Removal of fluoride from industrial wastewater by using different adsorbents: A review

Biopolymers to composite adsorbents for sulfate removal: From conventional to sustainable systems

Addressing elevated water salinity is a global water security issue listed among the UN's Sustainable Development Goals (UN-SDGs). Sulfate is a contributor to water salinity due to its high solubility and is a pollutant of increasing global concern. While various water treatment technologies are currently available, the high capital infrastructure and operational costs of such advanced methods have sustainability limits for their widespread adoption. By contrast, adsorption science and technology offers facile treatment and a sustainable mitigation strategy for the removal of oxyanions such as sulfate. A key challenge in adsorption science and technology relates to the molecular selective uptake of sulfate. This has catalysed significant effort towards achieving improved adsorption properties and the development of sustainable adsorbent technology. This review provides coverage of recent literature on synthetic adsorbents to current research on biosorbents that contain chitosan due to its multifunctional colloid and interface properties. The shift from conventional synthesis to green synthetic strategies are highlighted by the preparation of advanced biocomposite materials with unique sulfate adsorption properties. Diverse types of materials from inorganic minerals to polymer-based adsorbents (e.g., polycaprolactones, waste-based materials from fly ash, etc.) is described to highlight their sulfate adsorption properties. Specifically, chitosan and agricultural biomass waste in the form of lignocellulose materials are abundant and promising renewable platforms for the preparation of sulfate adsorbents. In particular, the adsorption properties of chitosan biocomposites are highlighted by its efficacy for adsorption-based remediation of sulfate oxyanions that reveal its promising utility as sulfate adsorbents with unique colloidal and interface properties.

Synthesis of a zeolite-a/MOF-5 composite for the defluoridation of groundwater

Consumption of excessive F- from groundwater harms human health and can cause bone and dental fluorosis. To reduce the excessive F- concentration from groundwater, a novel zeolite-A/MOF-5 (Z-A/MOF-5) composite was synthesized through the solvothermal method. The phase structure, functional group, weight loss, morphology, and elemental composition were characterized by using PXRD, FT-IR, TGA, SEM, and EDX, respectively. The surface charge of the Z-A/MOF-5 composite showed a positive surface up to a pH value of 8.1, which is accessible for the defluoridation of groundwater. The defluoridation efficiency of the Z-A/MOF-5 adsorbent was activated by optimizing defluoridation conditions. The maximum defluoridation efficiency (88.20%) and capacity (11.025 mg g-1) were recorded at a pH of 3, 1.2 g L-1 of adsorbent dose, 6 h of contact time, and 10 mg L-1 initial concentration of F- (C o) at ambient temperature. However, the defluoridation efficiency of the Z-A/MOF-5 composite still maintained its efficiency (85.50%) up to a pH of 7, which is applicable for the defluoridation of groundwater. The defluoridation data were well fitted with the Freundlich isotherm model and pseudo-second-order kinetics, confirming that defluoridation mainly proceeds via chemisorption on the heterogeneous surface of the Z-A/MOF-5 composite. The defluoridation performance of the Z-A/MOF-5 composite was tested on real water samples having 12.25 and 8.5 mg L-1 F- C o taken from Ziway and Kenteri towns, Ethiopia, that reduced the concentration of F- to 1.48 and 0.82 mg L-1, respectively. Interestingly, the recyclability study showed defluoridation efficiencies of 88.20%, 87.90%, 86.80%, 85.60%, 82.00%, and 70.10% for the 1st, 2nd, 3rd, 4th, 5th, and 6th runs, respectively. Consequently, the synthesized composite is a promising adsorbent for practical application.

Removal of Fluoride by Modified Adsorbents: A Review of Modification Methods and Adsorption Mechanisms

Fluoride is ubiquitously present in the natural environment, and its excessive levels can pose serious threats to human health and industrial production. Among various fluoride pollution control methods, adsorption is recognized for its optimal cost-effectiveness and adaptability. The mechanism of fluoride adsorption and the adsorption capacities of various modified adsorbents have been comparatively analyzed :natural minerals, biomass materials, metal oxides, and several emerging types of adsorbents, among which metal-based adsorbents show the best performance. Four modification methods to enhance the performance of adsorbents have been summarized: acid activation, thermal activation, surface functional group modification, and composite materials. Ultimately, this paper identifies the current limitations of adsorption methods for fluoride removal, including insufficient adsorption capacity and a narrow pH range of applicability. These findings are expected to offer valuable insights for the advancement of adsorbent materials research.

Ionic Recognition Controlled by Conformational Change: A DFT Investigation

Ions play a crucial role in the production of important materials and are associated with various health and environmental issues. Noncovalent interactions serve as fundamental tools for controlling the availability of cations and/or anions. Herein, we investigate the ability of two conformations of the 2,6-bis(1,2,3-triazol-4-yl)pyridine molecule to recognize cations (1), such as Li+, Na+, or K+, and anions (2), including F-, Cl-, or Br-. EDA-NOCV analysis demonstrates that the conformers preferentially recognize ions based on the size of the cations (K+ → Na+ → Li+) and anions (Br- → Cl- → F-). The preferential interaction with smaller cations (and anions) arises from the more attractive electrostatic and orbital interactions (N···.cation and C-H···.anion bonds). The presence of electron-donor groups (-NH2) in the first conformer (1) enhances cation recognition through stronger electrostatic N···.cation interactions. Conversely, the presence of electron-acceptor groups (-NO2) in the second conformer (2) facilitates anion recognition via more favorable electrostatic, orbital, and dispersion C-H···.anion interactions. Cation recognition is found to be more favorable in the first conformer than anion recognition in the second due to more attractive electrostatic energy and/or less Pauli repulsive energy associated with (O or primarily N)···.cation interactions in 1 ···.cations compared to (N or mainly C)-H···.anion bonds in 2 ···.anions. These findings provide significant insights into the mechanisms of cation and/or anion recognition through different conformations using the same base structure and can inform the design of molecules with enhanced functionalities.

Facile construction of zirconium/iron bimetallic organic frameworks for fluoride efficient removal from aqueous phase: An integrated experimental and theoretical investigation

This work presents the synthesis of Zr/Fe bimetallic organic frameworks (Zr/Fe-UiO-66) with varying compositions via a straightforward solvothermal method, targeting fluoride ions (F-) removal from the aqueous phase. Adsorption experiments elucidated the effect of factors (i.e., adsorbent dosage, initial concentration (C0), temperature, contact time and pH) on fluoride adsorption, and the parameters were optimized. The results show that the Zr/Fe-UiO-66(C) achieved the maximal uptake capacity of 164.4 mg/g, with the conditions of pH = 5.0, T = 298 K, C0 = 190 mg/L. The adsorption behavior of fluoride on Zr/Fe-UiO-66 can be well followed with the pseudo-second-order (PSO) kinetic model and the Sips isotherm model, described as the spontaneous, chemical driven and endothermic process. The adsorption mechanism was comprehensively explained by characterizations and microscopic simulations, such as molecular dynamics methods (MD) and independent gradient model analysis (IGM), which involves the chemical bonding, hydrogen-bond interaction and electrostatic interactions. Furthermore, Zr/Fe-UiO-66(C) exhibited excellent fluoride ion selectivity and superior stability. After 5 cycles of adsorption, Zr/Fe-UiO-66(C) maintained the removal efficiency of 83.4 % for F-. This research provides significant insights into the development of bimetallic metal-organic framework materials and fluoride removal research.

Morphoanatomical and metabolic changes in Bixa orellana L. (Bixaceae) exposed to atmospheric fluorine

Fluorine (F) is a toxic element for plants and can cause damage even at low concentrations. Brazil has several anthropogenic sources of F; however, relatively few native species have been studied. Thus, the objective of this study was to evaluate the responses promoted by F in Bixa orellana, a species native to South America and economically important for producing bixin, a pigment used as a natural dye in the food, cosmetic, and textile industries. The plants were subjected to simulated rain containing 0, 10, 20, and 40 mg/L of F. Visual analyses were performed during the experiment, and at the end, gas exchanges, photosynthetic pigments, and F were quantified, and leaf samples were collected for light and scanning electron microscopy and cell death testing. The concentration of F in B. orellana increased according to the concentration used in each treatment. There was a reduction in CO2 assimilation (A), stomatal conductance (gs), respiration (Rd), and photosynthetic pigment content in all plants exposed to the pollutant. Chloroses, necroses, and wrinkling occurred in the leaves of plants exposed to F. The stress also resulted in anatomical damage to the leaves, which showed atrophied epidermal cells and flaccid glandular trichomes. Laticifers and spongy and palisade parenchyma cells were plasmolyzed. Additionally, blue-stained cell groups indicating cell death were observed in the leaves of all treatments containing F. It is concluded that B. orellana is sensitive to F and responds quickly to the presence of this pollutant, making it a potential phytoindicator species for F in the atmosphere in possible biomonitoring programs.

Defluorination of water solutions and glass industry wastewater using a magnetic pineapple hydrochar nanocomposite modified with a covalent organic framework

This study investigates the development and use of a novel magnetic composite, PAH/MnFe2O4/COF, synthesized from pineapple hydrochar (PAH) and modified with a covalent organic framework (COF) for Fluoride (Flu) elimination from water and industrial wastewater. Fluoride contamination poses serious health risks, making its removal essential. The composite was analyzed using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and other methods, confirming its successful synthesis with a surface area of 102.960 m2/g and a saturation magnetization of 19.548 emu/g. The adsorption efficiency was modeled using a second-order polynomial, with a high R2 value of 0.9958, indicating excellent predictive accuracy. Optimal conditions for 99.54% Flu removal included a pH of 3.5, an adsorber mass of 1 g/L, a temperature of 50 °C, an adsorption time of 60 min, and a Flu concentration of 5 mg/L. The adsorption followed a pseudo-second-order model, indicating rapid chemical adsorption, while thermodynamic analysis revealed a spontaneous, endothermic process, supported by negative Gibbs free energy (ΔG°) values and an enthalpy (ΔH°) of 95.253 kJ/mol. The intraparticle diffusion model indicated multiple mechanisms were involved, including intraparticle diffusion and external surface adsorption. The composite showed a high adsorption capacity of 40.629 mg/g, outperforming the unmodified hydrochar. Additionally, the composite effectively reduced Flu ions, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and total dissolved solids (TDS) levels in industrial wastewater. These findings demonstrate that the PAH/MnFe2O4/COF composite is an efficient and promising adsorber for addressing the defluorination of water, offering a potential solution to environmental and public health issues.

Effects of Chelators on Fluoride Removal by AlCl3 and Al13 Coagulation: Performance and Mechanism

Aluminum (Al) coagulation is one of the most widely used techniques for the defluoridation of industrial effluents. This study examined the influence of two common chelating agents, i.e., ethylenediaminetetraacetic acid (EDTA) and citric acid (CA), on fluoride removal during coagulation using monomeric Al (AlCl3) and polymeric aluminum species [Al13O4(OH)24(H2O)127+, Al13]. The results revealed that EDTA reduced the fluoride removal efficiency by up to 95.4% with AlCl3 and by 28.3% with Al13. In contrast, CA inhibited fluoride removal by up to 100% with AlCl3 and 90.6% with Al13. Both chelators impaired fluoride removal primarily by disrupting floc formation. Advanced analytical techniques, including 19F/27Al NMR spectroscopy combined with DFT calculations, demonstrated that this interference was due to the formation of EDTA-Al-F ternary complexes and Al-CA binary complexes. Additionally, the formation of a bridging fluoride (μ-F) in the Al13 structure enhanced its thermodynamic stability against chelators. Specifically, Al13 maintained structural stability even in the presence of up to 1.50 mmol/L EDTA, whereas CA progressively destabilized the Al13 structure by forming soluble Al-CA complexes. These findings are believed to help guide the rational design of Al-based coagulants and optimize water treatment strategies aimed at defluoridation of industrial effluents.

The Role of Fluorine in Polyanionic Cathode Materials for Sodium-Ion Batteries

With the growing global demand for renewable energy and the increasing scarcity of lithium resources, sodium-ion batteries have received extensive attention and research as a potential alternative. Among many cathode materials for sodium-ion batteries, polyanion materials are favored for their high operating voltage, stable cycling performance, and good safety. However, the low electronic conductivity and low energy density of polyanionic materials limit their potential for large-scale commercial applications. To overcome this challenge, various strategies have been explored to improve their electrochemical performance. Among them, fluorine doping has been proven to be an effective means. In this study, we have systematically explored the effects of trace fluorine doping and mass fluorine substitution on the structure, dynamics, and electrochemistry of polyanionic cathode materials for sodium-ion batteries and deeply analyzed their reaction mechanisms. The analysis results show that trace fluorine doping can effectively improve the electronic conductivity of the material, thus enhancing its electrochemical performance. A large amount of fluorine substitution can effectively improve the voltage plateau of the material, thus enhancing its energy density. However, the environmental and safety challenges associated with the introduction of fluorine should also be addressed. Overall, the introduction of fluorine in polyanionic cathode materials can further optimize the electronic structure and electrochemical performance, thus realizing the wide application of high-performance sodium-ion batteries and making them a competitive battery technology.

Biodiesel production, calcium recovery, and adsorbent synthesis using dairy sludge

Dairy sludge (DS) consists of organic compounds such as lipids and valuable inorganic elements. Biodiesel recovery from dairy sludge extract (DSE), using conventional acid (trans)esterification yielded only 16.5 wt%. In contrast, non-catalytic (trans)esterification generated a substantially higher biodiesel yield of approximately 74.0 wt% due to the method's tolerance for impurities. Defatted dairy sludge (DDS) contained a higher Ca concentration than DS. DDS-produced biochar (DDSB) increased its Ca concentration predominantly in the form of CaO. 91.1% of the Ca was recovered from the DDSB containing Ca. The Ca remaining in the biochar residue (DDSBR) after Ca recovery was in the form of CaCO3. The porous structure developed as the Ca dissolved, implying that DDSBR could be an effective pollutant adsorbent. In this study, a method is proposed to maximize the utilization of DS by producing biodiesel, recovering Ca content, and using it as a pollutant adsorbent.

Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR)

Water treatment residual (WTR) is a burden for many water treatment plants due to the large volumes and associated management costs. In this study, we transform aluminum-salt WTR (Al-WTR) into ceramsite (ASC) to recover phosphate from challenging waters. ASC showed remarkably higher specific surface area (SSA, 70.53 m2/g) and phosphate adsorption capacity (calculated 47.2 mg P/g) compared to previously reported ceramsite materials (< 40 m2/g SSA and < 20 mg P/g). ASC recovered over 94.9% of phosphate across a wide pH range (3 - 11) and generally sustained > 90% of its phosphate recovery at high concentrations of competing anions (i.e., Cl-, F-, SO4 2-, or HCO3 -) or humic acid (HA). We challenged the material with real municipal wastewater at 10°C and achieved simultaneous phosphate (>97.1%) and COD removal (71.2%). Once saturated with phosphate, ASC can be repurposed for landscaping or soil amendment. The economic analysis indicates that ASC can be a competitive alternative to natural clay-based ceramsite, biochar, or other useful materials. Therefore, ASC is an eco-friendly, cost-effective adsorbent for phosphate recovery from complex waters, shedding light upon a circular economy in the water sector.

Controllable and selective fluoride precipitation from phosphate-rich wastewater

Industrial wastewater containing high levels of fluoride and phosphate poses significant environmental challenges and results in the waste of non-renewable resources. This study investigates the use of La(OH)3 as a precipitating agent to selectively remove and separate fluoride from phosphate in such wastewater. The findings indicate that fluoride removal efficiency is highly dependent on the pH level and La(OH)3 dosage. Using Response Surface Methodology, the optimal conditions for fluoride precipitation were identified as a pH range of 1.0 to 2.5, a reaction time of 60-80 min, a La/3F molar ratio of 2.0, and reaction temperature of 25 °C. Under these parameters, the fluoride removal efficiency exceeded 96.9 %, while phosphate removal remained around 7.2 %. Further Density Functional Theory calculations and characterization confirmed La(OH)3 has a strong affinity for fluoride than phosphate under acidic conditions, leading to the formation of a LaF3 precipitate without forming LaPO4, effectively separating fluoride from phosphate. These results demonstrate an efficient strategy for treating wastewater with high fluoride and phosphate content, enabling the selective precipitation and recovery of these elements for sustainable management.

Facile preparation of zirconium(IV) immobilized carboxymethyl cellulose/multiwalled carbon nanotubes gels by radiation technique and its selective fluoride removal

Removal of excessive fluorine in the waterbody environment and the Zn hydrometallurgical system is an urgent problem. In this paper, zirconium oxychloride immobilized carboxymethyl cellulose/carboxymethyl multiwalled carbon nanotube (CMC+MWCCNT-ZrOCl2) gels are facilely prepared by radiation technique. The addition of MWCCNT endows the CMC-ZrOCl2 gel a typical nanotubes/fiber structure, also increase the gel fraction of the gel. The selective adsorption of fluoride from single or co-existed anions was investigated. The adsorption isotherms can be well fitted by both the Langmuir and Freundlich model. The calculated maximum adsorption capacity was 36.657 mg/g. The selectivity coefficients of CMC+MWCCNT-ZrOCl2 for fluoride versus NO3-, PO43-, and SO42- are 140.34, 10.953, and 72.572, respectively. Also, CMC+MWCCNT-ZrOCl2 can be used as a potential adsorbent for selective removing F- from high concentration SO42- solution. The adsorption mechanism was investigated by XPS analyses.

Low cost materials for fluoride removal from groundwater

In several parts of the world, high fluoride concentrations in groundwater have been reported.Fluoride concentrations above the World Health Organization's (WHO) threshold level of 1.5 mg/L in drinkable water pose a health concern for communities and the environment. The distribution of fluoride is mainly related to the geological environment: rocks that contain fluorine, for example basalt, shale, and granite, release their respective minerals containing fluoride to the groundwater by dissolution. Excessive fluoride intake leads to dental and skeletal fluorosis, fragile bones, cancer, infertility, damage to the brain function, Alzheimer syndrome, and thyroid disorder. Cheap, abundant, and locally available fluoride removal techniques are needed to meet the requirement for fluoride-free drinking water in developing countries, especially in rural communities. Different conventional methods, such as membrane technologies, ion exchange, coagulation and precipitation techniques, are employed to remove fluoride from drinking water. However, only a few of these techniques can be applied at large-scale in developing countries due to their high investment costs, high maintenance and operating costs, and the possibility of producing toxic intermediates during the treatment process. Unlike conventional methods, adsorption is a promising technology due to its simple operation in a batch or continuous systems, simple design, low-cost of operation and wide range of locally available adsorbents. Adsorption is widely applied for removing fluoride from groundwater and wastewater, effectively maintaining water quality and taste. Based on the review, adsorption stands out as the best method for fluoride removal, considering surface modification and regeneration to increase the efficiency of adsorbent materials. This makes it an ideal solution for ensuring safe drinking water in resource-limited settings.

Experimental and DFT calculation study on the efficient removal of high fluoride wastewater from metallurgical wastewater by kaolinite

Fluoride pollution and water scarcity are urgent issues. Reducing fluoride concentration in water is crucial. Kaolinite has been used to study adsorption and fluoride removal in water and to characterize material properties. The experimental results showed that the adsorption capacity of kaolinite decreased with increasing pH. The highest adsorption of fluoride occurred at pH 2, with a capacity of 11.1 mg/g. The fluoride removal efficiency remained high after four regeneration cycles. The fitting results with the Freundlich isotherm model and the external diffusion model showed that the non-homogeneous adsorption of kaolinite fit the adsorption behavior better. Finally, the adsorption mechanism was analyzed by FT-IR and XPS. The binding energies of various adsorption sites and the chemical adsorption properties of atomic states were discussed in relation to DFT calculations. The results showed that Al and H sites were the main binding sites, and the bonding stability for different forms of fluoride varies, with the size of Al-F (-7.498 eV) > H-F (-6.04 eV) > H-HF (-3.439 eV) > Al-HF (-3.283 eV). Furthermore, the density of states and Mulliken charge distribution revealed that the 2p orbital of F was found to be active in the adsorption process and was the main orbital for charge transfer.

Bibliometric analysis and systematic review of fluoride-containing wastewater treatment: Development, hotspots and future perspectives

Water pollution with fluoride can cause dental fluorosis, skeletal deformities, and other diseases, posing serious harm to human health. To understand the development status, research hotspots, and frontier trends in fluoride-containing wastewater (FCW) treatment, this study employed bibliometric methods to visually analyze 2840 publications related to FCW treatment from the Web of Science Core Collection (WOSCC) database. The "bibliometrix" package in R language, VOSviewer, and CiteSpace visualization software were utilized for the analysis. The results revealed a fluctuating upward trend in the annual number of publications, indicating ongoing deepening and development of research in this field. India and China exhibited the strongest research capacity, forming a cooperation network centered around these two countries. High-impact journals such as Desalination and Water Treatment, Journal of Hazardous Materials, and Chemical Engineering Journal frequently publish research related to FCW treatment. Keyword co-occurrence and burst analysis revealed that the current research hotspots in FCW treatment primarily focus on treatment methods (ion exchange, chemical coagulation/precipitation, adsorption, electrochemical, membrane separation, and fluidized bed crystallization), adsorption mechanism, and adsorbent design and optimization. Future research will likely focus on developing efficient treatment technologies and adsorption materials for FCW, as well as the recovery of fluoride resources from FCW, highlighting a dual approach to environmental sustainability and resource management. By employing bibliometrics, this study outlines the development status of FCW treatment and predicts the field's future trends, providing insights for understanding the development trajectory of this field.

Insights of using microbial material in fluoride removal from wastewater: A review

Fluoride is an essential trace element for the human body, but excessive fluoride can cause serious environmental and health problems. Therefore, developing efficient fluoride removal technologies is crucial. This review summarizes the progress made in using microbial materials to remove fluoride from wastewater, covering strategies that involve pure cultures of bacteria, fungi, and algae, as well as modified microbial materials and bioreactors. Live microorganisms exhibit high efficiency in adsorbing low concentrations of fluoride, while modified microbial materials are more suitable for treating high concentrations of fluoride. The review discusses the adsorption mechanisms and influencing factors of these technologies, and evaluates their practical application potential through techno-economic analysis. Finally, future research directions are proposed, including the optimization of modification technologies and the selection of effective microbial species, providing theoretical guidance and a basis for future microbial defluoridation technologies.

Remediation of fluoride-contaminated wastes: Chelator-assisted washing and subsequent immobilization using CaO and H3PO4

Fluoride (F) contamination in industrial waste is a significant challenge for sustainable materials recycling. Existing techniques for mitigating F contamination focus on immobilization, converting F compounds to insoluble forms while leaving the total F content untreated. Chelator-assisted washing is considered a promising alternative remediation strategy that can indirectly release F by entrapping and dissolving F-bearing minerals. This study evaluates the effectiveness of chelator-assisted washing in removing F from three real F-contaminated waste samples (TCS-49, TCS-51, and TCS-52) by treating with four different chelators, ethylenediaminetetraacetic acid (EDTA), ethylenediamine N,N'-disuccinic acid (EDDS), diethylenetriaminepentaacetic acid (DTPA), and 3-hydroxy-2,2'-imino disuccinic acid (HIDS). The influence of key washing variables, including chelator type, solution pH, chelator concentration, washing time, and liquid-to-solid (L/S) ratio toward F extraction was assessed and optimized for attaining the maximum extraction. All chelators exhibited the highest F extraction from TCS-49 and TCS-51 at pH 11, whereas in TCS-52 it showed a discrete extraction pattern. Under optimized conditions (concentration, 10 mmol L-1; pH, 11; washing duration, 3 h; and L/S ratio, 10:1), EDTA outperformed the other chelators, enhancing F extraction by 2.1 and 1.2 times for TCS-49 and TCS-51, respectively, compared with those of control treatments. However, for TCS-52, the efficiency of EDTA was analogous to that of the control under the same washing conditions. The linear correlation between the extracted F and F-containing minerals suggests that the chelator-induced F removal from contaminated waste involves the entrapment and dissolution of F-bearing minerals, especially Ca and Fe. The subsequent post-washing immobilization of chelator-washed waste residues using CaO or H3PO4 significantly reduced the content of leachable F under the regulatory limit.

Fluoride exposure-induced gut microbiota alteration mediates colonic ferroptosis through N6-methyladenosine (m6A) mediated silencing of SLC7A11

Fluoride exposure is widespread worldwide and poses a significant threat to organisms, particularly to their gastrointestinal tracts. However, due to limited knowledge of the mechanism of fluoride induced intestinal injury, it has been challenging to develop an effective treatment. To address this issue, we used a series of molecular biology in vitro and in vivo experiments. NaF triggered m6A mediated ferroptosis to cause intestinal damage. Mechanistically, NaF exposure increased the m6A level of SLC7A11 mRNA, promoted YTHDF2 binding to m6A-modified SLC7A11 mRNA, drove the degradation of SLC7A11 mRNA, and led to a decrease in its protein expression, which eventually triggers ferroptosis. Moreover, NaF aggravated ferroptosis of the colon after antibiotics destroyed the composition of gut microbiota. 16 S rRNA sequencing and SPEC-OCCU plots, Zi-Pi relationships, and Spearman correlation coefficients verified that Lactobacillus murinus (ASV54, ASV58, and ASV82) plays a key role in the response to NaF-induced ferroptosis. Collectively, NaF-induced gut microbiota alteration mediates severe intestinal cell injury by inducing m6A modification-mediated ferroptosis. Our results highlight a key mechanism of the gut in response to NaF exposure and suggest a valuable theoretical basis for its prevention and treatment.

Fluoride induces immunotoxicity by regulating riboflavin transport and metabolism partly through IL-17A in the spleen

The impairment of the immune system by fluoride is a public health concern worldwide, yet the underlying mechanism is unclear. Both riboflavin and IL-17A are closely related to immune function and regulate the testicular toxicity of fluoride. However, whether riboflavin or IL-17A is involved in fluoride-induced immunotoxicity is unknown. Here, we first established a male ICR mouse model by treating mice with sodium fluoride (NaF) (100 mg/L) via the drinking water for 91 days. The results showed that fluoride increased the expression of the proinflammatory factors IL-1β and IL-17A, which led to splenic inflammation and morphological injury. Moreover, the expression levels of the riboflavin transporters SLC52A2 and SLC52A3; the transformation-related enzymes RFK and FLAD1; and the key mitochondrial functional determinants SDH, COX, and ATP in the spleen were measured via real-time PCR, Western blotting, and ELISA. The results revealed that fluoride disrupted riboflavin transport, transformation, metabolism, and mitochondrial function. Furthermore, wild-type (WT) and IL-17A knockout (IL-17A-/-) C57BL/6 J male mice of the same age were treated with NaF (24 mg/kg·bw, equivalent to 100 mg/L) and/or riboflavin sodium phosphate (5 mg/kg·bw) via gavage for 91 days. Similar parameters were evaluated as above. The results confirmed that fluoride increased riboflavin metabolism through RFK but not through FLAD1. Fluoride also affected mitochondrial function and activated neutrophils (marked with Ly6g) and macrophages (marked with CD68) in the spleen. Interestingly, IL-17A partly mediated fluoride-induced riboflavin metabolism disorder and immunotoxicity in the spleen. This work not only reveals a novel toxic mechanism for fluoride but also provides new clues for exploring the physiological function of riboflavin and for diagnosing and treating the toxic effects of fluoride in the environment.

Recovery of Li from waste Li-containing Al electrolytes with high F and Na contents by using a CaO roasting-water leaching process

With the increasing demand for Li, the recovery of Li from solid waste, such as Li-containing Al electrolytes, is receiving growing attention. However, Li-containing Al electrolytes often contain large amounts of F, leading to environmental pollution. Herein, a new method for preparing water-soluble Li salt from waste Li-containing Al electrolytes with high F and Na contents is proposed based on CaO roasting and water leaching. The effects of different roasting and leaching conditions on the Li leaching efficiency and reaction pathway were systematically investigated. Under the optimum processing conditions, the Li leaching efficiency reached 98%, while those of Na and F were 98.41% and 0.24%, respectively. Phase evolution analysis showed that the addition of CaO promoted the conversion of LiF and Na2LiAlF6 to Li2O, whereas F entered the slag phase as CaF2, which could be reused as a raw material for steel refinement. Overall, this study proposes an efficient and environmentally friendly method for the treatment and resource utilization of waste Al electrolytes with high F and Na contents.

Facile fabrication of graphene oxide and rare earth based metal organic frameworks decorated alginate and chitosan biopolymeric hybrid materials for defluoridation studies

Fluorosis disease can be prevented by the defluoridated water. Hence, the present work focused on the fabrication of hybrid materials using graphene oxide (GO) and Ce-based metal organic frameworks namely cerium fumarate (Ce-Fu) which gives GO/Ce-Fu for defluoridation of water. Further, the powdered GO/Ce-Fu was dispersed with alginate (Alg) and chitosan (CS) biopolymeric matrixes to give GO/Ce-Fu/Alg-CS biopolymeric hybrid beads for defluoridation investigations. The developed GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads have defluoridation capacities (DCs) of 4.410 and 4.753 mg/g within 30 min. The fabricated GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads were analyzed by XRD, FTIR, TGA, BET, SEM and EDAX studies. The performance of fluoride adsorption influencing parameters such as dosage, contact time, solution pH, interfering anions and temperature studies were optimized with batch scale. Thermodynamic, adsorption isotherms and kinetic studies were carried out using hybrid materials to find the nature and order of fluoride adsorption. The fluoride adsorption mechanism of GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads was investigated. The performance of recyclability of the hybrid materials was examined. In addition, the field studies of hybrid materials were also explored to identify their field suitability nature.

Formation of Aluminum-Fluoride Complexes Compromises Defluoridation Efficiency of Aluminum-Based Coagulation

Aluminum-based coagulation has long been regarded as a reliable and cost-effective process for the defluoridation of industrial effluents. However, such a well-recognized viewpoint is challenged by the underestimation of fluoride levels in treated effluents. Herein, we developed a systematic protocol to distinguish different fluoride species, including free F-, exchangeable fluoride (EF), and nonexchangeable fluoride (NEF). We demonstrated that EF forms complexes with octahedral aluminum (AlO6) on the surface of polyaluminum and can be exchanged with (1,2-cyclohexylenedinitrilo)-tetraacetic acid (CDTA). However, NEF is incorporated with tetrahedral aluminum (AlO4) at the core of polyaluminum, as confirmed by 19F/23Al NMR and ESI-MS analysis, and cannot be exchanged with CDTA due to steric hindrance. Increasing the aluminum coagulant dosage effectively reduced free F- levels in photovoltaic and electroplating effluents to below 1 mg/L. However, the total fluoride content, with over half in the form of EF and NEF, was above 2 mg/L, exceeding the discharge limit regulated by many local governments of China. Furthermore, both EF and NEF can gradually transform to free F- in natural waters. Our findings indicate that aluminum-based coagulation inevitably accompanies the formation of substantial amounts of EF and NEF, compromising its defluoridation efficiency toward industrial effluents.

Comprehensive review of industrial wastewater treatment techniques

Water is an indispensable resource for human activity and the environment. Industrial activities generate vast quantities of wastewater that may be heavily polluted or contain toxic contaminants, posing environmental and public health challenges. Different industries generate wastewater with widely varying characteristics, such as the quantity generated, concentration, and pollutant type. It is essential to understand these characteristics to select available treatment techniques for implementation in wastewater treatment facilities to promote sustainable water usage. This review article provides an overview of wastewaters generated by various industries and commonly applied treatment techniques. The characteristics, advantages, and disadvantages of physical, chemical, and biological treatment methods are presented.

Efficient recovery of highly pure CaF2 from fluorine-containing wastewater using an icy lime solution

Developing a feasible and low-cost strategy for the recovery of calcium fluoride efficiently from fluoride-containing wastewater is very essential for the recycle of fluoride resources. Herein, a modified lime precipitation method was employed to recover CaF2 from fluorinated wastewater using a special icy lime solution. Intriguingly, the highest F- removal was greater than 95% under the optimal condition, leaving a fluoride concentration from 200 to 8.64 mg/L, while the lime dosage was much lower than that of industry. Importantly, spherical-shaped CaF2 particles with a 93.47% purity and size smaller than 600 nm were recovered, which has a high potential for the production of hydrofluoric acid. Besides, the precipitation was significantly affected by Ca/F molar ratio, stirring time, temperature, and solution pH. Furthermore, the thermodynamics and kinetics were investigated in detail to reveal the crystallization process. As a result, the defluorination reaction followed the pseudo-second order reaction kinetics model. Also, CO2 in the air adversely influenced the CaF2 purity. Based on this facile method, a high lime utilization efficiency was applied to defluorination, which contributed to protecting the environment and saving costs. This study, therefore, provides a feasible approach for the green recovery of fluorine resources and has significance for related research.

Performance and mechanism of La-Fe metal-organic framework as a highly efficient adsorbent for fluoride removal from mine water

Water fluoride pollution has caused non-negligible harm to the environment and humans, and thus it is crucial to find a suitable treatment technology. In this study, La-Fe@PTA adsorbent was synthesized for the defluoridation of mine water. The results showed that the optimum conditions for defluoridation by La-Fe@PTA were pH close to 7.0, the initial F- concentration of 10 mg/L, the dosage of 0.5 g/L and the adsorption time of 240 min. Compared with SO42‒, Cl‒, NO3‒, Ca2+ and Mg2+, CO32‒ and HCO3‒ presented severer inhibition on fluoride uptake by La-Fe@PTA. The adsorption process fits well with the pseudo-second-order kinetic model and Freundlich model, and the maximum adsorption capacity of Langmuir model was 95 mg/g. Fixed-bed adsorption results indicated that fluoride in practical fluorinated mine water could be effectively removed from 3.6 mg/L to less than 1.5 mg/L within 130 bed volume (BV) by using 1.5 g La-Fe@PTA. Furthermore, the adsorbent still had good adsorption capacity after regeneration, which confirms the great application potential of La-Fe@PTA as a fluoride ion adsorbent. The mechanism analysis showed that La-Fe@PTA adsorption of fluorine ions is a physicochemical reaction driven by electrostatic attraction and ion exchange.

Carbon doping enhances the fluoride removal performance of aluminum-based adsorbents

Excessive fluoride presence in water poses significant environmental and public health risks, necessitating the development of effective remediation techniques. Conventional aluminum-based adsorbents face inherent limitations such as limited pH range and low adsorption capacity. To overcome these challenges, we present a facile solvent-thermal method for synthesizing a carbon-doped aluminum-based adsorbent (CDAA). Extensive characterization of CDAA reveals remarkable features including substantial carbon-containing groups, unsaturated aluminum sites, and a high pH at point of zero charge (pHpzc). CDAA demonstrates superior efficiency and selectivity in removing fluoride contaminants, surpassing other adsorbents. It exhibits exceptional adaptability across a broad pH spectrum from 3 to 12, with a maximum adsorption capacity of 637.4 mg/g, more than 110 times higher than alumina. The applicability of the Langmuir isotherm and pseudo-second-order models effectively supports these findings. Notably, CDAA exhibits rapid kinetics, achieving near-equilibrium within just 5 min. Comprehensive analyses utilizing Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) offer detailed insights into the mechanisms involving electrostatic attraction, ion exchange, and ligand exchange. Carbon-based groups play a role in ligand exchange processes, synergistically interacting with the unsaturated aluminum structure to provide a multitude of adsorption sites. The exceptional attributes of CDAA establish its immense potential as a transformative solution for the pressing challenge of fluoride removal from water sources.

Process Intensification for Enhanced Fluoride Removal and Recovery as Calcium Fluoride Using a Fluidized Bed Reactor

This study explored the feasibility of fluoride removal from simulated semiconductor industry wastewater and its recovery as calcium fluoride using fluidized bed crystallization. The continuous reactor showed the best performance (>90% fluoride removal and >95% crystallization efficiency) at a calcium-to-fluoride ratio of 0.6 within the first 40 days of continuous operation. The resulting particle size increased by more than double during this time, along with a 36% increase in the seed bed height, indicating the deposition of CaF2 onto the silica seed. The SEM-EDX analysis showed the size and shape of the crystals formed, along with the presence of a high amount of Ca-F ions. The purity of the CaF2 crystals was determined to be 91.1% though ICP-OES analysis. Following the continuous experiment, different process improvement strategies were explored. The addition of an excess amount of calcium resulted in the removal of an additional 6% of the fluoride; however, compared to this single-stage process, a two-stage approach was found to be a better strategy to achieve a low effluent concentration of fluoride. The fluoride removal reached 94% with this two-stage approach under the optimum conditions of 4 + 1 h HRT combinations and a [Ca2+]/[F-] ratio of 0.55 and 0.7 for the two reactors, respectively. CFD simulation showed the impact of the inlet diameter, bottom-angle shape, and width-to-height ratio of the reactor on the mixing inside the reactor and the possibility of further improvement in the reactor performance by optimizing the FBR configuration.

Approaches for the Efficient Removal of Fluoride from Groundwater: A Comprehensive Review

Contamination of groundwater with fluoride represents a significant global issue, with high concentrations posing serious public health threats. While fluoride is a critical element in water, excessive levels can be detrimental to human health and potentially life-threatening. Addressing the challenge of removing fluoride from underground water sources via nanotechnological approaches is a pressing concern in environmental science. To collate relevant information, extensive literature searches were conducted across multiple databases, including Google Scholar, PubMed, Scopus, Web of Science, the American Chemical Society, Elsevier, Springer, and the Royal Society of Chemistry. VOS Viewer software version 1.6.20 was employed for a systematic review. This article delivers an exhaustive evaluation of various groundwater fluoride removal techniques, such as adsorption, membrane filtration, electrocoagulation, photocatalysis, and ion exchange. Among these, the application of nanoparticles emerges as a notable method. The article delves into nano-compounds, optimizing conditions for the fluoride removal process and benchmarking their efficacy against other techniques. Studies demonstrate that advanced nanotechnologies-owing to their rapid reaction times and potent oxidation capabilities-can remove fluoride effectively. The implementation of nanotechnologies in fluoride removal not only enhances water quality but also contributes to the safeguarding of human health.

Optimization of Calcium Fluoride Crystallization Process for Treatment of High-Concentration Fluoride-Containing Semiconductor Industry Wastewater

This study utilized a fluidized bed reactor (FBR) for fluoride removal from high-concentration fluoride-ion-containing simulated semiconductor industry wastewater and recovered high-purity CaF2 crystals. The effects of hydraulic retention time (HRT), pH, Ca2+ to F- ratio, upflow velocity, seed size and seed bed height were investigated by performing lab-scale batch experiments. Considering fluoride removal and CaF2 crystallization efficiency, 5 h HRT, pH 6, seed height of 50 cm and [Ca2+]/[F-] ratio of 0.55 (mol/mol) were found to be optimum. The effect of the interaction between the important process parameters on fluoride removal was further analyzed using response surface methodology (RSM) experimental design. The results showed that all the individual parameters have a significant impact (p = 0.0001) on fluoride removal. SEM-EDX and FTIR analysis showed the composition of the crystals formed inside FBR. HR-XRD analysis confirmed that the crystalline structure of samples was mainly CaF2. The results clearly demonstrated the feasibility of silica seed material containing FBR for efficient removal and recovery of fluoride as high-purity calcium fluoride crystals.

Industrial fluoride emissions and their spatial characteristics in the Nansi Lake Basin, Eastern China

Excessive fluoride emissions threaten ecological stability and human health. Previous studies have noted that industrial sources could be significant. However, quantifying industrial fluoride emissions has not been yet reported. In this study, both bottom-up and top-down approaches were used to estimate the fluoride emissions in the Nansi Lake Basin. Global and local spatial autocorrelation were adopted to reveal the spatial agglomeration effects. The fluoride emissions calculated by the bottom-up approach were larger than those calculated by the top-down method. The highest fluoride input mainly occurred in Zoucheng and Mudan. The highest fluoride emissions mainly occurred in Zoucheng and Rencheng using the bottom-up approach. The highest fluoride emissions mainly occurred in Zoucheng and Yanzhou using the top-down approach. Mining and washing of bituminous coal and anthracite (BAW) was the most significant source of fluoride input and emissions. A significant spatial agglomeration effect of fluoride emissions was found. These findings could provide a method for accurate industrial fluoride emission estimation, complement the critical data on the fluoride emissions of main industrial sectors, and provide a scientific basis for tracing fluoride sources.

Development of innovative and green adsorbents for in situ cleanup of fluoride-polluted groundwater: Mechanisms and field-scale studies

In this study, the magnesium oxide (MgO)-based adsorbents [granulated MgO aggregates (GA-MgO) and surface-modified MgO powder (SM-MgO)] were developed to remediate a fluoride-contaminated groundwater site. Both GA-MgO and SM-MgO had porous, spherical, and crystalline structures. Diameters for GA-MgO and SM-MgO were 1-1.7 mm and 1-10 μm, respectively. The pseudo second-order dynamic adsorption and the Freundlich isotherm could be applied to express the chemical adsorption phenomena. The monolayer adsorption was the dominant mechanism at the initial adsorption period. During the latter part of fluoride adsorption, the multilayer adsorption became the dominant mechanism for fluoride removal from the water phase, which also resulted in the increased adsorption capacity. Higher hydroxide, phosphate, and carbonate concentrations caused a decreased fluoride removal efficiency due to the competition of sorption sites between fluoride and other anions with similar electronic properties. Fluoride removal mechanism using GA-MgO and SM-MgO as the adsorbents was mainly carried out by the chemical adsorption. Reaction paths contained two main processes: (1) formation of magnesium hydroxide after the reaction of MgO with water, and (2) the hydroxyl group of the magnesium hydroxide was replaced by fluoride ions to form magnesium fluoride precipitation. Results from column tests show that up to 61 and 73% of fluoride removal (initial fluoride concentration = 9.3 mg/L) could be obtained after 50 pore volumes of groundwater pumping with GA-MgO and SM-MgO injection, respectively. The GA-MgO system could be applied to contain and remediate fluoride-contaminated groundwater, and SM-MgO could be applied as an immediate fluoride removal alternative to achieve a rapid pollutant removal for emergency responses. Up to 71% of fluoride removal (fluoride concentration = 10.8 mg/L) could be obtained with GA-MgO injection after 30 days of operation. The developed GA-MgO system is a potential and green remediation alternative to contain the fluoride plume significantly.

Performance of three anion-exchange membranes in fluoride ions removal by electrodialysis

The performance of three anion-exchange membranes (AEMs) in the fluoride ions reduction by electrodialysis (ED) is performed on real and synthetic water. The electric potential method measures the potential difference (PD) between two synthetic anion solutions separated by ACS, AFN and AXE membranes. The selectivity of these three AEMs coupled with the membrane CMX, is a cation-exchange membrane (CEM) towards different ions. The removal rate is influenced by the thickness of the polarization layer (PL) which reduces the material transfer and provides an additional barrier. The greater the thickness δ of the PL, the longer the passage time and consequently the removal rate of anions is small. Using the unstirred layer model, δ for each ion will be determined. According to the potential measurement method, none of the tested AEMs are selective to fluoride ions and the order of selectivity is as follows: AFN> AXE> ACS. Best membrane couple selected for fluoride ion removal is ACS/CMX and ion selectivity follows the order: Cl-> NO-3>F-> HCO-3> SO42-. For ACS membrane, both the demineralization rate (DR) and δ of fluoride ions are influenced by the initial concentration of the co-ion according to the following order: NO-3> Cl-> HCO-3> SO2-4.

Enhancing fluoride removal from wastewater using Al/Y amended sludge biochar

This study explored the potential of utilizing aluminum and yttrium amended (Al/Y amended) sewage sludge biochar (Al/Y-CSBC) for efficient fluoride removal from wastewater. The adsorption kinetics of fluoride on bimetallic modified Al/Y-CSBC followed the pseudo-second-order model, while the adsorption isotherm conformed to the Freundlich equation. Remarkably, the material exhibited excellent fluoride removal performance over a wide pH range, achieving a maximum adsorption capacity of 62.44 mg·g-1. Moreover, Al/Y-CSBC demonstrated exceptional reusability, maintaining 95% removal efficiency even after six regeneration cycles. The fluoride adsorption mechanism involved ion exchange, surface complexation, and electrostatic adsorption interactions. The activation and modification processes significantly increased the specific surface area of Al/Y-CSBC, leading to a high isoelectric point (pHpzc = 9.14). The incorporation of aluminum and yttrium metals exhibited a novel approach, enhancing the adsorption capacity for fluoride ions due to their strong affinity. Furthermore, the dispersing effect of biochar played a crucial role in improving defluoridation efficiency by enhancing accessibility to active sites. These findings substantiate the significant potential of Al/Y-CSBC for enhanced fluoride removal from wastewater.

Phosphogypsum-Modified Vinasse Shell Biochar as a Novel Low-Cost Material for High-Efficiency Fluoride Removal

In this study, vinasse shell biochar (VS) was easily modified with phosphogypsum to produce a low-cost and novel adsorbent (MVS) with excellent fluoride adsorption performance. The physicochemical features of the fabricated materials were studied in detail using SEM, EDS, BET, XRD, FTIR, and XPS techniques. The adsorption experiments demonstrated that the adsorption capacity of fluoride by MVS was greatly enhanced compared with VS, and the adsorption capacity increased with the pyrolysis temperature, dosage, and contact time. In comparison to chloride and nitrate ions, sulfate ions significantly affected adsorption capacity. The fluoride adsorption capacity increased first and then decreased with increasing pH in the range of 3-12. The fluoride adsorption could be perfectly fitted to the pseudo-second-order model. Adsorption isotherms matched Freundlich and Sips isotherm models well, giving 290.9 mg/g as the maximum adsorption capacity. Additionally, a thermodynamic analysis was indicative of spontaneous and endothermic processes. Based on characterization and experiment results, the plausible mechanism of fluoride adsorption onto MVS was proposed, mainly including electrostatic interactions, ion exchange, precipitation, and hydrogen bonds. This study showed that MVS could be used for the highly efficient removal of fluoride and was compatible with practical applications.

Studies on ultrafast and remarkable removal of phosphate from sewage water by metal-organic frameworks

In the proposed research, a lanthanum-doped metal-organic framework (La-ATP) has been synthesised to remove phosphate from contaminated aqueous solutions. La-ATP was synthesised by a green energy-saving route using microwave irradiation and exhibited a phenomenal sorption capacity of 290 mg/g for the removal of phosphate. At a minimal dose of 0.1 g/L, 25 mg/L of phosphate gets reduced to 6.3 mg/L within 5 min and reaches equilibrium in 25 min. The isoelectric point of La-ATP was found to be 8.99, and it is efficient in removing phosphate over a wide range of pH 5-10. The existence of commonly occurring competing anions like sulphate, fluoride, chloride, arsenate, bicarbonate, and nitrate does not affect the uptake capacity of La-ATP towards phosphate ions. Furthermore, the robustness of La-ATP is demonstrated by its applicability to remove phosphate from real-life sewage water by reducing 10 mg/L of phosphorus from sewage water to < 0.02 mg/L. The primary mechanism governing phosphate removal was found to be ionic interaction and ligand exchange. Therefore, La-ATP can be considered a viable candidate for the treatment of eutrophic water streams because of its high sorption capacity, super-fast kinetics, and adaptability to contaminated sewage.

Efficient Fluoride Wastewater Treatment Using Eco-Friendly Synthesized AlOOH

Fluoride ion is essential for health in small amounts, but excessive intake can be toxic. Meeting safety regulations for managing fluoride ion emissions from industrial facilities with both cost-effective and eco-friendly approaches is challenging. This study presents a solution through a chemical-free process, producing a boehmite (AlOOH) adsorbent on aluminum sheets. Utilizing cost-effective Al foil and DI water, rather than typical precursors, yields a substantial cost advantage. The optimized AlOOH adsorbent demonstrated a high fluoride ion removal rate of 91.0% in simulated wastewater with fluoride ion concentrations below 20 ppm and displayed a similar performance in industrial wastewater. Furthermore, the AlOOH adsorbent exhibited excellent reusability through a simple regeneration process and maintained stable performance across a wide pH range of 4 to 11, demonstrating its capability to adsorb fluoride ions under diverse conditions. The efficiency of the AlOOH adsorbent was validated by a high fluoride ion removal efficiency of 90.9% in a semi-batch mode flow cell, highlighting its potential applicability in engineered water treatment systems. Overall, the AlOOH adsorbent developed in this study offers a cost-effective, eco-friendly, and sustainable solution for effectively removing fluoride ion from surface waters and industrial wastewaters.

Environmental implications of phosphate-based fertilizer industrial waste and its management practices

During the green revolution in the mid-twentieth century, the consumption of inorganic phosphorous and phosphate-based fertilizers (P-fertilizers) in the developing world skyrocketed, resulting in a proliferation of P-fertilizer industries. Phosphate-based fertilizer industries are ranked among the most environment-polluting industries. The worldwide phosphorus market, which was 68.5 million metric tons in 2020, is expected to increase at a compound annual growth rate (CAGR) of 2.5% to 81 million metric tons by 2027. The release of untreated hazardous pollutants from these fertilizer industries into the soil, water, and atmosphere has resulted in severe environmental health issues. Excessive surface runoff of phosphorus from agricultural fields and its deposition in water promote the growth of algae and macrophytes and lower dissolved oxygen concentration through eutrophication, which is detrimental to aquatic life. Fluorides (F-) and sulfur dioxide (SO2) and/or heavy metals (potentially toxic elements, PTEs) are also detected in the emissions from these fertilizer industries. The main solid waste generated from the phospho-gypsum plant produced up to 5 tons of di-hydrogen phosphate (H2PO4), including PTEs and radioactive substances. Phosphates and fluorenes from these industries are usually disposed of as sludge in storage ponds or trash piles. Humans inhaling poisonous gases released from the P-fertilizer industries can develop hepatic failure, autoimmune diseases, pulmonary disorders, and other health problems. The objectives of this review are to provide guidelines for eliminating the bottleneck pollutions that occur from the phosphate-based fertilizer industries and explore the management practices for its green development.

Investigation on water defluoridation via batch and continuous mode using Ce-Al bimetallic oxide: Adsorption dynamics, electrochemical and LCA analysis

With variable atomic ratios, Ce-Al bimetallic oxides were fabricated using the sol-gel combustion method and utilized for efficient fluoride removal. The synthesized bimetallic oxides were extensively studied using advanced characterization techniques, including TGA, XRD, FTIR, BET surface area analysis, EDX-assisted FESEM, XPS and impedance analysis. These techniques facilitate the interpretation of the chemical and physical properties of the synthesized material. The Ce-Al (1:1) bimetallic oxide was selected as an adsorbent for the defluoridation. The Ce-Al (1:1) oxide demonstrates a moderately high surface area of 108.67 m²/g. The sorption behaviour of fluoride on Ce-Al (1:1) was thoroughly investigated using batch and column modes. The maximum fluoride removal efficiency (99.4%) was achieved at a temperature of 45 °C and pH of 7.0 using an adsorbent dose of 0.18 g/L for 35 min. Pseudo-second-order kinetic model appropriately describes the sorption process. Freundlich's adsorption isotherm was more pertinent in representing fluoride adsorption behaviour. The maximum fluoride adsorption capacity is 146.73 mg/g at 45 °C. Thermodynamics study indicates fluoride adsorption on Ce-Al (1:1) bimetallic oxide is spontaneous and feasible. The adsorption mechanism was interpreted through XPS spectra, indicating that the physisorption process is mainly responsible for fluoride adsorption. An in-depth investigation of the adsorption dynamics was carried out using mass transfer models and found that the external diffusion process limits the overall adsorption rate. An electrochemical investigation was performed to understand the effect of fluoride adsorption on the electrochemical behaviour of bimetallic oxide. The fixed-bed column adsorption study suggested that the lower flow rate and increased bed height favourably impacted the overall defluoridation process, and column adsorption results were suitably interpreted through both the Adam-Bohart model and Yoon-Nelson dynamics model. The sustainable aspect of the defluoridation process was elucidated in terms of carbon footprint measurement using life cycle assessment analysis. The carbon footprint of the entire treatment process was calculated as 0.094 tons/year.

Porphyrin-based conjugated microporous adsorbent material for the efficient remediation of hexavalent chromium from the aquatic environment

The encapsulation and eradication of anions from water have received a lot of scrutinize and are extremely important for virtuous production and environmental treatment. To prepare extremely efficient adsorbents, a highly functionalized and conjugated microporous porphyrin-based adsorbent material (Co-4MPP) was synthesized using the Alder Longo method. Co-4MPP featured a hierarchical microporous and mesoporous layered structure containing nitrogen and oxygen-based functional groups with a specific surface area of 685.209 m2/g and a pore volume of 0.495 cm3/g. Co-4MPP demonstrated a greater Cr (VI) adsorption empathy than the pristine porphyrin-based material did. The effects of various parameters such as pH, dose, time, and temperature were explored on the Cr (VI) adsorption by Co-4MPP. The pseudo-second-order model and the Cr (VI) adsorption kinetics were in agreement (R2 = 0.999). The Langmuir isotherm model matched the Cr (VI) adsorption isotherm, demonstrating the optimum Cr (VI) adsorption capacities: 291.09, 307.42, and 339.17 mg/g at 298K, 312K, and 320K, correspondingly, with remediation effectiveness of 96.88%. The model evaluation further revealed that Cr (VI) adsorption mechanism on Co-4MPP was endothermic, spontaneous, and entropy-rising. The detailed discussion of the adsorption mechanism suggested that it could be a reduction, chelation, and electrostatic interaction, in which the protonated nitrogen and oxygen-containing functional groups on the porphyrin ring interacted with Cr (VI) anions to form a stable complex, thus remediating Cr (VI) anions efficiently. Moreover, Co-4MPP demonstrated strong reusability, maintaining 70% of its Cr (VI) elimination rate after four consecutive adsorptions.

Effects of Fe3O4 nanoparticles and nano hydroxyapatite on Pb and Cd stressed rice (Oryza sativa L.) seedling

Nowadays, Lead (Pb) and Cadmium (Cd) contamination in rice is an important worldwide environmental concern. Fe₃O₄ nanoparticles (Fe₃O₄ NPs) and Nano hydroxyapatite (n-HAP) are promising materials to manage Pb and Cd contamination. This study systematically investigated the effect of Fe₃O₄ NPs and n-HAP on Pb and Cd stressed rice seedlings' growth, oxidative stress, Pb and Cd uptake and subcellular distribution in roots. Furthermore, we clarified the immobilization mechanism of Pb and Cd in the hydroponic system. Fe₃O₄ NPs and n-HAP could reduce Pb and Cd uptake of rice mainly through decreasing Pb and Cd concentrations in culture solution and combining with Pb and Cd in root tissues. Pb and Cd were immobilized by Fe₃O₄ NPs through complex sorption processes and by n-HAP through dissolution-precipitation and cation exchange, respectively. On the 7th day, 1000 mg/L Fe₃O₄ NPs reduced the contents of Pb and Cd in shoots by 90.4% and 95.8%, in roots by 23.6% and 12.6%, 2000 mg/L n-HAP reduced the contents of Pb and Cd in shoots by 94.7% and 97.3%, in roots by 93.7% and 77.6%, respectively. Both NPs enhanced the growth of rice seedlings by alleviating oxidative stress and upregulating glutathione secretion and antioxidant enzymes activity. However, Cd uptake of rice was promoted at certain concentrations of NPs. The subcellular distribution of Pb and Cd in roots indicated that both NPs decreased the percentage of Pb and Cd in the cell wall, which was unfavorable for Pb and Cd immobilization in roots. Cautious choice was needed when using these NPs to manage rice Pb and Cd contamination.

Combing Seeding Crystallization with Flotation for Recovery of Fluorine from Wastewater: Experimental and Molecular Simulation Studies

For effective removal and utilization of fluorine resources from industrial wastewater, stepwise removal and recovery of fluorine were accomplished by seeding crystallization and flotation. The effects of seedings on the growth and morphology of CaF₂ crystals were investigated by comparing the processes of chemical precipitation and seeding crystallization. The morphologies of the precipitates were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements. The seed crystal, fluorite, helps improve the growth of perfect CaF₂ crystals. The solution and interfacial behaviors of the ions were calculated by molecular simulations. The existing perfect surface of fluorite was proven to provide the active sites for ion adhesion and formed a more ordered attachment layer than the precipitation procedure. The precipitates were then floated to recover calcium fluoride. By stepwise seeding crystallization and flotation, the products with a CaF₂ purity of 64.42% can be used to replace parts of metallurgical-grade fluorite. Both removal of fluorine from wastewater and the reutilization of the fluorine resource were realized.

Iron functionalized silica particles as an ingenious sorbent for removal of fluoride from water

The paucity of safe drinking water remains a global concern. Fluoride is a pollutant prevalent in groundwater that has adverse health effects. To resolve this concern, we devised a silica-based defluoridation sorbent from pumice rock obtained from the Paka volcano in Baringo County, Kenya. The alkaline leaching technique was used to extract silica particles from pumice rock, which were subsequently modified with iron to enhance their affinity for fluoride. To assess its efficacy, selected borehole water samples were used. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared and X-ray fluorescence spectroscopy was used to characterize the sorbent. The extracted silica particles were 96.71% pure and amorphous, whereas the iron-functionalized silica particles contained 93.67% SiO₂ and 2.93% Fe₂O₃. The optimal pH, sorbent dose and contact time for defluoridation of a 20 mg/L initial fluoride solution were 6, 1 g and 45 min, respectively. Defluoridation followed pseudo-second-order kinetics and fitted Freundlich's isotherm. Fluoride levels in borehole water decreased dramatically; Intex 4.57-1.13, Kadokoi 2.46-0.54 and Naudo 5.39-1.2 mg/L, indicating that the silica-based sorbent developed from low-cost, abundant and locally available pumice rock is efficient for defluoridation.

Removal of Fluoride from Aqueous Solution Using Shrimp Shell Residue as a Biosorbent after Astaxanthin Recovery

Natural astaxanthin has been widely used in the food, cosmetic, and medicine industries due to its exceptional biological activity. Shrimp shell is one of the primary natural biological sources of astaxanthin. However, after astaxanthin recovery, there is still a lot of chitin contained in the residues. In this study, the residue from shrimp (Penaeus vannamei) shells after astaxanthin extraction using ionic liquid (IL) 1-ethyl-3-methyl-imidazolium acetate ([Emim]Ac) was used as a bioadsorbent to remove fluoride from the aqueous solution. The results show the IL extraction conditions, including the solid/liquid ratio, temperature, time, and particle size, all played important roles in the removal of fluoride by the shrimp shell residue. The shrimp shells treated using [Emim]Ac at 100 °C for 2 h exhibited an obvious porous structure, and the porosity showed a positive linear correlation with defluorination (DF, %). Moreover, the adsorption process of fluoride was nonspontaneous and endothermic, which fits well with both the pseudo-second-order and Langmuir models. The maximum adsorption capacity calculated according to the Langmuir model is 3.29 mg/g, which is better than most bioadsorbents. This study provides a low-cost and efficient method for the preparation of adsorbents from shrimp processing waste to remove fluoride from wastewater.

Removal of fluoride ions from water by cerium-carboxymethyl cellulose beads doped with CeO2 nanoparticles

A novel adsorbent for fluoride ions (F^-) removal was prepared from cerium ion cross-linked carboxymethyl cellulose (CMC) biopolymer beads loaded with CeO₂ nanoparticles (NPs). The characterization of the beads was performed by swelling experiments, scanning electron microscopy and Fourier transforms infrared spectroscopy. The adsorption of fluoride ions from aqueous solutions was carried out with both cerium ion cross-linked CMC beads (CMCCe) and CeO₂-NPs added beads (CeO₂-CMC-Ce) in a batch system. Optimized adsorption conditions were obtained by testing the parameters such as pH, contact time, adsorbent dose, and shaking rate at 25 °C. The adsorption process is well described by the Langmuir isotherm and pseudo-second-order kinetics. The maximum adsorption capacity was found as 105 and 312 mg/g F^- for CMC-Ce and CeO₂-CMC-Ce beads, respectively. Reusability studies showed that, the adsorbent beads have exhibited excellent sustainable properties up to 9 cycle usage. This study suggests that, CMC-Ce composite with CeO₂ nanoparticles is a very effective adsorbent in removing fluoride from water.

Fluoride occurrence in environment, regulations, and remediation methods for soil: A comprehensive review

Fluoride, a naturally occurring chemical element, is largely insoluble in soils. More than 90% of the fluoride in soil is bound to soil particles and is unable to be dissolved. As part of the soil, fluoride is predominantly located in the colloid or clay fraction of the soil, and the movement of fluoride is strongly affected by the sorption capacity of the soil, which is affected by pH, the type of soil sorbent present, and the salinity. The Canadian Council of Ministers of the Environment soil quality guideline for fluoride in soils under a residential/parkland land use scenario is 400 mg/kg. In this review, we focus on fluoride contamination in soil and subsurface environments, and the various sources of fluorides are discussed in detail. The average fluoride concentration in soil in different countries and their regulations for soil and water are comprehensively reviewed. In this article, the latest advances in defluoridation methods are highlighted and the importance of further research addressing efficient and cost-effective methods to remediate fluoride contamination in soil is critically discussed. Methods used to mitigate fluoride risks by removing fluoride from the soil are presented. We strongly recommend that regulators and soil chemists in all countries explore opportunities to improve defluoridation methods and consider adopting more stringent regulations for fluoride in soil depending on geologic conditions.

Nrf2/PINK1-mediated mitophagy induction alleviates sodium fluoride-induced hepatic injury by improving mitochondrial function, oxidative stress, and inflammation

Mitophagy has distinct functions, which can lead to either protection or damage of tissues. Though current evidence indicated that NaF triggers mitophagy, the role and regulation of mitophagy in sodium fluoride (NaF)-induced liver injury still remain unclear. Therefore, we exployed the cell and mouse models and confirmed that NaF treatment activates mitophagy. Knocking down PTEN-induced putative kinase protein 1 (PINK1) expression attenuated mitophagy and increased the degree of mitochondrial impairment, oxidative stress, and apoptosis in NaF-treated HepG2 cells. In vivo experiments indicated that PINK1 deficiency weakened NaF-induced mitophagy. Moreover, PINK1-deficient mices aggravated NaF-induced hepatic mitochondrial injury, oxidative stress, and inflammation in livers, evidenced by the increased number of abnormal mitochondria, decreased adenosine triphosphate (ATP) and glutathione (GSH) levels, elevated reactive oxygen species (ROS) and malondialdehyde (MDA) content, enhanced hepatic macrophage infiltration and inflammatory cytokine levels. Notably, NaF exposure activated Nrf2 signaling both in vitro and in vivo. Nrf2 siRNA transfection blocked the upregulation of PINK1 expression and the induction of mitophagy in NaF-treated HepG2 cells. Also, ML385 (Nrf2 inhibitor) partially blocked the upregulation of PINK1 expression caused by NaF in mice livers. To sum up, the present study provided the demonstration that Nrf2/PINK1-mediated mitophagy activation offers a hepatoprotective effect by inhibiting NaF-induced mitochondrial dysfunction, oxidative stress, and inflammation.

Efficient removal of fluoride on aluminum modified activated carbon: an adsorption behavioral study and application to remediation of ground water

In recent times, ground water contamination by toxic elements is of great concern and it is to be addressed for consumption of human, animal, and plant growth. In this context, we have synthesized an adsorbent by modifying commercially available activated carbon with aluminum and tested for de-fluoridation studies. The activity results suggested that the optimized adsorbent is highly efficient in removing the fluoride from ground water. Adsorption maxima are obtained over a wide pH range from 4 to 9, with a contact time of 15 minutes at a dosage of 4 g/L. The results also revealed that the synthesized adsorbent is suitable for application in ground water without any pH adjustment and has exhibited 85%-95% tolerance for common anions in the range of 100-500 mg/L. Equilibrium adsorption isotherm models as well as kinetics of adsorption were applied for the system. An adsorption capacity of 20.4 mg/g and fast kinetics observed are most favorable for defluoridation. Reuse of adsorbent over repeated cycles was investigated. Residual amount of aluminum in treated water is found to be negligible. The removal of toxic elements like Pb, Cd, Cr, Cu, Ni, Zn, As, and Se under the optimized experimental conditions has also been investigated. Al-AC found to be a highly promising material for removal of fluoride and toxic metals from drinking water.

Application of artificial neural network for prediction of fluoride removal efficiency using neutralized activated red mud from aqueous medium in a continuous fixed bed column

The present research work approaches the removal of fluoride from aqueous medium using neutralized activated red mud (NARM) in a continuous fixed bed column. Artificial neural network (ANN) technique was applied effectively for optimization of the model for the practicability of the removal process. The consequences of various experimental variables, like bed length, adsorbate concentration, experimental time, and adsorbate solution flow rate are studied to know the breakthrough point and saturation times. The highest removal potentiality of NARM was considered to be 3.815 mg g^-1 of F^- in the bed height of 15 cm, starting concentration 1 ppm, susceptible time 120 min, adsorbate solution flow rate 0.5 mL min^-1, and constant room temperature, respectively. Bohart-Adams and Thomas models were considered to describe the fixed bed column effect to the bed height and adsorbate concentrations. The experimental data were applied to a back propagation (BP) learning algorithm programme with a four-seven-one architecture model. The artificial neural network model was considered to be functioning correctly as absolute relative percentage error throughout the learning period. Differentiation between the predicted outcomes from ANN model and actual results from experimental analysis affords a high degree of correlation (R² = 0.998) stipulating that the model was able to predict the adsorption efficiency. Experimented adsorbent materials were characterized using different instrumental analysis that is scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD).