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Thermodynamic Stability and Solubility of Molybdenum Minerals in Soils
Author(s) -
Vlek P. L. G.,
Lindsay W. L.
Publication year - 1977
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1977.03615995004100010016x
Subject(s) - solubility , molybdenum , soil water , chemistry , adsorption , mineralogy , inorganic chemistry , geology , organic chemistry , soil science
The chemical reactions of molybdenum in soils were studied in the laboratory. Solubility diagrams were constructed from thermodynamic data obtained from the literature and from measurements made on pure minerals. Included in these diagrams were solubility relationships for MoS 2 (molybdenite), Mo 3 O 8 (ilsemannite), Fe 2 (MoO 4 ) 3 (ferrimolybdite), CaMoO 4 (powellite), and PbMoO 4 (wulfenite). From these diagrams it appears that wulfenite is one of the most stable Mo minerals likely to form in soils. Lack of thermodynamic data on other Mo minerals prevents their evaluation as possible reaction products. The solubility of Mo in selected Colorado soils in the pH range of 5.5 to 7.7 was plotted on the wulfenite solubility diagram. Of the 13 soils used in this study, only one showed equilibrium with respect to wulfenite. When wulfenite was added to several other soils, the molybdenum solubility increased 10‐ to 100‐fold, confirming that wulfenite was not initially present. These wulfenite‐amended soils showed a close correspondence between soluble Mo and the wulfenite solubility isotherm. In the absence of solid phase Mo compounds, the solubility of Mo in soils is controlled by specific adsorption.