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Arsenic Mobilization Is Enhanced by Thermal Transformation of Schwertmannite

Version 2 2024-06-04, 13:46
Version 1 2018-05-23, 15:13
journal contribution
posted on 2024-06-04, 13:46 authored by SG Johnston, ED Burton, Ellen MoonEllen Moon
Fires in iron-rich seasonal wetlands can thermally transform Fe(III) minerals and alter their crystallinity. However, the fate of As associated with thermally transformed Fe(III) minerals is unclear, as are the consequences for As mobilization during subsequent reflooding and reductive cycles. Here, we subject As(V)-coprecipitated schwertmannite to thermal transformation (200, 400, 600 and 800 °C) followed by biotic reductive incubation (150 d) and examine aqueous- and solid-phase speciation of As, Fe and S. Heating to >400 °C caused transformation of schwertmannite to a nanocrystalline hematite with greater surface area and smaller particle size. Higher temperatures also caused the initially structurally incorporated As to become progressively more exchangeable, increasing surface-complexed As (AsEx) by up to 60-fold, thereby triggering enhanced As mobilization during incubation (∼70-fold in the 800 °C treatment). Although more As was mobilized in biotic treatments than controls (∼3-20×), in both cases it was directly proportional to initial AsEx and mainly due to abiotic desorption. Higher transformation temperatures also drove divergent pathways of Fe and S biomineralization and led to more As(V) and SO4 reduction relative to Fe(III) reduction. This study reveals thermal transformation of schwertmannite can greatly increase As mobility and has major consequences for As/Fe/S speciation under reducing conditions. Further research is warranted to unravel the wider implications for water quality in natural wetlands.

History

Journal

Environmental Science and Technology

Volume

50

Pagination

8010-8019

Location

United States

ISSN

0013-936X

eISSN

1520-5851

Language

English

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2016, American Chemical Society

Issue

15

Publisher

AMER CHEMICAL SOC