Fluoride Sorption Research Articles

Preparation and Properties of an Aluminum Hydroxide-Modified Diatomite Sorbent for Removal of Fluorides from Waters

A new sorbent (Al-D) for the removal of fluoride ions is prepared by modifying diatomite with aluminum ions. The sorbent is studied using X-ray diffraction, thermogravimetry, X-ray photoelectron spectroscopy, and adsorption structure analysis; its ability to remove fluoride ions from model aqueous solutions is measured under static conditions. The diatomite, which is modified by heterogeneous hydrolysis of an aluminum salt in the presence of diatomite suspension, has a higher specific surface area and a greater sorption pore volume and exhibits excellent characteristics in fluoride adsorption. Fluoride sorption isotherms measured under equilibrium conditions are modeled using the Langmuir, Freundlich, Langmuir−Freundlich, Brunauer−Emmett−Teller, and two-step Langmuir equations. The model parameters are calculated. The two-step Langmuir model gives the best fit to the experimental isotherms (R2 = 0.9836). Fluoride adsorption on the sorbent Al-D occurs via ion exchange: surface OH− groups are replaced with fluoride ions from solution to form aluminum fluoride complexes at the sorbent surface.

Clinoptilolite modified by calcium and hydroxyl ions for removal of fluoride from aqueous solution

In Mexico naturally occurring fluoride contamination of groundwater is widespread. Adsorption with local and low-cost materials has been recently studied. In this research, clinoptilolite was modified with hydroxyl, calcium, and hydroxyl followed by calcium to compare their fluoride removal capacity. The sorption of natural and modified materials was investigated for the initial fluoride concentrations from 1.5 mg/L to 15 mg/L, isotherms for these adsorbents were investigated and techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XDR) were used to characterize these adsorbents. It was found that removal fluoride was highest with calcium modified clinoptilolite from 60.2% with 1.5 mg F−/L to 43.0% with 15 mg F−/L. Sorption data for calcium modified clinoptilolite and hydroxyl and calcium modified clinoptilolite was found to fit Freundlich equations with equilibrium constants of 0.12 L/g and 0.021 L/g, respectively. SEM and XRD showed no significant changes of clinoptilolites after and before modification with calcium and sorption of fluoride, suggesting that interaction between adsorbent and adsorbate were only superficial. Modification of clinoptilolite with calcium enhanced its capacity for fluoride removal. This modification process was carried out using an economical and abundant mineral in central Mexico, which gives an additional advantage to the process.

Hydrothermal synthesis of magnetic iron oxide encrusted hydrocalumite-chitosan composite for defluoridation studies.

A magnetic adsorbent namely magnetic iron oxide encrusted hydrocalumite-chitosan (Fe3O4@HCCS) composite was prepared by the fabrication of magnetic iron oxide (Fe3O4) particles on hydrocalumite-chitosan (HCCS) composite for fluoride sorption studies in batch mode. The prepared magnetic Fe3O4@HCCS composite possesses an enhanced defluoridation capacity (DC) of 6.8mg/g compared to hydrocalumite (HC) which possesses the DC of 2.4mg/g. The various physico-chemical parameters such as contact time, pH, co-existing anions, initial fluoride concentration and temperature were optimized for the maximum fluoride removal. The structural changes of the sorbent, before and after fluoride sorption were studied using FTIR and SEM with EDAX techniques. The equilibrium data was well modeled by Freundlich and Langmuir isotherms. The thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of fluoride sorption. The field performance and efficiency of Fe3O4@HCCS composite was examined with the waste-water sample collected from a fluoride endemic area of Dindigul district, Tamilnadu, India using standard protocols.

Fluoride Removal from Groundwater by Technological Process Optimization

Abstract Fluoride removal from aqueous solutions was studied using nanofiltration and sorption techniques which have always been best key ways to deal with water contaminated by fluoride. In this presented work, we were firstly interested on fluoridated rejected water overcoming the drawback of RO membrane process of groundwater treatment plant in Baltic region (Kretinga, Lithuania). Opoka sorbent has shown effective results of fluoride sorption with efficiency higher than 77 %. In order to understand the sorption phenomenon and to validate the results obtained, we have applied experimental data on Freundlich and Langmuir isotherms which allow us to determine isotherms parameters (KF ; 1/n and KL ; q max) and to confirm the experiment. Because of the unacceptable tariff of drinking water treated by RO, defluoridation with nanofiltration method is proposed in this study as a solution which can replace reverse osmosis technique. For that, tests of nanofiltration for fluoride removal were carried out at laboratory scale by using nanofiltration flat sheet membranes (NF270 and NF90).

Studies on novel nano-bimetal doped cellulose nanofibers derived from agrowaste towards deflouridation.

Cellulose nanofibers were extracted from sugarcane bagasse. Zerovalent‑iron (ZVI)/Zirconium(IV) (Zr)/ZVI-Zr doped cellulose nanofibers were prepared, characterized and evaluated for fluoride removal. The prepared nanofibers could effectively remove fluoride within a wide pH range of 3.0 to 8.0. The equilibrium reached within 3 h and the adsorption capacities followed the order ZrZVICNF > ZrCNF > ZVICNF. The Langmuir adsorption capacity of ZrZVICNF was 35.70 mg/g, much higher than various commercial adsorbents. Nitrate, chloride, sulphate, phosphate, has insignificant effect on fluoride adsorption and higher concentrations of bicarbonate and silicate ions affected fluoride sorption. Furthermore insignificant amount of Zr(IV) ions were leached during adsorption owing to its efficient complexation with hydroxyl groups of cellulose and the adsorbent could be successfully regenerated. Spectroscopic analysis revealed that fluoride ion complexed with both Zr(IV) and Fe(II)/Fe(III) ions. Thus high fluoride uptake capacity, faster kinetics, applicability at wide pH range, makes ZrZVICNF as attractive sorbent for defluoridation.

Water defluoridation by carbonate calcined and uncalcined Layered Double Hydroxides (LDHs)

Carbonate Layered Double Hydroxides (LDHs) with different cationic composition and M2+/M3+ molar ratio were tested, both untreated and calcined, for water defluoridation. The defluoridation capacity of calcined LDHs, produced by intercalation during the reconstruction of lamellar structure, is more effective than the anion exchange of untreated LDHs. Among the calcined LDHs tested, that with 3Mg/(0.5Al+0.5Fe) molar ratio yields a maximum fluoride sorption capacity up to 92.3 mg/g, in spite of the high pH value (up to 12) of the experiments. After four cycles of regeneration by calcination and subsequent water defluoridation, this LDH composition maintains more than 80% of its fluoride removal capacity.

Experimental and kinetic study of fluoride adsorption by Ni and Zn modified LD slag based geopolymer

The present study aims at the synthesis of highly efficient, three dimensional, porous, alumino-silicate geopolymeric adsorbents derived from the steel plant LD (Linz–Donawitz) slag, a potential raw material for geopolymerisation, to remove toxic fluoride ions from wastewater. LD slag geopolymeric adsorbent (LDSGP) has been chemically modified by bivalent metallic ions i.e. Ni2+ and Zn2+ separately resulting formation of Ni-LDSGP & Zn-LDSGP adsorbents respectively; and their fluoride adsorption capacities have been investigated. The physico-chemical properties of all the geopolymeric adsorbents have been described by using standard characterization techniques including BET, FESEM & HRTEM, FTIR, XRD etc. showing micro-petal like morphology on its’ outer surfaces. The fluoride sorption onto the geopolymeric adsorbents have been investigated in batch adsorption studies where Zn-LDSGP adsorbent has the superior fluoride adsorption capacity followed by Ni-LDSGP and LDSGP (Qe,Zn−LDSGP=60mg/g>Qe,Ni−LDSGP=55.4mg/g>Qe,LDSGP=50.6mg/g). The equilibrium study shows best fit to Freundlich model while the adsorption kinetic data fitted best with pseudo-second-order model suggesting the nature of the adsorption to be chemisorption. The mass transfer occurred during the sorption process has been mathematically modeled and simulated to identify the rate-determining steps of mass transfer phenomena.

Biosorptive removal of fluoride from aqueous solution onto newly developed biosorbent from Ficus benghalensis leaf: Evaluation of equilibrium, kinetics, and thermodynamics

Need for developing an effective defluoridation method using locally available resources and recycling of agriculture waste is still encouraging the researchers for achieving sustainability. Greater attention was shown towards developing biosorbent for deflouridation utilisation of locally available plant biomass such as leaves. Present research envisages on developing a novel biosorbent from Ficus benghalensis leaf and tests its feasibility for removal of fluoride. Batch mode experimentations are conducted to evaluate its feasibility and determine the equilibrium, kinetic and thermodynamic characteristics of this biosorption process. The study revealed that the biosorption of fluoride onto this newly developed Ficus benghalensis leaf biosorbent obeys Langmuir isotherm with constants 'a' and 'b' calculated to be 2.242 mg/g and 0.647 L/mg at biosorbent dose of 8 g/L and temperature 26 ± 1ºC. The kinetic study indicates sorption data fits fine with Pseudo-second order kinetic model with kinetic constant calculated as K2 0.277 g/mg min at equilibrium contact period of 90 min. The thermodynamic study points out the spontaneous and endothermic nature of fluoride sorption with ΔH= 15.497 KJ/mol. Advanced analysis viz BET, SEM, and FTIR were done to know the characteristic of the newly developed biosorbent. When this biosorbent was tested on field groundwater sample, the efficacy for fluoride removal was found to be around 90%, and the concentration for treated water is well within drinking water standards for fluoride.

Removal of fluoride from groundwater using natural clay (kaolinite): Optimization of adsorption conditions

This article focuses on the application of clay, kaolinite, for the removal of fluoride ion from Saharan groundwater located in the Tindouf region (Algeria) because high concentrations are detected in potable water. Adsorption tests show that fluoride ion removal was efficient when the pH varies from 4.5 to 6. Under these conditions, the adsorption capacities were 0.442 and 0.448 mg/g, respectively. Kinetic and isotherm adsorption correlations were applied to describe the adsorption process. The results showed that the pseudo-second-order kinetic model and Freundlich isotherm fit well the experimental data. Thermodynamic calculation indicated that fluoride sorption into clay increased with increasing temperature from 30 to 55 °C, indicating the endothermic nature of sorption process. The investigation of the removal of fluoride from simulated potable water shows that the presence of nitrate and chloride ions did not influence the fluoride uptake. However, sulfate and carbonate ions decrease the adsorption capacity. Such results show that these ions may enter in competition with each other that may result in electrostatic repulsive forces between fluoride and clay surface. From this study, it can be concluded that the kaolinite is an effective and low-cost material for the removal of fluoride ions from groundwater.

Simultaneous Sorption of Arsenate and Fluoride on Calcined Mg–Fe–La Hydrotalcite-Like Compound from Water

The co-occurring pollution of arsenate (As(V)) and fluoride (F) in potable water has gained global concern due to its serious threat to the human health. In this work, calcined Mg/Fe/La hydrotalcit...

Development of aluminum and zirconium based xerogel for defluoridation of drinking water: Study of material properties, solution kinetics and thermodynamics

The present investigation reports the preparation and defluoridation efficiency of Al2O3/ZrO2 xerogel. The material was prepared by environment friendly sol-gel technique using respective metal salts as precursors. FTIR spectra indicated presence of bridged structure (Zr – O – Al) in the material and decrease in intensity of hydroxyl group vibration indicates substitution of surface hydroxyl groups by fluoride through formation of metal – fluoride bonding. The XRD of material showed amorphous characteristics of Al2O3/ZrO2. The morphological feature of the material indicate presence of micro-pore in the structure and the total specific surface area (m2 g−1) and average pore radius (nm) were calculated to be 3.68 and 1736.6, respectively. The molecular interaction/bonding between aluminum-zirconium contributed in enhancing the stability of the material, whereas, the kinetics of thermal degradation pattern is heterogeneous in characteristics. Al2O3/ZrO2 shows almost 98% fluoride removal efficiency where the material-anions equilibrium was reached within 20 min time interval. Fluoride adsorption characteristics was found to be pH dependent influenced by pore diffusion, where the presence of multiple active centers, i.e., Al and Zr in Al2O3/ZrO2 favors fluoride sorption in comparison to ZrO2 xerogel. Fluoride adsorption follows a pseudo-second order kinetic as well as intra-particle diffusion model with almost ≥ 0.99 accuracy. The thermodynamics of fluoride adsorption was found to be spontaneous and exothermic in nature. The adsorbent shows good regeneration efficiency up to 5th cycles of continuous operation with very little effect of co-anions that can be helpful for its sustainable commercial applications.

Defluoridation investigation of Yttrium by laminated Y-Zr-Al tri-metal nanocomposite and analysis of the fluoride sorption mechanism

In this study, a laminated nanocomposite of Y-Zr-Al with significantly high surface area of 256.6 m2/g was successfully prepared, and was used to investigate the defluoridation performance of sorbent based on Yttrium. The composite showed high fluoride sorption performance, especially at low F− concentration conditions. SEM, BET, Elemental Mapping and XPS were used to characterize physicochemical properties of the composite in detail. Several influence factors including pH, presence of coexisting anions and contacting time were detailly investigated. The sorption course was studied by equilibrium sorption isotherm and sorption kinetics. Based on experimental results, a mechanism for fluoride sorption onto Y-Zr-Al composite was proposed, which revealed that there were three main sorption models, including mesoporous diffusion sorption, electronic interaction sorption and ion exchange, in the sorption course. The composite was considered to be highly potential in treating fluoride polluted waste water due to its high efficiency, high anti-interference ability and easy operation, and the discovery of fluoride highly attractive rare earth element was important to further understand and develop defluoridation sorbents based on rare earth.

Fluoride removal studies using virgin and Ti (IV)-modified Musa paradisiaca (plantain pseudo-stem) carbons.

The preparation of carbons in virgin and Ti-modified forms under controlled conditions at low temperature from plantain pseudo-stem (Musa paradisiaca) was achieved. These prepared carbons were characterized for instrumental studies such as BET, FTIR, XRD, SEM with EDS and TGA to understand the chemistry and modification. The determination of IEP and pHZPC established the presence of positive surface sites on the virgin (VMPC) and Ti-modified (TiMPC) carbons to facilitate the sorption of fluoride. The fluoride removal efficiency as a function of time, pH, dose, initial fluoride concentration, temperature, and co-ion intervention was studied. The maximum fluoride removal of about 81.2 and 97.7% was achievable with VMPC and TiMPC, respectively, after 20min at the pH of 2.04 and continued for the equilibrium of 60min. Temperature was found to be influential both by way of initial increase followed by a decrease in the fluoride uptake of MPCs. Regeneration was very consistent up to 7cycles with the residual fluoride concentration below the WHO guide line of 1.5mgL-1. Highest intervention due to hydrogen carbonate ions was observed during the fluoride removal process. Kinetic (pseudo-first-order, pseudo-second-order, and intra-particle diffusion) and isotherm models (Langmuir, Freundlich, and DKR) were checked for their compliance with the present sorption system. These low temperature synthesized MPCs are found to be effective candidates in the process of fluoride abatement in water.

Sorption of fluoride using chemically modified Moringa oleifera leaves

Contamination of drinking water due to fluoride is a severe health hazard problem. Excess of fluoride (> 1.5 mg/L) in drinking water is harmful to human health. Various treatment technologies for removing fluoride from groundwater have been investigated. The present study showed that the leaves of Moringa oleifera, a herbal plant is an effective adsorbent for the removal of fluoride from aqueous solution. Acid treated Moringa oleifera leaves powder showed good adsorption capacity than alkali treated Moringa oleifera leaves powder. Batch sorptive defluoridation was conducted under the variable experimental condition such as pH, contact time, adsorbent dose and initial fluoride ion concentration. Maximum defluoridation was achieved at pH 1. The percentage of fluoride removal increases with adsorbent dose. The equilibrium sorption data were fitted into Langmuir, Freundlich and Temkin isotherms. Of the three adsorption isotherms, the R2 value of Langmuir isotherm model was the highest. The maximum monolayer coverage (Qmax) from Langmuir isotherm model was determined to be 1.1441 mg/g, the separation factor indicating a favorable sorption experiment is 0.035. It was also discovered that the adsorption did not conform to the Freundlich adsorption isotherm. The heat of sorption process was estimated from Temkin Isotherm model to be − 0.042 J/mol which vividly proved that the adsorption experiment followed a physical process.

Assessing the applicability of an agro-industrial waste to Engineered Bio-char as a dynamic adsorbent for Fluoride Sorption

A potential feedstock, de-oiled Pongamia-pinnata seed cake is used to prepare engineered Bio-char (EBC) for the removal of fluoride from ground water. EBC was characterized and batch biosorption studies were conducted at different initial fluoride concentrations, EBC dosages and pH values. A maximum fluoride adsorption occurred at pH-7 with an equilibrium time of 90 min and EBC dosage of 10 mg/L. Different isotherm models were investigated, among which Langmuir was found to best fit with a maximum adsorption capacity of 0.985 ± 0.025 mg/g. The chemisorption was defined by Ritchie-pseudo-second-order kinetics with intra-particle diffusion contributing to the rate determining step. Column studies with variable operating conditions (initial fluoride concentration, bed depth, flow rate) and modeling of the breakthrough curves showed modified dose response model in excellent agreement with a maximum uptake of 1.12 ± 0.025 mg/g. EBC regeneration, comparison with contemporary sorbents and its real time application are also explored in the present study.

Effects of Changing pH, Incubation Time, and As(V) Competition, on F- Retention on Soils, Natural Adsorbents, By-Products, and Waste Materials.

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F−) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F− sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F− sorption even at alkaline pH, and pine sawdust showed low F− sorption for any pH value. Specifically, F− sorption was close to 100% for both ashes at pH < 6, and around 70% at pH 10, while for forest soil it was close to 90% at pH < 2, and around 60% at pH values near 8. Regarding the effect of incubation time on F− sorption, it was very low for both soils, pyritic material, granitic material, and both kinds of ashes, as all of them showed very rapid F− sorption from the start, with differences being lesser than 10% between sorption at 30 min and 1 month of incubation. However, sawdust and slate fines sorbed 20% of added F− in 30 min, remaining constant up to 12 h, and doubling after 30 days. And finally, mussel shell sorbed 20% at 30 min, increasing to close to 60% when incubation time was 30 days. This means that some of the materials showed a first sorption phase characterized by rapid F− sorption, and a slower sorption in a second phase. As regards the effect of the presence of As(V) on F− sorption, it was almost negligible, indicating the absence of competition for sorption sites. In view of that all, these results could aid to appropriately manage soils and by-products when focusing on F− removal, in circumstances where pH value changes, contact time vary from hours to days, and potential competition between F− and As(V) could take place.

Adsorption of fluoride on a chitosan-based magnetic nanocomposite: equilibrium and kinetics studies

Abstract A new derivative of chitosan functionalized with chloroacyl chloride and 2-(2-aminoethylamino) ethanol was synthesized for the preparation of a magnetic nanocomposite containing Fe3O4@TiO2 nanoparticles. Characterizations were done by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The nanocomposite was examined for the defluoridation of water, and the effect of contact time, pH, initial fluoride ion concentration, and adsorbent dosage were investigated. The Langmuir model showed the best agreement with the experimental data. The maximum adsorption capacity for the fluoride removal from aqueous solutions was 15.385 mg/g at 318 K and pH = 5.0. The adsorption mechanism matches the pseudo-second-order kinetic model with a rate constant (k2) of 0.68 g/mg·min. The thermodynamics study of the nature of adsorption showed that ΔH and ΔS were 13.767 kJ/mol and 0.066 kJ/mol·K respectively. A mechanism for the fluoride sorption was proposed by considering the electrostatic and hydrogen bonding interactions.

Biosorption of fluoride from aqueous medium by Indian sandalwood (Santalum Album) leaf powder

Sandalwood leaf powder prepared from mature, dried Indian sandalwood (Santalum album) leaves was investigated to assess its ability to remove fluoride from aqueous solutions using adsorption process. Effects of solution pH, contact time, adsorbent amount and solution temperature on fluoride sorption had been investigated. The biosorbent was effective at the pH range of 5.0–7.0 and its fluoride removal capacity was found to be above 75.0%. The kinetics of the interactions was measured with pseudo first order Lagergren equation (mean k1: 2.22 × 10−2 min−1), simple second order kinetics (mean k2: 4.43 × 10−1 g/mg/min), and intra-particle diffusion (mean ki: 8.31 × 10−2 mg/g/min0.5) mechanism. The adsorption data gave good fits with Langmuir, Freundlich and Temkin isotherms and yielded Langmuir monolayer capacity of 4.66 mg/g. The negative values of the thermodynamic parameters, ΔH, ΔS and ΔG showed the adsorption process to be exothermic in nature and thermodynamically favourable at lower temperature. These results indicated that Sandalwood leaf powder might be an effective adsorbent for treatment of water contaminated with fluoride.

Comparison of La3 + and mixed rare earths-loaded magnetic chitosan beads for fluoride adsorption

La3+ and mixed-rare earth magnetic chitosan beads (MCLB and MCLRB) were successfully prepared for fluoride removal, respectively. The adsorbents were characterized by scanning electron microscope and magnetic response. Batch experiments were carried out to investigate the adsorbent performance based on the influence of various factors such as adsorbent dosage, contact time, initial solution pH and co-existing anions on the fluoride adsorption. Results showed that MCLB and MCLRB followed the pseudo-second-order kinetic model with the correlation coefficient value of 0.9925 and 0.9985 respectively. The adsorption process was mainly chemical adsorption. The isotherm data was well fitted both Langmuir model and Freundlich model. The adsorption capacity of the adsorbents were 20.53 and 22.35mg/g respectively. The optimum pH value for fluoride ion removal was 5.0. The effects of co-existing anions on the fluoride sorption followed the decreasing order of CO32–>HCO3–>SO42−>NO3−>Cl−. Fluoride adsorption on MCLB and MCLRB could be attributed to ion exchange between fluoride and OH groups with the FeO coordinate bond promotion. Our study revealed that MCLB and MCLRB performed strong adsorption capacity for fluoride ion. In particularly, MCLRB could be a more cost-effective adsorbent to remove fluoride from aqueous solution.

Removal of Cr(VI) and fluoride by membrane capacitive deionization with nanoporous and microporous Limonia acidissima (wood apple) shell activated carbon electrode

Abstract Membrane capacitive deionization (MCDI) is an attractive desalination technique to achieve pure water by adsorbing ions in charge porous electrodes. In the current study nano-porous and micro porous activated carbon was derived from Limonia acidissima shells. The Limonia acidissima shell activated carbon (LASAC) prepared with chemical and thermal modification. The characterization techniques such as SEM, TGA, DTA, DTG, and N2 adsorption–desorption isotherm analysis were used for analysis LASAC. The LASAC electrode was used in MCDI lab scale self-made set up for simultaneous sorption of Cr(VI) and fluoride from the aqueous system. The LASAC electrode performance of was found effective for simultaneous removal of Cr(VI) and fluoride from mixed feed solution with maximum electrosorption capacity of Cr(VI) and fluoride were found to 0.8086 mg/g and 0.7805 mg/g for 10 mg/L; 3.227 mg/g and 2.7554 mg/g for 100 mg/L respectively. The parameters estimation of the monocomponent isotherm, multicomponent isotherm models and kinetic models were carried out in the present study. Thus MCDI with LASAC electrode could be useful for treatment of low concentrated Cr(VI) and fluoride wastewater.