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Heats of Immersion Studies on Anion-Treated Ferric Oxide¹

ABSTRACT

Microcalorimetry was used to obtain heats of immersion data for Fe₂O₃ (hematite) treated with SO₄^-2, H₂PO₄^-1 or MoO₄^-2 at pH 4.0. The data were compared with values from a reference OH saturated iron oxide. Using water adsorption data, the net integral heats of adsorption as functions of outgassing temperature (25 to 470C) were calculated. The energies of adhesion were also determined. Anion penetration lowered the surface energy of hematite, as manifested by a lowering of the immersional heats with increasing outgassing temperature. At pH 4.0 the relative bonding strengths of the anions on hematite were concluded to be MoO₄^-2 > H₂PO₄^-1 > SO₄^-2 > OH^-1. The heat of immersion values after 25C outgassing indicated limited anion effect as well as a physical interaction of water with Fe₂O₃. The molybdate ion had the greatest effect on surface energy at all outgassing temperatures.

The energy of rehydration (hydroxylation) of the Fe₂O₃ surface was also calculated from the data.

¹ Partial support of this work by the California Water Resources Center Grant WRC 31366 is gratefully acknowledged.

² Associate Soil Chemist and Assistant Professor of Soil Science, Dep. of Soils and Plant Nutrition, Univ. of California, Davis, respectively. The Senior Author's present address is: Professor of Soil Chemistry, Utah State Univ., Logan, Utah.

Received for publication March 15, 1967. Accepted for publication July 7, 1967.