HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Reyes, E. D. Articles by Jurinak, J. J. Search for Related Content PubMed Articles by Reyes, E. D. Articles by Jurinak, J. J. Agricola Articles by Reyes, E. D. Articles by Jurinak, J. J.

A Mechanism of Molybdate Adsorption on Fe₂O₃¹

ABSTRACT

The adsorption of molybdate on Fe₂O₃ (hematite) was studied at pH 4.0 and 7.75 by equilibrium dialysis at 22.0 and 40.0C. Two distinct adsorption reactions, both following the Langmuir equation, occurred at pH 4.0. The first reaction was insensitive to a change in temperature and appeared saturated at an equilibrium concentration of about 10 ppm Mo. The second reaction was saturated at 55 ppm Mo and was endothermic. The reactions were ascribed to the adsorption of monomeric molybdate ions at two different sites on the iron oxide. The endothermic nature of the adsorption at the higher concentration was considered dues to the formation of polymolybdate from monomeric condensation. At pH 7.75, the adsorption of molybdate on the oxide surface was about 5 times less than at pH 4.0. The reaction in the alkaline system was not sensitive to temperature change.

A comparison of the surface areas of three molybdate forms with nitrogen surface areas of the molybdated oxides indicated that the monomeric, H_xMoO_2^x–2, form was principally adsorbed. It was concluded that the condensation of the paramolybdate form, Mo₇O₂₄^–6, was initiated as the temperature was increased at the high Mo concentrations. The behavior of the equilibrium function with increasing surface coverage for the second adsorption reaction supported the suggested mechanism.

Key Words: ferric oxide • hematite • molybdenum

¹ Portion of the thesis presented by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Soil Science, University of California, Davis.

² Assistant Professor of Soils, University of the Philippines, College, Laguna, and Associate Soil Chemist, Dep. of Soils and Plant Nutrition, University of California, Davis, respectively. The junior-author is now Professor of Soil Chemistry, Dept. of Soils and Meterorology, Utah State University, Logan.

Received for publication February 24, 1967. Accepted for publication April 27, 1967.