As(III) involves Mn(IV) reduction to Mn(II), although the resulting MnOOH byproduct inhibits further As(III) oxidation. By contrast, photocatalytic oxidation using birnessite achieved superior As(III) removal efficiency, as the process minimized MnOOH interference, highlighting its regulatory role in arsenic speciation and environmental mobility (Figure 4) [67]. Additionally, manganese oxides function as heterogeneous catalysts in advanced oxidation processes. For instance, hydrothermally aged natural manganese oxides exhibited enhanced catalytic ozonation performance in 4-chlorophenol degradation, attributed to redox cycling between Mn³⁺/Mn²⁺ and Fe³⁺/Fe²⁺, which amplified the generation of reactive oxygen species (ROS) [68]. Similarly, natural manganese ores activated PMS to efficiently degrade phenol, TBBPA, and RhB, underscoring their broad applicability in pollutant remediation [69]. The structural adaptability and redox plasticity of manganese oxides position them as multifunctional materials for environmental applications. However, challenges persist in optimizing their stability, recyclability, and selectivity under real-world conditions.

To elucidate the enhancement mechanism of natural minerals in pollutant degradation, we selected typical metal oxide materials for performance comparison (

Table 3. The degradation of pollutants by metal oxide materials.

Mineral	Target Pollutant	Oxidant Concentration	Catalyst Dosage	Time	pH	Degradation Efficiency	Ref.
Hematite	Roxarsone	Oxalate, 2.0 mM	0.5 g L−1	6 h	4.5	85.10%	[46]
Hematite	Cefazolin	PAA, 0.4 mM	0.3 g L−1	80 min	7	98.10%	[49]
Siderite	2-chlorophenol	PDS, 0.5 mM	0.05 g⋅L−1	180 min	8.1	82.50%	[70]
Goethite	Bisphenol A	H2O2, 1 mM	0.5 g L−1	240 min	3.5	87.60%	[71]
Magnetite	Rhodamine B	PMS, 1 mM	0.2 g L−1	60 min	7	94.78%	[54]
Natural manganese-containing minerals	4-Chlorophenol	O3, 0.6 mg min−1	1.0 g L−1	15 min	7	84.11%	[68]
Ferrihydrite	Enoxacin	H2O2, 10 mM	0.4 g L−1	120 min	3	89.70%	[72]
Ilmenite	Sodium butyl xanthate	H2O2, 2 mM	4.0 g L−1	80 min	8.7	92.52%	[73]

). Notably, the introduction of mineral components significantly improved degradation efficiency while also achieving cost savings and mitigating the risk of metal leaching contamination.

3.2. Metal Sulfide Materials

3.2.1. Pyrite

The degradation effects of natural metal sulfide minerals on pollutants are summarized in

Table 4. The degradation of pollutants by metal sulfide materials.

Minerals	Target Pollutants	Oxidant Concentration	Catalyst Dosage	Time	pH	Degradation Efficiency	Ref.
Pyrite	Cyclohexanoic acid	PS, 4.0 mM	2.0 g L−1	120 min	3–11	85.10%	[74]
Pyrite	Tetracycline	H2O2, 5 mM	1.0 g L−1	60 min	4.1	85%	[77]
Pyrite	V(IV)-citrate	PMS, 5 mM	8.0 g L−1	180 min	N.A.	99.40%	[76]
Pyrite	Acetaminophen	PDS, 5 mM	2.0 g L−1	300 min	4	100%	[78]
Pyrite	sulfamethoxazole	PAA, 460 μM	0.3 g L−1	50 min	5.8	93.67%	[79]
Chalcopyrite	Bisphenol A	PMS, 0.3 mM	0.1 g L−1	20 min	6	99.70%	[80]
Chalcopyrite	Rhodamine B	H2O2, 43 mM	0.75 g L−1	50 min	5.1	97.20%	[81]
Chalcopyrite	metronidazole	PAA, 460 μM	4.0 g L−1	30 min	3	83.92%	[82]
Bornite	Tetracycline	PDS, 11.1 mM	3.5 g⋅L−1	180 min	4.5	87.50%	[83]

. As the most abundant and most widely distributed metal sulfide mineral on the Earth, pyrite (FeS₂) has become a research hotspot due to its excellent catalytic performance, which was considered to have great advantages in environmental remediation, cost-effectiveness of pyrite as catalyst for aqueous pollutant solutions is confirmed by numerous researchers. In typical applications, pyrite is often used as a heterogeneous catalyst to drive the persulfate-based advanced oxidation reaction due to the high content of Fe²⁺. Zhu et al. constructed a pyrite/persulfate system for the removal of cyclohexanoic acid in real petroleum wastewater. Under optimal conditions (2 g/L of pyrite, 4 mM PS), more than 90% of cyclohexanoic acid can be removed in a wide pH range. It was revealed that the Fe²⁺ serves as the active reaction sites for persulfate activation, and SO₄^•−, Fe(IV), and •OH contribute to cyclohexanoic acid degradation. Moreover, the interaction between Fe³⁺ and S played a positive role in promoting the cycle of Fe³⁺/Fe²⁺, endowing the pyrite with outstanding recycling performance. The reaction process is shown in Figure 5a [74]. Interestingly, the pyrite/persulfate system was also applied for the innovative removal of Microcystis aeruginosa [75]. Additionally, the pyrite-driven persulfate activation showed good performance for the treatment of the metal ion–organic complex; for example, the V(IV)–citrate complex in groundwater can be efficiently degraded with the natural pyrite/PMS system assisted with alkali precipitation, providing an efficient way for actual complex wastewater treatment [76].

In addition to the persulfate-based advanced oxidation process, pyrite/H₂O₂ Fenton-like processes have also been widely reported. The functional mechanism of pyrite/H₂O₂ systems for naphthalene degradation was investigated. The results indicated that the homogeneous reaction mainly contributed to hydrogen peroxide disintegration and naphthalene degradation in the pyrite/H₂O₂ system. Moreover, the sulfur species from pyrite was confirmed as an important factor for promoting the Fe²⁺/Fe³⁺ cycle, which further facilitated the continuous production of reactive oxygen species, thus enhancing the degradation of naphthalene [84]. Wang et al. proposed an ingenious pre-reaction scheme to improve the reaction activity of the pyrite/H₂O₂ system, where the contaminant solution was added after a period of pre-reaction between pyrite and H₂O₂. As illustrated in Figure 5b, the pre-reaction of pyrite and H₂O₂ caused the in situ formation of H⁺ and thus promoted the Fe²⁺ release, which further boosted the generation of ROS and led to the efficient degradation of dyes [85]. In addition, Dai et al. demonstrated that FeS₂ effectively activates PAA to degrade tetracycline (TC), with sulfur speciation critically influencing ROS generation and Fe(II) regeneration [86]. DFT calculations revealed that sulfur species facilitate electron transfer between CH₃COO• radicals and FeS₂, driving dual roles in regulating ROS and sustaining Fe(II)/Fe(III) cycling. This theoretical insight aligns with experimental observations showing sulfur-mediated enhancement in SO₄^•− production and PAA activation efficiency. Furthermore, the integration of electrospun hydrophilic FNC fiber films with the FeS₂/PAA system maintained robust TC degradation in real wastewater, showcasing its practical applicability.

The modification of pyrite via ball milling is considered efficient for improving the catalytic activity of pyrite. It was found that the production of S vacancies (V_S) and the improved reducibility of S(-II) on the pyrite induced by the ball-milling process played multiple roles in promoting the catalytic activation of the persulfate, with the reaction mechanism shown in Figure 5c. It accelerated Fe(III) reduction and Fe(II) dissolution in the pyrite/persulfate system and thus promoted the production of reactive species (RS) for monochlorobenzene degradation. Interestingly, it was also found that the ball-milling treatment improved the contribution of Fe^IV for monochlorobenzene degradation, indicating that the RS generation pathway was changed [87]. Sun et al. emphasized the dominant function of the size effect on improvements in the catalytic performance of pyrite in the pyrite/persulfate system induced by the mechanical treatment of pyrite. Different grinding treatment times result in different pyrite particle sizes. The fitting results showed that the decomposition rate was almost linearly related to the particle size of pyrite [88]. In recent work, by optimizing the ball-milling conditions, the catalytic efficiency of modified pyrite was increased by 60-fold compared to natural pyrite, and the ball-milled pyrite Fenton system was able to degrade dyes and a series of antibiotics within 30 min [89].

Figure 5. (a) The efficient removal of naphthenic acids from real petroleum wastewater by the natural-pyrite-activated persulfate system [74], Copyright © 2023, Elsevier; (b) the reaction scheme in pyrite/H₂O₂ system assisted by pre-reaction [85], Copyright © 2021, Elsevier; and (c) the reaction mechanism of the ball-milled pyrite/PDS system [87], Copyright © 2024, Elsevier.

Figure 5. (a) The efficient removal of naphthenic acids from real petroleum wastewater by the natural-pyrite-activated persulfate system [74], Copyright © 2023, Elsevier; (b) the reaction scheme in pyrite/H₂O₂ system assisted by pre-reaction [85], Copyright © 2021, Elsevier; and (c) the reaction mechanism of the ball-milled pyrite/PDS system [87], Copyright © 2024, Elsevier.

3.2.2. Chalcopyrite

Chalcopyrite (tetragonal system) is one of the most widely distributed sulfur-containing minerals, with Cu, Fe, and S mass fractions of 35.78, 32.73, and 28.31%, respectively. It accounts for more than 70% of the total copper content in the Earth’s crust. The effective electron transfer properties of chalcopyrite, due to its complex metal oxidation states, such as Cu(I), Cu(II), Fe(II), and Fe(III), enable it to exhibit excellent catalytic performance in the degradation of organic pollutants through peroxide activation. Wang et al. used natural chalcopyrite (NCP) to activate peroxymonosulfate (PMS) for the remediation of groundwater contaminated with aged leachate [90]. As illustrated in Figure 6a, the exceptional performance of NCP-activated PMS is primarily attributed to the promotion of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ cycling facilitated by S²⁻. Moreover, SO₄•⁻ and •OH were identified as the dominant reactive oxygen species (ROS) in the NCP/PMS system under varying initial pH conditions [91].

Compared with single metal sulfides such as FeS and CuS, Cu/Fe bimetallic sulfides exhibit high catalytic activities due to the synergistic effect of Cu-Fe active sites. Nie et al. compared the PMS activation of BPA removal between CuFe₂O₄ and CuFeS₂. According to reports, bimetallic sulfides are much more effective than bimetallic oxides due to the role of S²⁻ in improving Fe³⁺/Fe²⁺and Cu²⁺/Cu⁺ cycling [80]. In addition, chalcopyrite (CuFeS₂) is a copper iron bimetallic sulfide mineral and a promising heterogeneous Fenton catalyst. The synergistic effect exhibited by Cu and Fe in minerals stimulates the activation of H₂O₂, resulting in the production of more active hydroxyl radicals (•OH). Yang et al. investigated the use of thermally activated natural chalcopyrite for the Fenton-like degradation of organic dye Rhodamine B (RhB). This study showed that thermal activation at 300 °C changed the valence of surface elements of natural chalcopyrite, rather than altering its main chemical phase. Heat-activated chalcopyrite significantly improved the Fenton-like degradation of RhB. The Cu⁺ and Fe²⁺ species on the surface of chalcopyrite can activate H₂O₂ to produce • OH through electron transfer reaction, accompanied by Cu²⁺/Fe³⁺, and the reaction process is shown in Figure 6b [81].

3.2.3. Sphalerite

Sphalerite is a widely distributed natural semiconductor mineral with the theoretical chemical composition of ZnS, which is a wide-band-gap semiconductor (E_g = 3.68 eV) [90]. However, natural sphalerite generally contains various impurities, such as Fe²⁺, Cd^{2 +}, and Cu²⁺, resulting in the narrowing of its band gap [92,93]. Therefore, natural sphalerite usually shows good photocatalytic performance under sunlight or visible-light irradiation. Lu et al. detected the chemical composition of natural sphalerite by electron microprobe analysis (EMPA) (as shown in

Table 5. XPS binding energies and the corresponding atom ratio for comparisons between natural and pure sphalerite [94].

Catalyst	Binding Energy (eV)					Atom Ratio
	Zn 2p	S 2p	O 1s	Fe 2p	Cu 2p	Zn/S	Fe/S	Cu/S
Natural sphalerite	1022.15	161.68, 162.86, 169.14	532.11	712.48	932.26	0.694	0.329	0.033
Pure sphalerite	1021.58	161.7	531.64	-	-	1.06	-	-

). In addition to Zn, several other metal elements, including Fe, Cu, Cd, Ag, and Mn, were detected, and the Fe content was highest (13.74–18.65%). The results showed that the band gap (E_g) of natural sphalerite (2.8 eV) was significantly narrower than that of pure ZnS (3.4 eV). It was proposed that the Fe 3d and S 3p orbitals both contributed to the valence band of natural sphalerite and thus led to a negative shift in the valence band, thereby decreasing the band gap of natural sphalerite. Moreover, the trace non-isoelectronic substitution of Ag⁺ for Zn ²⁺ also produced a negative charge, which could serve as the capture sites for holes. As a result, the natural sphalerite exhibited a higher photocatalytic MB degradation activity than pure ZnS under visible-light irradiation [94]. Based on the photocatalytic effect of natural sphalerite, it could also be applied for the treatment of halohydrocarbons and oily wastewater. The hydrometallurgical process, especially solvent extraction technology, exhibits good application prospects in metal recovery from spent lithium-ion batteries. However, the solvent extraction process will inevitably produce oily wastewater, causing environmental issues. It was reported that natural sphalerite could achieve an efficient degradation of oily wastewater (from solvent extraction) under visible-light irradiation with the assistance of H₂O₂, and 86.20% total organic carbon can be removed under optimal conditions. The natural doped Fe in sphalerite could introduce an impurity level, thus narrowing the band gap of sphalerite. Meanwhile, Fe could also serve as the capture site for electrons to promote the separation of electron–holes [95,96]. Moreover, the applications of natural sphalerite in photocatalytic sterilization have also been reported [97,98].

3.3. Silicates

Silicates are widely used as catalyst support in water treatment due to their abundance, low cost, and stability. Their high surface area, developed pore structure, and strong cation exchange capacity enhance adsorption, catalysis, and reusability. Studies have focused on integrating catalysts with clay minerals to improve performance and provide additional active sites for peroxide activation in water treatment.

Kaolinite, a classic 2D layered mineral, consists of a silicon–oxygen tetrahedron layer and an aluminum–oxygen octahedron layer, with distinct basal and edge planes. Its abundant surface-bound and structural hydroxyl groups, adsorption sites, and micro-scale properties make kaolinite a promising catalyst for activating PMS. Li et al. reported that natural kaolinite’s weak photochemical activity can be enhanced by constructing Kaol/NiFe-LDO heterostructures. As shown in Figure 7a, the interfacial chemical bonds and Z-scheme band structure enable efficient PMS activation, generating sulfate radicals via photo-generated hole oxidation. Compared to natural kaolinite, the Kaol/NiFe-LDO heterostructure achieved a significantly improved degradation of RhB and orange II, emphasizing its potential in environmental applications [99]. Li et al. explored the use of natural negatively charged kaolinite with abundant hydroxyl groups to activate PMS for atrazine degradation. The results showed that hydroxyl and sulfate radicals are the key reactive species, and factors such as catalyst loading, pH, PMS dosage, and inorganic ions significantly affect the degradation efficiency. Notably, the natural kaolinite used for PMS activation possessed excellent stability, and the structure is shown in Figure 7b [100]. Zhang et al. utilized the natural layered clay mineral kaolinite as a carrier, combining it with g-C₃N₄ to load single iron atoms (FeSA-NGK), resulting in the fabrication of a novel composite material. This material demonstrated outstanding pollutant degradation performance under the synergistic action of PMS and visible light. The introduction of kaolinite not only increased the loading amount of single Fe atoms by 14.2% but also enhanced the concentration of N vacancies, optimizing the electronic structure and thereby significantly enhancing the catalytic activity of the material [101].

Halloysite nanotubes, a type of clay mineral, possess a distinctive nanotube morphology, predominantly composed of Al₂Si₂O₅(OH)₄·nH₂O, where n = 4 for a 1.0 nm wall-packing spacing (row halloysite) and 2 for a 0.72 nm spacing (dried sample). These nanotubes exhibit diameters between 0.1 and 0.4 µm and a length that does not exceed 0.5 µm [102]. Characterized by their expansive specific surface area, distinctive hollow cylindrical form, remarkable stability, exceptional biocompatibility, and low biotoxicity, these HNTs offer remarkable adaptability across a spectrum of uses such as adsorption, energy storage, and catalytic processes [102,103]. Zhang et al. demonstrated that halloysite nanotubes (HNTs), modified with nanomanganese cobaltate (MCO@HNTs), effectively activate PMS for antibiotic degradation, as shown in Figure 3c. The system degrades ornidazole (ONZ) over a wide pH range (6.08–11.00) with minimal ion leaching and strong resistance to natural water interference. Singlet oxygen (¹O₂) was identified as the main ROS driving ONZ degradation [104]. Another study developed a novel catalyst using nano-CoFe₂O₄-decorated halloysite nanotubes (CoFe₂O₄/HNT), which efficiently degrades the antibiotic ornidazole (ONZ) through the activation of PMS. HNT served as a carrier to enhance the dispersion of CoFe₂O₄ and, due to its positively charged inner wall, facilitated the loading of anionic macromolecules, which is essential for enhancing catalytic efficiency. The CoFe₂O₄/HNT plus PMS system nearly completely degraded ONZ within an hour, demonstrating good pH tolerance and resistance to anion interference [105]. Zhao et al. utilized the Coulomb interaction to deposit 1,10-phenanthroline-coordinated Co²⁺ onto the surface of HNTs, and then incorporated atomically dispersed cobalt sites into nitrogen-doped hollow carbon nanotubes to fabricate the CoNC/NHCNTs-900 material. This material activated PMS effectively, leading to the efficient degradation of tetracycline (TC) pollutants with an unprecedented mineralization rate of 89.07%. The use of HNTs as a template prevented the aggregation of cobalt species and enhanced the material’s specific surface area, which facilitated the exposure of active sites and the transfer of reactants [106].

Montmorillonite is a monoclinic crystalline layered structure aluminosilicate clay mineral with the chemical formula (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O. It has received widespread attention due to its large specific surface area, excellent cation exchange capacity, and significant water absorption and swelling properties. Figure 7e shows the adsorption mechanism of cationic and anionic dyes on montmorillonite clay minerals [107]. The adsorption efficiency of montmorillonite can be significantly enhanced through appropriate modification. Its surface is covered with abundant hydroxyl functional groups, which can activate peroxides and act as active sites. Gao et al. enhanced the strong interaction between CoO and montmorillonite through a molten salt induction method, preparing an efficient CoO/Mt catalyst for the activation of PMS to degrade tetracycline (TC). In this work, the introduction of montmorillonite not only provided abundant surface hydroxyl groups to enhance the electronic structure of CoO nanoparticles but also significantly improved the stability and activity of the catalyst, and the reaction process is shown in Figure 7d. Treating montmorillonite with molten NaPO₃ mitigated its dehydroxylation process, thereby more effectively modulating the electronic structure of CoO. This resulted in the CoO/Mt catalyst exhibiting excellent performance in the activation of PMS, achieving a 99% TC degradation efficiency within 7 min and maintaining a 96% removal rate after eight cycles, while also significantly reducing the leaching of Co ions [108]. Shi et al. developed a nanoscale zero-valent iron/montmorillonite (NZVI/Mt) composite material for the efficient removal of hexavalent chromium (Cr(VI)) from aqueous solutions. The NZVI, synthesized through a liquid-phase reduction method, when combined with natural montmorillonite, not only enhances the dispersion of NZVI to prevent aggregation but also leverages the adsorptive properties of montmorillonite to further increase the composite’s removal efficiency for Cr(VI). Under optimal conditions, the NZVI/Mt composite achieved a removal efficiency of up to 92.41% for Cr(VI) and demonstrated a maximum adsorption capacity of 67.75 mg/g [109]. Furthermore, Rehman et al. synthesized a cost-effective paired mineral–carbon material (PMC) by synergistically integrating montmorillonite, goethite, and rice-husk-derived carbon. The hierarchical porous structure (187 m²/g) with abundant defects enabled superior PMS activation, achieving rapid diethyl phthalate (DEP) degradation (k₁ = 0.923 min⁻¹, pH 6.0). DFT calculations revealed targeted radical (SO₄•⁻/•OH/¹O₂) attack on DEP’s electron-rich sites (f₀: 0.0837–0.1027). Beyond performance, the study emphasized circular economy benefits: agricultural waste (rice husk) was valorized into functional catalysts, while the PMC/PMS system significantly reduced DEP phytotoxicity, restoring the healthy growth of seedlings (biomass recovery > 90%). Eco-friendly synthesis by avoiding energy-intensive calcination steps and a radical-dominated metal-free pathway minimizes secondary pollution risks. Economically, the production cost of PMC on the lab-scale was estimated at USD 8.08/kg, 20% lower than that of commercial activated carbon (USD 10/kg), with scalable processes leveraging low-cost minerals and biomass. This work exemplifies a sustainable paradigm integrating “waste-to-resource” conversion, high-efficiency decontamination, and ecological risk mitigation, offering a competitive alternative for industrial wastewater treatment [110].

Figure 7. (a) The proposed mechanism for the improved photocatalytic ability of NFK HCs [99], Copyright © 2024, Elsevier; (b) the highly efficient activation of peroxymonosulfate by natural negatively charged kaolinite with abundant hydroxyl groups for the degradation of atrazine [100], Copyright © 2019, Elsevier; (c) nanomanganese cobaltate-decorated halloysite nanotubes for the degradation of ornidazole via peroxymonosulfate activation [104], Copyright © 2023, Elsevier; (d) Co₃O₄ and montmorillonite for promoted peroxymonosulfate activation toward tetracycline degradation [108], Copyright © 2024, Elsevier; (e) the mechanism of adsorption of cationic and anionic dyes onto smectite clay minerals [109], Copyright © 2022, Elsevier.

Figure 7. (a) The proposed mechanism for the improved photocatalytic ability of NFK HCs [99], Copyright © 2024, Elsevier; (b) the highly efficient activation of peroxymonosulfate by natural negatively charged kaolinite with abundant hydroxyl groups for the degradation of atrazine [100], Copyright © 2019, Elsevier; (c) nanomanganese cobaltate-decorated halloysite nanotubes for the degradation of ornidazole via peroxymonosulfate activation [104], Copyright © 2023, Elsevier; (d) Co₃O₄ and montmorillonite for promoted peroxymonosulfate activation toward tetracycline degradation [108], Copyright © 2024, Elsevier; (e) the mechanism of adsorption of cationic and anionic dyes onto smectite clay minerals [109], Copyright © 2022, Elsevier.

4. Conclusions and Outlook

The application of natural minerals in environmental remediation has demonstrated substantial promise, particularly as heterogeneous catalysts for pollutant degradation. These minerals, enriched with metallic elements and endowed with distinct physicochemical properties, exhibit inherent multi-metallic compositions, defect sites, and porous structures that serve as naturally optimized platforms for regulating radical/non-radical pathways. While current research predominantly focuses on pyrite, chalcopyrite, and magnetite, emerging candidates, such as ilmenite, apatite, and tourmaline, have untapped potential due to their unique redox-active metal combinations and crystallographic defect densities. Existing studies emphasize the critical role of surface grain boundaries and redox-active metals in mediating electron transfer, yet the atomic-scale reaction kinetics and their structure–activity relationships with mineral-specific features remain poorly elucidated. Key challenges impeding technological translation include (1) poorly understood dynamic adsorption–catalysis coupling mechanisms at mineral–pollutant–oxidant ternary interfaces, particularly in municipal wastewater degradation scenarios where adsorption-dominated mineral carriers may compete with catalytic pathways; (2) the lack of a balanced assessment of energy efficiency from a lifecycle perspective; and (3) the irreversible deactivation of active sites in complex environmental matrices.

Future advancements require the synergistic integration of computational materials science and advanced characterization. For instance, DFT simulations could decide how defect engineering in minerals such as chalcopyrite redistributes electron clouds to suppress electron–hole recombination. Meanwhile, mineral-based heterojunction composites can be developed through band-gap engineering for electron transfer channel modulation. By artificially synthesizing crystal structures that mimic natural minerals (e.g., double-layered hydroxide [111,112,113], nanostructured composites [114,115]), researchers can overcome the inherent limitations of natural counterparts, achieving the precise regulation of active sites and stability [116]. This synthetic strategy and the utilization of unmodified natural minerals are complementary pillars in mineral-mediated catalysis; while synthetic approaches enable tailored control over electronic and structural properties, natural minerals inherently minimize environmental disruption due to their geochemical compatibility. To synergistically advance both pathways, future research on all-natural mineral composites must integrate multidimensional evaluation frameworks that concurrently assess synthetic analogs in terms of mining feasibility, regeneration potential, and ecotoxicological impacts. Such dual-focused efforts will bridge lab-scale innovations to engineered catalytic systems, optimizing the performance of these systems without compromising sustainability.