Fluoride Adsorption Kinetics Research Articles

Comprehensive batch studies on removal of fluoride from aqueous solution by acid and alkali-activated adsorbents prepared from Dal lake weeds: Mechanism, Kinetics and Thermodynamics

An efficient and economical way of eliminating fluoride from water is being investigated by employing the buoyant aquatic plant (Dal weed). Two post-pyrolysis chemical activation alteration techniques were implemented: acidic activation by employing sulfuric acid (H-activation) and alkaline activation using sodium hydroxide (OH-activation). The batch kinetic studies have been carried out considering varying starting fluoride levels such as 2–10 mg/L. The impact of diverse procedural factors, including dosage of Dal weed, starting fluoride level, pH and contact duration was observed to determine their influence on fluoride adsorption kinetics. Based on analyzed exploratory results, removal efficacy of 63% for the OH-activated carbon and 83% for H-activated carbon was achieved at commencing fluoride level of 10 mg/L, adsorbent dosage of 0.8 g, at 25 °C after 120 min. The maximal fluoride uptake capacity for H-activated carbon was observed to be 78.158 mg/g. Kinetic investigations showed that the Freundlich isotherm model provided a satisfactory match with an R2 value of 0.99. The reaction order nature adhered to kinetics resembling pseudo second order. Thermodynamic investigation revealed endothermic sorption, with negative ΔG indicating spontaneous fluoride uptake. In comparison, the positive number for ΔS suggested random behavior at the contact involving the adsorbent and adsorbate. The investigations into the regeneration capabilities of the adsorbent material revealed that even after undergoing for five consecutive cycles of adsorption and regeneration, the adsorbent exhibited an uptake potential of 45%. The presence of competing ions in the solution negatively impacted defluoridation efficacy, with the influence following the order of HCO3−< NO3−< Cl−< SO42−< PO43−.

Production of activated carbon from exhausted coffee grounds chemically modified with natural eucalyptus ash lye and its use in the fluoride adsorption process.

The objective of this research was to produce an activated carbon (AC) from exhausted coffee grounds (ECG) and chemically activate it with natural lye from eucalyptus ash to subsequently evaluate the fluoride adsorption process in an aqueous medium. The thermal analysis of ECG was determined as well as solubilized extraction, alkalinity and calcium content of eucalyptus ashes. AC was characterized by elemental analysis, scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), analysis of textural properties, pH and point of zero charge (PZC). The AC presented macroporosity and XRD confirmed the amorphous characteristic of cellulose-containing materials. Carboxylic acid functional group was identified in the AC surface, which can contribute to the adsorption of fluoride. The specific surface area of ECG and AC were 189.01 and 21.74 m2/g. The adsorption kinetics of fluoride revealed that equilibrium is reached around 800min and the data followed the pseudo-second order model. The Freundlich model fitted the experimental data with the best quality and Freundlich's constant n allowed inferring that the adsorption is favorable and the isotherm appears to be L-type, with an initial downward curvature, which suggests less availability of active sites when increasing the adsorbent concentration.

Evaluation of Scales of Tilapia Sp. and Sciaenops ocellatus as Low Cost and Green Adsorbent for fluoride Removal From Water.

Water containing more than 1.5 mg/L of fluoride is considered toxic as it causes dental, kidney, and other health problems. With the purpose of helping alleviate these problems by exploring a treatment method for fluoride contamination, this study was to assess the suitability of scales of Tilapia Sp. and Sciaenops ocellatus as a cheaper source of adsorbent for the removal of fluoride from drinking water. The samples which were obtained from the Lapaz Market in Accra, Ghana, underwent treatment to eliminate any impurities. They were then ground into powder and treated with aluminum hydroxide [Al(OH)3]. The treated samples were used for the removal of fluoride from spiked solutions prepared in the laboratory. Batch adsorption was performed by varying parameters such as adsorbent dose (1–8 g/L), initial concentration (2 mg/L to 10 mg/L), and contact time (30–300 min) at pH of 7. A one-way ANOVA was used to validate the significance of the defluoridation process with respect to the different experimental conditions. The optimum adsorbent dose, initial concentration, and contact time were found to be 4 g/L, 10 mg/L, and 300 min, respectively. The results revealed that the maximum percentage removal of fluoride was 76% by Tilapia Sp. and 70% by Sciaenops ocellatus at the optimum conditions. This is an indication that both Tilapia Sp. And Sciaenops ocellatus scales are suitable adsorbents for the removal of fluoride from water. The fluoride adsorption kinetics followed the pseudo-second-order model, and the adsorption isotherm fitted the Freundlich Isotherm model better than the Langmuir Isotherm model. The adsorption intensity and adsorption capacity for Tilapia Sp. were 3.484 L/mg and 0.065 mg/g, and that of Sciaenops ocellatus 3.195 L/mg and 0.045 mg/g respectively.

Removal of fluoride from water using aluminum hydroxide-loaded zeolite synthesized from coal fly ash

The removal of fluoride from wastewater is essential as the excess accumulation of fluoride in environment is harmful to the health of humans. In this study, the defluorination of water by aluminum hydroxide-coated zeolite (AHZ), which was synthesized from coal fly ash, was investigated in batches. The Langmuir maximum adsorption capacity of fluoride by AHZ reached 18.12 mg/g. Aluminum hydroxide was shown to be the major component that adsorbed fluoride. More than 92% removal of fluoride was achieved within 2 h, and the fluoride adsorption kinetics were well fitted to a pseudo-second-order model. The point of zero charge (pHpzc) of the AHZ was determined to be 5.52. Fluoride adsorption by AHZ depended greatly on pH, and maximum performance was obtained at pH 5.5–6.5. The AHZ showed good selectivity for the adsorption of fluoride in the presence of chloride, nitrate, sulfate, bicarbonate, and acetate ions, and the fluoride was nearly exhausted at a sufficiently high dose. The release of OH− due to fluoride adsorption was confirmed. FTIR and XPS studies further illustrated that the adsorption mechanism of fluoride adsorption on AHZ was ligand exchange with hydroxyl groups and the formation of F–Al bonds.

Facile Synthesis of Hollow MgO Spheres and Their Fluoride Adsorption Properties

In the present work, the hollow MgO spheres were synthesized through a facile wet-chemistry method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrum are employed to characterize the as-prepared sample. Those results indicate that the average size of the as-prepared MgO hollow spheres is about 2 μm. Also, the MgO hollow spheres have the polycrystalline and porous structure, which would provide large specific surface area and plenty active sites for fluoride adsorption. The adsorption properties of the MgO hollow spheres towards fluoride are investigated. The fluoride adsorption kinetics of the MgO hollow spheres fits well the pseudo-second-order model. Also, the kinetic data revealed that the fluoride adsorption was rapid, more than 83% of fluoride could be removed within 40 min. The fluoride adsorption capacity of the hollow MgO spheres is larger than 182.4 mg/g at a pH of 7.0. The as-prepared products maintain excellent adsorption performance in the pH range of 3–11. In addition, the adsorption mechanism also has been discussed. From the FTIR results, a hydroxyl and carbonate coexchange mechanism is proposed. It is believed that the hollow MgO spheres are a potential candidate for fluoride removal.

Kinetics of fluoride adsorption onto native and Mg(OH)2-amended limestone

The adsorption kinetics of fluoride onto limestone (LS) and Mg(OH)2-amended LS were investigated using batch adsorption technique. Data were best fitted to second-order and Elovich models. The Mg(OH)2-ameded LS showed substantial increases in F− adsorption relative to native LS. Similarity of ionic radii and charge of both F− and OH− were hypothesized to be the major cause of such increases. The OH− functional group of the surface Mg(OH)2 could be exchanged by aqueous F− through surface complexation (ligand exchange). No background effect of naturally occurring anions in F−-rich groundwater on adsorption capacity of Mg(OH)2-amended LS. The results reveal that the Mg(OH)2-amended LS can be environmentally safe and economical for F− removal.

Removal of fluoride and hardness by layered double hydroxides: property and mechanism

Calcined layered double hydroxides are typical anionic adsorbents with excellent fluoride removal capabilities. However, in actual water bodies, cationic substances such as hardness are often widespread. This research explored the performance of simultaneous fluoride and hardness removal by the adsorbents. The results showed that adsorption kinetics of fluoride and hardness substances followed the quasi-second order. The adsorption isotherms for fluoride and hardness agents followed the Langmuir and Freundlich models, independently. The capability of calcined layered double hydroxides to remove magnesium ions is much higher than that of calcium ion. The removal of fluoride is mainly utilized the “memory effect”. The removal of magnesium occurred by forming metal oxide bond with magnesium and aluminum ions on the surface of the adsorbents and was embed in the gap on the surface of the material. To remove calcium, the -OH generated by fluoride entered into the interlayer of the material to form Ca (OH)2 precipitate.

Removal of Fluoride and Arsenate from Aqueous Solutions by Aluminum-Modified Guava Seeds

The contamination of groundwater by arsenic and fluoride is a major problem worldwide, causing diseases in the population that uses these waters for their consumption. Therefore, the removal of these types of pollutants from groundwater is a very important issue. In this work, the removal of arsenate and fluoride from aqueous solutions by using aluminum-modified guava seeds (Al-GSs) was evaluated. Batch-type adsorption experiments were carried out with aqueous solutions of As(V) and F− and Al-GSs. The kinetic and equilibrium parameters of adsorption were determined, as well as the effects of adsorbent dose and pH. The adsorbent was characterized by scanning electron microscopy and infrared spectroscopy in order to determine its morphology and the functional groups present in the material. The results showed that hydroxyl and carboxyl are the main groups involved in the adsorption of As(V) and F−. The fluoride adsorption kinetics indicate that the equilibrium time was reached at 150 min and it can be described by the Lagergren model, while for As(V) the equilibrium time was lower (120 min) and the kinetic data were fitted well to the pseudo-second-order model. The Langmuir-Freundlich model can describe the adsorption equilibrium data in all cases. The fluoride adsorption capacity by Al-GS was 0.3445 mg/g, and for As(V) it was 4 mg/g. It can be established that the removal of arsenates and fluoride in Al-GSs is due to chemisorption on a heterogeneous surface.

Simultaneous and efficient removal of fluoride and phosphate by Fe-La composite: Adsorption kinetics and mechanism

We report the synthesis of a novel Fe-La composite adsorbent by one-pot hydrothermal method for removing fluoride and phosphate simultaneously. The as-obtained adsorbent shows rod-like morphology and large specific surface area of 113.13 m2/g. A series of adsorption experiments were carried out to investigate the influence of various factors on the simultaneous adsorption of fluoride and phosphate, such as different adsorbent dosage, pH, temperature and co-existing anion. The results demonstrate that the Fe-La adsorbent exhibited high adsorption capacity for fluoride and phosphate in a wide pH range (3.8–7.1). The adsorption kinetics of fluoride and phosphate by Fe-La composite could be well described by the Langmuir model and the pseudo-second-order model. The simultaneous removal of fluoride and phosphate by Fe-La composite could be ascribed to ion exchange between fluoride and La-OH groups, as well as the formation of metal phosphates precipitation, respectively. Our results may provide some insight to develop new adsorbents for removing fluoride and phosphate simultaneously.

Optimization of molar concentration of AlCl3 salt in the sol–gel synthesis of nanoparticles of gamma alumina and their application in the removal of fluoride of water

Nanoparticles of gamma alumina prepared by sol–gel method, using alcoholic aluminum chloride (AlCl3) precursor has been demonstrated as an effective adsorbent for fluoride removal of water. Increasing the molar concentration of AlCl3 from 0.1 to 0.25 M was found to increase the nanoalumina content in the same ratio with good yield. Different analytical techniques like thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and Brunauer, Emmett and Teller surface area analysis were employed for the characterization of the synthesized nanoparticles whereas batch adsorption studies were performed for the understanding of adsorption kinetics of fluoride in water of neutral pH. Adsorption kinetics has exhibited excellent fluoride removal capability of ~23 mg/g from the nanoparticles derived using up to 0.2 M AlCl3 precursor. Nanoparticles derived from 0.25 M AlCl3 have shown comparatively less fluoride removal (~18 mg/g). Langmuir equilibrium model was found more suitable for describing the fluoride adsorption mechanism. Presence of sulphate, carbonate, nitrate, and chloride anions in water influenced the fluoride removal efficiency noticeably.

Adsorption kinetics of fluoride on bone char and its regeneration

Adsorption kinetics of fluoride on bone char and its regeneration

Removal of fluoride from drinking water using aluminum hydroxide coated activated carbon prepared from bark of Morinda tinctoria

The aim of this study is to design and develop a novel cost effective method for fluoride removal, applicable to rural areas of developing countries. Adsorption is widely considered as one of the appropriate technologies for water defluoridation. This study investigates the feasibility of using low-cost biomass based activated carbon from the bark of Morinda tinctoria coated with aluminum hydroxide (AHAC) for water defluoridation, at neutral pH range. Characterization of AHAC was done through IR, SEM with EDAX studies before and after fluoride treatment. The fluoride adsorption capacity of AHAC as a function of contact time, pH and initial fluoride concentration was investigated. The role of co-existing interfering ions also was studied. The isotherm and kinetic models were used to understand the nature of the fluoride adsorption onto AHAC. Freundlich isotherm and intra-particle diffusion were the best-fitting models for the adsorption of fluoride on AHAC. Fluoride adsorption kinetics well fitted with pseudo-second order model. The results showed excellent fluoride adsorption capacity was found to be 26.03 mg g−1 at neutral pH.

Defluorination of drinking water using surfactant modified zeolites

The prevalence of high concentrations of fluoride (i.e. > 1.5 mg/l) in groundwater in the Northernpart of Ghana especially around the Bongo communities has been an issue of concern.Owingto the arid nature of these localities, the inhabitants (who are mainly peasant farmers), relymore on groundwater sources for their drinking water. With the strenuous nature of their joband the warm weather conditions, the farmers generally consume more water, thus becomingmore vulnerable to dental and skeletal fluorosis. This study focused on the removal of fluoridefrom groundwater by employing surfactant modified zeolites (SMZ) synthesized using locallyavailable kaolin material as precursor. The zeolite synthesis involved calcination of kaolin, alkaline fusion and hydrothermal treatment. The final product was modified with 5g/L Hexadecyltrimethylammonium bromide (HDTMABr). The zeolite was characterised by Xray Diffraction(XRD), Energy Dispersive Xray (EDX) and Scanning Electron Microscopy (SEM) and the modified form employed in batch fluoride removal studies. The fluoride adsorption kinetics was studiedusing model water with varying initial fluoride concentration. From the EDX analysis, the synthesized zeolite NaLSX was found to comprise predominantly Oxygen (60%), Silicon (15%), and Aluminium (13%). The SEM showed the zeolite NaLSX crystals to be octahedrally shaped. The unmodified zeolite NaLSX was incapable of adsorbing fluoride ions but the surfactant modified zeolite adsorbed fluoride. The fluoride adsorption capacity of the modified zeolite was pH dependent and peaked at pH 6.0 – 7.0. Keywords : characterization, defluoridation, groundwater, surfactant, zeolites

Removal of fluoride from drinking water using modified ultrafine tea powder processed using a ball-mill

A low-cost and highly efficient biosorbent was prepared by loading zirconium(IV) onto ball-milled, ultrafine tea powder (UTP-Zr) for removal of fluoride from drinking water. To evaluate the fluoride adsorption capacity of UTP-Zr over a wide range of conditions, the biosorbent dosage, contact time, initial pH, initial fluoride concentration and presence of other ions were varied. UTP-Zr performed well over the considerably wide pH range of 3–10. The residual concentration of Zr in the treated water was below the limit of detection (0.01mg/L). Fluoride adsorption by the UTP-Zr biosorbent followed the Langmuir model, with a maximum adsorption capacity of 12.43mgF/g at room temperature. The fluoride adsorption kinetics fit the pseudo-second-order kinetic model. The synthesized biosorbent was characterized by BET, SEM, EDS, XRD and XPS to reveal how UTP-Zr interacts with fluoride. Results from this study demonstrated that UTP-based biosorbents will be useful and safe for the removal of fluoride from drinking water.

Characterization and adsorption properties of a lanthanum-loaded magnetic cationic hydrogel composite for fluoride removal

In this study, a novel lanthanum-loaded magnetic cationic hydrogel (MCH-La) was synthesized for fluoride adsorption from drinking water. The adsorption kinetics, isotherms, and effects of pH and co-existing anions on fluoride uptake by MCH-La were evaluated. FTIR, Raman and XPS were used to analyze the fluoride adsorption mechanism of MCH-La. Results showed that MCH-La had positive zeta potential values of 23.6–8.0 mV at pH 3.0–11.0, with the magnitude of saturation magnetization up to 10.3 emu/g. The fluoride adsorption kinetics by MCH-La fitted well with the fractal-like-pseudo-second-order model, and the adsorption capacity reached 93% of the ultimate adsorption capacity within the first 10 min. The maximum fluoride adsorption capacity for MCH-La was 136.78 mg F−/g at an equilibrium fluoride concentration of 29.3 mg/L and pH 7.0. Equilibrium adsorption data showed that the Sips model was more suitable than the Langmuir and Freundlich models. MCH-La still had more than 100 mg of F−/g adsorption capacity at a strongly alkaline solution (pH > 10). The adsorption process was highly pH-dependent, and the optimal adsorption was attained at pH 2.8–4.0, corresponding to ligand exchange, electrostatic interactions, and Lewis acid–base interactions. With the exception of both anions of HCO3− and SiO44−, Cl−, NO3−, and SO42− did not evidently prevent fluoride removal by MCH-La at their real concentrations in natural groundwater. The fluoride adsorption capacity of the regenerated MCH-La approached 70% of the fresh MCH-La from the second to fifth recycles. FTIR and Raman spectra revealed that C–O and CO functional groups on MCH contributed to the fluoride adsorption, this finding was also confirmed by the XPS F 1s spectra. Deconvolution of C 1s spectra before and after fluoride adsorption indicated that the carboxyl, anhydride, and phenol groups of MCH were involved in the fluoride removal.

Review of fluoride removal from water by adsorption using soil adsorbents – an evaluation of the status

The fate of excessive fluoride in water is cause for serious public health concerns worldwide. Water defluoridation using various technologies therefore continues to attract disproportionate research interest from around the world. Defluoridation studies using soil adsorbents, in particular, have remained the focus of intense research efforts since the last few decades. So as to assess the research status in this area, soil adsorbents commonly reported for water defluoridation over the last few decades were reviewed. This paper presents a compilation of defluoridation capacities and a summary of requisite parameters for water defluoridation using soil adsorbents. Comparison of defluoridation efficiencies of soil adsorbents is also presented, and the fluoride adsorption kinetics and adsorption equilibrium characteristics of adsorbents discussed. The results indicate that the soil adsorbents that have attracted highest research interest in this regard include hydroxyapatites, montmorillonites, hydrotalcite, zeolites, pumice and kaolinites. On average, however, the minerals that have shown the highest capacities for water defluoridation are: ferrihydrites, hydrotalcite, palygorskites, boehmite/bauxite, and pumice. Fluoride adsorption for most soil adsorbents is fitted by the Langmuir and Freundlich isotherms. Most of the kinetic data, in contrast, were described by the pseudo-second-order kinetics model. Water pH and temperature were the dominant solution factors that controlled fluoride adsorption onto soil adsorbents.

Optimizing adsorption of fluoride from water by modified banana peel dust using response surface modelling approach

The present work highlighted the effective application of banana peel dust (BPD) for removal of fluoride (F−) from aqueous solution. The effects of operating parameters such as pH, initial concentration, adsorbent dose, contact time, agitation speed and temperature were analysed using response surface methodology. The significance of independent variables and their interactions were tested by the analysis of variance and t test statistics. Experimental results revealed that BPD has higher F− adsorption capacity (17.43, 26.31 and 39.5 mg/g). Fluoride adsorption kinetics followed pseudo-second-order model with high correlation of coefficient value (0.998). On the other hand, thermodynamic data suggest that adsorption is favoured at lower temperature, exothermic in nature and enthalpy driven. The adsorbents were characterised through scanning electron microscope, Fourier transform infrared spectroscopy and point of zero charges (pHZPC) ranges from pH 6.2–8.2. Finally, error analysis clearly demonstrates that all three adsorbents are well fitted with Langmuir isotherm compared to the other isotherm models. The reusable properties of the material support further development for commercial application purpose.

Fluoride adsorption properties of three modified forms of activated alumina in drinking water.

The study describes the removal of fluoride from drinking water using activated alumina (AA). AA was modified with H2SO4, FeCl3 and a combination of the two to enhance fluoride adsorption. The AA adsorbents were characterized using Brunauer-Emmett-Teller surface area analysis and X-ray fluorescence. The maximum adsorption capacity of H2SO4- and FeCl3-modified AA adsorbents was 4.98 mg/g, which is 3.4 times higher compared with that of normal AA. The results showed that the surface area of AA increased when modified with H2SO4. AA modified with FeCl3 enhanced fluoride adsorption ability through ion-exchange between chlorine ions and fluoride ions. The fluoride adsorption properties of AA modified with both H2SO4 and FeCl3 were consistent with the Langmuir model. The fluoride adsorption kinetics of the adsorbents were well described by the pseudo-second-order kinetic model.

Synthesis and characterization of cotton-like Ca–Al–La composite as an adsorbent for fluoride removal

Abstract Cotton-like Ca–Al–La composite as an adsorbent for fluoride removal was successfully synthesized by an easy one-step hydrothermal process. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the samples have uniform and cotton-like morphology. Batch sorption experiments were conducted to study the influence of various factors such as pH, initial fluoride concentration, equilibrium contact time, co-existing anions on the sorption of fluoride. The fluoride adsorption over the Ca–Al–La composite follows the Langmuir model. The maximum adsorption capacity of the adsorbent is 29.30 mg/g. The fluoride adsorption kinetics over the adsorbent can be well described by the pseudo-second-order kinetic model. In addition, the cotton-like Ca–Al–La composite showed high fluoride removal efficiency over a wide range of pH (3–11).

Titanium(IV) hydrate based on chitosan template for defluoridation from aqueous solution

A cost effective bio-adsorbent, titanium(IV) hydrate based on chitosan template (Ti-CHI), was synthesized using Ti(SO4)2 and chitosan for defluoridation from aqueous solutions. The Ti-CHI material was characterized using FTIR, SEM with EDX, XRD, XPS and Zeta potential. The adsorption kinetics of fluoride onto Ti-CHI followed pseudo-second-order and intra-particle diffusion models. The Ti-CHI was effective for defluoridating systems with low fluoride concentrations (4.52mg/L), exhibiting a 87.50% removal rate and permitting a residual fluoride concentration (0.55mg/L). The most stable pH range for fluoride removal was from 4 to 9. After combining the results of pH effects, FTIR and Zeta potential, the NH groups and TiOH groups were revealed as the fluoride adsorption sites on Ti-CHI. In addition, the carbonate ions present in the aqueous solutions adversely impact the fluoride adsorption. The Langmuir, Freundlich, and Langmuir–Freundlich models were used to illustrate the isotherms of the adsorption process. The adsorption of fluoride onto Ti-CHI fits the Langmuir and Langmuir–Freundlich isotherm models well. The maximum adsorption capacity for fluoride on the Ti-CHI was 16.12mg/g. Thermodynamic studies revealed that the adsorption process was spontaneous.