title: Early stage formation of iron oxyhydroxides during neutralization of simulated acid mine drainage solutions.
abstract: The phases and stability of ferric iron products formed early during neutralization of acid mine drainage waters remain largely unknown. In this work, we used in situ and time-resolved quick-scanning X-ray absorption spectroscopy and X-ray diffraction to study products formed between 4 min and 1 h after ferric iron sulfate solutions were partially neutralized by addition of NaHCO(3) ([HCO(3)(-)]/[Fe(3+)] < 3). When [HCO(3)(-)]/[Fe(3+)] = 0.5 and 0.6 (initial pH ∼ 2.1 and 2.2, respectively), the only large species formed were sulfate-complexed ferrihydrite-like molecular clusters that were stable throughout the duration of the experiment. When [HCO(3)(-)]/[Fe(3+)] = 1 (initial pH ∼ 2.5), ferrihydrite-like molecular clusters formed initially, but most later converted to schwertmannite. In contrast, when [HCO(3)(-)]/[Fe(3+)] = 2 (initial pH ∼ 2.7), schwertmannite and larger ferrihydrite particles formed immediately upon neutralization. However, the ferrihydrite particles subsequently converted to schwertmannite. The schwertmannite particles formed under both conditions aggregated extensively with increasing time. This work provides new insight into the formation, stability and reactivity of some early products that may form during the neutralization of natural acid mine drainage.
authors: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. mzhu@lbl.gov
authors: Mengqiang
authors: M
authors: Zhu
authors: Benjamin
authors: B
authors: Legg
authors: Hengzhong
authors: H
authors: Zhang
authors: Benjamin
authors: B
authors: Gilbert
authors: Yang
authors: Y
authors: Ren
authors: Jillian F
authors: JF
authors: Banfield
authors: Glenn A
authors: GA
authors: Waychunas
mesh_terms: D000143:Acids; D003116:Color; D005290:Ferric Compounds / Q000138:chemical synthesis*; D008906:Mining; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D000143:Acids; D005290:Ferric Compounds; D012996:Solutions; C021024:ferric hydroxide