Spectroscopic studies of the progress of humification processes in humic substances extracted from refuse in a landfill

Humic acids (HA) and fulvic acids (FA) extracted from refuse in a landfill at different landfill ages were characterized by elemental composition, GPC, FTIR, and ¹³C CP/MAS NMR. The elemental composition analysis revealed high O/C and low H/C ratios in the FA, indicating a high proportion of O-alkyl and carboxylic acids in the FA. The M_w and M_n values and M_w/M_n ratios indicated that the HA had a higher molecular weight and were more homogeneous with respect to molecular weight. FTIR spectra showed that the FA had relatively more intense bands assigned to aliphatic structures and were abundant in oxygen-containing function groups. The analytical results of ¹³C CP/MAS NMR suggested that there were more oxygenated aliphatic carbons and fewer aromatic carbons in the FA than in the HA. All the results demonstrated that the degree of humification increased with landfill age.