Dissolution of aluminum hydroxide to provide Al and to neutralize acidity for the removal and recovery of fluoride through cryolite crystallization. (10th June 2023)

• Record Type: Journal Article
• Authors: Ouedraogo, Sabine Jessica; Vinh, Ya; Noophan, Pongsak (Lek); Naddeo, Vincenzo; Li, Chi-Wang
• Is Part Of: Journal of cleaner production. Volume 404(2023)
• Publication Date: 2023-06-10
• Subjects: Fluoride -- Crystalline aluminum hydroxide -- Amorphous aluminum hydroxide -- Complexation -- Crystallization; Factory and trade waste -- Management -- Periodicals; Manufactures -- Environmental aspects -- Periodicals; Déchets industriels -- Gestion -- Périodiques; Usines -- Aspect de l'environnement -- Périodiques; 628.5
• DOI: 10.1016/j.jclepro.2023.136987
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: Dissolution of aluminum hydroxide (Al(OH)3 (s)) was investigated for providing Al and at the same time neutralizing the acidity generated in the recovery of fluoride through the crystallization of cryolite. The alkalinity provided by the dissolution of Al(OH)3 (s) combined with Na2 CO3 reduces the total treatment cost for fluoride recovery by 45%, compared to when other aluminum salts were used. In this study, two types of aluminum hydroxide having different degrees of crystallinity of 61.53% and 25.57%, denoted as crystalline Al(OH)3 (s) (CAH) and amorphous Al(OH)3 (s) (AAH), respectively, were investigated. The results showed that the dissolution of AAH was very efficient but an excess amount of AAH adsorbed the freshly formed A l F x 3 − x complexes, impairing the purity of cryolite. On the other hand, the dissolution of the CAH was mostly dependent on the time, the Al dosage, and the initial pH of the solution. Upon reaching equilibrium, the dissolved Al to the initial F molar ratio reached 2/6. With the mixed volume ratio of 1:1 between the raw HF solution and the HF solution being equilibrated with CAH initially, the removal of F reached 96% and the cryolite formation was positively confirmed based on the XRD analysis of the resulting solid. Graphical abstract: Image 1 Highlights: Al(OH)3 (s) provided a low-cost Al for cryolite formation. 45% of the treatment cost was saved using Al(OH)3 (s) for cryolite formation. Equilibrium Al/F of 2/6 obtained by Phreeqc was verified experimentally. XRD confirms the successful production of cryolite at the fixed Al/F of 1/6. Cryolite formation efficiency by Phreeqc was experimentally confirmed.