Journal
CHEMICAL GEOLOGY
Volume 488, Issue -, Pages 162-170Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2018.04.030
Keywords
Coexistence of Fe-aq(2) and Mn-aq(2+); Oxidation; Goethite; Lepidocrocite; Crystallinity
Categories
Funding
- National Natural Science Foundation of China [41571228, 41425006, 41330852]
- Fok Ying-Tong Education Foundation [141024]
- Fundamental Research Funds for the Central Universities [2662015JQ002]
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Iron and manganese oxides are ubiquitous in soils and sediments, and their formation and conversion processes affect the migration and transformation of heavy metals and organic pollutants. Mn2+ was found to affect the formation of iron oxides from Fe2+ oxidation. However, little attention has been paid to the oxidation process at the initial stage and generation of manganese oxides in the reaction system of Fe-aq(2+) and Mn-aq(2+). This work investigated the formation process and mechanism of iron and manganese oxides in a mixed solution system of Fe-aq(2+) and Mn-aq(2+) under oxic condition. The effect of pH (5.0-9.0) on the reaction process and products was further studied. The results indicated that Fe-aq(2+) was oxidized to goethite and lepidocrocite, and Mn2+ adsorbed on the surface of iron oxides was catalytically oxidized to poorly crystalline manganese oxides by dissolved O-2 in a mixed solution of Fe-aq(2+) and Mn-aq(2+). Compared with the absence of Mn-aq(2+), the presence of Mn-aq(2+) caused no obvious changes in the species of iron oxides, but significantly increased the oxidation rate of Fe-aq(2+). Formation of manganese oxides on the surface decreased the crystallinity of the iron oxides. The increase of pH enhanced the oxidation of Fe-aq(2+) and Mn-aq(2+) and formation of lepidocrocite. This work expands our understanding of the interactions and geochemical processes of Fe-aq(2+) and Mn-2+(aq)
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