Cryolite (Na3AlF6) crystallization for fluoride recovery using an electrolytic process equipped with a sacrificail aluminum anode

doi:10.1016/j.jhazmat.2019.01.033

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Title:	Cryolite (Na3AlF6) crystallization for fluoride recovery using an electrolytic process equipped with a sacrificail aluminum anode
Authors:	Ya, Vinh;Li, Chi-Wang
Keywords:	Electro-crystallization;Cryolite;Fluoride;Recovery;Chemical equilibrium modeling
Date:	2019-12-13
Issue Date:	2020-06-01 12:16:41 (UTC+8)
Abstract:	An electro-crystallization process equipped with a sacrificial aluminum anode was operated under an optimum condition to promote the formation of crystalline cryolite for the recovery of fluoride from synthetic F-containing wastewater. The effects of pH, Al/F molar ratio, initial F concentration, and electrolytes were investigated experimentally, and the results were compared with data obtained from chemical equilibrium modeling. Cryolite was successfully produced under optimum pH values of 5 to 6 and Al/F molar ratios of less than 1/6. The F removal increased with increasing Al/F molar ratio until reaching the molar ratio of 1/6 and decreased thereafter due to the formation of AlFn3−n species. The adsorption of AlFn3−n by Al(OH)3 precipitates contributed part of F removal. The removal efficiency reached 100% when the initial fluoride concentration was high while it was around 90% with the low initial fluoride concentration. XRD and SEM/EDX analysis showed that the obtained solids matched well to the commercial cryolite. Finally, the operating costs of chemical-crystallization (the process with Al ions added chemically) and electro-crystallization were compared, and the cost of the former was less than the latter. Energy consumption was the main contributor to the operating cost of the electro-crystallization process.
DOI:	10.1016/j.jhazmat.2019.01.033
Appears in Collections:	[Graduate Institute & Department of Water Resources and Environmental Engineering] Proceeding

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