C - Lublin

attributed to the transition of free electronic pairs belonging to the nucleophilic
atoms (mainly oxygen, for one, in the C=O group and its heteroanalogs).
Hypsochromic shift of this absorption band increasing with the increase of
incubation period of the P-treated soil could probably be due to the appearance of
new polar P=O groups in the P-modified HS.
To gain insight into the mechanism of reactions resulting in the formation of
new bonds in humic ligand, the prepared Fe-HA complex was tested as the metalhumus
sorbent for P anions. Figure 2 shows that control and P-modified complexes
differed structurally. There are the absorption bands at 1610 and 1402 cm -1 in the
control IR spectrum which can be attributed to the coordinated C=O groups. The P
treatment resulted in the disappearance of these frequencies. At the same time,
some new absorption bands arose in the spectrum. Among them are the bands at
1250 and 1170 cm -1 which can be attributed to the vibration frequencies of the P=O
groups having the dissimilar surroundings.
The data obtained prove the possibility of intra-complex formation of P=O
bonds in humic macroligand through the substitution of prior C=O groups. It is
known that compounds with P=O group are more capable of binding metal ions in
the forms of very inert soluble complexes than compounds with C=O group. This
fact allows to explain the increased elimination of metals from the P-modified
humus molecules and their accumulation in FA (Table 1).According to the IR
spectra of HA and FA (Fig. 2), the O-containing functional groups tended to
accumulate in FA whereas C=C bonds tended to accumulate in HA. As evident
from Fig.1, in the spectrum of the P-modified FA there is a hypsochromic shift of
the absorption band concerned with the transition of electrons belonging to oxygen
atoms. This shift can be attributed to the P=O groups passing to FA fraction of HS.
CONCLUSION
Consecutive changes in spectral and chemical properties of alkali-extractable
humus substances have been revealed in the soil incubated with orthophosphate
salt. The most considerable changes were observed at the end of the incubation
period (3 years). The P-modified humus molecules were characterized by the
accumulation of C=C bonds and P-containing polar groups. Structural changes
corresponded to the observed changes in chemical properties of humus substances.
It is shown that chemical composition of humic and fulvic acids varied
significantly in the course of incubation of the P-enriched soil. The longer was
incubation period, the lower were contents of metals and phosphorus in humic acid.
The P incorporation in humus molecules promoted elimination of metals in the
forms of soluble P-containing complexes and their discovery in fulvic acid fraction.
101