Characterization of chromium and copper complexes with fulvic acids isolated from soils in Slovenia

Fulvic acids (FA) were isolated from Slovenian peat and forest soils in order to prepare their chromium (Cr) and copper (Cu) complexes. The elemental composition and the COOH content of FA were measured. Both FA and FA complexes were characterized by gel permeation chromatography (GPC) and infrared spectroscopy (IR). Conditional stability constants (Kst) and complexation capacities (CC) of FA complexes were determined by the method based on ion exchange equilibrium. Both FA showed similar composition, average molecular weight and IR spectra. Substantial differences were found in IR spectra, Kst and CC between Cu and Cr complexes of the same FA as well as between different FA and the same metal. Cr complexes exhibited higher stability and larger CC values in comparison with Cu complexes. The same is true for peat FA in relation to forest FA. According to the IR spectra, Cu is predominantly bound to COO− groups while in Cr complexes other functional groups or different mechanisms might also be involved.