Adsorption of Fluoride from Aqueous Solution by a Synthetic Iron(III)−Aluminum(III) Mixed Oxide

Abstract

This paper presents the synthesis of iron(III)-aluminum(III) mixed oxide with some of its physicochemical characteristics and fluoride adsorption behavior thereon. Results showed that the optimum initial pH for fluoride adsorption is 4.0-10.0, and the equilibrium time required is 1.5 h. The isotherm data follow the order Redlich-Peterson g Langmuir > Freundlich > Temkin. The Langmuir monolayer adsorption capacity of the adsorbent is determined to be 17.73 mg/g, which is higher than that of either of the pure oxides. The enthalpy change (∆H°) and entropy change (∆S°) for the adsorption reaction are +29.31 kJ/mol and +116.75 J mol -1 K -1 , respectively. The adsorption is endothermic in nature. The kinetics follows a pseudo-second-order rate equation, and the reaction rate is a multistage-controlled diffusion process. The activation energy for this adsorption reaction is 6.35 kJ/mol.

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

“…As shown in Fig. 8(b) and Table 2, the constant k 2 , the initial sorption rate h 0 and equilibrium adsorption capacity (q e ) values all increased with the increase of temperature from 25 to 50 • C. The increase in adsorption capacity and rate of fluoride with increasing temperature is presumably because of the endothermic nature of fluoride adsorption on magnetic adsorbents [9].…”

“…Several researchers have reported the possible adsorption mechanism of fluoride on floc Al(OH) 3 which was either by electrostatic adsorption [8,9] or surface complexation [10,30], or a combination of both. The surface of mineral oxides is negative charged when pH value is above the pH ZPC (zero point charge) and positive charged when pH value is below the ZPC.…”

“…Several methods have been applied to remove excessive fluoride from aqueous environments, such as adsorption [2,[8][9][10], precipitation [6], ion-exchange [11], electrodialysis [12] and electrochemical methods [13]. Among them, precipitation and adsorption are two most important techniques used for water defluoridation.…”

“…Various low-cost materials such as activated alumina [7,8], clay [14], soil [15], bone char [8,12], light weight concrete [16], fly ash and other materials [2,13] have been tested for removing fluoride from drinking water, but the fluoride adsorption capacities of those materials are not high enough for wide application [8]. In the past few years, novel adsorbents with strong affinity towards fluoride have been developed for fluoride removal, such as synthetic ion exchangers calcined Mg-Al-CO 3 layered double hydroxides (LDH) [7], zirconium-impregnated collagen fiber [2], Fe-Al-Ce trimetal oxide [17] and iron-aluminum mixed oxide [9]. Rare earth elements also have been investigated as potential adsorbents because of their selective affinity to fluoride, high adsorption capacity, cause little pollution, and easy preparation [18].…”

Effect of aluminum fluoride complexation on fluoride removal by coagulation

“…6. The peaks in the 400-1500 cm −1 region corresponded to the stretching and bending modes of Al O [16]. Peaks of flocs in coagulation at 590 and 995 cm −1 shrinked and shifted compared with that of Al(OH) 3 flocs in adsorption.…”