Ageing of synthetic and natural schwertmannites at pH 2 - 8

Author(s)

Sirpa Kumpulainen, Marja-Liisa Räisänen, Frank von der Kammer, Thilo Hofmann

Abstract

The transformation of schwertmannite to goethite was studied by ageing one

synthetic and five natural schwertmannites in water at room temperature. Additionally, one synthetic

and two natural schwertmannites were kept at variable pH (2, 4, 6 and 8). After one year, only the

synthetic sample and one natural schwertmannite had transformed to goethite. However, the oxalate

solubility of Fe and trace elements in all the samples decreased, whereas the total Fe/S ratios and

specific surface areas of all samples increased. Arsenic and organic matter appeared to suppress the

schwertmannite-to-goethite phase transformation. At pH 2, synthetic schwertmannite fullytransformed

to goethite, but at pH 46 only minor transformation occurred. Depending on pH,

many trace elements were released into solution during ageing of the natural schwertmannites. In

general, Co, Mn, Zn and Si were released to solution, whereas As was enriched in the remaining iron

oxide fraction. Al was dissolved at pH

Organisation(s)

External organisation(s)

University of Helsinki, Geological Survey of Finland

Journal

Clay Minerals: journal of the European Clay Groups

Volume

43

Pages

437-448

No. of pages

12

ISSN

0009-8558

Publication date

2008

Peer reviewed

Yes

Austrian Fields of Science 2012

105904 Environmental research

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