title: Acid transformation of bauxite residue: Conversion of its alkaline characteristics.
abstract: Bauxite residue (BR) is a highly alkaline solid hazardous waste produced from bauxite processing for alumina production. Alkaline transformation appears to reduce the environmental risk of bauxite residue disposal areas (BRDAs) whilst potentially providing opportunities for the sustainable reuse and on-going management of BR. Mineral acids, a novel citric acid and a hybrid combination of acid-gypsum treatments were investigated for their potential to reduce residue pH and total alkalinity and transform the alkaline mineral phase. XRD results revealed that with the exception of andradite, the primary alkaline solid phases of cancrinite, grossular and calcite were transformed into discriminative products based on the transformation used. Supernatants separated from BR and transformed bauxite residue (TBR) displayed distinct changes in soluble Na, Ca and Al, and a reduction in pH and total alkalinity. SEM images suggest that mineral acid transformations promote macro-aggregate formation, and the positive promotion of citric acid, confirming the removal or reduction in soluble and exchangeable Na. NEXAFS analysis of Na K-edge revealed that the chemical speciation of Na in TBRs was consistent with BR. Three acid treatments and gypsum combination had no effect on Na speciation, which affects the distribution of Na revealed by sodium STXM imaging.
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China.
authors.forename: Xiangfeng
authors.initials: X
authors.lastname: Kong
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China.
authors.forename: Meng
authors.initials: M
authors.lastname: Li
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China. Electronic address: sgxue@csu.edu.cn.
authors.forename: Shengguo
authors.initials: S
authors.lastname: Xue
authors.affiliation: Crop and Environment Sciences Department, Harper Adams University, Newport, Shropshire, TF10 8NB, United Kingdom.
authors.forename: William
authors.initials: W
authors.lastname: Hartley
authors.affiliation: Griffith School of Environment, Griffith University, Nathan Campus, Qld 4111, Australia.
authors.forename: Chengrong
authors.initials: C
authors.lastname: Chen
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China.
authors.forename: Chuan
authors.initials: C
authors.lastname: Wu
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Li
authors.affiliation: School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan, 410083, PR China.
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Li
keywords: Alkaline transformation; Bauxite residue; Gypsum combination; NEXAFS analysis; Organic acid