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A B S T R A C TMagnesium-doped nano ranged hematite was prepared following surfactant (cationic surfactant cetyltrimethyl ammonium bromide, [CTAB]) mediation-precipitation technique. The chemical composition of the synthesized sample was: Fe 63.8% and Mg 1.35%. Presence of crystalline hematite phase was confirmed from the X-ray diffraction pattern. The transmission electron microscopy (TEM) image showed spherical particles varying in the range of 40-200 nm. Fluoride adsorption studies were carried out in batch mode under different experimental conditions, which included time, pH, and amount of adsorbent and adsorbate. The contact time data were fitted to a number of rate equations. The fluoride adsorption reached a maximum at a pH of 7.0 and then, decreased with further increase of pH. The equilibrium data followed both the Langmuir and Freundlich models. DG˚values were estimated to be À6.695, À5.399, À3.819, À3.568, and À2.740 kJ/mole at 293, 303, 308, 313, and 323 K, respectively. DH˚and DS˚were À47.12 kJ/mole and À138.58 J/mole/deg, respectively. The negative DH˚value confirmed the adsorption process to be exothermic in nature, while the negative DS˚indicated decreased randomness at the solid solution interface during adsorption. The fluoride loaded sample was characterized using TEM, selected area electron diffraction, and energy dispersive analysis of x. The present results show that the nano structured Mg-doped hematite synthesized by the present procedure can be regarded as a potential adsorbent for fluoride removal from aqueous solutions, as it can be effectively used at pH values of 5.75 and 7.0 which are applicable to the treatment of actual fluoride contaminated water. Fluoride containing water sample collected from nearby location was tested for defluoridation to establish real time use of adsorbent.

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ABSTRACT:In this study, high surface area (312 m 2 g −1 ) nano-sized Ca-Mgdoped ferrihydrite was synthesized using surfactant mediation-precipitation technique. The micrographs obtained by transmission electron microscopy confirmed the particle size to be in the range of 2-5 nm. The weak crystalline nature of powder was indicated by the selected area electron diffraction pattern. Here, we studied the adsorption of four cations [Pb(II), Cd(II), Cu(II) and Co(II)] onto self-prepared nano-sized powder under various experimental conditions. The contact time data followed pseudo-second-order kinetics model for all the four cations giving regression coefficient values >0.99. The isothermic data fitted well to both Langmuir and Freundlich models for Pb(II), Cd(II) and Cu(II) with corresponding Langmuir monolayer capacities of 312.5, 333.3 and 333.3 mg g −1 , respectively. For Co(II) isothermic data, only Freundlich model showed good fit and the experimentally obtained maximum loading capacity was 225 mg g −1 . Desorption studies confirmed that Pb(II)-or Cd(II)-loaded adsorbent can be regenerated/reused. Studies up to five cycles of adsorption-desorption confirmed increase in uptake capacity upon regeneration. Although Cu(II)-or Co(II)-loaded adsorbents could not be regenerated, toxicity characteristic leaching procedure tests confirmed that they were safe for disposal. This is the first study of its kind to report high-loading capacities for various cations and an increase in Pb(II) or Cd(II) uptake capacities after regeneration on an adsorbent. Therefore, the prepared sample can be regarded as a super adsorbent.