Molybdenum Reactions With Soils and the Hydrous Oxides of Iron, Aluminum, and Titanium

Abstract

Abstract The absorption reactions of molybdate with soils and soil‐forming materials can be predicted from the Freundlich equation modified to include a term for pH. The modified equation is applicable over a wide range of soil acidites and Mo concentrations within the region of physiological importance for plant nutrition, and for the higher Mo levels influencing quality of plant materials as forage. Molybdate sorption reactions with the hydrous oxides of Fe, Al, Ti, and of acid soils all show analagous patterns. The sorption of molybdate by Fe 2 O 3 · xH 2 O is accompanied by a stoichiometric release of two hydroxyl ions and one molecule of water. These conditions are satisfied by equations for the reaction of Na 2 MoO 4 with Fe(OH) 3 in an acid system forming Fe 2 (MoO 4 ) 3 , or by chemisorption of molybdate on complex iron‐water‐hydroxyl solid phase materials. The importance of these factors in predicting plant absorption is discussed.