Highly efficient fluoride extraction from simulant leachate of spent potlining via La-loaded chelating resin. An equilibrium study

A review on fluoride contamination in groundwater and human health implications and its remediation: A sustainable approaches

Contamination of drinking water due to fluoride (F-) is a major concern worldwide. Although fluoride is an essential trace element required for humans, it has severe human health implications if levels exceed 1.5 mg. L-1 in groundwater. Several treatment technologies have been adopted to remove fluoride and reduce the exposure risk. The present article highlights the source, geochemistry, spatial distribution, and health implications of high fluoride in groundwater. Also, it discusses the underlying mechanisms and controlling factors of fluoride contamination. The problem of fluoride-contaminated water is more severe in India's arid and semiarid regions than in other Asian countries. Treatment technologies like adsorption, ion exchange, precipitation, electrolysis, electrocoagulation, nanofiltration, coagulation-precipitation, and bioremediation have been summarized along with case studies to look for suitable technology for fluoride exposure reduction. Although present technologies are efficient enough to remove fluoride, they have specific limitations regarding cost, labour intensity, and regeneration requirements.

New easily recycled carrier based polyurethane foam by loading Al-MOF and biochar for selective removal of fluoride ion from aqueous solutions

The production of Integrated circuits (ICs) generates wastewater with a high concentration of residual fluoride ions, necessitating highly efficient fluorine removal methods. In this study, a novel composite carrier was developed using a hydrothermal synthesis method to load Al-MOF and biochar (BC) onto polyurethane foam (PUF), resulting in the composite foam of Al-MOF-PUF@BC. The results showed that the composite carrier exhibited a stable fluoride removal effect, with a maximum adsorption capacity of 16.52 mg/g at room temperature. The adsorption isotherm curves were consistent with the Langmuir isotherm model, and the adsorption kinetics were well-described by the pseudo-first-order model. The mechanism of fluorine adsorption on Al-MOF-PUF@BC was ligand exchange with hydroxyl groups and the formation of FAl bonds. Density functional theory (DFT) calculations revealed that the adsorption energy reached -246.7 eV, indicating stable adsorption for fluoride ions. The composite foam demonstrated excellent regenerative properties and was effective for fluoride removal in actual IC wastewater.

Fe(II)/LXQ-10 bifunctional resin materials for boosting synergistic adsorption/oxidation of benzene in industrial waste gas

A series of adsorption/oxidation bifunctional material with different Fe(II) loading amounts was prepared by using ultrahigh crosslinking adsorption resin (LXQ-10) as a carrier and FeCl2 as an impregnating solution. The bifunctional material was characterized by BET, SEM, XRD, XPS, and EPR. The effects of Fe loading, reaction temperature, and space velocity on benzene adsorption efficiency were investigated using self-made experimental equipment to explore the optimal reaction condition. The adsorption results were fitted and analyzed by using four typical models: the quasi-first-order kinetic model, the quasi-second-order kinetic model, Elovich's kinetic model, and the Weber and Morris kinetic model. The quasi-first-order kinetic model had the highest R2 value (0.998) and the best applicability. The fitting effect of the Freundlich equation (R2 = 0.997) was better than that of the Langmuir equation (R2 = 0.919). Furthermore, the effects of Fe loading, H2O2 concentration, benzene inlet concentration, and temperature on the catalytic oxidation efficiency of benzene were studied. The catalytic oxidation efficiency of 3-Fe(II)/LXQ-10 was maintained at about 95% at a temperature of 303 K and an H2O2 concentration of 150 mmol/L. Compared with the adsorption efficiency, the catalytic oxidation efficiency of bifunctional resin materials in a heterogeneous Fenton system was remarkably improved and had excellent stability. A possible migration and transformation path during benzene removal was proposed according to the results of the analysis of GC-MS intermediates. This study provided a novel process for the adsorption and oxidative degradation of VOCs.

Porous Lanthanum-Zirconium phosphate with superior adsorption capability of fluorine for water treatment

Bimetal oxide is a popular defluorinating material. Hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant successfully synthesizes a novel lanthanum-zirconium phosphate to remove fluorine from groundwater. Lanthanum-zirconium phosphate at a Zr/La molar ratio of 2 exhibited a specific surface area of 455.14 m2/g with a wide pore size, which was achieved by incorporating lanthanum into materials and removing CTAB through calcination. The maximum fluoride adsorption capacity is 109.17 mg/g, which is tenfold that of mesostructured zirconium phosphate. Specifically, analysis revealed that mZrP and LamZrP2-1 were amorphous, which is consistent with HAADF-STEM. The fluoride adsorption fitted well with the pseudo-second-order equation model and Langmuir isotherm mode. LamZrP2-1 had potent anti-interference ability without PO43-. Moreover, LamZrP2-1 was reusable for at least six cycles of adsorption-desorption with little influence. The adsorption mechanism of fluoride was discussed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis, and Fourier transform infrared (FTIR) spectroscopy. Fluoride was captured by LamZrP2-1 via charge attraction, ligand exchange of different bond strengths, and ion exchange. Lanthanum-zirconium phosphate is important not only in the research and development of bimetal oxides but also in the treatment of groundwater for fluoride removal.

Adsorption studies of a multi-metal system within acetate media, with a view to sustainable phosphate recovery from sewage sludge

Phosphate shortages and the ensuing pressures on food security have led to an interest in processed sewage sludge as a substitute for commercial fertilisers. The presence of heavy metals in this nutrient source causes concerns around environmental release and pollution. This work builds towards a resin-in-pulp sludge detoxification process. It showcases the kinetic and thermodynamic adsorption capabilities of the ion-exchange resins C107E (carboxylic acid functionality), MTS9301 (iminodiacetic acid) and TP214 (thiourea), with respect to Cu(II), Fe(II), Pb(II) and Zn(II), within a simulated sewage sludge weak acid (acetate) leachate. The isotherms produced in this complex system were quite different to those generated when single metals were investigated in isolation, with desorption of lower affinity species clearly observed at higher equilibrium concentration values. Mixed-metal isotherm data were fitted to common two-parameter isotherm models and also a novel modified Langmuir model, which better accounted for the effects of desorption and competition. Kinetic data were also fit to common two-parameter models; results suggesting the system was likely film diffusion-controlled and followed pseudo-2nd-order kinetics. C107E displayed rapid adsorption of lead (t_1/2 = 26 ± 3min), and significant uptake of all metals. MTS9301 showed high affinity for copper ions, with concurrent desorption of all the other metals, and also displayed the fastest kinetics (t_1/2 = 14.1 ± 0.9, 130 ± 20, 25 ± 5 and 49 ± 6 min for copper, iron(II), lead and zinc, respectively). C107E and MTS9301 showed far slower adsorption for iron(II) than the other three metals, which invited the possibility of kinetic separations. TP214 had reasonable effectiveness in removal of copper, but poor affinity for all other metals. The greatest difficulty in modelling the multi-metal system was the two-stage trends observed in equilibrium experiments, as metal-proton exchanges become metal-metal exchanges. While not having the highest capacity, MTS9301 was recommended as the most appropriate resin for rapid and efficient removal of Cu, Pb and Zn from the acetate medium.

Fluoride-immobilized co-processing and resource utilization of aluminum-electrolyzed spent cathode carbon in brick-fired kiln

Spent cathode carbon (SCC) is hazardous waste from the electrolytic aluminum industry due to its high levels of soluble fluoride, while brick-fired kiln provides the clay and heating conditions needed to immobilize fluoride. However, SCC reusing is still understudied, meanwhile co-processing and resource utilization of SCC in brick-fired kiln were still not reported in the literatures in addition to a Chinese patent of the authors. Here, the effects of firing temperatures, firing time, clay doses and calcium doses on the fluoride-immobilized performance of SCC co-processing were explored in a simulated brick-firing kiln, and their mechanisms were analyzed by SEM and XRD. The results indicated that clay-added co-processing in brick-fired kiln was a preferred choice without required additional additives or operations. The leached fluoride met Chinese standards by clay-added co-processing at ≥ 800 °C/ ≥ 40 g clay/ ≥ 120 min. Clay and calcium-added co-processing in brick-fired kiln was another alternative choice with higher fluoride-immobilization rates. The leached fluoride met Chinese standard (GB5085.3-2007) by clay and calcium-added co-processing at ≥ 500 °C/ ≥ 30 min/ ≥ 5 g clay/ ≥ 0.5 g CaCO₃. SEM and XRD indicated that SiO₂ in clay reacted with sodium in SCC and formed vitreous analog (Na_1.55Al_1.55Si_0.45O₄) to prevent fluoride ion migration and the newly-formed k-Feldspar (K₂O.Al₂O₃.6SiO₂) may adsorb fluoride ions in clay-added co-processing. Soluble fluoride NaF in SCC were converted into water-insoluble cuspidine in clay and calcium-added co-processing, in addition to the crystalline phase conversion in clay-added co-processing. Therefore, the risks of finished bricks to human health and the environment were greatly reduced after clay-added or clay and calcium-added treatments.

Performance and mechanism of lanthanum-modified zeolite as a highly efficient adsorbent for fluoride removal from water

Defluoridation of water is still challenging due to the fluoride pollution of both groundwater and surface water worldwide. In this study, lanthanum-modified zeolite (LMZ) was synthesized from coal fly ash and was investigated for fluoride removal from water by conducting batch and column experiments. Our results indicated that the process of fluoride adsorption was endothermic and the adsorption kinetics on LMZ followed the pseudo-second-order model. A higher temperature increased both the capacity and the rate of adsorption. The maximum fluoride adsorption capacity of LMZ reached 141.5 mg/g with a F/La molar ratio of 4.21, as estimated from the Langmuir model which best fitted the isotherm data. Fluoride adsorption greatly depended on pH, with optimal performance being achieved within ∼5.0-∼7.0. The point of zero charge of LMZ was pH 8.8, at which only bicarbonate ions greatly affected fluoride removal. However, no competing effect was observed at pH 6.3 for all tested anions including chloride, sulphate, nitrate, bicarbonate and acetate. The dominant adsorption mechanism was the ligand exchange of fluoride with hydroxyls on LMZ, as illustrated by the rise in pH due to fluoride adsorption and by the molecular scale spectroscopic FTIR, Raman and XPS studies. Fluoride adsorbed on LMZ was successfully desorbed using NaOH solution, and regenerated LMZ could be reused. The results of column studies showed that LMZ granulated with alginate performed well in treating F^--containing water. In conclusion, LMZ is a promising material for efficient defluoridation from water.

Complementary advantages of spent pot lining and coal gangue in the detoxification and valuable components recovery process

As a hazardous solid waste rich in carbon and fluorine, spent pot lining (SPL) is a huge threat to sustainable production and environmental security. As abundant carbon and fluorine resources, the use of such valuable components has great practical and economic significance. Based on the environmental concerns and the component characteristics of SPL, coal gangue (CG), the largest output of solid wastes in the coal-producing industry and rich in aluminum and silicon, was introduced in the utilization and detoxification process of SPL in this work. The substance flow of the co-utilization process presents a circular economy and complementary advantages of SPL and CG. Pure regular fibrous silicon carbides were obtained owing to the synergy effect of SPL and CG. Aluminum from CG and SPL was utilized to prepare dawsonite combined with the sodium from the impurities removal process. Pure cryolite was obtained via mixing wastewater from the silicon carbide purification process and the dawsonite extraction process. Almost all components in SPL and CG were converted into valuable products, and no wastewater and residue was discharged. Thus, a sustainable process of trash to treasure and circular economy for treating CG and SPL was established here with environmental and economically friendly characteristics, which gave a new insight into utilizing wastes with complementary advantages.

Functionality screening to help design effective materials for radioiodine abatement

This paper is part of a growing body of research work looking at the synthesis of an optimal adsorbent for the capture and containment of aqueous radioiodine from nuclear fuel reprocessing waste. 32 metalated commercial ion exchange resins were subjected to a two-tier screening assessment for their capabilities in the uptake of iodide from aqueous solutions. The first stage determined that there was appreciable iodide capacity across the adsorbent range (12–220 mg·g⁻¹). Candidates with loading capacities above 40 mg·g⁻¹ were progressed to the second stage of testing, which was a fractional factorial experimental approach. The different adsorbents were treated as discrete variables and concentrations of iodide, co-contaminants and protons (pH) as continuous variables. This gave rise to a range of extreme conditions, which were representative of the industrial challenges of radioiodine abatement. Results were fitted to linear regression models, both for the whole dataset (R² = 59%) and for individual materials (R² = 18–82%). The overall model determined that iodide concentration, nitrate concentration, pH and interactions between these factors had significant influences on the uptake. From these results, the top six materials were selected for project progression, with others discounted due to either poor uptake or noticeable iodide salt precipitation behaviour. These candidates exhibited reasonable iodide uptake in most experimental conditions (average of >20 mg·g⁻¹ hydrated mass), comparing favourably with literature values for metallated adsorbents. Ag-loaded Purolite S914 (thiourea functionality) was the overall best-performing material, although some salt precipitation was observed in basic conditions. Matrix effects not withstanding it is recommended that metalated thiourea, bispicolylamine, and aminomethylphosphonic acid functionalized silicas warrant further exploration.

Applications of biomass-based materials to remove fluoride from wastewater: A review

Fluoride is one of the essential trace elements for the human body, but excessive fluoride will cause serious environmental and health problems. This paper summarizes researches on the removal of fluoride from aqueous solutions using newly developed or improved biomass materials and biomass-like organic materials in recent years. These biomass materials are classified into chitosan, microorganisms, lignocellulose plant materials, animal attribute materials, biological carbonized materials and biomass-like organic materials, which are explained and analyzed. By comparing adsorption performance and mechanism of adsorbents for removing fluoride, it is found that carbonizing materials and modifying adsorbents with metal ions are more beneficial to improving adsorption efficiency and the adsorption mechanisms are various. The adsorption capacities are still considerable after regeneration. This paper not only reviews the properties of these materials for fluoride removal, but also focuses on the comparison of materials performance and fluoride removal mechanism. Herein, by discussing the improved adsorption performance and research technology development of biomass materials and biomass-like organic materials, various innovative ideas are provided for adsorbing and removing contaminants.

Tailored design of a novel composite foam of sodium alginate used for fluoride ion removal

Fluoride is an essential micronutrient for humans. Nonetheless, when the amount of fluoride ion is greater than required, it will cause skeletal fluorosis and dental fluorosis to threaten human health. In this paper, a series of sodium alginate (SA)-based foam materials are prepared by freeze-drying technique and anchored with the nano-activated alumina (nAl₂O₃) in the SA to obtain a novel adsorbent of SA-nAl₂O₃ foam used for fluoride ions removal. The SA-nAl₂O₃ foam morphology was further explored and confirmed that nAl₂O₃ existed stably in the SA. The adsorption results showed that the maximal fluoride ion adsorption capacity was 5.09 mg/g with 20 mg/L fluorine solutions at a pH of 3. The adsorption isotherm fitted adequately to the Langmuir isotherm model, which demonstrated that the adsorption process is closer to monolayer adsorption. The adsorption kinetics behavior of SA-nAl₂O₃ foam was described by a pseudo-second-order model, and the adsorption process occurred by chemisorption. Adsorption thermodynamics analysis emphasized that the adsorption process was spontaneous and endothermic. The main mechanism of the foam is ion exchange. The SA-nAl₂O₃ foam exhibited excellent regeneration performance and stability after three cycles.

Capture of aqueous radioiodine species by metallated adsorbents from wastestreams of the nuclear power industry: a review

Abstract

Iodine-129 poses a significant challenge in the drive towards lowering radionuclide emissions from used nuclear fuel recycling operations. Various techniques are employed for capture of gaseous iodine species, but it is also present, mainly as iodide anions, in problematic residual aqueous wastestreams, which have stimulated research interest in technologies for adsorption and retention of the radioiodine. This removal effort requires specialised adsorbents, which use soft metals to create selectivity in the challenging chemical conditions. A review of the literature, at laboratory scale, reveals a number of organic, inorganic and hybrid adsorbent matrices have been investigated for this purpose. They are functionalised principally by Ag metal, but also Bi, Cu and Pb, using numerous synthetic strategies. The iodide capacity of the adsorbents varies from 13 to 430 mg g−1, with ion-exchange resins and titanates displaying the highest maximum uptakes. Kinetics of adsorption are often slow, requiring several days to reach equilibrium, although some ligated metal ion and metal nanoparticle systems can equilibrate in < 1 h. Ag-loaded materials generally exhibit superior selectivity for iodide verses other common anions, but more consideration is required of how these materials would function successfully in industrial operation; specifically their performance in dynamic column experiments and stability of the bound radioiodine in the conversion to final wasteform and subsequent geological storage.

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A novel carboxylated polyacrylonitrile nanofibrous membrane with high adsorption capacity for fluoride removal from water

To deal with the drinking water safety caused by fluoride, a novel carboxylated polyacrylonitrile nanofibrous membrane (C-PAN NFM) is designed and fabricated massively for the first time by adopting synchronously biaxial stretching and carboxylation. The C-PAN NFM is composed of the layered stack structure by cross-linked nanofibers. Due to its high specific surface area, excellent hydrophilicity, a large amount of carboxyl and amine groups, C-PAN NFM owns high fluoride adsorption capacity and outstanding selectivity. Both the carboxylation and acid treatment of C-PAN NFM improved the fluoride adsorption capacity remarkably. Specifically, C-PAN NFM shows excellent reusability without secondary pollution. The fluoride adsorption behavior of C-PAN NFM is dominated by chemical adsorption, and the adsorption mechanism is mainly driven by hydrogen bonding and ion exchange. The mass-produced C-PAN NFM is a novel polyacrylonitrile-based porous membrane that shows a great application potential for fluoride removal with good efficiency and recyclability.

A Novel and Efficient Metal Oxide Fluoride Absorbent for Drinking Water Safety and Sustainable Development

Inefficient and non-environmentally friendly absorbent production can lead to much resource waste and go against low carbon and sustainable development. A novel and efficient Mg-Fe-Ce (MFC) complex metal oxide absorbent of fluoride ion (F−) removal was proposed for safe, environmentally friendly, and sustainable drinking water management. A series of optimization and preparation processes for the adsorbent and batch experiments (e.g., effects of solution pH, adsorption kinetics, adsorption isotherms, effects of coexisting anions, as well as surface properties tests) were carried out to analyze the characteristics of the adsorbent. The results indicated that optimum removal of F− occurred in a pH range of 4–5.5, and higher adsorption performances also happened under neutral pH conditions. The kinetic data under 10 and 50 mg·g−1 were found to be suitable for the pseudo-second-order adsorption rate model, and the two-site Langmuir model was ideal for adsorption isotherm data as compared to the one-site Langmuir model. According to the two-site Langmuir model, the maximum adsorption capacity calculated at pH 7.0 ± 0.2 was 204 mg·g−1. The adsorption of F− was not affected by the presence of sulfate (SO42−), nitrate (NO3−), and chloride (Cl−), which was suitable for practical applications in drinking water with high F− concentration. The MFC adsorbent has an amorphous structure, and there was an exchange reaction between OH− and F−. The novel MFC adsorbent was proven to have higher efficiency, better economy, and environmental sustainability, and be more environmentally friendly.

Experimental and modeling studies for adsorbing different species of fluoride using lanthanum-aluminum perovskite

We investigated the adsorption mechanisms for removing fluoride based on experimental and modeling studies. Lanthanum-aluminum perovskite was designed for treating wastewater contaminated by fluoride. A fluorine-species model was developed to calculate the concentrations of different species of fluorine: F^-, HF, HF₂^-. Multiple kinetic models were examined and the pseudo-second order model was found the best to fit the experimental data, implying fast-chemisorption. The thermodynamic data were fitted by the Langmuir model and Freundlich model at different temperatures, indicating heterogeneous adsorption at low temperature and homogeneous adsorption at high temperature. The La₂Al₄O₉ material had less influence from negative ions when adsorbing fluoride. The adsorption mechanisms were further studied using experiments and Density Functional Theory calculations. The adsorption experiments could be attributed to the lattice plane (1 2 1) and La, O, Al sites. More Al sites were required than La sites for the increase of fluoride concentration. By contrast, more La sites than Al sites were needed for increased pH.

Water-soluble fluorine detoxification mechanisms of spent potlining incineration in response to calcium compounds

In this study, the detoxification mechanisms of water-soluble fluorine in the bottom ash and the distribution of fluorine during the spent potlining (SPL) incineration were characterized in response to four calcium compounds using an experimental tube furnace. CaSiO₃, CaO, Ca(OH)₂, and CaCO₃-assisted SPL incineration converted NaF to low toxicity compounds in the bottom ash yielding a conversion range of 54.24-99.45% relative to the individual SPL incineration. The two main mechanisms of the fluorine transformation were the formations of CaF₂ and Ca₄Si₂O₇F₂. The fluorine transformation efficiency was greater with CaSiO₃ than CaO, Ca(OH)₂, and CaCO₃. Our simulations demonstrated that SiO₂ enhanced the conversion of NaF. The fluorine leaching content of the bottom ash was estimated at 13.71 mg⋅L^-1 after the SPL co-incineration with CaSiO₃ (Ca:F = 1.2:1). The acid-alkali solutions had no significant effect on the fluorine leaching content of the bottom ash when 3 ≤ pH ≤ 12. Fluorine during the SPL co-incineration with CaSiO₃ (Ca:F = 1.2:1) at 850 °C for 60 min was partitioned into 83.37, 13.90, and 2.72% in the bottom ash, fly ash, and flue gas, respectively. The transformation and detoxification mechanisms of water-soluble fluorine provide new insights into controls on fluorine emission from the SPL incineration.

Water-Gated Transistor Using Ion Exchange Resin for Potentiometric Fluoride Sensing

We introduce fluoride-selective anion exchange resin sorbents as sensitisers into membranes for water-gated field effect transistors (WGTFTs). Sorbents were prepared via metal (La or Al)-loading of a commercial macroporous aminophosphonic acid resin, Puromet^TM MTS9501, and were filled into a plasticised poly(vinyl chloride) (PVC) phase transfer membrane. We found a potentiometric response (membrane potential leading to WGTFT threshold shift) to fluoride following a Langmuir-Freundlich (LF) adsorption isotherm with saturated membrane potential up to ~480 mV, extremely low characteristic concentration c_1/2 = 1/K, and picomolar limit of detection (LoD), even though ion exchange did not build up charge on the resin. La-loading gave a superior response compared to Al-loading. Membrane potential characteristics were distinctly different from charge accumulating sensitisers (e.g., organic macrocycles) but similar to the Cs⁺ (cation) selective ion-exchanging zeolite mineral 'mordenite'. We propose a mechanism for the observed threshold shift and investigate interference from co-solutes. Strong interference from carbonate was brought under control by 'diluting' metal loading in the resin. This work sets a template for future studies using an entirely new 'family' of sensitisers in applications where very low limit of detection is essential such as for ions of arsenic, mercury, copper, palladium, and gold.

Adsorption mechanism for removing different species of fluoride by designing of core-shell boehmite

Many kinds of adsorbents have been developed for removing fluoride from water. However, the unclear actual mechanism of fluoride adsorption greatly restricts the structural design and application of novel adsorbents. Based on the understanding of the interaction between hydroxyl and fluoride, a novel core-shell nanostructure of boehmite was synthesized via an in-situ-induced assembly for removing fluoride. The formed polycrystalline boehmite (γ-AlOOH) nanostructure significantly enhances adsorption performance. The transformation of fluoride forms (including F^-, HF, HF₂^-) is closely related to the solution property. The acidic solution is more favorable, mainly because of the conversion of HF (pyrazine) and HF₂^- (the bifluoride ion) with a strong hydrogen bond effect from fluoride (F^-) with pH < 3.18. The lattice plane of (0 0 2) belongs to the dominant face for removing fluoride in this structure. According to the experimental and theoretical calculation, strong bonding of Al, O and H sites with fluoride species (F^-, HF, HF₂^-) in acidic solution are demonstrated, but not in alkaline solution due to OH^- interference. The possible mechanism of fluoride adsorption on boehmite (AlOOH) structures is proposed. Our findings show a new potential prospect of structural designing for novel fluoride adsorbent.

Multiple bimetallic (Al-La or Fe-La) hydroxides embedded in cellulose/graphene hybrids for uptake of fluoride with phosphate surroundings

To insight into the selective adsorption mechanism of fluoride in the bimetallic system, Fe-La or Al-La composites were comparatively embedded onto the cellulose/graphene hybrids (CG hybrids) to fabricate the Fe-La@CG hybrids or Al-La@CG hybrids for fluoride uptake with existing phosphate. The results showed that Al-La@CG hybrids were mainly in the amorphous nature, while Fe-La@CG hybrids have the identical diffraction peaks as compared with those of hydrated lanthanum oxides (HLO) and hydrated iron oxides (HFO). Fluoride capture by Al-La@CG and Fe-La@CG hybrids followed the similar tendencies with the pH altering, but the adsorption performance of Al-La@CG hybrids was better than that of Fe-La@CG hybrids at the same pH levels. Adsorption of fluoride onto Al-La@CG hybrids exhibited less sensitivity and high selectivity with existing phosphate as compared with that of Fe-La@CG hybrids, which further indicated that the Al-La@CG hybrids were more preferable for fluoride adsorption. The fraction areas of La-F and Al-F accounted for 79.1 % and 20.9%, which indicated that the fluoride onto the Al-La@CG hybrids was mainly based on the La species. Similarly, La-F in exhausted Fe-La@CG hybrids accounted for 55.6%, higher than that (44.4%) of Fe-F.

Fluoride uptake by three lanthanum based nanomaterials: Behavior and mechanism dependent upon lanthanum species

Excess fluoride in water can be efficiently removed by lanthanum based material, however, different lanthanum species exhibited distinct fluoride removal capability. In this study, three typical lanthanum based nanoparticles denoted as L1, L2 and L3 in the form of La(OH)₃, La₂O₃·nH₂O and LaCO₃OH respectively were synthesized and well characterized for fluoride removal. They differ in terms of morphology, surface charge, water content, specific surface area and crystallinity. L2 (La₂O₃·nH₂O) exhibited the highest adsorption capacity (~28.9 mg/g) and selectivity towards fluoride, followed by L3 (LaCO₃OH) (~25.1 mg/g) and L1 (La(OH)₃) (~6.03 mg/g). Despite the relatively low capacity for L1, it could be efficiently regenerated by alkaline solution for repeated use. However, both L2 and L3 suffered significant from capacity loss after regeneration. X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis and molecular configuration modelling suggested the distinct mechanism of fluoride adsorption onto the three materials. Fluoride was captured by L1 and L3 via electrostatic attraction and ligand exchange of different bond strength. However, a stronger LaF interaction via chemical adsorption by L2 was observed. This study provided new insights into the role of commonly used La species for fluoride removal.

Precipitation Methods Using Calcium-Containing Ores for Fluoride Removal in Wastewater

F-containing wastewater does great harm to human health and the ecological environment and thus needs to be treated efficiently. In this paper, the new calcium-containing precipitant calcite and aided precipitant fluorite were adopted to purify F-containing wastewater. Relevant reaction conditions, such as reaction time, oscillation rate, dosage of hydrochloric acid, calcite dosage and the assisting sedimentation performance of fluorite, and action mechanism are analyzed. The experiment showed that the removal rate of fluoride in simulated wastewater reached 96.20%, when the reaction time, the dosage of calcite, the dosage of 5% dilute hydrochloric acid, and the oscillation rate was 30 min, 2 g/L, 21.76 g/L, and 160 r/min, respectively. Moreover, the removal rate of fluoride in the actual F-containing smelting wastewater reaches approximately 95% under the optimum condition of calcite dosage of 12 g/L, reaction time of 30 min, and oscillation rate of 160 r/min. The addition of fluorite significantly improves the sedimentation performance of the reactive precipitates. The experimental results showed that calcite and fluorite can effectively reduce the concentration of fluoride ions in F-containing wastewater and solve the problem of slow sedimentation of reactive precipitates.

Efficient Removal of Fluoride by Complexation Extraction: Mechanism and Thermodynamics

A complexation extraction system was designed to develop a new process for the efficient removal of fluoride from solutions, such as zinc or copper electrolytes or wastewater derived from flue gas. The effects of the boron fluoride molar ratio, organic phase composition, initial pH, temperature, and phase volume ratio on the extraction efficiency were investigated. The extraction efficiency was found to increase with the increase in the boron fluoride molar ratio, Alamine336 concentration, and phase volume ratio, whereas it decreased with the increase in temperature. For the simulated electrolyte or wastewater derived from flue gas, the majority of metallic ions were insensitive to the extraction, with the exception of Al³⁺ and Fe³⁺. Fluoride decreased from 5 g/L to 0.05 g/L after two-stage cross-flow extraction alone; with an extraction efficiency of 99%. Both the stripping and cycling properties were excellent when sodium hydroxide was employed as the stripping reagent. Furthermore, the loading capacity was 43.4 g/L, and increased by four times, when boric acid was added. This novel process implies a wide range of potential applications, such as the removal of unwanted fluoride ions from various high-fluoride polluted solutions and the simplification of brine phase diagram.

Selective Environmental Remediation of Strontium and Cesium Using Sulfonated Hyper-Cross-Linked Polymers (SHCPs)

Sulfonated hyper-cross-linked polymers based on 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP) were synthesized via metal-free (SHCP-1) and conventional Lewis acid-catalyzed (SHCP-2) Friedel-Crafts alkylation routes. The sulfonated polymers possessed BET surface areas in excess of 500 m²·g^-1. SHCP-1 was investigated for its ability to extract Sr and Cs ions from aqueous solutions via the ion-exchange reaction of the sulfonic acid moiety. Equilibrium uptake data could be accurately modeled by the Dubinin-Radushkevich isotherm, with maximum calculated loading values of 95.6 ± 2.8 mg·g^-1 (Sr) and 273 ± 37 mg·g^-1 (Cs). Uptake of both target ions was rapid, with pseudo second-order rate constants calculated as 7.71 ± 1.1 (×10^-2) for Sr and 0.113 ± 0.014 for Cs. Furthermore, the polymer was found to be highly selective toward the target ions over large excesses of naturally occurring competing metal ions Na, K, Mg, and Ca. We conclude that hyper-cross-linked polymers may offer intrinsic advantages over other adsorbents for the remediation of aqueous Sr and Cs contamination.