Using chromatographic and spectroscopic parameters to characterize preference and kinetics in the adsorption of humic and fulvic acid to goethite.

Humic substances (HS) are very heterogeneous, and preferential adsorption of certain components takes place during their interaction with minerals. Our results indicated that for fulvic acid (FA) the relatively large (3.6-18.2 kDa) particles were preferred in the adsorption to goethite, whereas for humic acid (HA) the intermediate sized (3.6-12.0 kDa) fractions were preferred. Correlations between molar mass (Mw) and specific UV absorption values (SUVA) with ratios of UV light absorbance (E2/E3, E4/E6) were observed. The adsorption did not change the relation between E2/E3 and Mw, E4/E6 and SUVA. The E2/E3 and E4/E6 can probably be used as indicators of molar mass and aromaticity of HS in studying the preferential adsorption. The adsorption of HA and FA to goethite was fast and reached a steady state in about 6 h. The intermediate sized HA particles (3.6-12.0 kDa) were adsorbed quickly, and part of them was subsequently replaced by somewhat larger particles (>50 kDa). For FA, preferential adsorption of relative large particles (3.6-18.2 kDa) took place quickly, and there was a limited substitution by particles with higher aromaticity. Without specifying the property especially the molar mass range of HS under study, confusion can arise from researches using different HS materials.