Initial Fluoride Concentration Research Articles

Simultaneous removal of fluoride and nitrate from an aqueous mixture and semiconductor wastewater by sodium chloride mediated electro-generated aluminas (EGAs): Conversion of recovered fluoride into fluorapatite using plasterboard waste

Electro-generated aluminas (EGAs) were synthesized using sodium chloride electrolyte of 100 mM with Al/Al and Al/Fe electrodes operated at 800 mA for 1.5 h. The synthesized mesoporous EGAs, EGA (Al) and EGA (Fe) belonging to H2 type hysteresis contain the boehmite and bayerite phases as confirmed by XRD analysis and whose proportions are estimated to be 49.6 ± 0.3% and 50.4 ± 0.3% respectively by thermo-gravimetric study. The batch adsorption studies were conducted using the binary (F−/NO3−) mixture from which the adsorption efficiency was studied as a function of time (0–60 min), pH (3–10), initial concentration of fluoride or nitrate (100, 300, 500 and 1000 mgL−1) and temperature (15 °C, 25 °C, 35 °C and 45 °C) using EGA (Al) and EGA (Fe) adsorbents. The adsorptive removal of fluoride and nitrate from real effluent samples using EGAs was significant particularly in effluents E1 and E3 with residual concentrations within the safe limit of World Health Organization (WHO). Regeneration using 100 mM NaOH was quite consistent up to five consecutive cycles and the recovered fluoride was converted into fluorapatite. Taking into account the regeneration aspect, the cost analysis showed that 1 g EGA (Al) and EGA (Fe) was 0.464 USD and 0.508 USD respectively. The endothermic nature of adsorption through chemical forces was confirmed by the compliance of pseudo – second – order (kinetic), Langmuir and DKR (isotherm) models (R2 ≈ 0.99) along with thermodynamic parameters. Characterization of EGAs using FTIR, FESEM, XRD, XPS and BET was done to understand the adsorptive behavior between EGAs and the adsorbate (F−/NO3−) ions. The exhausted EGAs after fifth cycle of regeneration was mixed with ariake clay, plasterboard waste and cement in proper proportions and, made as specimens for the construction of bank bodies.

Fluoride removal using tartaric acid-modified rice husk biochar: Comprehensive batch and column studies

Tartaric Acid-modified Rice Husk biochar (TARH) was evaluated as an efficient and cost-effective adsorbent to eliminate Fluoride (F¯) ions from aqueous solutions. F¯ is a major contaminant in groundwater, and current conventional treatment methods have certain drawbacks in treating higher concentrations of fluoride. The adsorption efficiency of TARH was improved by pre-treating rice husk biochar using tartaric acid (organic acid), which was confirmed by FT-IR measurement, indicating the presence of carboxylic acids, hydroxyl groups, and amine surface functional groups. The study optimized fluoride batch adsorption experiments by considering the parameters affecting adsorption, including pH, contact time, initial concentration, and adsorbent dosage using the Central Composite Design (CCD) from Response Surface Methodology (RSM). Maximum fluoride adsorption of 74.73% was attained by TARH under ideal circumstances (an initial fluoride concentration of 32 mg/L, a pH of 7, 0.25 g/100 mL of adsorbent dosage, and 180 minutes contact duration). The CCD models showed an exceptional R2 value of 0.988 for fluoride adsorption, illustrating their efficacy. Three-dimensional response surface plots were visualized to analyse the effects of control parameters on %adsorption, and statistical analysis supported the validity of the CCD model. Isotherm models and adsorption kinetics were investigated. The adsorption exhibited monolayer adsorption according to the Langmuir isotherm model and a pseudo-second-order rate-limiting phase due to chemisorption. The column adsorption studies were performed for various experimental factors such as influent fluoride concentration (4–16 ppm), influent flow rate (4–8 mL/min), and fixed-bed depth (4–8 cm). The experimental data were examined using the Yoon-Nelson, Thomas, and BDST models, which revealed a substantial correlation between the experimental findings and model predictions. The effectiveness of TARH was examined by regeneration study and case study was performed to evaluate the fluoride removal from actual water samples.

Harnessing the potential of zinc oxide nanoparticles from Strychnos potatorum seeds impregnated with activated carbon for an effective removal of fluoride in deep soil water

Abstract Fluoride (F−) contamination in global water sources is a growing concern, prompting the need for innovative solutions. This explores a novel method using zinc oxide nanoparticle-activated carbon (ZnO-NP/AC) composite for efficient fluoride removal from deep soil water, aiming to evaluate its effectiveness in attracting fluoride contaminants. The focus is on treatment of water sample collected from Dharmapuri, Tamil Nadu, using green synthesis method for ZnO-NP/AC column filter. Employed an exclusive column adsorption method, investigated on physiochemical parameters in water before and after running the column. Fluoride concentration and TDS where significantly harnessed in water after running the green synthesis composite column filter. Characterization of green synthesized nanoparticles of Strychnos potatorum seed powder synthesis with ZnO NPs. Green synthesis successes were confirmed in two ways; one way is UV-visible spectrophotometer technique in depth quantity peak and another one is graphically peak from SEM, density and crystalline structure in XRD techniques. Column composite with S.potatorum ZnO-AC NPs has removed fluoride efficiently (80.5%) at range of 20 g/L for a contact time of 60 minutes, surpassing World health organization (WHO) guidelines for safe drinking water. In conclusion ZnO-AC NPs composite is a sustainable and cost-effective method for effective removal of fluoride contaminants from deep soil water, addressing a pressing global issue.

Synthesis, characterization, and evaluation of fluoride removal capacity of calcium-impregnated Euphorbia neriifolia carbon (Ca-Enc).

Fluoride ions must be removed from drinking water in order to prevent fluorosis. Many conventional techniques have been examined for the defluoridation of water all over the world. As far as fluoride ions are concerned, adsorption is the most promising method for the removal of them from aqueous environments. In the present study, we aim to find out how well Euphorbia neriifolia plants can remove fluoride from water using activated and carbonized adsorbents. The Euphorbia neriifolia plant stem was pulverized, dried, and activated using calcium ions extracted from used eggshells collected nearby. The synthesized adsorbent material before and after adsorption of fluoride ions was systematically characterized using FTIR, XRD, SEM with EDAX, TGA, and zero-point charge. The defluoridation capacity of the as-prepared adsorbent material was investigated using batch adsorption studies. Various influencing factors such as contact time, solution pH, initial fluoride concentration, mass of the adsorbent, temperature, and co-existing ions were systematically investigated towards the removal of fluoride ion on prepared adsorbent material. This study was conducted to identify the optimal conditions of prepared adsorbent for the maximum removal of fluoride ions from aqueous solution. A groundwater sample with fluoride content of more than 1.5ppm was taken and studied in this present work. A basic quality indicator of the synthesized material was examined, and its ability to remove fluoride was determined. The findings provide insight into the selective elimination of fluoride ions from aqueous environment.

Removal of Fluoride from Drinking Water by Utilizing Modified Bagasse Sugarcane as Low-Cost Adsorbents for Bilaspur City, Chhattisgarh

Recently, there has been a noticeable increase in fluoride contamination in drinking water, leading to evident harmful effects in various locations. Tackling the challenge of reducing fluoride levels in potable water has become a significant concern for drinking water supply agencies. In our current study, we focused on creating and characterizing different adsorbents, namely sugarcane bagasse, coconut husk, and rice husk, for their ability to effectively remove fluoride. These adsorbents are not only cost-effective and readily available but also straightforward to prepare. We conducted thorough characterizations of all three adsorbents to assess their performance under various conditions. This included investigating the impact of pH on removal efficiency, evaluating removal efficiency with varying doses of adsorbent, analyzing removal efficiency across different temperatures, studying the influence of the initial concentration of fluoride on the total amount of adsorbent per unit mass, and examining the impact of altering initial fluoride concentrations while maintaining a constant temperature of 30 ± 2 °C. Our findings revealed noteworthy insights into the effects of these parameters on removal efficiency. fluoride contamination in the groundwater of Bilaspur, Chhattisgarh, originates not only from anthropogenic sources but also from geogenic sources. The efficiency of contamination reduction rises as the pH increases, reaching a plateau after a certain point. When employing an adsorbent dose of 0.5 g/100 mL of modified bagasse sugarcane (MBS) and a contact time of 75 minutes, along with a temperature of 323 K, the highest efficiency is observed in the MBC. Subsequently, the efficiency is lower in aluminum-hydroxide-coated rice husk and then in modified coconut husk. Analysis indicates that as the initial fluoride concentration increases, the removal efficiency di- minishes due to the capacity limitations of the adsorbent materials.

Successful removal of fluoride from aqueous environment using Al(OH)3@AC: column studies and breakthrough curve modeling.

In this study, we discuss the removal of fluoride from water through column adsorption methods using Al(OH)3@AC as a functional granular activated carbon. The height of the bed, fluoride concentration, and flow rate are the experimental factors used to obtain the breakthrough curves. As the flow rate increased, the breakthrough and saturation times decreased. The analysis of simplified column models, such as the Adams-Bohart, Thomas, and Yoon-Nelson models, revealed that the Clark model best described the adsorption process when fitting the experimental data. The obtained breakthrough curves agreed with the corresponding experimental data. The highest capacity for adsorption obtained during the column procedure was found to be 41.84 mg g-1 with a bed height of 3 cm, an initial fluoride concentration of 10 mg L-1 and a flow rate of 7.5 mL min-1.

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

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

Gum Arabic tree biomass derived activated carbon for fluoride sequestration in batch and fixed bed processes: kinetics, thermodynamics and column adsorption modeling

The biomass obtained from the stem of Gum Arabic tree was used to prepare a thermally activated carbon through pyrolysis at 800 °C. The activated carbon tagged GAAC-800 was used as adsorbent for the fluoride sequestration in a batch and a fixed-bed reactor in a continuous column systems. The surface morphology, elemental composition as well as particle size distribution of the adsorbent was investigated with Scanning Electron Microscopy (SEM), Elemental and Particle Size Analyzers. Also, the influence of initial fluoride concentrations, column packing height and the flow rate on the column efficiency were examine while the efficiency of batch process as a function of contact time and temperature was also investigated. It was found that the kinetic of the process was best fitted with second order model, while the mechanism was best explained by interparticle diffusion model. In addition, the Langmuir Isotherm model showed that the maximum monolayer adsorption capacity of fluoride removal was 71.93 mg/g. The breakthrough curve from the fixed bed adsorption data were well modeled by Adams-Bohart, Yoon-Nelson and Clark model. The models were judged using Akaike Information Criteria (AIC) values after statistical evaluation. GAAC-800 removed fluoride from aqueous solution comparably higher than other adsorbent in its category in batch and continuous column systems.

A sustainable approach for fluoride treatment using coconut fiber cellulose as an adsorbent

In developing countries like India, an economically viable and ecologically approachable strategy is required to safeguard the drinking water. Excessive fluoride intake through drinking water can lead to dental fluorosis, skeletal fluorosis, or both. The present study has been under with an objective to investigate the feasibility of using cellulose derived from coconut fiber as an adsorbent under varying pH conditions for fluoride elimination from water. The assessment of equilibrium concentration of metal ions using adsorption isotherms is an integral part of the study. This present finding indicates the considerable effect of variation of adsorbent dosages on the fluoride removal efficiency under constant temperature conditions of 25 ± 2 °C with a contact period of 24 h. It is pertinent to mention that maximum adsorption of 88% has been observed with a pH value of 6 with 6 h time duration with fluoride dosage of 50 mg/L. The equilibrium concentration dwindled to 0.4 mg/L at fluoride concentration of 20 mg/L. The Langmuir model designates the adsorption capacity value of 2.15 mg/L with initial fluoride concentration of 0.21 mg/g with R2 value of 0.660. Similarly, the adsorption capacity using Freundlich isotherms is found to be 0.58 L/g and 0.59 L/g with fluoride concentration of 1.84 mg/L and 2.15 mg/L respectively. The results from the present study confirm that coconut fiber possesses appropriate sorption capabilities of fluoride ion but is a pH dependent phenomenon. The outcomes of the study indicate the possible use of cellulose extracted from waste coconut fiber as a low-cost fluoride adsorbent. The present study can be well implemented on real scale systems as it will be beneficial economically as well as environmentally.

Efficient Fluoride Removal from Aqueous Solution Using Graphene/Ce Composite Supported on Activated Carbon

Background: More than 260 million people worldwide are affected by excess fluoride (F- > 1.5 mg/L) in their drinking water. Fluorosis of the teeth and skeleton, among other health issues, is caused by it. Objective: The aim of this study is to evaluate the fluoride removal from contaminated water using graphene-based new adsorbent material. Method: Graphene (G) was prepared by a facile liquid-phase exfoliation method. CeO2 nanoparticles (NPs) were synthesized by the co-precipitation method. G was treated with CeO2 NPs in a probe sonicator to generate G/Ce material in solution. Finally, the impregnation evaporation process synthesized the G/Ce supported on activated carbon composite (G/Ce/AC). Results: FE-SEM analysis shows that the crumpling and scrolling sheets of G, the nanosized spherical shape of CeO2 NPs and a thick layer of nano-sized spherical particles has built up on the surface of graphene in G/Ce/AC composite. After conversion to G/Ce/AC Composite, the specific surface area of graphene was increased from 3.08 to 485.3621 m2/g. The adsorption of fluoride on G/Ce/AC was investigated using batch systems (effects of pH, contact time, adsorbent dosage and the initial fluoride concentration), adsorption isotherm and kinetic studies. The pseudo-second order was the one that best described the kinetic data, while the Langmuir isotherm best described the equilibrium data with a maximum adsorption capacity equal to 27.9 mg/g. Conclusion: Therefore, the results show that the G/Ce/AC composite was well synthesized and has excellent fluoride adsorption capacity compared to other materials already evaluated for this purpose.

Application of a novel zirconium coagulant in the coagulation-ultrafiltration process: Fluoride removal and membrane fouling alleviation

Groundwater fluoride pollution is a worldwide problem that threatens human health and drinking water. Economical and efficient coagulation is the most widely used defluorination technology. The fluoride removal efficiency depends on the complexation and adsorption capacities of the hydrolyzed metal salt coagulant, so the development of new metal coagulants is the key to coagulation defluorination technology. In this study, novel polymeric zirconium salt coagulants (ZXCs) were prepared by the sol-gel method. Their capabilities in coagulation and coagulation-ultrafiltration processes were evaluated and compared with those of the traditional polyaluminum chloride (PAC) and polyferric sulfate (PFS) coagulants. ZXC exhibited more effective fluoride removal than PAC and PFS, and the fluoride removal rates of ZXC, PAC and PFS were 81.0 %, 24.7 % and 5.4 % with the optimized dosages of 0.30 mM and pHs of 5.0, 6.0 and 5.0, respectively. With an initial fluoride concentration of 4.0 mg/L, 0.30 and 1.5 mM doses of ZXC reduced the fluoride concentrations to 0.76 and 0.13 mg/L. The structures and properties of ZXC and the flocs were characterized with Fourier Transform Infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), X-ray photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area determinations. The series characterization and hydrolysis precipitation area map showed that adsorption onto hydroxyl groups and ion exchange with surface hydroxyl groups were the main pathways for fluoride removal by ZXC. In the coagulation-ultrafiltration defluorination process, the highly polymerized ZXC was fully hydrolyzed under acidic conditions to form larger and looser flocs with almost no dissolved residue, which substantially reduced membrane fouling. This work provides new insights into the development of materials and technologies for fluoride removal from drinking water.

Architecture of GO/CoFe2O4/ZnO nanocomposite for efficient fluoride removal: An approach using RSM, ANN and GRU modeling

The presence of fluoride in wastewater possesses a significant risk to the environment. Graphene oxide-based nanocomposites were prepared as potential adsorbents for fluoride removal from water. Various techniques including X-ray diffraction (XRD), Scanning Electron Microscopy (FE-SEM), Energy dispersive X-ray (EDX), Fourier Transform Infrared Spectroscopy (FTIR), RAMAN spectroscopy, Ultraviolet-Visible spectroscopy (UV–vis), Vibrating Sample Magnetometer (VSM), X-ray Photoelectron Spectroscopy (XPS), Brunauer Emmett Teller (BET), and Electrochemical Impedance Spectroscopy (EIS) were employed to investigate the morphological, structural, chemical composition, elemental analysis, surface area, optical band gap, etc. of the CoFe2O4, CoFe2O4/ZnO composite and GO/CoFe2O4/ZnO nanocomposite. XRD analysis confirmed a reduction in crystallite size to 15.7 nm of GO/CoFe2O4/ZnO. Batch adsorption studies were conducted for fluoride removal with input independent variables (pH, temperature, initial fluoride concentration, time, and an adsorbent GO/CoFe2O4/ZnO dosage). The Response Surface Methodology (RSM) and Gated Recurrent Unit (GRU) models predicted the fluoride removal process, with RSM achieving an optimal fluoride removal of 94.3%, GRU achieving 94.5% and Artificial neural network (ANN) attaining 93.72%. A kinetic investigation was carried out using Pseudo first order (PFO) and Pseudo second order (PSO). Results confirmed that the adsorption of fluoride followed the PSO kinetic model with an (R2 = 0.999). Isotherm studies were conducted using Langmuir, Temkin, Freundlich, and Dubinin Radushkevich isotherms. Among them, the best model follows an adsorption mechanism, with (R2 = 0.984) and an adsorption capacity of 10.68 mgg−1 was Langmuir Isotherm. The real water sample of Ravi River, Pakistan also investigated for fluoride removal capability. This research contributes to the promotion of RSM and GRU modeling with high sustainability for water purification. The contemplated nanocomposite (GO/CoFe2O4/ZnO) is a potential adsorbent for the mechanism of water detoxification containing fluoride which may be useful for environmental remediation as well.

An efficient separation for fluoride-ions from water supplies by ion precipitate flotation: Pilot scale study with generation of coagulative bubbles

Bubble surface modification is a promising technique that enables to increase the efficiency of a treatment that aims to remove a certain particle with lower consumption of chemical inputs. In this study, the so-called coagulative bubbles were generated from a mixed system consisting of amphoteric surfactant (Cocamidopropyl betaine, CAPB) and inorganic polymer coagulants (aluminum sulfate and calcium chloride) for the removal of fluoride ions present in groundwater destined for human supply. The critical micellar concentration (CMC) of CAPB was 0.26 mmol L−1. The coagulant bubbles (CB) were generated from pressurizing the coagulant solution in distilled water and applied continuously in a helical tubular reactor. The CB treatment method provided higher fluoride removal compared to conventional treatment with simple coagulant application. The CBs generated with Al made it possible to remove approximately 98 % of the initial amount of fluoride measured (3.5 mg L−1) with a dosage of 31 mg L−1 of Al; feed flow rate of 20 L min−1; pH 6 ± 0.5; and saturation pressure of 3 atm. This same operation, but without generation of CBs (regular atmospheric pressure), allowed the removal of 67 % of the initial fluoride concentration.

Facile synthesis of Aluminium fumarate metal–organic framework and hydroxyapatite composite with improved adsorption characteristics for efficient fluoride removal from water

An aluminium fumarate (AlFu)-hydroxyapatite (HAP) composite (AlFu-HAP) with numerous functional groups for fluoride binding was synthesised by a simple solid–solid mixing process. The produced AlFu-HAP composite with numerous functional groups results in outstanding adsorption capability in the sequence AlFu-HAP > AlFu > HAP. This composite was studied under different pH, initial fluoride concentrations, temperatures, and contact times. The adsorption kinetics and isotherms were pseudo-second-order model and Freundlich adsorption isotherm, respectively. XRD, SEM, FTIR, Raman spectroscopy, and XPS analysis of the samples before and after the adsorption reaction indicate that the fluoride removal mechanism was controlled by anion exchange of the OH– group in AlFu-HAP and F- in water. At high concentrations (150–200 mg F-/L) in groundwater and industrial effluent, the AlFu-HAP showed > 90 % fluoride removal. Thus, the current study will provide an effective strategy for developing an AlFu-HAP composite adsorbent to be used for the effective elimination of fluoride from wastewater.

Novel MOF(Zr)-on-MOF(Ce) adsorbent for elimination of excess fluoride from aqueous solution

Herein, we used a one-pot method to fabricate a novel MOF-on-MOF adsorbent, namely MOF(Zr)-on-MOF(Ce). The adsorbent demonstrated a high maximum fluoride-ions capture capacity of 164.47 mg g−1. The morphology, elemental distribution, pore size distribution, and thermal stability were studied using SEM-EDS, XRD, BET, and TGA. The influence of the temperature, solution pH, fluoride concentration, and coexisting ions was explored using intermittent experiments. The results suggested that MOF(Zr)-on-MOF(Ce) had a fast capture rate for fluoride. MOF(Zr)-on-MOF(Ce) maintained an excellent fluoride removal performance over a wide pH range with an initial fluoride concentration of 20 mg L−1. The optimal effect was obtained at a pH of 4, but a high removal efficiency of 94% was maintained even at a pH of 9. Interference experiments showed that only the PO43– had an adverse inhibition influence. The field experiments demonstrated that MOF(Zr)-on-MOF(Ce) can keep the safety threshold levels of fluoride in drinking water. The Langmuir and pseudo-second order kinetic models were well fitted for the defluoridation process, demonstrating that the adsorption of fluoride ions on MOF(Zr)-on-MOF(Ce) was dominated by monolayer chemisorption. With the further characterization and kinetic thermodynamic studies indicates that the removal mechanism involves ion exchange, electrostatic interactions and complexation effect.

In situ synthesis of MIL-53-type eco-MOF from high-alumina fly ash for efficiently removing fluoride from water

Facing ubiquitous fluoride pollution in aquatic environments and ever-increasing discharge of coal fly ashes, this study aims to in situ synthesize a kind of Al-based metal–organic framework eco-material (eco-MOF) using high-alumina fly ash as metal raw material, and apply the obtained adsorbent to efficiently adsorb fluoride in water. The synthesized eco-MIL-53(Al) exhibits excellent thermal stability, showcasing a consistent morphology of fine columnar crystals and possessing a high specific surface area (353 ​m2·g−1). Moreover, the adsorption isotherm demonstrates a strong agreement with the Langmuir isotherm model, indicative of a maximum uptake quantity of 160 ​mg·g−1 ​at 318 ​K. In addition, fluoride adsorption experiments demonstrate that an increased dosage enhances the adsorption efficiency, the higher water pH value diminishes the removal efficiency, and the impact of coexisting anions is minimal. Also, the adsorption capacity is augmented with increasing temperature at high initial fluoride concentrations, but shows negligible variation at low initial fluoride concentrations. It is worth noting that the desiliconization filtrate can be applied to synthesize ZSM-5 zeolite, realizing the total utilization of fly ash. The present work provides a novel platform that would serve as a mutually beneficial reference for managing the environmental risks of fluoride and waste resource utilization.

Modeling, optimization and comparative study on abatement of fluoride from synthetic solution using activated laterite soil and fly ash

The supply of potable water by proper treatment of fluoride laden ground water is a challenging task. Batch experiments were executed with activated laterite soil and fly ash individually for removal of fluoride. The process parameters such as particle size (100–620 μm), dose of adsorbent (10–60 g/L), initial concentration of fluoride (2–12 mg/L), agitation speed (20–120 rpm), contact time (0.5–10 h) and pH (4.5–9.5) were investigated and it was observed that activated laterite soil had better fluoride removal efficiency than fly ash. At pH 4.5, contact time 10 h, particle size 100 μm, adsorbent dose 60 g/L, initial concentration of fluoride 12 mg/L, and agitation speed 120 rpm, maximum removal efficiencies of fluoride using activated laterite soil and fly ash were found as 85.91 ± 0.62% and 77.1 ± 0.39%, respectively. Kinetic study was performed and Pseudo 2nd order kinetic model was found to fit the kinetic data best. The Freundlich isotherm model fit the equilibrium data fairly well. The values of adsorption equilibrium constant as used in Freundlich isotherm model vis-à-vis adsorption capacity (KF) for activated laterite soil and fly ash were obtained as 0.1331 and 0.0772 ((mgg−1)(Lmg−1)1/n). A thermodynamic analysis was conducted to examine the process behaviour. In order to determine whether the adsorbent may be used for further cases, regeneration of the adsorbents was also done. Generally, two types of adsorption mechanisms happen like electrostatic attraction and ion exchange. The electrostatic force of attraction favours the adsorption of negatively charged fluoride ions on positively charged adsorbent surfaces. In ion exchange, fluoride ions are exchanged by hydroxyl and hydronium ion. Based on experimental data, Multi-Gene Genetic Programming (MGGP) model could accurately predict the removal efficiency of fluoride under various operating situations. Finally, using Genetic Algorithm (GA) optimization the maximum output values for both adsorbents were estimated as 99.14% and 99.02%.

Effective defluoridation using lanthanum-organic frameworks encapsulated hydrotalcite based bio-hybrid beads

Herein, hydrotalcite (HT) integrated lanthanum-metal organic frameworks (LaMOFs) cross-linked alginate and chitosan (Alg-CS) biopolymers that are HT-LaMOFs@Alg-CS beads was prepared and successfully utilized for defluoridation investigations. The prepared HT-LaMOFs@Alg-CS beads were evaluated with the help of various instrument analyses. The adsorption capacity of the prepared HT-LaMOFs@Alg-CS beads for fluoride retention was investigated, across a broad choice of pH levels, and in the occurrence of interfering ions identified in water. The batch optimized condition for fluoride adsorption using HT-LaMOFs@Alg-CS beads were contact time (30 min), pH 7, initial fluoride concentration (10 mg/L), dosage (0.1 g) at room temperature. The fluoride adsorption capacity of HT-LaMOFs@Alg-CS beads is 4905 mgF− kg−1 within 20 min. To distinguish the defluoridation behavior on HT-LaMOFs@Alg-CS bio-hybrid beads, the adsorption isotherm, kinetics, and thermodynamic studies were performed. Thermodynamic results suggest that the fluoride adsorption route on the developed HT-LaMOFs@Alg-CS beads was endothermic process with spontaneous nature. The experimental data result of HT-LaMOFs@Alg-CS bio-hybrid beads for fluoride removal was majorly fitted Langmuir isotherm and pseudo-second-order kinetics. The reusability and real water sample examination results of the attained HT-LaMOFs@Alg-CS hybrid beads for defluoridation was demonstrated that the prepared HT-LaMOFs@Alg-CS beads were regenerable nature with more fitting at field level.

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.

Fluoride Removal from Water Sources by Adsorption on MOFs

Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according to WHO). Among the numerous technologies for removing fluoride from waters, metal–organic framework (MOF) materials are considered to be promising adsorbents due to their advantages of high porosity, high specific surface area, diverse functions and easy modification. In this study, the synthesis of MOFs and the progress of their application to the removal of fluoride from contaminated water, as published in the recent literature mainly over the past five years, are reviewed. The adsorption mechanism(s) and its main characteristics, such as effect of initial fluoride concentration, adsorbent dosage, solution pH, contact time, adsorption capacity, thermodynamic and regeneration studies, etc., for the removal of fluoride with the addition of different MOFs are compared. According to these comparisons, the hydrothermal/solvothermal synthesis method is most commonly used for the preparation of MOFs, whereas higher BET surface areas are shown by specific MOFs based on aluminum metal ions. The main fluoride adsorption mechanisms were found to be electrostatic attraction and/or complexation. The most common pH for conducting experiments was 7.0, but several examined materials were found to be effective over a wide pH range. Four to six regeneration cycles were successfully applied on average, regarding the MOFs under review, whereas in the majority of these cases, the sorption process was found to be endothermic.