Sodium removal from bauxite desilication product (sodalite) aided by chelating effects of inorganic and organic acids. (15th July 2023)

• Record Type: Journal Article
• Authors: Wang, Sicheng; Nguyen, Tuan; Peng, Hong; Wu, Songlin; Parry, David; Urban, Anja; Huang, Longbin
• Is Part Of: Journal of environmental management. Volume 338(2023)
• Publication Date: 2023-07-15
• Subjects: Bauxite Desilication product -- Sodalite -- Dealkalization -- Bauxite residue -- Organo-mineral complex -- Acid leaching -- Mineral weathering; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2023.117837
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Dealkalization is a prerequisite to converting bauxite residue into non-hazardous materials that can be used for various upcycling applications. Structural alkali (Na + ) lodged inside the densely packed aluminosilicate-cages of sodalite, the dominant desilication product from refining alumina, is a common culprit in the persistence of strong alkalinity of bauxite residue. The present study unravelled chemical and mineralogical processes involved in sodalite dealkalization, driven by organic and inorganic acids. These acids have different H + dissociation coefficients and their anions have different chelation abilities with surface metal atoms of aluminosilicate minerals. The efficacy of sodium removal by exposure to the acids was found not only dependent on the acid strength (pKa ), but also on the chelating property of dissociated conjugate anions. Following an initial H + -Na + exchange, Na + removal from sodalite was correlated with partial hydrolysis of aluminosilicate network and resultant chelating reactions with acid anions. The selection of organic and inorganic acids whose conjugate bases possess good chelating capability in the pH buffer zone 7–9 (e.g., oxalate or phosphate), would provide significant aid to the dealkalization process. The findings in this study are crucial in understanding the conversion of bauxite residue into a soil-like growth media (technosol) for sustainable mined land rehabilitation. Graphical abstract: Image 1 Highlights: Alkali (Na + ) removal from densely packed aluminosilicate-cages of sodalite is acid specific. Sodium removal efficacy depends on acidic strength (pKa) and chelating property of acid's conjugate anions. The dealkalization of sodalite begins with a H + -Na + exchange process that causes minimal damage to the β -cages. Partial aluminosilicate network hydrolysis and anion chelation assist sodalite dealkalization. Acids with chelating capability in pH buffer zone 7–9 provide significant aid to the dealkalization.