Physicochemical speciation of molybdenum in rain water

Abstract

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of molybdenum in natural and synthetic rain water samples. The concentration ( C L) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration ( C T) of molybdenum was determined after the acid decomposition of the sample to calculate the non-labile concentration ( C T− C L). From the speciation results, molybdenum species in the successive rainfall sample were found in a fraction with smaller molecular weights <10 3 Da and characterized as labile forms, i.e. simple molybdate ions. Non-labile molybdenum existed in particulate matter (≥0.45 μm in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the formation of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (≥0.45 μm). This type of molybdenum was associated with the formation of humic iron aggregates.