Structural and mineralogical variation upon reoxidation of reduced Fe-bearing clay minerals during thermal activation

Wenwen Zhang; Xiaodong Li; Yao Zhao; Zongquan Sun; Meichen Yao; Xuefei Zhou; Fasheng Li; Fujun Ma; Qingbao Gu

doi:10.1016/j.scitotenv.2023.166243

Structural and mineralogical variation upon reoxidation of reduced Fe-bearing clay minerals during thermal activation

Sci Total Environ. 2023 Dec 1:902:166243. doi: 10.1016/j.scitotenv.2023.166243. Epub 2023 Aug 16.

Authors

Wenwen Zhang¹, Xiaodong Li², Yao Zhao², Zongquan Sun², Meichen Yao¹, Xuefei Zhou³, Fasheng Li², Fujun Ma², Qingbao Gu⁴

Affiliations

¹ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
³ State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
⁴ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Electronic address: guqb@craes.org.cn.

PMID: 37595928
DOI: 10.1016/j.scitotenv.2023.166243

Abstract

The hydroxyl radicals (OH) produced from Fe(II) oxidation upon reoxidation of reduced Fe-bearing clay minerals (RFC) have received increased attention and thermal activation was used to enhance Fe(II) oxidation to improve OH production. However, changes in mineral morphology and structure during thermally-activated RFC reoxidation are not yet clear. Herein, the Fe(II) oxidation extent was measured by chemical analysis during the reoxidation of model RFC (reduced nontronite (rNAu-2) at elevated temperatures. Mineralogical variation of rNAu-2 particles was observed by scanning electron microscopy (SEM), Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS). The structural Fe(II) oxidation in rNAu-2 was accelerated with increasing temperature, accompanied by the transformation of structural entities and the dissolution of Fe and Si, while the overall structure of rNAu-2 minerals was relatively intact. The surface microstructure of particles showed the dissolved holes, net-shape flocs, and even large pore channels after Fe(II) oxidation by thermal activation. Moreover, the rearrangement of structural Fe(II) entities, the regeneration of edge Fe(II), and the electron transport from the interior to the edge were enhanced during rNAu-2 reoxidation by thermal activation. The increasing electron transfer at elevated temperatures could possibly be owing to the increasing number of reactive sites by increasing the internal disorder of rNAu-2. This work provides novel insights into the structural and mineralogical changes in promoting electron transfer upon RFC reoxidation.

Keywords: High temperatures; Mineral morphology; RFC reoxidation; Structural Fe(II); electron transfer.