Recovery of fluoride from water through adsorption using orange-waste gel, followed by desorption using saturated lime w
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ORIGINAL ARTICLE
Recovery of fluoride from water through adsorption using orange‑waste gel, followed by desorption using saturated lime water Hari Paudyal1,2 · Keisuke Ohto2 · Hidetaka Kawakita2 · Katsutoshi Inoue2 Received: 15 April 2019 / Accepted: 9 April 2020 © Springer Japan KK, part of Springer Nature 2020
Abstract In this study, a new process for the recovery of fluoride from water with orange-waste gel loaded with Zr(IV) is investigated using saturated Ca(OH)2 as the desorption agent to desorb fluoride from a fluoride-loaded adsorbent. The maximum adsorption capacities of Zr(IV)-loaded orange-waste gel at pH values of 2.5, 3, 4, 6, and 8 were found to be 1.23, 1.52, 1.74, 1.10, and 0.53 mmol/g, respectively. The white precipitate obtained after the desorption using saturated Ca(OH)2 solution was characterized by scanning electron microscopy, X-ray diffraction, and dynamic light scattering techniques. The leakage of the total organic carbon during the desorption using Ca(OH)2 (7.31 mg/L) was found to be considerably less than that using NaOH (71.48 mg/L) at a solid/liquid ratio of 5 g/L. It is considered that fluoride was first desorbed by the saturated Ca(OH)2 solution, after which it combined with the Ca(II) ions provided by lime water to form a CaF2 precipitate, which is a raw material employed in various industrial processes, including cement manufacturing. Therefore, the saturated Ca(OH)2 solution investigated in this study can be considered as an efficient, economically viable, and promising desorbent for the removal of fluoride from fluoride-loaded adsorbents in an aqueous solution. Keywords Fluoride recovery · Orange-waste gel · Desorption · Saturated lime water · CaF2 precipitate
Introduction Fluoride compounds, particularly calcium fluoride (CaF2), are used in cement production, lubricant additives, phosphors, photonics, imaging, light amplification, display monitors, ceramic processing, and the glass industry [1, 2]. CaF2 is a host for luminescent ions due to its low refractive index, low phonon energy, high stability, non-hygroscopic nature, and highly transparent behavior [3, 4]. Additionally, C aF2 is used as a laser material after doping with rare earth metals [5, 6]. The presence of toxic and hazardous ions, such as fluoride ions, in portable water bodies is detrimental to human health and aquatic life [7]. Wastewater containing a high fluoride content is produced by electro-plating, metal refining, semiconductor production, and other high-tech industrial techniques [8–10]. The presence of fluoride in * Katsutoshi Inoue [email protected] 1
Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal
Department of Applied Chemistry, Saga University, Honjo 1, Saga 840‑8502, Japan
2
drinking water in the concentration range of 0.5–1.0 mg/L is beneficial for prevention of dental caries; however, a fluoride concentration higher than 1.5 mg/L (WHO standard) may have serious negative effects on the human health, causing disorders such as dental and skeletal
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