Molybdenum retention by Kenyan soils

Abstract

Studies on the adsorption of molybdenum on sixteen Kenyan soils representing seven soil orders showed that the adsorption was strongly dependent on the amount of crystalline iron in the soil and on the pH measured in water of the soil. The maximum amount of adsorption of molybdenum occurred at about the pI(. of molybdic acid. The studies also showed that the adsorption conformed to the Langmuir adsorption isotherm, with only two exceptions. There were also significant correlations between the calculated adsorption maximum and the percentage organic carbon content, DCBextractable iron, oxalate-extractable iron, DCB-extractable aluminum, DCB-extractable manganese and the specific surface of the soil. A surface complexation model, the constant capacitance model, was used to model the adsoption data. The model predicted the right order of magnitude of the maximum adsorption for these soils. However, it overestimated the significance of iron oxides in the retention of molybdenum by Kenyan soils.