Adsorption and desorption of divalent mercury (Hg2+) on humic acids and fulvic acids extracted from typical soils in China

A series of batch equilibration experiments were conducted to assess the adsorption and desorption of divalent mercury (Hg2+) by humic acids (HAs) and fulvic acids (FAs) extracted from black soil and red soil in China. The Fourier transform infrared (FTIR) spectroscopy, cross-polarization (CP) with magic-angle spinning (MAS) C-13 nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM) were jointly adopted to characterize the humic substances (HSs) samples and HSs-Hg complexes. The FTIR spectra showed that the adsorption of Hg2+ mainly acted on O-H, C-O and C=O groups of HAs and FAs. The NMR spectra indicated that HAs are higher in Paraffin and carbonyl C content compared with corresponding FAs, while FAs exhibit higher methoxy C, O-alkyl C and carboxyl C contents. The SEM images revealed the different surface structures of HAs, FAs and HSs-Hg complexes, which explains Hg2+ complexation phenomenon on HSs. The study also showed that HAs have higher adsorption capacity for Hg2+ than those of FAs. Hg2+ adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. The desorbed percentages of all HSs samples were less than 1%, which indicated their high binding strength for Hg2+. Furthermore, HAs samples have a lower desorption ratio than FAs, HAs can play a more important role in pollution control of Hg2+ in environment. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.