Conditions For Removal Of Fluoride Research Articles

Removal of fluoride from aqueous phase by biosorption onto algal biosorbent Spirogyra sp.- IO2: Sorption mechanism elucidation

This communication presents results pertaining to the adsorptive studies carried out on fluoride removal onto algal biosorbent ( Spirogyra IO2). Batch sorption studies were performed and the results revealed that biosorbent demonstrated ability to adsorb the fluoride. Influence of varying the conditions for removal of fluoride, such as the fluoride concentration, the pH of aqueous solution, the dosage of adsorbent, the temperature on removal of fluoride, and the adsorption–desorption studies were investigated. Sorption interaction of fluoride on to algal species obeyed the pseudo first order rate equation. Experimental data showed good fit with the Langmuir's adsorption isotherm model. Fluoride sorption was found to be dependent on the aqueous phase pH and the uptake was observed to be greater at lower pH. Maximum fluoride sorption was observed at operating 30 °C operating temperature. Adsorption–desorption of fluoride into inorganic solutions and distilled water was observed and this indicated the combined effect of ion exchange and physical sorption phenomena. Significant changes in the FT-IR spectra was observed after fluoride sorption which is indicative of the participation of surface function groups associated with hydrogen atoms in the carboxylic groups in sorption interaction. From X-ray photoelectron spectroscopy (XPS) analysis a marginal increase in the area for the binding energy peak at 287.4 eV was observed which could be due to the formation of –C–F– bonds. Thermogravimetric (TGA) analysis of the fluoride loaded sorbent showed that the biosorbent underwent three steps decomposition process when heated from 25 to 100 °C. The maximum weight loss was observed to be between 200 and 400 °C and 700 and 800 °C.

Factors influencing the removal of fluoride from aqueous solution by calcined Mg–Al–CO 3 layered double hydroxides

Layered double hydroxides (LDH) calcined at different temperatures (denoted as CLDH) have been demonstrated to recover their original layered structure in the presence of appropriate anions. In the light of this so-called “memory effect”, a study of removal of fluoride from aqueous solution by calcined Mg–Al–CO 3-LDH has been carried out. The LDH calcined at 500 °C had the highest capacity of removal of fluoride ion, because of retention of its intrinsic structure. The CLDH with an Mg/Al ratio of 2 has a remarkable ability to adsorb anions. The adsorption loading is higher for the calcined Mg–Al-LDH than for calcined Zn–Al and Ni–Al-LDH. The influence of varying the conditions for removal of fluoride, such as the pH of aqueous solution, the initial fluoride concentration, the dosage of adsorbent, and temperature on removal of fluoride have been investigated. The influence of co-existing anions in fluoride aqueous solution indicates that the percentage of removal of fluoride increased in order PO 4 3− < Cl − ≈ SO 4 2− < Br − ≪ NO 3 −. It was found that maximum removal of fluoride from aqueous solutions was obtained in 6 h at pH 6.0 with an initial concentration of 50 mg/L, and that the retention of fluoride ions by the CLDH material was 98% or higher. The residual fluoride concentration was found to be 0.4 mg/L with an initial concentration of 20 mg/L, which meets the national standard for drinking water quality. The Freundlich isotherm and Langmuir isotherm were used to fit the data of equilibrium experiments. The results of X-ray diffraction, FT-IR and TG-MS demonstrate that the adsorption phenomenon is accompanied by rehydration with concomitant uptake of fluoride ions to rebuild the initial layered structure.

Study of interaction of polymeric aluminium hydroxide with fluoride

The interaction between polymeric aluminium hydroxide, Alp, and fluoride has been investigated to optimize the conditions for removal of fluoride from waste waters of aluminium manufacturing plants using Alp. The results of these studies have shown that the nature of products formed between Alp and fluoride depends on the molar concentration ratio of fluoride to aluminium (rF), pH, and initial fluoride concentration. In the absence of interfering ions, fluoride can be effectively precipitated as Al13(OH)29F10 with Alp, using [Formula: see text] and 4 &lt; pH ≤ 7. At rF &gt; 1, Alp dissociates and fluoride is precipitated as cryolite, and the residual fluoride concentration is controlled by its high solubility.