The dissolution of micas by fulvic acid

Abstract

Three micas commonly occurring in soils, that is, biotite, phlogopite and muscovite, were shaken with 0.2% (W/V) aqueous fulvic acid (FA) solution for 710 h at room temperature. Proportions of major constituent elements extracted (Fe, Al, Mg, K and Si from biotite, Al, Mg, K and Si from phlogopite and Al, K and Si from muscovite) were determined. Depending on the type of mineral and its Fe content, substantial amounts of Fe, Al, Mg, K and Si were brought into aqueous solution by the FA under mild conditions. The ease with which the micas were attacked by the FA decreased in the following order: biotite > phlogopite > muscovite. IR and ESR analyses indicated the formation of metal—FA complexes as a major reaction mechanism by which the minerals were dissolved. Our data show that aqueous FA solution can dissolve from micas relatively large amounts of metals and Si, which may then become more available to plant roots and microbes, active in soil genesis processes, as well as participants in the synthesis of new minerals.