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Submitted on 1 Jan 1980
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MÖSSBAUER SPECTROSCOPIC STUDIES OF HUMIC ACID AND FULVIC ACID SOIL FRACTIONS
D. Dickson, L. Heller-Kallai, I. Rozenson
To cite this version:
D. Dickson, L. Heller-Kallai, I. Rozenson. MÖSSBAUER SPECTROSCOPIC STUDIES OF HUMIC
ACID AND FULVIC ACID SOIL FRACTIONS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-
409-C1-410. �10.1051/jphyscol:19801158�. �jpa-00219644�
JOURNAL DE PHYSIQUE Colloque C1, supplkment au n
"
1 , Tome 41, janvier 1980, page c1-409~@SSBAUER SPECTROSCOPIC STUDIES OF HUFIIC ACID AND FULVIC ACID SOIL FRACTIONS
D.P.E. Dickson, L. ~eller-ICallaix and I. Rozenson X
Department of Physics, the University of Liverpool, Liverpool, England.
x Department of Geology, the Hebrew University, Jerusalem, I s r a e l .
I. Introduction.- Humic and fulvic acids are known to be efficient chelators of metallic ions and it is of considerable interest to know how and to what extent iron is found bound to these materials in soils. When looking for evidence of organically-bound iron in humic or fulvic acids it should be remembered that relatively drastic chemical treatments are required to isolate these fractions.
2. Experimental.- Samples of humic and fulvic acid were obtained from a dark grey calcareous clog loam by the usual procedures /I/ after de- calcification with 0.1 N HCl. Sample H A 1 (ash content 294) was the first precipitate obtained after acidifying the alkali extract. Sample HAII (ash content 2%) was the lyophilized supernatant after adding H SO to an aliquot of sample H A 1
2 4
redissolved in NaOH at pH 1 1 . The fulvic acid fraction, which remained in solution after pre- cipitation of sample HAI, was passed through a cation exchange column and concentrated to one tenth of its volume. Part of this sample was concentrated by evaporation (FAI, ash content 15%) while the remainder was purified by dialysis and dissolved in 0.2ml of the original fulvic acid solution (FA II, ash content 2%).
The 5 7 ~ e Mijssbauer spectra are plotted with the centre of the room temperature iron metal spectrum as zero velocity and this is also the reference for the chemical shifts.
3. Results and Discussion.- Fig. 1 shows the Kdssbauer spectra of samples HA I and HA II.
-1 0 1 2
VELOCITY (mm/sec)
Fig. 1. Room temperature Mdssbauer spectra of freeze-dried humic acid samples: a) HAII (2% ash, weight 350 mg), b) H A 1 (29% ash, weight 250 m g ) .
The solid line is the computer fit.
These spectra were computer fitting to a single doublet component, both fits yielding the same parameters (Table 1). The difference between the Msssbauer spectra of samples H A 1 and HAII lies in their absorption intensities. These correspond to an iron concentration in the low ash sample of only about one-sixth of that in the high ash sample.
The M6ssbauer parameters are the same, within the uncertainties, as those obtained for iron in kaolinite /2,3/. Synthetic complexes of I?e3+ with humic and fulvic acid give rise to doublets with larger quadrupole splittings /4,5,6/. It thus appears that the Mtissbauer spectra of samples H A 1 and HAII are predominantly associated with inor- ganic iron in the ash fraction rather than with any
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801158
c1-410 JOURNAL DE PHYSIQUE organically-bound iron. The ash content of sample
H A 1 was reduced by a factor of 14.5 on purifi- cation to sample HAII while the iron content was decreased by a factor of only 6, indicating that iron-containing compounds may be resistant impurities in humic acid.
Fig. 2 shows the Mdssbauer spectra of fulvic acid samples F A 1 and F A X at 82K. These spectra
0 . 5 1 ,
, , , , , ,1
- 3 - 2 - 1 0 1 2 3 4
VELOCITY (mm/sec)
Fig. 2 . 82K Mossbauer spectra of frozen samples of concentrated fulvic acid solutions: a) FAII (2% ash, dry weight 115 mg), b) F A 1 (15% ash, dry weight 135 mg). The solid line is the computer fxt were computer fitted to a single doublet component, both fits yielding the same parameters (Table 1).
These parameters show that the iron is in a di- valent form and are unlike those of any silicate oxide or hydroxide which might reasonably be assumed to be present and also differ from those of synthetic Fe 2+ humates and fulvates /7,4,5/. They closely resemble those obtained from measurements on frozen solutions containing [F~'I(H~O)~~ 2+
ions in a study which showed that the spectra are essentially the same, irrespective of the nature of the anion /a/. Hydrated ferrous ions are generally soluble. The fact that they were not
Table 1
Sample Temperature Chemical Quadrupole Shift Splitting (m/sec) (mlsec) HAI, HA11 R.T. 0.3540.1 0.5140.01 FAI, FAII 82K 1.39k0.02 3.2540.05 Iron in kaolinite 12/ R.T. 0.3940.05 0.5040.05 F ~ I I ( ~ ~ 0 ) 62+
in frozen solutions18/ 82K 1 .&Of 0.05 3.35'0.05 entirely removed on decalcification of the loam or on dialysis of sample F A 1 suggests that they are adsorbed by some components of the fulvic acid fraction. There is only a small difference in the Mdssbauer absorption intensities between samples F A 1 and FAII. On normalizing to the different dry weights of material in the two samples there is no significant differences in their iron concentrat- ions, despite the different ash contents. Whether iron is present in the divalent form in the original sample or was reduced in the course of the chemical treatments cannot be established from the present data.
4. Conclusions.- The M8ssbauer spectra give no evidence for the presence of any iron directly bound to organic material in the samples we have investigated.
References
/I/ Schnitzer, M. and Khan, S.U., "Humic sub- stances in the environment" (Marcel Dekker, Basel) 1972, p.203.
/2/ Malden, P.J. and Meads, R.E., Nature
215
(1967) 844.
/3/ Jefferson, D.A., Tricker, M.J. and Winter- bottom, A.P., Clays, Clay Minerals
27
(1975) 355.
141 Hansen, E.H. and Mosbaek, H., Acta.Chem.
Scand.
2
(1977) 3083./5/ Lakatos, B., Korecz, L. and Meisel, J., Geoderma
19
(1977) 149.161 Goodman, B.A. and Cheshire, M.V., J. soil. ~ c i . 30 (1979) 85.
-
171 Hoering, T.C., Carnegie Institution Year Book (1972) 682.
/8/ Dlzsi, I., Keszthelyi, L., PBcs, L. and Korecz, L., Phys.Lett.
