Characterization of organo-mineral aggregates of chernozem in northeast China and their adsorption behavior to phenanthrene

Organo-mineral aggregares in various fractions including clay, silt, fine sand, and coarse sand were isolated from a Chernozem in northeast China by ultrasonic dispersion in water followed by sedimentation. The physicochemical properties of different fractions were determined and the organo-mineral aggregates were characterized jointly with Fourier-transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM), x-ray diffraction (XRD), and cross-polarization (CP) with magic-angle spinning (MAS) ¹³C nuclear magnetic resonance (NMR) spectrometry. The XRD patterns showed that clay was dominated by quartz and calcite, while the mineral assemblage of silt was composed of quartz, calcite, plagioclase, and trace amounts of mica and chlorite. The results from FTIR spectra were consistent with those from XRD. The SEM images indicated that the particle surface became smoother with increasing particle size. The CP-MAS ¹³C NMR spectra showed that the contents of aromatic C in clay, silt, fine sand, and coarse sand were 25.6, 28.19, 17.22, and 26.32%, respectively. The adsorprion and desorption behaviors of polycyclic aromatic hydrocarbons on four soil fractions were investigated using phenanthrene as a model substrate. The adsorption and desorption isotherms for all the fractions were well described by the modified Freundlich equation, and batch experiments demonstrated that the adsorption capacity increased with decreasing particle size. The desorption capacities of phenanthrene on clay and silt were larger than that of sand. The organic C normalized adsorption coefficients were positively correlated with the contents of nonpolar and aromatic C. The adsorption mechanism may be that phenanthrene undergoes a .-. interaction with organic matter of aggregates and is adsorbed on the aggregates.