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SELECTIVE EXTRACTION OF AMORPHOUS IRON OXIDE BY EDTA FROM A MIXTURE OF AMORPHOUS IRON OXIDE, GOETHITE, AND HEMATITE
Author(s) -
BORGGAARD O. K.
Publication year - 1976
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1976.tb02017.x
Subject(s) - ammonium oxalate , goethite , hematite , chemistry , iron oxide , extraction (chemistry) , amorphous solid , inorganic chemistry , ammonium hydroxide , oxalate , solubility , nuclear chemistry , oxide , hydroxide , chromatography , mineralogy , organic chemistry , adsorption
Summary Iron (III) was extracted by EDTA and ammonium oxalate from a model substance consisting of amorphous iron oxide, goethite, and hematite precipitated in the presence of quartz sand. Even by varying the EDTA concentration between 0.02 and 0.1 M, pH between 4.40 and 6.00, the solid:solution ratio between I:25 and I:250, and using extraction times up to go days, it was found that EDTA was able to extract only a limited amount of iron. In contrast, 0.2 M ammonium oxalate at pH 3.0 is able to dissolve all the iron compounds if the extraction time is sufficient. Nevertheless, the amount of EDTA‐extractable iron is equal to the amount of iron extracted after 4–5 hours with ammonium oxalateat pH 3.0. From X‐ray analysis, DTA curves, a solubility product determination, and a kinetic investigation, it is concluded that the EDTA‐extractable fraction consists of X‐ray amorphous iron oxide, less soluble than polymeric iron hydroxide, and presumably only one compound. Therefore, it is concluded that it may be possible by means of EDTA to carry out a selective extraction of X‐ray amorphous iron oxides mixed with goethite and hematite.