“…Figure 3c shows that ionic strength variation in the range of 0 to 100 mM had insignificant effects on F − removal, although an increase in ionic strength increases charge screening and reduces the electrostatic repulsion on the surface (Yang et al, 2007). This effect of electrolyte also indicates that outer sphere electrostatic interactions had a negligible role in F − adsorption on this soil in our pH range of interest, consistent with other studies for F − adsorption on different materials, e.g., laterite (Vithanage et al, 2012), where F − adsorption was primarily described by inner sphere complexation.…”
Core Ideas
A surface complexation model for F− adsorption on soil was developed.
Dissolved Al and Al–F complex adsorption added to the model better explained F− adsorption.
The model can be extended to study the effect of existing co‐anions or humic substances.
The adsorption processes of F− on a natural soil as a function of varying pH and F− concentration were evaluated by applying a surface complexation model (SCM) based on a single surface functional group with monodentate binding sites. A granitic soil from Tsukuba, Japan, was chosen as an example, and the SCM was developed to explain the pH dependency of F− sorption isotherms on the soil. Four possible surface complexation reactions were postulated with and without including dissolved Al. Optimized constants for F− surface complexation, and those for protonation and deprotonation, were used for the simulations. The SCM including dissolved Al and the adsorption of Al–F complex can simulate the experimental results, the decreasing trend of F− adsorption with the increase in pH, quite successfully. Also, including dissolved Al and the adsorption of Al–F complex to the model explained the change in solution pH after F− adsorption. Therefore, incorporation of dissolved Al and Al–F complex in model calculations of a soil–F system is an important improvement to predict F− concentrations of soil solutions.
“…Figure 3c shows that ionic strength variation in the range of 0 to 100 mM had insignificant effects on F − removal, although an increase in ionic strength increases charge screening and reduces the electrostatic repulsion on the surface (Yang et al, 2007). This effect of electrolyte also indicates that outer sphere electrostatic interactions had a negligible role in F − adsorption on this soil in our pH range of interest, consistent with other studies for F − adsorption on different materials, e.g., laterite (Vithanage et al, 2012), where F − adsorption was primarily described by inner sphere complexation.…”
Core Ideas
A surface complexation model for F− adsorption on soil was developed.
Dissolved Al and Al–F complex adsorption added to the model better explained F− adsorption.
The model can be extended to study the effect of existing co‐anions or humic substances.
The adsorption processes of F− on a natural soil as a function of varying pH and F− concentration were evaluated by applying a surface complexation model (SCM) based on a single surface functional group with monodentate binding sites. A granitic soil from Tsukuba, Japan, was chosen as an example, and the SCM was developed to explain the pH dependency of F− sorption isotherms on the soil. Four possible surface complexation reactions were postulated with and without including dissolved Al. Optimized constants for F− surface complexation, and those for protonation and deprotonation, were used for the simulations. The SCM including dissolved Al and the adsorption of Al–F complex can simulate the experimental results, the decreasing trend of F− adsorption with the increase in pH, quite successfully. Also, including dissolved Al and the adsorption of Al–F complex to the model explained the change in solution pH after F− adsorption. Therefore, incorporation of dissolved Al and Al–F complex in model calculations of a soil–F system is an important improvement to predict F− concentrations of soil solutions.
“…The observed value of zero point charge (pH zpc = 8.13) suggests the presence of some weakly acidic groups on the surface of the adsorbent γ-Fe 2 O 3 nanoparticles. According to literature data, the calculated pH ZPC is comparable with experimentally measured pH ZPC (8.13) [ 34 ]. Fig.…”
BackgroundFluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide and hence its removal attracted much attention to have clean aquatic systems. In the present work, removal of fluoride ions from drinking water tested using synthesized γ-Fe2O3 nanoparticles.MethodsNanoparticles were synthesized in co-precipitation method. The prepared particles were first characterized by X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). Density functional theory (DFT) calculations on molecular cluster were used to model infrared (IR) vibrational frequencies and inter atomic distances.ResultsThe average size of the particles was around 5 nm initially and showed a aggregation upon exposure to the atmosphere for several hours giving average particle size of around 5–20 nm. Batch adsorption studies were performed for the adsorption of fluoride and the results revealed that γ-Fe2O3 nanoparticles posses high efficiency towards adsorption. A rapid adsorption occurred during the initial 15 min by removing about 95 ± 3 % and reached equilibrium thereafter. Fluoride adsorption was found to be dependent on the aqueous phase pH and the uptake was observed to be greater at lower pH. Fourier transform infrared spectroscopy (FT-IR) was used for the identification of functional groups responsible for the adsorption and revealed that the direct interaction between fluoride and the γ-Fe2O3 particles.ConclusionsThe mechanism for fluoride removal was explained using the dehydoxylation pathway of the hydroxyl groups by the incoming fluoride ion. FT-IR data and other results from the ionic strength dependence strongly indicated that formation of inner-spherically bonded complexes. Molecular clusters were found to be good agreement with experimental observations. These results show direct chemical interaction with fluoride ions.
“…A novel bimetallic oxide adsorbent was synthesized by the co-precipitation of Fe(II) and Ti(IV) sulphate solution using ammonia titration at room temperature for fluoride removal from water [51]. Mg-doped nano ferrihydrite powder [52], Fe(III) modified montmorillonite [53], iron rich laterite [54], as an adsorbents for F − removal from aqueous solutions. See Table 3 for details.…”
Fluoride is a persistent and non-biodegradable pollutant that accumulates in soil, plants, wildlife and in human beings. Therefore, knowledge of its removal, using best technique with optimum efficiency is needed. The present survey highlights on efficacy of different materials for the removal of fluoride from water. The most important results of extensive studies on various key factors (pH, agitation time, initial fluoride concentration, temperature, particle size, surface area, presence and nature of counter ions and solvent dose) fluctuate fluoride removal capacity of materials are reviewed.
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