摘要：Humin (HU) is the least understood humic substance (HS) fractions due to its close associations with soil mineral colloids. Here, humic acid (HA), fulvic acid (FA), HU, iron-bound HU (HUi), claybound HU (HUc) and residual HU (HUr) were sequentially extracted from an Alfisol of northeast China. Elemental analysis, solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize HS fractions. The adsorption isotherms of Cu(II) on HS fractions were obtained using batch equilibrium method. Among these HS fractions, HA contained higher proportion of phenols, whereas HUc exhibited higher proportion of aliphatic hydrocarbons. For the different HU fractions, n-alkanes/n-alkenes were particularly abundant in HUc, whereas polysaccharides were abundant in HUr. The adsorption of Cu(II) on HS fractions well fitted both Freundlich and Langmuir equations. The maximum amounts of Cu(II) adsorbed was FA > HUi > HA > HUc > HU > HUr, which was positively correlated with their O/C ratio and carbonyl C whereas negatively correlated with C/N ratio (p < 0.01). The results suggested that HU is highly heterogeneous in terms of their chemical compositions and plays important role in controlling the behavior and fate of Cu(II) in the environment.
