A review of emerging adsorbents and current demand for defluoridation of water: Bright future in water sustainability.

Enhanced fluoride removal from water by rare earth (La and Ce) modified alumina: Adsorption isotherms, kinetics, thermodynamics and mechanism

Nano-magnetically modified activated carbon prepared by oak shell for treatment of wastewater containing fluoride ion

Fluoride occurrences, health problems, detection, and remediation methods for drinking water: A comprehensive review.

The present investigation describes the synthesis and characterization of nanocrystalline adsorbent, hydroxyapatite (HAp) from Limacine artica shells and its application towards fluoride removal from aqueous solution. The high content of calcium carbonate (92.9%) analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed the snail shell to be a good precursor for HAp synthesis. The X-ray diffraction (XRD) and Braunauer-Emmet-Teller (BET) analyses supported the formation of a nanocrystalline material with a surface area and pore diameter of 152.45m 2 /g and 4.2 nm, respectively. The observed decrease in crystallite size after fluoride ion adsorption was attributed to the dispersion of agglomerated HAp particles due to H-bonding between adsorbed fluoride ions with bulk water molecules. The good fitting of Lagergren pseudo second-order kinetics and Elovich model indicated the rate limiting step to be of chemisorptions type. The adsorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms satisfactorily supporting both monolayer and multilayer physisorption at HAp-water interface. Thermodynamic study revealed the adsorption process to be spontaneous and endothermic in nature. Electrostatic attraction, ion exchange and hydrogen bonding are mainly responsible for the adsorption mechanism. The used HAp could be reused for fourth cycle without a significant loss of adsorption ability.

Kinetics and mechanistic interpretation of fluoride removal by nanocrystalline hydroxyapatite derived from Limacine artica shells

Fluoride in drinking water is beneficial at low concentrations but is considered harmful for the human health when present at concentrations exceeding 1.5 mg/L. Prevalence of high concentration of fluoride in drinking water, combined with the nonavailability of alternate viable sources, makes the treatment of the contaminated water an essential task. In this study, we report the synthesis and characterization of a hybrid adsorbent; hydroxyapatite-modified activated alumina (HMAA) prepared by dispersing nanoparticles of hydroxyapatite inside activated alumina granules. The composite adsorbent provided a synergy toward fluoride removal from contaminated drinking water. The hybrid adsorbent possesses a maximum adsorption capacity of 14.4 mg F/g which is at least five times higher than the virgin-activated alumina, which has been used extensively for fluoride removal. HMAA was regenerated using six bed volumes of a solution containing commonly available innocuous chemicals. The adsorbent was subjected to multiple numbers of operating cycles within a column, each cycle consisting of one adsorption run followed by regeneration.

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A. Thareja

Papers

Enhanced fluoride removal by hydroxyapatite-modified activated alumina