Fluoride Sorption Research Articles

Fluoride removal using a rotating anode electro-coagulation reactor: Parametric optimization using response surface methodology, isotherms and kinetic studies, economic analysis and sludge characterization

The presence of fluoride in drinking water can cause various diseases, such as dental fluorosis and skeletal fluorosis. The present study aims to intensify the fluoride removal using a rotating anode electro-coagulation (EC) reactor with providing the proper hydrodynamics conditions. This fluoride removal is modeled and optimized using Response Surface Methodology (RSM) and central composite design (CCD) with varying operational parameters (rotation speed: 20–80 RPM, current: 0.2–1.0 A, initial fluoride concentration: 8–40 mg/L and time: 15–75 min). The maximum fluoride removal is obtained as 96.87% (predicted) and 95.40% (experimental) for the optimized process parameters, initial concentration of 32 mg/L, 0.8 A current, 60 min, and 60 RPM of rotating speed. Kinetic analysis reveals that the removal process adheres to a second-order kinetic model, suggesting that the rate of fluoride removal is dependent on the concentration of fluoride ions present. Isothermal studies indicate that the effective sorption of fluoride onto the generated flocs follows a sips isotherm. The optimal cost analysis is carried out to determine the operational cost as 0.256 USD/m3 for F removal of 93.49% at initial concentration 24 mg/L, time 50 min, current 0.7 A, and rotation 70 rpm and presenting a cost-effective solution for fluoride mitigation. Further, characterizations of the resultant sludge through X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and the Toxicity Characteristic Leaching Procedure (TCLP) confirmed the safe disposal potential of the sludge. The findings show a promising approach for fluoride removal, combining high efficiency, economic viability, and environmental safety.

Development of magnetic La doped Al2O3 core-shell nanoparticle loaded hydrogel for selective recovery of fluoride from aquatic medium

The selective removal of pollutants from water bodies is regarded as a conciliation between the rapid expansion of industrial activities and need of clean water for sustainability. Fluoride is one such geogenic pollutant, and various materials have already been reported. Developing an efficient field employable material is however a challenge. Herein, we report the synthesis and competencies of strategically designed magnetic La-doped Al2O3 core-shell nanoparticle loaded polymeric nanohybrid as a benchmark fluoride sorbent. A facile synthesis strategy involved fabrication of Fe3O4 magnetic core followed by growth of La doped Al2O3 shell using sol-gel method. Doping of La2O3 into Al2O3 structure was optimised (6%), resulting in Fe3O4-Al0.94 La0.06O1.5 core-shell particles which provided exceptional fluoride affinity. The obtained magnetic Fe3O4-Al0.94La0.06O1.5 core-shell nanoparticles were then loaded (22%) into alginate to form cross-linked hydrogel beads (Fe3O4-Al0.94 La0.06 O1.5-Ca-ALG). These prepared hydrogel beads were characterised and utilized for selective recovery of fluoride under different ambient conditions. Driving forces for enhanced fluoride uptake by La doped Al2O3 were investigated and explained with the help of both experimental observation and theoretical simulation. Density functional theory calculations indicated significant expansion in the cell volume of Al2O3 due to La doping which favoured the fluoride sorption. The calculated defect formation energy for the incorporation of F into Al2O3 was found to decrease in the presence of La. XPS analysis suggested direct interaction of fluoride with Al, forming Al-F bond and breaking Al-O bond. Different vital parameters for uptake were optimised. Also, kinetics, isotherm and diffusion models were evaluated. Developed hydrogel beads attained record sorption capacity of 132.3mgg-1 for fluoride. Overall, excellent stability, no leaching of constituents, effectiveness for selective fluoride recovery from groundwater, brand it a perfect epitome of sustainable water treatment application.

Taguchi’s optimization technique for water deflouridation through electrocoagulation

Excess fluoride in drinking water is posing serious health concern to humankind. Electrocoagulation is an emerging technique for water defluoridation, and recent research is focused on the optimization of process variables for achieving maximum fluoride removal. As such, the Taguchi optimization technique is adopted to arrive at optimum values process parameters which can provide maximum fluoride removal with more accuracy and fewer experimental runs. In the present research a laboratory-scale batch EC reactor with four aluminum electrodes (98% pure) connected to a DC supply for a wide range of fluoride concentrations which were not studied in earlier researches. Taguchi’s L 16 orthogonal array was applied for optimization of the process variable It revealed maximum efficiency of 86.67% for defluoridation at optimum conditions of process variables with pH: 6 ± 0.1, initial adsorbate concentration: 5 mg/L, EC time: 45 min, voltage: 25 V, and IED: 2 cm. The percentage contribution of process variables was obtained by ANOVA in descending order as initial adsorbate concentration (45.31%) > pH (33.83%) > voltage (13.68%) > EC time (4.2%) > IED (2.98%). Freundlich isotherm and second-order kinetic models were found to be the best suitable for water defluoridation using the EC process. FTIR and XRD analysis for EC sludge also confirmed the fluoride sorption onto A l ( O H ) 3 flocs. The electrode consumption of 0.263 kg/ m 3 , and total operational cost of USD 0.6004/ m 3 were estimated for water defluoridation using the EC process.

Studies on Taguchi’s optimization for biosorbent developed from waste eggshell material for water defluoridation

Excess fluoride intake from drinking water is a serious concern for human health posing mainly dental/skeletal fluorosis and other multiorgan manifestation. Recent research is being focus on developing a new biosorbent from calcium-rich waste materials with thermal treatment for removal from water since it has high affinity and greater potential for deflouridation. The present research developed a new biosorbent from waste eggshell for deflourdation from water. Taguchi’s orthogonal array was used for process variables optimization to acquire the maximum removal. The fluoride uptake capacity of 10.69 and fluoride removal percentage of 86.67% were acquired for the eggshell sorbent at optimum values of process variables of pH: 7 0.1, adsorbate concentration: 15 agitation time: 60 min, eggshell dose: 14 and temperature: 303 K. ANOVA analysis indicates the contribution of process variables in descending order as adsorbate concentration 39.76% > pH 39.33% > temperature 12.34% > biosorbent dose 6.42% > agitation time 2.14%. Freundlich isotherm and second-order kinetic model were best fitted for the sorption of fluoride. Thermodynamic parameters (ΔH = 42.33 and ΔS = 0.240 ) indicate endothermic and spontaneous fluoride sorption. The sorption elution studies with 0.1 N NaOH suggest the eggshell sorbent could be reused up to three cycles. The influence of co-ions was obtained as < < < The eggshell sorbent was also shown feasibility for defluoridation from real water samples.

Role of starch in one pot fabrication of mesoporous gamma-alumina with excellent fluoride sorption capacity

Green synthesis of mesoporous γ-AƖ2O3, a cutting-edge material for sustainable application in medicine, engineering, energy, and water treatment, is still challenging. Our study used a one-pot strategy for facile synthesis of γ-AƖ2O3 by sol-gel method using starch from cassava waste. AƖ(OH)3 were bound to the O-H groups of the starch molecule to form the AƖ(OH)3-starch complex in a nano-network confined in starch polymer cages. Its calcination at 500 ℃ produced a mesoporous, highly crystalline water stable γ-AƖ2O3 with a pore size of 2.07 nm and an extensive BET surface area (215 cm2/g). Using the response surface methodology (RSM), the as-synthesized γ-AƖ2O3 was optimized for efficient fluoride removal from water. A central composite design (CCD) was used to study the effect of initial fluoride concentration, pH, contact time, and sorbent dose on fluoride removal efficiency and optimization of the process. The relative importance of the sorption process variables to the fluoride removal process was assessed using ANOVA. The quadratic model showed that the predicted response was significantly correlated with the experimental response (R2 = 0.9667), with sorbent dose and pH being the process's most influential factors. Optimum conditions for 93.6% fluoride removal efficiency were sorbent dose of 0.5 g, initial fluoride concentration of 10 mg/L, pH 7, and contact time of 137.5 min. A weakly acidic medium favored fluoride removal from water, while the presence of PO43- and HCO3- retarded the process. The sorption data fitted well in the Langmuir isotherm (0.9783) and pseudo-second-order kinetic model (0.9999), indicative of a chemisorption process. The maximum sorption capacity towards fluoride was 207.5 mg/g. A thermodynamic study indicated that the sorption process was spontaneous and endothermic, with increased randomness at the solid-solution interface. Sorption, desorption, sustainability, and leaching tests showed that the sorbent could be used for sustainable fluoride removal at 8.3 USD/1000 liters of safe drinking water.

Understanding fluoride adsorption from groundwater by alumina modified with alum using PHREEQC surface complexation model

Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy, point of zero charge and X-ray diffraction. Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate a PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor, and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available aluminium waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.

Fluoride sorption using Al and Mg modified Dicerocaryum eriocarpum leaves mucilage

The occurrence of fluoride at elevated levels remains a potential risk to public health globally. This study was performed to the test the potency of modified precipitate derived from the mucilage extracted from Dicerocaryum eriocarpum (DE) leaves. The mucilage was precipitated and modified using 0.1 M of aluminium and magnesium, respectively. The sorbents (AlDE and MgDE) were characterized with Fourier transform infrared spectrometer, scanning electron microscopy and energy-dispersive X-ray, Brunauer–Emmett–Teller, X-ray fluorescence and Thermo-gravimetric analyzer. Batch sorption studies including the effects of dosage, pH, time, temperature and change in water chemistry were investigated. The sorption studies recorded 84.23% removal by applying 0.25 g of AlDE for 2 h in a 100 mL aqueous solution containing 10 mgF −/L. The AlDE and MgDE recorded a significant difference in removal efficiencies when using natural water over deionized water. The highest fluoride sorption capacity recorded with the use of AlDE (69.65 mg/g) over MgDE (41.84 mg/g). The pseudo-second-order kinetic model best described the sorption kinetics using both sorbents. The sorption process was feasible and exothermic. Electrostatic interaction and ion exchange were responsible for the update of fluoride by the sorbents. De-ionize water was recorded as a good desorbing agent for the sorbents.

Fluoride adsorption enhancement of Calcined-Kaolin/Hydroxyapatite composite

The use of waste or natural resources is an interesting approach to preparing adsorbent materials. Most adsorption materials are powder-based, making them impractical for a variety of applications. In this work, the natural kaolin clay and hydroxyapatite synthesized from biogenic waste were studied as defluoridation materials. The point of zero charge (pH PZC ), the fluoride adsorption capability and the adsorption isotherm of calcined kaolin and mixed calcined kaolin/hydroxyapatite in both powdered and moulded forms were investigated. The hardness of the moulded (post-formed) samples was tested before and after in immersion in a fluoride solution. The maximum hardness was 15.8 kilo-pounds for the post-formed calcined kaolin sample. Sample hardness values slightly decreased after immersion in a fluoride solution due to the formation of micro-cracks. Most samples presented high pH PZC values, implying that these materials are suitable for the capture of fluoride anions. The adsorption properties varied with the ratio of calcined kaolin to hydroxyapatite. These properties for post-formed samples were different from those in powdered form. Post-formed samples showed higher fluoride adsorption. The maximum fluoride adsorption capacity and efficiency of the post-formed samples (calcined kaolin) at pH 3 were 1.74 F − mg/g and 87%, respectively. The sorption of fluoride of hydroxyapatite and mixed calcined kaolin/hydroxyapatite powders was found to have the form of the Langmuir isotherm, which indicates a monolayer adsorption on the adsorbent surface. Isotherms of calcined kaolin powder, post-formed calcined kaolin and mixed calcined kaolin/hydroxyapatite samples followed the Freundlich isotherm, which indicates multilayer adsorption on a heterogenous adsorbent surface.

Taguchi L16 orthogonal array approach for optimization of fluoride removal from aqueous solution using Saccharum spontaneum weed grass novel biosorbent

Optimization of operating and design parameters is needed for the greater application to achieve higher quality, performance, and minimum cost. The paper mainly concentrates on, the optimization of process parameters influencing the deflouridation of water by Analysis of mean (ANOM) approach. The current work mainly aims at the utilization of the Taguchi approach to optimize influencing operating parameters for maximizing the removal of fluoride under batch experimental studies by using biosorbent developed from Saccharum spontaneum, weed plant. The optimum conditions were found at pH 7, sorbate content 5 mg/L, period of contact 120 min, sorbent dosage 10 g/L, and temperature 30 °C. The percent part of various process parameters is obtained in the successive sequence pH 56.21% > initial concentration of adsorbate 33.94% > biosorbent dose 5.49% > contact time 3.35% > temperature 1.01%. The equilibrium study indicates fluoride sorption on Saccharum spontaneum adsorbent fulfill the Langmuir model with parameters ‘a' and ‘b' determined as 1.617 mg/g and 0.473 L/mg. The kinetic study with sorption data suggested the Pseudo-second order kinetic model as best fitting with kinetic rate k2 0.218 g/mg min. The thermodynamic analysis suggested a spontaneous and endothermic nature (ΔH = 16.268 kJ/mol). Characterization of adsorbent was done using BET, SEM, and also by the determination of textual properties. Regeneration of the biosorbent is done for three cycles and is used for fluoride removal.

Use of mining waste as a novel low-cost material for fluoride removal from groundwater in CKDu endemic areas of Sri Lanka

A cost-effective fluoride removal process from groundwater using locally sourced waste materials was postulated for use in remote areas such as northern Sri Lanka. The process is relatively simple to operate, reduces fluoride levels to meet WHO guidelines and uses locally available waste from lime extraction. The “Natural Red Earth” (NRE) waste was a mixture of clays (12.43 wt%) and iron oxides (8.13 wt%) deposited on quartz (64.04 wt%). The smallest mesh size (<63 μm) of NRE was preferred to remove fluoride due to enrichment with aluminium and iron materials. Fluoride exchange kinetics were relatively fast (ca. 5 min) for NRE which was ascribed to sorption sites present in an active coating. Equilibrium studies revealed a low fluoride loading (0.009 meq/g). Thermal modification of the NRE at 350 °C increased the maximum fluoride uptake to 0.014 meq/g. Exposure of NRE to 1 M hydrochloric acid solution was preferred as the fluoride sorption capacity was promoted to 0.02 meq/g. Protonated surface sites on NRE were considered responsible for the enhanced fluoride sorption capacity. Acid activated NRE successfully batch treated simulated groundwater contaminated with fluoride ions to meet WHO guidelines. Practically, NRE may be used in addition to a sand filter and charcoal bed if required to remove organic matter. The economics for constructing and using a new NRE based treatment system is suitable for rural farming communities in Sri Lanka.

Testing of Sorbents for Removal of Acid Gases from Biomass Gasification

A number of various commercial technologies are available to remove contaminants from gasification gases, particularly those from biomass. However, new cheaper technologies are needed to meet the stringent requirements in gas cleaning, especially for biomass gas production. In this paper, we discuss the suitability of various sorbents prepared by us based on oxides or carbonates of various metals (Al2O3, CaO, CuO, Fe2O3, MgO, MnO, Na2O and ZnO) for the removal of acid gases from flue gas during biomass gasification process at elevated temperatures. The acid gas removal efficiencies were experimentally verified for all prepared sorbents under specific conditions such as raw gas composition and temperature. The experimental results showed that the sorbents based on aluminum, copper and zinc oxides have high sorption capacity for selective sorption of hydrogen chloride and hydrogen fluoride. In the case of sulfane, sorbents based on copper and zinc oxides have a high sorption capacity. All these sorbents can then be used to remove acid gases from biogas produced by biomass combustion at elevated temperatures.

Sorption of Fluoride and Bacterial Disinfection Property of Biosynthesized Nanofibrous Cellulose Decorated Ag-MgO-Nanohydroxyapatite Composite for Household Water Treatment.

An innovative and sustainable approach to integrating modified Ag–MgO–nanohydroxyapatite on a nanofibrous cellulose template (CNF-AgMgOnHaP) as a multifunctional adsorbent via a hydrothermal bioreduction route using Citrus paradisi peel extract was developed and examined. The surface morphology and mineralogical properties of CNF-AgMgOnHaP by UV–vis spectroscopy, SEM-EDS, XRD, FTIR, TEM, and BET techniques are reported. Batch fluoride sorption studies and its disinfection potential against common bacteria in surface water were evaluated. The results showed the successful synthesis of a modified multistructural CNF-AgMgOnHaP composite with an improved BET surface area of 160.17 m2/g. The sorption of fluoride by the adsorbent was found to strongly depend on the different sorption conditions with a maximum F− sorption capacity of 8.71 mg/g at 303 K, and pH of 5 with 0.25 g dosage at 10 min contact time (25 ± 3 °C). Equilibrium fluoride sorption onto the CNF-AgMgOnHaP was best described by the Freundlich isotherm model across all the operating temperatures. The overall kinetic results showed that the adsorption mechanisms not only depend on using the pseudo-second-order process but are also governed by the mass transfer of the adsorbate molecules from the external surface onto the pores of the adsorbent. The thermodynamic parameters revealed that the adsorption process of F− onto CNF-AgMgOnHaP was endothermic and spontaneous at the sorbent/solution interface. The synthesized composite also provides some antibacterial activity against common infectious microbes from contaminated drinking water. The overall results suggested that the CNF-AgMgOnHaP nanocomposite possesses the potential for the simultaneous decontamination of pollutants and microbes in drinking water.

Fluoride remediation from on-site wastewater using optimized bauxite nanocomposite (Bx-Ce-La@500): Synthesis maximization, and mechanism of F─ removal

Bauxite is a widely available Al-O-rich mineral with great potential for abating fluoride. However, low adsorption capacity, a narrow workable pH range, and a lack of clarity on the best removal mechanism hinder its application. In this work, a highly efficient bauxite nanocomposite (Bx-Ce-La@500) was synthesized via doping and pyrolysis, and its fluoride adsorption in industrial wastewater was examined. Doping Ce/La synergistically improved the fluoride adsorption affinity of the composite (from pHPZC 8.0 ~ 10.0) and enhanced the •OH. The materials were characterized by SEM-EDS, BET, XRD, and TGA while XPS, FTIR, and DFT were used to investigate the mechanism of fluoride sorption. Results show that Bx-Ce-La@ 500 has a positive zeta potential of 26.3–23.1 mV from pH 1~ 10. The Langmuir model was the best fit with a maximum adsorption capacity of 88.13 mg/g and removal efficiency up to 100% in 50 ppm F− solution. The high F− removal was attributed to the enhanced surface affinity and the formation of adequate •OH on the material. Except for carbonate and phosphate ions, other ions exhibited negligible effects and the selective removal of F− in real wastewater was high. The main mechanism of adsorption was the ligand/ion exchange and electrostatic attraction.

Fluoride Bio-Sorption Efficiency and Antimicrobial Potency of Macadamia Nut Shells.

This paper presents the potential application of macadamia nut shells (MNS) in the bio-sorption of fluoride and its antimicrobial potency against common pathogens encountered in surface water resources. The efficiency of MNS in the sorption of fluoride was determined using batch mode experiments, while the antimicrobial potency was investigated using the well disc diffusion assay method. The maximum fluoride sorption capacity of 1.26 mg/g was recorded at an initial fluoride concentration of 5 mg/L, adsorbent dosage of 0.5 g/100 mL, contact time of 120 min and initial pH of 6. The adsorption kinetics data were better described with a pseudo second order model, indicating the dominance of the chemisorption mechanisms. The Langmuir adsorption isotherm model described the isotherm data suggesting a monolayered adsorption. The thermodynamic parameters, ∆Gº and ∆Hº, confirmed that F− sorption by MNS is a spontaneous and endothermic process. The bio-sorbent was regenerated for seven continuous cycles when HCl was used as regenerating solution. The antimicrobial studies revealed that MNS has minimal activity towards Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. The MNS showed potentials for application in bio-sorption of fluoride. However, the doping of MNS with metal ions is recommended to enhance its anti-microbial potency.

Fluoride ions sorption using functionalized magnetic metal oxides nanocomposites: a review.

Fluoride is an anionic pollutant found superfluous in surface or groundwater as a result of anthropogenic actions from improper disposal of industrial effluents. In drinking water, superfluous fluoride has been revealed to trigger severe health problems in humans. Hence, developing a comprehensive wastewater decontamination process for the effective management and preservation of water contaminated with fluoride is desirable, as clean water demand is anticipated to intensify considerably over the upcoming years. In this regard, there have been increased efforts by researchers to create novel magnetic metal oxide nanocomposites which are functionalized for the remediation of wastewater owing to their biocompatibility, cost-effectiveness, relative ease to recover and reuse, non-noxiousness, and ease to separate from solutions using a magnetic field. This review makes an all-inclusive effort to assess the effects of experimental factors on the sorption of fluoride employing magnetic metal oxide nanosorbents. The removal efficiency of fluoride ions onto magnetic metal oxides nanocomposites were largely influenced by the solution pH and ions co-existing with fluoride. Overall, it was noticed from the reviewed researches that the maximum sorption capacity using various metal oxides for fluoride sorption was in the order of aluminium oxides >cerium oxides > iron oxides > magnesium oxides> titanium oxides, and most sorption of fluoride ions was inhibited by the existence of phosphate trailed by sulphate. The mechanism of fluoride sorption onto various sorbents was due to ion exchange, electrostatic attraction, and complexation mechanism.

Effectiveness of Zr(IV)-Loaded Banana Peels Biomass for the Uptake of Fluoride Anion from Water

The present study reports the fluoride uptake potential of Zr(IV)-loaded saponified banana peels (Zr(IV)-SBP) from water. Zr(IV)-SBP was synthesized by loading Zr(IV) onto banana peel biomass after saponification and sorbent characterization was performed by using different techniques including FE-SEM (Field Emission Scanning Electron Microscopy), FTIR (Fourier Transform Infra-Red) spectroscopy and zeta potential analysis. Batch experiments were carried out to examine the monitoring factors for the uptake of fluoride onto the investigated adsorbent. The optimal pH and contact time were found to be 2.94 and 300 minutes, respectively. The results from characterization techniques concurred that Zr(IV)-SBP have prominent adsorption sites favorable for the sorption of fluoride ions. The sorption behavior of fluoride onto Zr(IV)-SBP was best fitted with the Langmuir adsorption isotherm and pseudo-second-order kinetics model. The maximum adsorption capacity of Zr(IV)-SBP was 36.02 mg/g using the Langmuir isotherm model. The coexisting ions like chloride and nitrate caused very small interference, elevated concentration of sulphate notably lowers the fluoride adsorption percentage in the binary system, and the sorption using multiple systems was lowered significantly which is due to the synergistic effect of co-existing interfering ion. The adsorbed fluoride was completely desorbed using 2M NaOH solution. Fluoride sorption performance of Zr(IV)-SBP demonstrated that it can be a low cost, environmentally benign and one of the highly potent alternatives for the remediation of fluoride ions to avoid ablation on the water.

Studies on biosorbent developed from Rohu fish scales waste for defluoridation of water

ABSTRACT Development of waste-derived biosorbent for fluoride reduction is gaining wider interest to achieve sustainable and cost-effective water treatment. Biosorbent from Rohu fish scales waste produced from the fish market is developed for defluoridation of water. The morphological characteristics of the sorbent surface were analysed by BET, SEM, and EDAX analysis. Sorption experiments were performed in batch mode to estimate the equilibrium, kinetic and thermodynamic parameters. The equilibrium analysis indicates the sorption capacity increases linearly with the concentration of adsorbate ions and follows Freundlich isotherm. Fluoride uptake capacity of 2.972 mg/g with maximum fluoride removal of 92.12% was obtained at optimum values of process parameters: adsorbate initial concentration of 5 mg/L, pH 3, agitation rate of 150 rpm, mixing period of 90 min, temperature 303 K, and dose of 6 g/L. The E value (2.236 kJ/mol) obtained from the DR isotherm suggests the physisorption mechanism for fluoride sorption. The kinetic study indicates that fluoride sorption follows the second-order kinetic model. Thermodynamic parameters ∆H = −14.72 kJ/mol and ∆S = 0.049 kJ/mol which indicates the spontaneous and exothermic sorption nature of adsorption for fluoride reduction using fish scales sorbent. The reuse and regeneration of the exhausted Rohu fish scales sorbent was performed with 0.1 N NaOH to explore the possibility of reuse and found that it could be effectively reused up to six cycles with about 80% regeneration. The study to check practical applicability of defluoridation of field water using Rohu fish scales adsorbent indicates the adsorbent significantly reduced the fluoride.

Sorption of NdF3 and ThF4 from the LiF\u2013NaF\u2013KF Melt

The sorption of neodymium and thorium fluorides by AG-3 activated carbon from molten alkali metal fluorides LiF–NaF–KF has been studied. The sorption isotherm of neodymium fluoride at 650°C has a pronounced convex and is adequately described by the Langmuir equation. The sorption of thorium fluoride under the same conditions is much weaker than that of neodymium fluoride, which is determined by the size of the neodymium and thorium fluoride complexes. The kinetic dependence of the sorption of neodymium fluoride at a temperature of 650°С is adequately described by a first-order equation for a reversible reaction. The temperature dependence of sorption capacity in the range 550–750°С passes a maximum within 600–650°С.

Enhanced Fluoride Uptake by Layered Double Hydroxides under Alkaline Conditions: Solid-State NMR Evidence of the Role of Surface >MgOH Sites.

Layered double hydroxides (LDHs) are potential low-cost filter materials for use in fluoride removal from drinking water, but molecular-scale defluoridation mechanisms are lacking. In this research, we employed 19F solid-state NMR spectroscopy to identify fluoride sorption products on 2:1 MgAl LDH and to reveal the relationship between fluoride sorption and the LDH structure. A set of six 19F NMR peaks centered at -140, -148, -156, -163, -176, and -183 ppm was resolved. Combining quantum chemical calculations based on density function theory (DFT) and 19F{27Al} transfer of populations in double resonance (TRAPDOR) analysis, we could assign the peaks at -140, -148, -156, and -163 ppm to Al-F (F coordinated to surface Al) and those at -176 and -183 ppm to Mg-F (F coordinated to surface Mg only). Interestingly, the spectroscopic data reveal that the formation of Al-F is the predominant mode of F- sorption at low pH, whereas the formation of Mg-F is predominant at high pH (or a higher Mg/Al ratio). This finding supports the fact that the F- uptake of 2:1 MgAl LDH was nearly six times that of activated alumina at pH 9. Overall, we explicitly revealed the different roles of the surface >MgOH and >AlOH sites of LDHs in defluoridation, which explained why the use of classic activated alumina for defluoridation is limited at high pH. The findings from this research may also provide new insights into material screening for potential filters for F- removal under alkaline conditions.

Modeling defluoridation of real-life groundwater by a green adsorbent aluminum/olivine composite: Isotherm, kinetics, thermodynamics and novel framework based on artificial neural network and support vector machine

The kinetic, isotherm, and thermodynamics of adsorptive removal of fluoride from the real-life groundwater was evaluated to assess the applicability of a green adsorbent, aluminum/olivine composite (AOC). The isotherm and kinetics were demonstrated by the Freundlich and Elovich model indicating significant surface heterogeneity of AOC in favouring the fluoride sorption. The fluoride removal efficiency of AOC was achieved as 87.5% after 240 min of contact time. The diffusion kinetic model exhibited that both the intra-particle and film diffusion together control the rate-limiting step of fluoride adsorption. A negative value of ΔG0 (−19.919 kJ/mol) at 303 K confirmed the spontaneous adsorption reaction of fluoride, and its endothermic nature was supported by the negative value of ΔH0 (39.504 kJ/mol). A novel framework for a predictive model by artificial neural network (ANN), and support vector machine (SVM) considering the real and synthetic fluoride-containing water was developed to assess the efficiency of adsorbent under different scenarios. ANN model was observed to be statistically significant (RMSE: 1.0955 and R2: 0.9982) and the proposed method may be instrumental in a similar area for benchmarking the synthetic and real-life samples. The low desorption potential of the spent adsorbent exhibited safe disposal of sludge and the secondary-pollutant-free treated water by the efficient and green adsorbent AOC enhanced the field-scale applicability of the green technology.