Fluoride Pollution Research Articles

Endogenous calcium mediates seedling growth and fluoride stress tolerance in four bean genotypes

Fluoride (F) pollution is a global environmental problem representing a severe risk for food and vegetables grown in contaminated soils. Phaseolus vulgaris L. is widely cultivated in arid and semi-arid regions and in F contaminated areas of the world. For that reason, F tolerance during germination and seedling growth was evaluated for four bean genotypes: Borlotto nano (commercial variety) and three African genotypes (Lyamungu 85, Lyamungu 90 and Jesca). Seeds were grown in sand enriched with NaF or KF at three different levels (0, 80 and 200 mg kg-1). NaCl was used as a benchmark to determine the potential effect of different Na levels in plant. Total F content and mineral accumulation (Na, K and Ca) in roots and shoots were measured. The translocation factor, growth ratio, F tolerance index were evaluated to estimate plant-salt response. Germination rate decreased with increased F level. Borlotto was more F sensitive (0% germination with 200 mg kg-1of KF and NaF) than the African genotypes. Under the highest F concentration (200 mg kg-1), F preferentially accumulated in shoots (Jesca 75.7 mg kg-1, Lyamungu 85 100.1 mg kg-1 and Lyamungu 90 115.4 mg kg-1). Ca content in roots was negatively correlated to F absorption, suggesting its antagonistic role to F mobility. Based on these parameters, Jesca and Lyamungu 85 were the most tolerant species, recording a low F uptake and a high Ca content in the root. This study highlighted the central role of Ca, as a key secondary messenger in regulating the plant growth and development under F stress. Highlights - F stress negatively affected bean germination and seedling growth - F mainly accumulated in the shoots of bean varieties - Ca concentration in the roots played a crucial role in mitigating F accumulation

Outstanding performance of thiophene-based metal-organic frameworks for fluoride capture from wastewater

Worsening fluoride pollution in water poses a great threat to human life. Because of the unique properties of the 2, 5-thiophenedicarboxylate (H2TDC) ligand, a series of TDC-MOFs were prepared by altering the central metal ions (i.e., Al3+, Ce4+ and Zr4+) and they were subsequently used to adsorb fluoride from aqueous solution. Characterization of the materials (SEM, XRD, BET, and TGA) showed that TDC-MOFs had high thermal stability, well-defined microstructure and high specific surface area. The maximum adsorption capacities of Al-TDC, Ce-TDC, and Zr-TDC at 298 K were 107.5 mg g−1, 94.9 mg g−1, and 97.0 mg g−1, these were superior to the values for most adsorbents reported in the literature. Adsorption of fluoride on TDC-MOFs accorded with the Langmuir adsorption isotherm model, and the quasi-second-order kinetic model, in which chemisorption was the kinetic control step. The optimized parameters (including pH, time, interfering ions, and ionic strength) indicated that TDC-MOFs were suitable for fluoride removal over a broad pH range (4.0–10.0) without interference. Fourier transform infrared spectroscopy (FTIR), Zeta potential, and X-ray photoelectron spectroscopy (XPS) analyses confirmed that the main mechanisms of fluoride adsorption onto TDC-MOFs were the combination of electrostatic attraction and ligand exchange. Fluoride-loaded on TDC-MOF can be eluted with dilute NaOH solution, and the adsorbent can be used for at least 4 cycles of adsorption/desorption. These results indicated that the prepared TDC-MOFs were promising candidate materials for fluoride removal from actual and complex water.

Fluoride pollutants removal from industrial wastewater

BackgroundThe main object of the present study is the industrial wastewater effluent treatment resulting from a solar cell manufacturing process, which is a Joint Egyptian Chinese Renewable Energy laboratory, in Sohag Governorate. Fluoric and hydrochloric acids are the main pollutants causing a pH of 1 to 3. The effluent is neutralized by the addition of both potassium hydroxide and calcium hydroxide to permit the precipitation of the resulting sparingly soluble calcium fluoride. The chlorides are partially precipitated as calcium chloride, and the further addition of hydrated aluminum sulfate is used to precipitate the remaining extra chloride as an insoluble complex to reach the allowable chloride concentration in the treated effluent. Set of experiments at bench and pilot scales were run to achieve the optimum conditions for defluorination and dichlorination taking into consideration not exceeding the allowable ranges of pollutants as soluble salts in the final effluent.ResultsExperimental results showed that the performance of a pilot scale was satisfactory in fluorides, chlorides, and dissolved solids by 97.64, 78.85, and 79.4% removal, respectively. Based on these results a full-scale industrial treatment unit was designed for construction and operation as a treatment unit for industrial wastewater contaminated with fluorides as main pollutant.ConclusionsThe recommended treatment procedure succeeded in the removal of fluorides and chlorides as main contaminants in the effluent which permit the use of treated water in the irrigation of non-edible plants, according to Egyptian Code No. (501/2015).

Preparation of Al-loaded magnetic Chinese medicine residue-derived biochar and application of it in fluoride removal

The development and application of new materials for the extreme fluoride pollution problem has drawn increasingly wide attention. Here, Chinese medicine residue, FeSO4.7 H2O, FeCl3.6 H2O and Al(NO3)3 were used as raw materials to create an novel Al-loaded magnetic Chinese medicine residue-derived biochar (Al/Fe3O4/CMRB) adsorbent for effective fluoride adsorption. Al/Fe3O4/CMRB was characterized and used to conduct fluoride adsorption. In the pH range of 4–11, the fluoride adsorption reduced from 37.38 mg/g to 15.84 mg/g. The pseudo-second-order equation and Freundlich equation was the ideal model to describe the adsorption. The thermodynamic study confirmed the spontaneous and exothermic nature of fluoride adsorption by Al/Fe3O4/CMRB. Chloridion, nitrate, and sulfate had no influence on fluoride adsorption when a single anion and all three anions were present. phosphate created a more significant reduction of fluoride adsorption with rising concentrations, whether or not the other three anions were present. Al/Fe3O4/CMRB was an potential composite for aqueous fluoride removal. In addition, Al/Fe3O4/CMRB showed high separation efficiency in a contactless magnetic field, which demonstrated its potential use for large-scale applications in real samples.

Adsorption of fluoride by using sodium alginate coated poly-aluminium chloride (PAC) sludge: preparation, characterisation and mechanism

ABSTRACT Poly-aluminium chloride (PAC) sludge is a waste product created during drinking water treatment, usually generated in large quantities and typically landfilled. More attention must be directed to environmental-friendly management and economically sustainable of Al-based sludge. In this work, a low-cost and environmental-friendly adsorbent prepared by sodium alginate coated PAC sludge (SPS) was investigated for fluoride removal. Basic preparing parameters including heating temperature (200–800°C), sodium alginate concentration (0.5–5 wt%), particle size (1–2 mm, 2–3 mm, 3–4 mm) and operating parameters including dosage (1–14 g/L), solution pH (4–11), temperature (10–35°C), co-existing anions (NO3 −, Cl−, SO4 2-, PO4 3-) were examined to evaluate the optimum defluoridation capacity. The prepared SPS adsorbents reached a high removal efficiency of 95.6% with initial fluoride concentration of 10 mg/L, dose of 8 g/L, contact time of 24 h, pH value of 7 and temperature of 10°C. The kinetic study indicated that fluoride adsorption followed the pseudo-second-order kinetics well (R2 = 0.9942), and adsorption isotherms can be well described by Freundlich model (R2 = 0.9952). Thermodynamic studies showed the fluoride adsorption was spontaneous and exothermic. The elements and functional groups of SPS adsorbents were analysed by using EDS and FTIR, respectively. The adsorption mechanism involved physisorption, ligand-exchange and electrostatic attraction. According to N2 adsorption–desorption isotherm, the SPS was mesoporous material which facilitated the adsorption of fluoride ions. Also, aluminium presented in form of Al-OH in SPS adsorbents had significant contribution in fluoride adsorption. The concentration of the residual aluminium ions was 4.48 × 10−3 mg/L which is lower than the China Drinking Water Standard. The encouraging results of this preliminary study indicated that SPS is an environmental-friendly and cost-effective treatment option for groundwater with fluoride pollution.

Fabricating ultrafine zirconium oxide based composite sorbents in “soft confined space” for efficiently removing fluoride from environmental water

The fluoride pollution in environmental water can cause serious health problems, and the fluoride removal by sorbent is an effective strategy, and challenges by its poor selectivity and low capacity. Herein, we reported a new insight into the fabricating ultrafine zirconium oxide (ZrO2) based composite sorbents (E-ELP-Zr) in “soft confined space” and efficient fluoride removal from water. It relies on the confined aqueous phase of Oil-in-Water (O/W) high internal phase emulsions (HIPEs) as droplet reactor, and ultrafine ZrO2 particles (<10 nm) were achieved via the controllable in situ growth onto lipase immobilized poly(styrene-co-glycidyl methacrylate) nanospheres. E-ELP-Zr exhibited outstanding capacity for defluorination (135.8 mg g−1 at 298 K), quick adsorption rate in the first 10 min, and the superior selectivity against co-occurring anions (Cl-, SO42−, NO3– and CO32–). The adsorption mechanism of fluoride on E-ELP-Zr was strong electrostatic attraction as well as the specific affinity of zirconium. After five regeneration cycles, the adsorption capacity of E-ELP-Zr slightly decreases to 88.55% of the initial value, and the excellent interfacial stability was benefited from covalently attached lipases. More importantly, this hybrid sorbent can be successfully applied for low level (7.15 mg L-1) of fluoride decontamination from actual sample of fluorinated wastewater, which endowed a distribution coefficient (Kd) as high as 6.3 L g−1.

Spatial and seasonal variability, control factors and health risk of fluoride in natural water in the Loess Plateau of China

Hundreds of millions of people around the world are currently exposed to excessive amounts of fluoride (F-) in drinking water. Although the factors controlling the spatiotemporal distribution of F- contents have been analyzed, their contributions have rarely been quantified. In this study, 510 water samples were collected in the dry and wet seasons in China’s Loess Plateau to investigate the spatial and seasonal distribution, controlling factors, and potential health risks of F- in natural water. High-F- waters were mainly distributed in valley areas of the Loess Plateau, and more severe fluoride pollution of streamwater and groundwater was found in the wet and dry seasons, respectively. Mineral dissolution, competitive adsorption, adsorption/desorption and cation exchange jointly controlled F- enrichment. Spatiotemporal distribution of high-F- levels was mainly determined by climate and streamwater-groundwater connectivity in the dry season, with contribution rates of 41.7% and 37.6%, and by terrain and anthropogenic activities in the wet season, with contribution rates and 49.9–55.6% and 30.7%, respectively. Fluoride in groundwater through oral intake posed the greatest health risks to infants, followed by children, teenagers and adults in the dry and wet seasons. This study provides a scientific basis for the effective management of high-F- water in arid regions.

Defluorination mechanism related to the activity of hydroxyl groups: A combined density functional theory calculations and experimental study

Aluminum-based (Al-based) materials are of great significance to solve the global fluoride pollution problem. Hydroxylation modification is one of the effective methods to improve the surface activity and defluorination performance of aluminum matrix materials. However, the lack of in-depth understanding of the role of hydroxyl gourp at the molecular level restricts the preparation and application of Al-based adsorbents. In this work, based on the interface of Al-based two-dimensional materials, the effects of anionic ligands, doped metals and solution H+ on the structural activity of surface hydroxyl groups were explored by DFT theoretical calculation and experimental design. Simultaneously, quantitative analysis of the contribution of each possible mechanism in the defluorination process was carried out. Both anionic exchange reaction and chemical co-adsorption determined the defluorination process. The high polarizability and more negative charge of anionic ligands was found to facilitate reducing the activity of hydroxyl groups in weak acid environment. H+ can enhance the activity of hydroxyl, and thereby strengthening the hydrogen bond (H-bond) effect, but it will have a synergistic effect with anionic ligands. Metal doping will change the electron density on O atoms, which will affect the F- adsorption effect of hydroxyl via H-bond. Compared with the existing research, we carefully studied the influence of hydroxyl group activity on the defluorination performance of aluminum matrix materials, which can provide a feasible basis for structural design of the subsequent adsorbents.

Mechanisms of fluoride uptake by surface-modified calcite: A 19F solid-state NMR and TEM study

Fluoride pollution in groundwater is a serious problem threatening millions of people worldwide. Calcite is considered an ideal adsorbent for defluoridation owing to its widespread presence and low cost. To further enhance its performance, we synthesize a series of phosphate-modified calcites with varying phosphate concentrations. The surface modification led to the formation of a nanosized hydroxyapatite (HAP) coating on the calcite surface. With increasing concentrations of phosphate used for modification, the BET specific surface area of the adsorbents was dramatically enhanced, resulting in a great enhancement of F uptake. At low F concentrations (i.e., <1 mM), surface-modified calcite can achieve up to 25 times higher F removal efficiency than calcite. The 19F solid-state MAS NMR spectra yielded three distint peaks at δ(19F) = −86 ppm, −99 ppm, and −122 ppm, representing the formation of carbonate fluorapatite (CFA), fluorapatite (FAP), and coprecipitated F, respectively. This provides strong evidence for the contribution of newly formed HAP to F removal. In contrast, at high F concentrations (e.g., >2 mM), surface modification did not enhance F uptake by calcite. The 19F solid-state MAS NMR analysis revealed that the predominant deflurodation mechanism is the formation of CaF2 precipitates (δ(19F) = −108 ppm) for both pristine and modified calcite at high F concentrations. Under this condition, the contribution of the newly formed nanosized HAP to F uptake is insignificant. Taken together, our results demonstrated the potential of surface modification of calcite as a cost-effective technique for defluoridation for most F-rich groudwater.

Effects of soil fluoride pollution on wheat growth and biomass production, leaf injury index, powdery mildew infestation and trace metal uptake

Fluoride (F) is an emerging pollutant that originates from multiple sources and adversely affects plant growth and nutrient bioavailability in soil. This greenhouse study investigated the effects of soil F (0, 10, 20, 50, 100, 200 mg kg−1) on morpho-physiological growth characteristics of wheat, soil F contents, and bioavailability and uptake of F, phosphorus (P), sulphur (S), potassium (K), calcium (Ca), magnesium (Mg), aluminium (Al), iron (Fe), manganese (Mn), silicon (Si) and zinc (Zn) by wheat. Higher F significantly reduced plant height and number of leaves particularly at early growth stages and increased visible leaf injury index. Powdery mildew infestation coincided with leafy injury and was higher in elevated soil F treatments. Fluoride treatments (>50 mg kg−1) significantly increased water (H2O)- and calcium chloride (CaCl2)-extractable F contents in soil. Water-extractable soil F contents from soil in all concentration were higher than CaCl2-extractable F. This increased F bioavailability resulted in significantly higher F uptake and accumulation in live leaves, dead leaves and grains of wheat which followed order: live leaves > dead leaves > grains. Leaf injury index and number of dead leaves correlated significantly positively with soil H2O- and CaCl2-extractable F contents. Patterns of nutrient (P, K, S) and trace metals (Al, Ca, Mg, Fe, Mn, Si, Zn) varied significantly with F concentrations and between live and dead leaves, and grains except for Zn. Dead leaves generally had higher nutrients and trace metals than live leaves and grains. Fluoride contents in live leaves, dead leaves and grains showed positive correlations with nutrient elements but negative with trace metals. Number of dead leaves correlated negatively with Al, Ca, Fe, Mg, S and Si but positively with P and Zn contents in dead leaves whereas leaf injury index showed positive correlation with Fe, K, P, Si, Zn, S but negative with Al, Ca and Mg contents. These observations provided evidence of higher F uptake and associated impairment in nutrient and trace metal accumulation which caused leaf injury accompanied by powdery mildew infestation in wheat. However, further research in the region is required to confirm the relationship between F pollution, leaf injury and trace metal accumulation in crops under field conditions.

Efficient fluoride removal from water by amino Acid-enriched Artemia Cyst motivated Sub-10 nm La(OH)3 confined inside superporous skeleton

• Artemia Cyst-shell in-situ growth of La(OH) 3 nanoparticles for fluoride removal. • the sub-10 nm La(OH) 3 provides ultrahigh capacity (124 mg/g) • three-dimensional macropous structure of matrix provides fast kinetics. • yielding a satisfactory capacity of ∼ 6700 L/kg sorbent for application. The fluoride pollution in water has aroused great concern worldwide, and the fluoride removal by adsorbent is effective technique, and challenges by its weak selectivity and low capacity. Herein, we reported a new insight into the small size of La(OH) 3 nanoparticles preparation and efficient fluoride removal from waters. It relies on the charged amino-acids inside discarded Artemia Cyst-shell, motivated sub-10 nm La(OH) 3 formation (< 10 nm) with high activity, its super-porous (several μm) of three-dimensional skeleton further favors for the fluoride diffusion and kinetics. This hybrid nano-adsorbent exhibits outstanding capacity for defluorination (124 mg/g, 6.53 meq/g), the superior selectivity against various foreign ions, endows a distribution coefficient ( K d ) as high as 1000 mL/g. The super-porous skeleton also brings about rapid kinetic diffusion with ∼ 30 min for equilibrium, yielding a satisfactory capacity of ∼ 6700 L/kg sorbent for the application by the drinking water standards in China. The saturated adsorbent can be readily regenerated and reused without decrease in performance, this technology is promising for mitigating the fluoride contamination problem of worldwide.

Investigation on Efficient Removal of Fluoride from Ground Water Using Activated Carbon Adsorbents

Groundwater seems to be the most significant natural source of potable water for millions of individuals. Fluoride pollution in groundwater is a big problem in Tamil Nadu’s Dharmapuri area. According to a survey done in a school in the Dharmapuri area, dental and skeletal fluoroses afflict almost 75% of school kids. There is no proven or recommended cost-effective strategy for lowering fluoride levels in the home. This study proposes cost-effective and efficient natural treatment approaches for lowering fluoride levels. In this experiment, fluorides in groundwater are eliminated to a suitable extent utilizing natural adsorbents. Neem stem charcoal (activated carbon), neem leaves powder, dry coconut husk, coconut shell charcoal (activated carbon), and rice husk powder are natural adsorbents. The adsorbents were utilized at different concentrations until the best concentration was found. The ideal concentration removes the bulk of fluoride from groundwater and delivers adequate treatment. People could adopt this cost-effective procedure because just a few components are enough. As per the Bureau of Indian Standards, the concentration should not exceed 1.5 ppm, and it should not be lesser than 1 ppm; keeping this in mind, the neem stem charcoal which has higher efficiency in removing fluoride can be used in extensive environments, but in this selected place, it reduces the concentration even below 1 ppm, which relays below the standard level. As a result, adopting these procedures helps prevent dental and skeletal fluoroses, which is common among young people.

A Brief and Critical Review of Chronic Fluoride Poisoning (Fluorosis) in Domesticated Water Buffaloes (Bubalus bubalis) in India: Focus on its Impact on Rural Economy

In the rural areas of India, fluoridated drinking water, industrial fluoride pollution and fluoride-rich feed phosphate supplements are the major sources of fluoride exposure for domesticated water buffaloes (Bubalus bubalis). However, the fluoridated drinking groundwater is the commonest and principal source of fluoride exposure for these ruminants. Chronic fluoride exposure for long-time deteriorate the animal health and causes the fluorosis disease. In the country, the drinking groundwater sources of villages are contaminated with fluoride beyond the threshold value, 1.0 or 1.5 mg/L. At 1.5-1.7 ppm fluoride concentration in drinking water, 62.2% and 21.6% calves and 55.9% and 48.3% adult buffaloes are found to be afflicted with dental and skeletal fluorosis, respectively. The maximum prevalence of dental and skeletal fluorosis, 96.8% and 34.4% in calves and 66.9% and 60.2% in adult buffaloes has also been reported at or &gt; 3.0 ppm fluoride in drinking water, respectively. However, calves are found to be more sensitive and susceptible to chronic fluoride toxicity or fluorosis. Besides the deterioration of the animal health, chronic fluoride intoxication in buffaloes also weakens the rural economy which has been focussed in the present review. In this communication, besides the status of chronic fluoride intoxication in the form of osteo-dental and non-skeletal fluorosis in buffaloes, determinations, bio-indicators and bio-markers of fluorosis and prevention and control of chronic fluoride poisoning in these animals are also considered and briefly and critically reviewed. Simultaneously, research gaps are also identified and highlighted them for further research study on chronic fluoride intoxication in buffaloes. Findings of this review may help in preparation of health policy for improving the health and mitigation of fluorosis in economically important buffalo animals in the country.

Selenomethionine alleviated fluoride-induced toxicity in zebrafish (Danio rerio) embryos by restoring oxidative balance and rebuilding inflammation homeostasis.

Fish are target organisms that are extremely susceptible to fluoride pollution, and an increase in fluoride load will damage multiple systems of fish. Selenomethionine (Se-Met) at low levels has been reported to alleviate oxidative damage and inflammation caused by toxic substances, but whether it can alleviate fluoride-induced toxicity in zebrafish embryos has not been elucidated. In this study, the intervention effects of Se-Met on developmental toxicity, oxidative stress and inflammation in zebrafish embryos exposed to fluoride were determined. Our results showed that fluoride accumulated in larvae and induced developmental toxicity in zebrafish embryos, caused oxidative damage and apoptosis, increased significantly the MPO and LZM activities and the levels of the inflammation-related genes IL-1β, IL-6, TNF-α, IL-10 and TGF-β. Moreover, fluoride significantly increased the levels of ERK2, JNK, p38 and p65 in MAPKs and NF-κB pathways. Se-Met-treatment alleviated the adverse effects induced by fluoride, and all of the above indicators induced by fluoride returned to near control levels with increasing concentrations and time. However, treatment with Se-Met-alone also markedly increased the levels of IL-6, TNF-α, IL-10, TGF-β, ERK2 and JNK. In short, these data demonstrated that Se-Met-could alleviate fluoride-induced toxicity in zebrafish embryos by restoring oxidative balance and rebuilding inflammation homeostasis, although low levels of Se-Met-alone had certain toxic effects on zebrafish embryos. Taken together, Se-Met-plays an important role in preventing toxic damage induced by fluoride in zebrafish embryos, although it has certain toxic effects.

Adsorption of fluoride from industrial wastewater using polymer adsorbents: a review

Fluoride pollution in ground and surface water originates from naturally occurring reactions and industrial activities such as the disposal of industrial wastewater. Amongst different fluoride removal technologies including chemical precipitation, membrane filtration, ion exchange processes, and electrodialysis, adsorption is an attractive method for fluoride removal from wastewater due to its low operational cost, simplicity, and good sustainability. Various adsorbents are used for fluoride removal including, metal oxides and hydroxide, carbonaceous adsorbents, zeolite, polysaccharides, and polyresin adsorbents. This review studies the application of modified polysaccharides and polyresin adsorbents for the removal of fluoride from wastewater. The relationship between the adsorption conditions and the resulting adsorption capacity is thoroughly discussed. Based on the reported studies, modified polysaccharides and polyresins adsorbents can effectively remove fluoride from wastewater achieving high adsorption capacity, the highest being 92.39 mg/g for aluminum impregnated amberlite at pH 3. Furthermore, aluminum impregnated adsorbents reported a higher fluoride adsorption capacity than other modification methods where the three adsorbents with the highest fluoride adsorption capacity are: aluminum impregnated amberlite 92.39 mg/g at pH 3> zirconium immobilized crossed linked chitosan 48.26 mg/g at pH 6 > chitosan/aluminum hydroxide beads 17.68 mg/g at pH 4. In addition, polymeric adsorbents are also highly sustainable as they can be regenerated multiple times to be reused. Therefore, the high adsorption capacity and good regeneration potential allow polymeric adsorbents to serve as promising and sustainable adsorbents to remove fluoride from industrial wastewater.

Comparison of Water Defluoridation Using Different Techniques

Fluoride pollution in subsurface water is a significant problem for different nations across the world because of the intake of excessive fluoride caused by the drinking of the contaminated subsurface. Water pollution by flouride can be attributed to the natural and human-made agents. Increased levels of fluoride in drinking water may result in the irretrievable demineralization of bone and tooth tissues, a situation called fluorosis, and other disorders. There has long been a need for fluoride removal from drinking water to make it safe for human use. Among the various fluoride removal methods, adsorption is the method most popularly used due to its cheap cost, ease of utilization, and being a scalable and simple physical technique. According to the findings of this study, the highest concentration of fluoride (0.1–15.0 mg/L) was found in Sweden and the lowest (0.03–1.14 mg/L) in Italy. We collected the values of adsorption capacities and fluoride removal efficiencies of various types of adsorbents from valuable released data accessible in the literature and exhibited tables. There is still a need to find the actual possibility of using biosorbents and adsorbents on a commercial scale and to define the reusability of adsorbents to decrease price and the waste generated from the adsorption method. This article reviews the currently available methods and approaches to fluoride removal of water.

Chemical characteristics, evolution, and quality of groundwater and processes controlling its fluoride concentration features: case study of a typical high-fluoride areas in the Southwestern Shandong Plain, China.

In this study, the groundwater (GW) in the high-fluorine area of the Southwestern Shandong Plain was divided according to the characteristics of high Na% (> 75%), and its water chemistry characteristics and causes were discussed separately, and the hydrochemical process of the formation of high-fluorine GW was determined. Finally, the GW quality of the study area was evaluated. The results proved that silicate hydrolysis can significantly promote the release of F- in fluorine-containing minerals; high %Na can be used as one of the early-warning conditions for judging high-fluoride areas. To this end, 132 GW samples were collected from 66 wells during the dry and wet seasons. The study area was found to have weakly alkaline GW (pH 7.1-8.9) and could be divided into high %Na areas (HNA) and non-HNA. GW exhibited different hydrochemical characteristics between HNA and non-HNA. In non-HNA, total hardness (TH) exceeded 200mg/L, and total dissolved solids (TDS) ranged from 514.1 to 5246.1mg/L; in HNA, TH was less than 200mg/L, TDS ranged from 552.8 to 1298.3mg/L, and Na+ increased with TDS, whereas Ca2+ and Mg2+ contents were low. The main water type in HNA was HCO3-Na and in non-HNA was SO4·Cl-Ca·Mg and SO4·Cl-Na. The study area is experiencing serious fluoride pollution. GW in HNA is mostly controlled by carbonate and silicate hydrolysis and evaporation, whereas GW in non-HNA is controlled by dolomite dissolution and cation exchange in the main. Moreover, GW in HNA has significantly been altered by albite hydrolysis, which produces Na+ and HCO3- and triggers various reactions promoting the release of F- from fluorine-containing minerals (FCM). Regarding the water quality for irrigation, GW in HNA was found to be less suitable than that in non-HNA. Nevertheless, in terms of the water quality index (WQI), GW is moderate for drinking and poor for irrigation. Therefore, extensive attention should be paid to the exploitation and management of high-sodium GW in the plain area.

Leaching behavior and environmental safety evaluation of fluorine ions from shotcrete with high-fluorine alkali-free liquid accelerator.

High-fluorine alkali-free liquid accelerator (AF-hf, F- concentration was about 2.31g/L) was still used in engineering because of its low cost, excellent stability, and coagulation-promoting effect. The main purpose of this study was to explore the leaching behavior of fluorine ions in shotcrete for tunnel lining with high-fluorine alkali-free liquid accelerator and whether there was fluoride pollution. The setting time and mechanical properties of cement paste and mortar with AF-hf were tested. Under different environmental conditions, F- leaching concentration from sprayed concrete was studied comparatively. Moreover, XRD and SEM were used to analyze the crystal composition and micro morphology of hydration products. The experimental results showed that with the increase of AF-hf dosage, the setting time of cement paste was greatly shortened, and later strength of mortar and shotcrete could meet the construction requirements. In addition, when the leaching solution type (including Na2CO3, Na3PO4, Na2SO4, and NaNO3) and testing conditions (particle size, soaking temperature, leaching solutions) were different, F- leaching concentration changed regularly, and the minimum value was more than 20 mg/L, which might cause fluorine pollution to groundwater and soil. After shotcrete samples were soaked, the CaF2 peaks' intensity was relatively weaker and Ca(OH)2 decreased obviously. Meanwhile, cement hydration products became looser and abundant of flaky C-S-H gel transformed into fibrous and chained structure.

Capacitive Removal of Fluoride Ions via Creating Multiple Capture Sites in a Modulatory Heterostructure

Fluoride pollution has become a major concern because of its adverse effects on human health. However, the removal capacity of defluorination agents in traditional methods is far from satisfactory. Herein, capacitive removal of F- ions via creating multiple capture sites in a modulatory heterostructure has been originally demonstrated. The heterostructure of uniformly dispersed Al2O3 coating on hollow porous nitrogen-doped carbon frameworks was precisely synthesized by atomic layer deposition. An exceptional F- ion removal efficiency at 1.2 V (95.8 and 92.9% in 5 and 10 mg/L F- solutions, respectively) could be finally achieved, with a good regeneration ability after 20 consecutive defluorination cycles. Furthermore, we investigated the removal mechanisms of F- ions by in situ Raman, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy measurements. The promotional removal capacity was realized by the multiple capture sites of the reversible conversion of Al-F species and the insertion of F- ions into the carbon skeleton. This work offers an important new pathway and deep understanding for efficient removal of F- ions from wastewater.

Assessment of shallow aquifer vulnerability to fluoride contamination using modified AHP-DRASTICH model as a tool for effective groundwater management, a case study in Yuncheng Basin, China

Vulnerability assessment is an effective tool for the precaution of groundwater quality to specific pollutants. Groundwater fluoride pollution is severe and universal in the world, however, the method of groundwater risk assessment to fluorine is never built. The objective of this study was to establish an effective method to assess the potential level of groundwater vulnerability to fluoride by a modification of the typical DRASTIC model. The hydrogeochemical (H) factor (pH and TDS) was designed as a complementary parameter in the DRASTICH model. The weights of the parameters were revised by Analytical Hierarchy Process (AHP) method. The built AHP-DRASTICH model was applied to evaluate the groundwater vulnerability to fluoride contamination in Yuncheng basin, northern China, where groundwater with high fluoride concentration occurred extensively. The assessment result indicates that about 40 percent of the area belonged to relatively high and high vulnerability zones, which mainly distributed at the central part of the basin with strong evaporation and longer water-rock interaction time. The AHP-DRASTICH model shows a stronger positive correlation between risk scores and F concentration, giving better vulnerability assessment to F pollution compared with DARSTIC and DRASTICH models. The AHP-DRASTICH model is reliable and useful for guiding government and policy maker to take effective actions protecting groundwater from specific pollution.