THE SOLUBILITY OF MOLYBDENUM IN SIMPLIFIED SYSTEMS AND AQUEOUS SOIL SUSPENSIONS

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Abstract
Summary: Studies of the precipitation of molybdate by ferric iron and aluminium show that ferric molybdate has minimum solubility at pH 2.7 and that it is less soluble than aluminium molybdate which has minimum solubility at pH 4.8. Ferric molybdate is much less crystalline than aluminium molybdate.The sorption of molybdate by hydrous ferric oxide, aluminium oxide, and clay minerals depends on pH and the concentration of molybdate in solution. When sorption by the solids is compared, hydrous ferric oxide is outstanding and the order of the others is: aluminium oxide> halloysite> nontronite> kaolinite.The main process in the sorption studies was probably adsorption of molybdate by anion exchange with hydroxyl ions. Precipitation of aluminium molybdate was detected by X‐rays when aluminium oxide and halloysite were treated with concentrated molybdate solutions.The sorption of molybdate by soils depends on the pH and the concentration of molybdate in solution. A krasnozem which was high in free ferric oxide sorbed the largest quantities of molybdate from solution. Its ability to sorb molybdate was substantially reduced after removing the free ferric oxide by the Mg‐oxalate method.