Chemical Regeneration of Bone Char Associated With a Continuous System for Defluoridation of Water

Abstract

Sources of fluoride contaminated water are found around the world and their treatment is required before human consumption. This paper contributes to advances in the use of bone-char as an adsorbent for fluoride, associating steps of chemical regeneration and fluoride adsorption in continuous systems, thereby making feasible the multiple use of the adsorbent. Following the development of low cost treatment of water defluoridation in a fixed bed column, using bone-char, regeneration was carried out with NaOH (0.5 mol/L) solution in subsequent adsorption/desorption cycles. The continuous system was modeled applying Thomas, Yoon-Nelson, Adams-Bohart, Wolborska and Yan models, and the Yan model showed the best adjustment. The adsorption capacity of 6.28 mg/g was obtained from the breakthrough curve. Chemical regeneration of bone-char was feasible, and a reduction in adsorption capacity of 30% was observed only after five adsorption/desorption cycles.

Bone char from an invasive aquatic species "devilfish" as a sustainable adsorbent for the removal of fluoride in water for human consumption

“…The values of pore volume and diameter for each of the bone chars are within the range reported by other authors for bone chars (Alkurdi et al 2019;Murillo et al 2012;Nigri et al 2019).…”

“…It can be seen that there is an increase in the intensity of the 556, 600, 961 and 1016 cm -1 bands, corresponding to the PO4 3groups, when the bone is pyrolysed (C500) and at the same time these bands maintain their intensity when saturated with fluoride (CF500). In addition, the 3566 cm -1 band corresponding to the OHincreases when the Bone sample is pyrolysed, revealing the formation of hydroxyapatite, and this band is attenuated when saturated with fluoride, which may indicate an interaction between the hydroxyl groups of hydroxyapatite and fluoride (Nigri et al 2019). The mass-loss (TG) and derivative mass-loss (DTG) curves of Bone, C500 and CF500 samples are exhibited in Fig.…”

“…Therefore, at solution pH below their respective pHPZC, electrostatic attraction favors fluoride adsorption. The positive charge of the surface increases by lowering the pH below the pHPZC (Nigri et al 2019).…”

“…In addition, as shown in XRD analysis, the main constituent of bone char is hydroxyapatite, so the groups on the surface of solid that affect its surface charge are phosphates, ≡P-OH, and hydroxyl, ≡Ca-OH, this groups can interact with the solvent and the ions in aqueous solution (Nigri et al 2019). Therefore, when the solution temperature is increased, fluoride ions have more energy and therefore more fluoride ions can be adsorbed on the surface of the bone char as they have enough energy (Cooney 1998).…”

Evaluation of Fluoride Adsorption Mechanism and Capacity of Different Types of Bone Char

“…In addition, several studies have reported that hydroxyapatite is an alternative material for fluoride removal. Hydroxyapatite can remove fluoride by exchanging between OH-group on hydroxyapatite and fluoride ion in water [ 14 , 21 , 33 , 38 ].…”