Dissolution of Fe from Fe-bearing minerals during the brown-carbonization processes in atmosphere

• Published in: The Science of the total environment Vol. 791; p. 148133
• Main Authors: Wang, Yi, Ling, Jingyi, Gu, Cheng, Zhou, Shaoda, Jin, Xin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2021
• Subjects: AZTD; Guaiacol; IMt-2; Polymerization; Structural Fe; SWy-2; SWy-2; Polymerization; Structural Fe; Guaiacol; IMt-2; AZTD
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.148133

Previous studies found Fe dissolution in atmosphere correlates to biomass burning, while the underlying mechanisms need to be further investigated. In this study, we reported a laboratory investigation about Fe dissolution behavior of two model Fe-bearing clay minerals of montmorillonite (SWy-2) and illite (IMt-2), and one standard mineral dust of Arizona test dust (AZTD) in atmospheric condition (pH = 2), after the minerals engaging into the brown-carbonization reaction with guaiacol, which is a commonly detected volatile phenol substance in biomass burning. The results show that the pre-brown-carbonization reaction promoted Fe dissolution from all the three minerals, attributing to the reduction of Fe(III) by gaseous guaiacol. The Fe dissolution from SWy-2, IMt-2 and AZTD were also compared under both light and dark conditions to simulate the daytime and nighttime atmospheric processes. As a result, model solar irradiation further promoted Fe dissolution from IMt-2 and AZTD, since both minerals contain moderate photo-reducible Fe(III) oxide or/and Fe(III) oxyhydroxide. The promotive effect of solar irradiation on Fe dissolution from AZTD would be gradually diminished because the photo-reactive Fe(III) is also guaiacol-reducible. Whereas, it was on the contrary for SWy-2 which does not contain the Fe(III) (oxyhydr-)oxide phase. And more dependently, the photo-induced hydroxyl radical (OH) on SWy-2 would re-oxidize the formed Fe(II), unless sufficient amount of guaiacol or brown-carbonization products on SWy-2 consumed the OH and complexed with surface coordinated Fe(III) forming photo-reducible Fe(III). The results of this study suggested the brown carbonization process on minerals would greatly mediate the Fe dissolution behavior from the Fe-bearing mineral dusts in atmosphere. Similar processes might need to be taken into consideration to accurately evaluate the input of Fe from atmosphere to open oceans. [Display omitted] •Pre-brown-carbonization reaction promoted Fe dissolution from mineral dust.•The promotive effect is derived from the reduction of Fe(III) by guaiacol.•Structural Fe(III) in the expandable silicate sheet is the most reactive.•The adsorbed and formed organics further affect Fe dissolution when lighting.