Arsenic Mobilization Is Enhanced by Thermal Transformation of Schwertmannite

作者：Johnston, Scott G.^*; Burton, Edward D.; Moon, Ellen M.

来源：Environmental Science & Technology, 2016, 50(15): 8010-8019.

DOI：10.1021/acs.est.6b02618

• NICKELIFEROUS GOETHITE
• REDUCTIVE TRANSFORMATION
• IRON
• DISSOLUTION
• SPECIATION
• MOBILITY
• DEHYDROXYLATION
• FERRIHYDRITE
• SORPTION
• SULFUR

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 degrees 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 (As-Ex) by up to 60-fold, thereby triggering enhanced As mobilization during incubation (similar to 70-fold in the 800 degrees C treatment). Although more As was mobilized in biotic treatments than controls (similar to 3-20x), in both cases it was directly proportional to initial As-Ex and mainly due to 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.

• 出版日期2016-8-2