Fluoride Removal In Water Research Articles

Fluoride Removal in Water Using Kaolin and Eggshell Powder Blend Adsorbents

Fluoride contamination in water has emerged as a significant global concern due to its adverse health effects when consumed in excess. This study is focused on developing an eco-friendly, cost-effective adsorbent for fluoride removal using eggshells and kaolin. Adsorbent blends were prepared by mixing kaolin and eggshell powder in six different ratios, namely; 100:0, 80:20, 65:35, 50:50, 35:65, and 20:80. Cylindrical-shaped pellets were produced from each of the blends and subjected to the thermal treatment at 950 ◦C. Fluoride adsorption capacities of the pellets were investigated at different pH conditions (from pH 2 to pH 10) for a 5 mg/L fluoride solution with 1 g of adsorbent dosage and 60 min of contact time. Pellets with a 50:50 ratio (CKE3) were found to be the most effective adsorbent considering the adsorption capacity and stability at all the studied pH conditions. At pH 6, CKE3 showed an adsorption capacity of 0.06 mg/g compared to 0.02 mg/g of kaolin-only pellets. XRD, TGA-DSC, EDX and SEM analysis were used to characterize the adsorbent. XRD analysis showed that the raw adsorbent contained phases of CaCO3 and kaolinite, whereas the calcined material comprised Ca(OH)2 and metakaolinite. Batch experiments were carried out with CKE3 for adsorbent dosage, pH, contact time, and initial fluoride concentration. An adsorbent dosage of 4 g was capable of resulting in a 53% removal of fluoride for a 5 mg/L solution after 60 min of contact time. Pseudo-first-order and pseudo-second-order kinetic models were applied in the study, and pseudo-second-order exhibited the best fit. The isotherm data were studied for Langmuir and Freundlich models, and the results were satisfactorily fitted with Langmuir isotherm.

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.

Adsorption of Fluoride from Aqueous Solution by Zirconium-Modified Artificial Zeolites: Kinetics, Thermodynamics and Mechanism

Artificial zeolites (AZ) and AZ modified with zirconium cation (AZZ) were fabricated in this work. AZ and AZZ, which were characterized by SEM and XRD, showed that AZZ was the composite of AZ and ZrO2. The adsorption kinetics and isotherms of AZ and AZZ towards fluoride removal in water were consistent with the Langmuir and pseudo-second-order models, respectively. AZZ had better fluoride adsorption capacity than AZ. The maximal adsorption capacity of fluoride onto AZZ reached up to 128.2 mg/g. Moreover, the thermodynamic studies illustrated that the adsorption procedure was spontaneous and endothermic. The effect of solution pH on AZZ fluoride adsorption was also investigated, and the results showed that the more acidic the fluoride solution, the better the fluoride adsorption capacity. After five cycles of regeneration, the adsorption capacity of AZZ was maintained at 78 %. Based on zeta potential measurements, this work proposed that the electrostatic attraction between AZZ and fluoride ions (F-) should be the mechanism for F- adsorption onto AZZ in water.

Removal of Fluoride in Water Using Sustainable Strontium Ferrite Graphene Nano Composite

Removal of Fluoride in Water Using Sustainable Strontium Ferrite Graphene Nano Composite

Development of a tea waste-based mixture for the removal of fluoride in water: A case study with selected concentrations of fluoride in water

Development of a tea waste-based mixture for the removal of fluoride in water: A case study with selected concentrations of fluoride in water

Structure–performance correlation guided cerium-based metal–organic frameworks: Superior adsorbents for fluoride removal in water

Fluoride in the hydrosphere exceeds the standard, which could be critically hazardous to human health and the natural environment. The adsorption method is a mature and effective way to remove pollutants in water, including fluoride. In this study, we synthesized three kinds of cerium-based metal–organic frameworks (Ce-MOFs) with different structures and properties by modulating the organic ligands (i.e., trimesic acid (BTC), 1,2,4,5-benzenetetracarboxylic acid (PMA), and terephthalic acid (BDC)) via the solvothermal method. The adsorption kinetics of Ce-MOFs on fluoride well fit the pseudo second order model, and their adsorption isotherms also conform to Langmuir isothermal model. The thermodynamic study reveals that the adsorption process is a spontaneous endothermic reaction. The maximum saturated adsorption capacities of Ce-BTC, Ce-PMA, and Ce-BDC are 70.7, 159.6, and 139.5 mg g−1, respectively. Ce-MOFs have stable and excellent adsorption capacity at pH = 3–9. Coexisting anions (Cl−, SO42−, and NO3−) do not affect the performance of Ce-MOFs for fluoride removal. Moreover, Ce-MOFs also show their broad prospect as superior fluoride adsorbents because of their excellent performance and reusability in real water samples. Organic ligands have a remarkable influence on the defluoridation performance of Ce-MOFs. This work will provide a feasible idea for designing MOFs as superiors adsorbents for defluoridation.

Recent advances in metal–organic framework-based materials for removal of fluoride in water: Performance, mechanism, and potential practical application

Clean water is necessary in all areas of life, especially for our body. Fluoride in water has serious negative effects on human health and the environment. Effectively repairing fluoride-polluted water remains a critical mission. Among the numerous technologies for removing fluoride from water, metal–organic framework (MOF) materials are regarded as promising adsorption materials. In this study, the synthesis of MOFs and their application progress in aquatic defluoridation in recent years, which are classified according to the central metal ions, are reviewed. In particular, an understanding of the effect factors for water remediation is provided, and the potential environmental application is analyzed. The adsorption mechanism and the evaluation on potential practical applications for fluoride removal by different MOFs are elucidated. Finally, future research opportunities and prospects of MOF-based materials for fluoride removal are proposed.

Efficient removal of fluoride from neutral wastewater by green synthesized Zr/calcium sulfate whiskers: An experimental and theoretical study

A convenient and effective method was developed to fabricate zirconium-based calcium sulfate whiskers (Zr-CSWs), an environmentally friendly adsorption material designed to clean excessive fluoride from wastewater. Zr-CSWs, which potentially provide high adsorption activity toward fluoride in wastewater, overcome an aggregation problem typical of Zr-based species that may block the pore structure of the supporting material and degenerate its treatment performance. The results indicate that Zr-CSWs show excellent equilibrium adsorption capacity compared to other Zr-based materials in practical water solutions with pH values of 6–7. The adsorption of fluoride on Zr-CSWs was further evaluated in accordance with the Langmuir equation and the pseudosecond-order model. Coexisting anions had a minor effect on the removal of fluoride, and a strong alkali solution regenerated the used adsorbent. Density functional theory (DFT) calculations were performed to determine the mechanism of fluoride removal. The calculations demonstrated that the removal of fluoride by Zr-CSWs was mainly achieved by ion exchange between fluoride ions and OH - on the surface of the adsorbent, where a protonation process created low-coordination Zr atoms. • Zirconium decorated calcium sulfate whisker (Zr-CSW) was prepared in a simple and low-cost way. • Zr-CSW has high capacity and good selectivity for the removal of fluoride in water. • The adsorption follows Langmuir model and pseudosecond-order dynamic equation. • The mechanism for fluoride removal has been revealed by density of functional theory (DFT).

High-performance lanthanum-based metal–organic framework with ligand tuning of the microstructures for removal of fluoride from water

Excess fluoride in water poses a threat to ecology and human health, which has attracted global attention. In this study, a series of lanthanum-based metal–organic frameworks (La-MOFs) were synthesized by varying the organic ligands (i.e., terephthalic acid (BDC), trimesic acid (BTC), biphenyl-4,4-dicarboxylic acid (BPDC), 2,5-dihydroxyterephthalic acid (BHTA), and 1,2,4,5-benzenetetracarboxylic acid (PMA)) to control the microscopic structure of the MOFs and subsequently apply them for the removal of fluoride in water. The maximum capture capacities of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC at 298 K are 105.2, 125.9, 145.5, 158.9, and 171.7 mg g−1, respectively. The adsorption capacity is greater than most reported adsorbents. The adsorption isotherms of La-MOFs for fluoride are well fit to the Langmuir isotherm model. In addition, the adsorption kinetics of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC follows the pseudo-second-order kinetic model, and the kinetic rate-limiting step of adsorption is chemical adsorption. Thermodynamics revealed that temperature is favorable for the adsorption of fluoride. Meanwhile, La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC are suitable for the removal of fluoride in a relatively wide pH range (4.0–9.0). Simultaneously, from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis, electrostatic attraction and ligand exchange are identified as the main action mechanisms for the adsorption of fluoride of La-MOFs. The prepared La-MOFs are used as efficient adsorbents for removal of fluoride in actual water, indicating that they have great potential in removing fluoride in real and complex environmental water. This work provides a new strategy for designing adsorbents with adjustable microstructure and expected function to effectively recover fluorosis in water.

Assessment of fluoride removal in a batch electrocoagulation process: A case study in the Mount Meru Enclave.

The presence of excessive amounts of fluoride than prescribed standards has been reported in various sources of domestic water supply around the slopes of Mount Meru and other parts in Tanzania. Efforts to remove the excessive fluoride have been carried out using various technologies. In this study, electrocoagulation experiments were carried out to assess its efficiency on fluoride removal. The fluoride concentration tested ranged from 1.37 to 48 mg/L in both synthetic and natural waters. The voltage applied in the electrocoagulation (EC) process ranged from 0 to 50 V while maintaining pH values of 4 to 9. The representative experimental results for the Ngarenanyuki river water with initial fluoride concentration of 29.5 mg/L accomplished a removal efficiency of 90% at an optimal electrolysis time of 30 min, an applied voltage of 30 V and an optimal pH of 6. The method showed efficient fluoride removal in water to allowable limits by World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) (1.5 mg/L). Despite the voltage applied (30 V), the pH at neutrality remained unchanged thus making the process more efficient. At this voltage (30 V) the process has been reported previously also to have the capability of disinfecting the water and hence rendering such water safe for use.

Multiple coated graphite oxide – sand composites for fluoride removal in water

In drinking water treatment, sand filters are frequently used to remove turbidity. We enhanced the performance of the sand by a chemical modification using graphite oxide (GO). Repeated coating of sand granules with graphite oxide (GO) followed by low temperature (120 °C) pyrolysis yielded hierarchical core-shell structures. The sand granules can be coated with GO in a single (hereafter S-GO1) or multiple (presently five cycles, hereafter S-GO5) coating steps. The GO coated sand composites were characterized using spectroscopic, microscopic, and conventional techniques. When compared to S-GO1, the GO coatings on S-GO5 show enhanced stability in contact with water. The S-GO5 removes over 70% fluoride around pH 6.30 ± 0.02 according to Hill adsorption model. We also used a simulated water sample to assess the efficacy of sand/GO composites to remove fluoride and turbidity. When S-GO5 is used, the solution turbidity has reduced by 87% (from 0.08 to 0.01 NTU). However, in the presence of S-GO1, the turbidity has increased by + 75% (from 0.08 to 0.14 NTU). The gradual dissolution of adhered GO on S-GO1 enhanced the turbidity of treated water. The S-GO5 can be used to regulate excess fluoride and turbidity in water, simultaneously.

Experimental and model study for fluoride removal by thermally activated sepiolite.

The present investigation demonstrates the preparation of thermally activated sepiolite for effective removal of fluoride via adsorption from an aqueous solution. The thermal treatments on sepiolite were conducted at different temperatures (300-950 °C) for 4 h in an N2 atmosphere, and the thermally activated sepiolite was characterized using a field emission scanning electron microscope (FESEM), X-ray diffractometry (XRD), X-ray fluorescence (XRF), a differential scanning calorimetry-thermogravimetric analyzer (DSC-TGA), and a surface area analyzer. Sepiolite that was treated at 950 °C was shown to have a higher fluoride removal efficiency than other temperatures. The fluoride removal was evaluated under different experimental conditions such as solution pH, adsorbent dose, reaction time, initial concentration, temperature, presence of co-existing ions, and reuses. The kinetic and equilibrium adsorption results were well described by the pseudo-second-order kinetic model and Langmuir isotherm, respectively, and adsorption of fluoride onto thermally activated sepiolite was endothermic and spontaneous in nature. The Langmuir maximum adsorption capacity (169.95 mg/g) was superior to the literature value. The thermally activated sepiolite was also effective in a continuous flow system for treating fluoride. Thus, this thermally activated sepiolite is expected to be used as an effective adsorbent for the removal of fluoride in water.

Adsorptive removal of fluoride using polymer-modified ceria nanoparticles: determination of equilibrium, kinetic and thermodynamic parameters

ABSTRACT Polyaniline/Ceria nanocomposite is prepared in two steps: CeO2 by gel combustion method and it’s polymer nanocomposite by in situ polymerization. The as-synthesized nanocomposite is characterized by X-Ray Diffractometer, Scanning Electron Microscopy, Brunauer–Emmett–Teller technique, etc. Its efficacy in adsorptive removal of fluoride in water is investigated by the batch method under various experimental conditions including contact time, pH, initial concentration, temperature, etc. The maximum adsorption capacity is obtained at neutral pH within 1 h. The adsorption kinetics data is well fitted into the pseudo-second order model and Langmuir model. The results of the adsorption thermodynamic study evidenced a spontaneous, exothermic and entropy-driving adsorption process.

Fluoride in Drinking Water and Nanotechnological Approaches for Eliminating Excess Fluoride

Arising awareness of health hazards due to long-term exposure of fluoride has led researchers to seek for more innovative strategies to eliminate excess fluoride in drinking water. Fluoride-bearing chemicals in both natural and anthropogenic sources contaminate drinking water, which mainly cause for human fluoride ingestion. Hence, developing sustainable approaches toward alleviation is essential. Among many emerging techniques of defluoridation, nanotechnological approaches stand out owing to its high efficiency, and hence, as in many areas, nanotechnology for excess fluoride removal in water is gaining ground compared to other conventional adsorbents and process. The present review focuses on some of the advanced and recent nanoadsorbents including their strengths and shortcomings (e.g., CNT, LDH, graphene-based nanomaterials, and magnetic nanomaterials) and other processes involving nanotechnology while discussing basic aspects of hydrochemistry of fluoride and geological conditions leading for water fluoride contamination. Considering all the findings in survey, it is evident that developing more sustainable techniques is essential rather than conducting batch-type experiments solely.

Enhanced adsorption of fluoride on Al-modified boron nitride nanosheets from aqueous solution

Though fluoride is a necessity for human body, excessive intake probably leads to irreversible damages such as dental fluorosis, skeletal fluorosis and lesions of the endocrine glands, thyroid and liver. Herein boron nitride nanosheets (BNNSs) and a series of Al-modified BNNSs (BNNSs-Al-X) with different Al amounts were first prepared to remove superfluous fluoride in aqueous solution. The modified Al was proved to be amorphous Al2O3 on the surface of BNNSs. Batch adsorption results show that both BNNSs and BNNSs-Al-2, which fits pseudo-second-order model well, have high adsorption rate for fluoride. The maximum adsorption capacity calculated by Langmuir model is 50.510 mg/g for BNNSs-Al-2, which is better than vast majority of reported adsorbents. The excellent adsorption capacity of BNNSs-Al-2 could be attributed to the synergy of porous BNNSs and amorphous Al2O3. Primary BNNSs can adsorb fluoride mainly by physical interaction, while chemical adsorption is predominant on the Al-modified BNNSs, which can be deduced from the fitted model and corresponding parameters. All of the above results prove that BNNSs-Al-2, as a promising adsorbent, can play an important role for removal of fluoride in water.

Fluoride removal in water by a hybrid adsorbent lanthanum–carbon

Various health problems associated with drinking water containing high fluoride levels, have motivated researchers to develop more efficient adsorbents to remove fluoride from water for beneficial concentrations to human health. The objective of this research was to anchor lanthanum oxyhydroxides on a commercial granular activated carbon (GAC) to remove fluoride from water considering the effect of the solution pH, and the presence of co-existing anions and organic matter. The activated carbon was modified with lanthanum oxyhydroxides by impregnation. SEM and XRD were performed in order to determine the crystal structure and morphology of the La(III) particles anchored on the GAC surface. FT-IR and pKa’s distribution were determined in order to elucidate both the possible mechanism of the lanthanum anchorage on the activated carbon surface and the fluoride adsorption mechanism on the modified material. The results showed that lanthanum ions prefer binding to carboxyl and phenolic groups on the activated carbon surface. Potentiometric titrations revealed that the modified carbon (GAC–La) possesses positive charge at a pH lower than 9. The adsorption capacity of the modified GAC increased five times in contrast to an unmodified GAC adsorption capacity at an initial F− concentration of 20mgL−1. Moreover, the presence of co-existing anions had no effect on the fluoride adsorption capacity at concentrations below 30mgL−1, that indicated high F− affinity by the modified adsorbent material (GAG–La).

Millimeter-sized Mg–Al-LDH nanoflake impregnated magnetic alginate beads (LDH-n-MABs): a novel bio-based sorbent for the removal of fluoride in water

Mg–Al-LDH nanoflake impregnated magnetic alginate beads (LDH-n-MABs) were successfully synthesized and their defluoridation performance was systematically evaluated. Batch experiments showed that the LDH-n-MABs outperformed many other reported adsorbents with higher adsorption capacities. The effects of various limiting factors including pH, contact time, initial fluoride concentration, temperature, and co-existing substances were investigated. XPS and FT-IR measurements evidenced the complex uptake mechanism of fluoride onto the LDH-n-MABs. The advantages of this adsorbent are as follows: (1) Mg–Al-LDH nanoflakes with a higher adsorption capacity for F− were immobilized into alginate beads without leaching, taking the safety issues concerning nanomaterials into consideration; (2) the prepared beads had a high magnetic sensitivity to an external magnetic field providing an easy and efficient way to separate them from aqueous solution; (3) the bio-based sorbents offer advantages such as biodegradability, hydrophilic properties, natural origin and a high abundance. Furthermore, the results from the real fluoride contaminated groundwater study confirmed the feasibility of LDH-n-MABs for fluoride removal.

Development of amine functionalized co-polymeric resins for selective fluoride sorption

This study describes the development of various synthetic co-polymeric resins modified by ethylenediamine such as vinylbenzyl chloride/divinylbenzene-ethylenediamine (VBC/DVB-ED), styrene/divinylbenzene/vinylbenzylchloride-ethylenediamine (ST/DVB/VBC-ED) and acrylonitrile/divinylbenzene/vinylbenzylchloride-ethylenediamine (AN/DVB/VBC-ED) for the removal of fluoride in water. Fluoride sorption experiments were carried out in batch mode. Among the synthetic resins, AN/DVB/VBC-ED resin possessed higher defluoridation capacity (DC) than ST/DVB/VBC-ED and VBC/DVB-ED resins. The fluoride removal studies were carried out to optimize the various equilibrium parameters viz., contact time, pH, co-anions, different initial fluoride concentration and temperature. The equilibrium data were fitted with isotherms and kinetic models to find the best fit for the sorption process. The sorbents were characterized using FTIR, elemental analysis, BET surface area and SEM with EDAX analysis. Field trial studies indicated that the synthesized resins could be used as effective sorbents for fluoride removal.

Synthesis and characterization of lanthanum impregnated chitosan flakes for fluoride removal in water

In the present research work, biopolymer chitosan has been modified by impregnation of lanthanum to enhance the fluoride removal capacity of chitosan. The effect of various synthesis parameters like lanthanum loading, stirring time and drying temperature, on fluoride removal has been studied. It was observed that the synthesis parameters have significant influence on development of LCF and in turn on fluoride removal capacity. The adsorbent has been characterized with XRD, SEM and FTIR studies. The optimal condition for synthesis of LCF includes lanthanum loading: 20 wt.%, stirring time: 6 h, drying temperature: 75 °C for 2 h with maximum adsorption capacity of 1.27 mg/g. XRD Pattern of LCF was compared with bare chitosan which shows that chitosan structure is retained after lanthanum impregnation. SEM of LCF shows the presence of spherical particles spread over the chitosan matrix. The experimental data fitted well in Freundlich isotherm and follows pseudo-second order kinetics and governed by intra-particle diffusion and it is a complex process. Effect of pH and effect of presence of interfering ions on adsorption of fluoride were studied. The performance of LCF was compared with many other reported adsorbent for fluoride removal. Reuse and regeneration capacity of LCF was also explored.

Enhanced adsorptive removal of fluoride using mesoporous alumina

Two different kinds of mesoporous alumina samples were prepared using aluminum tri- sec-butoxide in the presence of either cetyltrimethylammonium bromide (MA-1) or stearic acid (MA-2) as a structure-directing agent, and tested for adsorptive removal of fluoride in water. Both materials contain a wormhole-like mesopore structure, but exhibited different textural properties: surface area (421 or 650 m 2/g) and pore volume (0.96 or 0.59 cm 3/g). These mesoporous aluminas demonstrated significantly improved adsorption capacity and faster kinetics to those of the commercial activated aluminas in fluoride removal by adsorption process. MA-2 prepared using stearic acid, in particular, demonstrated an adsorption capacity (14.26 mg/g) and initial adsorption rate (14.6 mg/g min) that were respectively 2.2 and 45 times higher than those of a commercial gamma alumina. The textural features of larger surface area and relatively smaller pore size in MA-2 compared to the activated aluminas are believed to be responsible for this enhancement in adsorption process.