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Synthesis and stability of hetaerolite, ZnMn2O4, at 25??C

Geochimica et Cosmochimica Acta

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Abstract

A precipitate of nearly pure hetaerolite, ZnMn2O4, a spinel-structured analog of hausmannite, Mn3O4, was prepared by an irreversible wprecipitation of zinc with manganese at 25??C. The synthesis technique entailed constant slow addition of a dilute solution of Mn2+ and Zn2+ chlorides having a Mn/Zn ratio of 2:1 to a reaction vessel that initially contained distilled deionized water, maintained at a pH of 8.50 by addition of dilute NaOH by an automated pH stat, with continuous bubbling of CO2-free air. The solid was identified by means of X-ray diffraction and transmission electron microscopy and consisted of bipyramidal crystals generally less than 0.10 ??m in diameter. Zn2+ ions are able to substitute extensively for Mn2+ ions that occupy tetrahedral sites in the hausmannite structure. Hetaerolite appears to be more stable than hausmannite with respect to spontaneous conversion to ??MnOOH. The value of the standard free energy of formation of hetaerolite was estimated from the experimental data to be -289.4 ?? 0.8 kcal per mole. Solids intermediate in composition between hetaerolite and hausmannite can be prepared by altering the Mn/Zn ratio in the feed solution. ?? 1987.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Synthesis and stability of hetaerolite, ZnMn2O4, at 25??C
Series title:
Geochimica et Cosmochimica Acta
Volume
51
Issue:
6
Year Published:
1987
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochimica et Cosmochimica Acta
First page:
1539
Last page:
1547
Number of Pages:
9