Simulation study for the formation of alkaline efflorescence on bauxite residue disposal areas following the phosphogypsum addition. (20th July 2020)

• Record Type: Journal Article
• Authors: Wu, Yujun; Li, Meng; Fu, Ding; Santini, Talitha C.; Jiang, Jun; Hartley, William; Xue, Shengguo
• Is Part Of: Journal of cleaner production. Volume 262(2020)
• Publication Date: 2020-07-20
• Subjects: Bauxite residues -- Efflorescence -- Phosphogypsum -- Alkaline substance -- Alkalinity migration; 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.2020.121266
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: Bauxite residue is a solid, highly alkaline byproduct generated in the alumina refining process. The process that forms the fine white salt deposits on the surface of bauxite residue disposal areas (BRDAs) following prolonged dry periods, and which also forms on products made from reused residues (sintered bricks, etc.), is known as efflorescence. It not only seriously affects the utilization of bauxite residue in building materials, but also creates potential dust pollution around the BRDAs, which means it would require sustained and intensive resources to manage and transform its alkalinity. Through a laboratory simulation experiment using soil leaching columns, we show that the extent of bauxite residue efflorescence is affected by many factors, including porosity, initial water content, bauxite residue particle size. The main soluble mineral precipitates of efflorescence are Na2 CO3 and NaHCO3 . Addition of phosphogypsum, a common amendment to reduce dispersion and promote removal of Na + through leaching, shifted the composition of effloresced salts to favor Na2 SO4 ·10H2 O. SEM and Na K-edge X-ray absorption near-edge structure (XANES)spectroscopy demonstrated that free alkali migrates to the residue surface to precipitate as a uniform agglomerate in the efflorescence process, which also changes the chemical form of Na-containing minerals in the bauxite residue and the mesoscale spatial distribution of Na (soft X-ray scanning transmission microscopy imaging). Free alkali migration with water is the main driver of efflorescence, and this work also demonstrated that phosphogypsum can reduce the generation of alkaline efflorescence for ameliorating alkaline dust pollution from bauxite residue. Graphical abstract: Image 1 Highlights: . The mechanism for the efflorescence formation affected by phosphogypsum was studied. . Phosphogypsum can reduce the generation of alkaline efflorescence. . The phase equilibrium diagram showed the transformation of trona and Na2 SO4 . . Free alkali migration with water is the main driver of efflorescence. . XANES revealed that free alkali migrates to the surface as a uniform agglomerate.