title: Freezing-Enhanced Dissolution of Iron Oxides: Effects of Inorganic Acid Anions.
abstract: Dissolution of iron from mineral dust particles greatly depends upon the type and amount of copresent inorganic anions. In this study, we investigated the roles of sulfate, chloride, nitrate, and perchlorate on the dissolution of maghemite and lepidocrocite in ice under both dark and UV irradiation and compared the results with those of their aqueous counterparts. After 96 h of reaction, the total dissolved iron in ice (pH 3 before freezing) was higher than that in the aqueous phase (pH 3) by 6-28 times and 10-20 times under dark and UV irradiation, respectively. Sulfuric acid was the most efficient in producing labile iron under dark condition, whereas hydrochloric acid induced the most dissolution of the total and ferrous iron in the presence of light. This ice-induced dissolution result was also confirmed with Arizona Test Dust (AZTD). In the freeze-thaw cycling test, the iron oxide samples containing chloride, nitrate, or perchlorate showed a similar extent of total dissolved iron after each cycling while the sulfate-containing sample rapidly lost its dissolution activity with repeating the cycle. This unique phenomenon observed in ice might be related to the freeze concentration of protons, iron oxides, and inorganic anions in the liquid-like ice grain boundary region. These results suggest that the ice-enhanced dissolution of iron oxides can be a potential source of bioavailable iron, and the acid anions critically influence this process.
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, Korea.
authors.forename: Daun
authors.initials: D
authors.lastname: Jeong
authors.affiliation: Korea Polar Research Institute , Incheon 406-840, Korea.
authors.forename: Kitae
authors.initials: K
authors.lastname: Kim
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, Korea.
authors.forename: Dae Wi
authors.initials: DW
authors.lastname: Min
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, Korea.
authors.forename: Wonyong
authors.initials: W
authors.lastname: Choi
mesh_terms: D000838:Anions / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D004391:Dust; D005290:Ferric Compounds / Q000737:chemistry*; D005615:Freezing; D006851:Hydrochloric Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007053:Ice; D007501:Iron / Q000737:chemistry; D008027:Light; D008903:Minerals / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry; D012995:Solubility; D013431:Sulfates / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D000838:Anions; D002712:Chlorides; D004391:Dust; D005290:Ferric Compounds; D007053:Ice; D008903:Minerals; D009566:Nitrates; D013431:Sulfates; D013464:Sulfuric Acids; C000499:ferric oxide; D007501:Iron; C033158:sulfuric acid; D006851:Hydrochloric Acid