Bulletin of the Tomsk Order of the October Revolution and Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov

Vol. 297 1975

On the Association of Antimony with Humus-Type Organic Matter in Natural Waters and Aqueous Solutions

P. A. Udodov, R. S. Solodovnikova,
N. M. Shvartseva, E. S. Rychkova

The hydrogeochemistry of antimony has scarcely been studied; this applies especially to the question of its association with organic matter. It is known that a number of chemical elements (Pb, Cu, Bi, Zn, and others) form complex compounds with humus-type organic matter [1, 2].

To determine the influence of organic matter on the behavior of antimony in aqueous solutions and natural waters, field work was carried out in the area of the Semiluzhenskoe antimony ore occurrence (Tomsk Oblast), as well as experimental laboratory work. In the area of the Semiluzhenskoe site in 1970-72, 83 samples were collected, including 40 samples from surface watercourses, 20 from springs, and 23 from wells. In all these samples, total organic matter, \(C_{\mathrm{total}}\), was determined simultaneously by the Tyurin method [5], and the antimony content was determined by the polarographic method according to E. M. Malkov [4]. The content of organic matter ranges from 0.5 to 23 mg/l, averaging 5-7 mg/l \(C_{\mathrm{total}}\). Correspondingly, the antimony content in these waters varies from 2.5 to 100 microg/l, averaging 20-50 microg/l. The results of these determinations are presented in Figs. 1 and 2.

From Fig. 1 it is evident that organic matter was encountered in all types of waters: surface waters, waters of Paleozoic deposits, and waters of zones of rupture disturbances. Organic matter is present in small amounts in the waters of zones of rupture disturbances (\(C_{\mathrm{org}} = 0.2-0.3\) mg/l). It is possible that deep waters become enriched in organic matter at the expense of overlying surface waters that seep along fractures. The possibility that these waters contain their own organic matter cannot be ruled out. Analysis of the data obtained revealed a certain regularity: the antimony content increases with increasing organic matter in surface waters; in waters of zones of rupture disturbances this is not observed, while fissure waters occupy an intermediate position between them (Fig. 2).

From this it may be concluded that antimony in surface waters is possibly present in the form of antimony-organic compounds.

It was of interest to clarify the role of organic matter in the enrichment of natural waters with antimony. For this purpose, an experiment was set up on the solubility of antimonite in various solvents. Weighed portions of antimonite of the 2 mm fraction, 50 mg each, washed free of dust, were placed in 0.5 l beakers and treated with 250 ml, respectively, of bidistillate, bidistillate with humic acid, and bidistillate with fulvic acid, with acid concentrations of 10 and 50 mg/l in terms of carbon content. The results of the experiment

Fig. 1. Content of total organic carbon in various types of waters of the Semiluzhensk ore occurrence.

Fig. 2. Dependence of antimony content on the amount of total organic carbon in waters.

are shown in Figs. 3 and 4. From Fig. 3 it is evident that antimony passes from antimonite into aqueous solution in all samples. However, the antimony content in them differs at different pH values. The highest antimony contents in all variants are found in strongly acidic and alkaline media; at the same time, it was observed that after ashing of the organic matter in the samples, the antimony content increases. This indicates an interaction of antimony with organic matter, which is also confirmed by the isolation of humate and

Fig. 3. Solubility of antimonite as a function of pH in bidistillate with the addition of humic acid and fulvic acid in an amount of 10 mg/L. 1 — in the control sample; 2 — with addition of sodium humate without its ozonation; 3 — with ozonation of sodium humate; 4 — with addition of fulvic acid without its ozonation.

Fig. 4. Solubility of antimonite as a function of pH in bidistillate with the addition of humic acid and fulvic acid in an amount of 50 mg/l. 1 — in the control sample; 2 — with addition of sodium humate; 3 — antimony humate, washed with alkali; 4 — with addition of sodium fulvate; 5 — antimony fulvate, washed with alkali.

of antimony fulvate from dry residues during their extraction with a 1% NaOH solution (Fig. 4). The presence of antimony humates and fulvates in neutral and alkaline media indicates the formation of complex antimony–organic compounds. To confirm the possibility of complex formation between humic acids and antimony, we obtained titration curves for humic acids and their systems with \(\mathrm{Sb}^{3+}\) at \(\mathrm{Sb}^{3+}\) concentrations of 100 and 1000 µg/ml and humic-acid concentrations of 100 and 200 µg/ml of solution (Figs. 5, 6). The curves obtained indicate the presence of a pH effect, since additional amounts of 0.1 solution of NaOH are consumed in the titration of humic acids with antimony; this is associated with the release of hydrogen ions, their replacement by antimony ions in the molecules of humic acids, and, consequently, with the process of complex formation [3]. To determine the nature of the complexes formed

Fig. 5. Curves of potentiometric titration of humic acids (HA) and their systems with antimony (at concentrations: Sb — 1000 µg/ml, HA — 2000 µg/ml of solution). 1 — humic acid; 2 — \(\mathrm{SbCl}_3\); 3 — humic acid + \(\mathrm{SbCl}_3\).

Fig. 6. Curves of potentiometric titration of humic acids (HA) and their systems with antimony (at concentrations: Sb—100 µg/ml, HA—100 µg/ml solution). 1—humic acid; 2—SbCl₃; 3—humic acid + SbCl₃

(methods of electrophoresis and electrodialysis were used to determine the sign of the charge, its mobility, and other properties).

At the beginning of the experiment, electrophoresis was carried out on solutions of the salt SbCl₃, and then on solutions of SbCl₃ with humic acid in weakly acidic and alkaline media, taken in the ratio of 1 mg of Sb³⁺ and 2 mg of humic acid. This showed that antimony from an acidic solution of SbCl₃, in the absence of organic matter, migrates along the electropherogram toward the cathode in the form of SbCl₃. The electropherogram of an alkaline solution of SbCl₃ indicates the presence on the electropherogram of the complex anion SbO₂⁻, formed as a result of hydrolysis of the salt taken. In the presence of organic matter in a weakly acidic medium, a complex of antimony with humic acid is formed; it is less mobile than the simple complex anion of antimony. However, the greater part of the antimony remains in the form of Sb³⁺ (at the cathode), another part of it (much smaller) is found at the anode in the form of SbO₂⁻, and only an insignificant part of it passes into a complex with humic acid. The formation of a complex compound of antimony with humic acid is confirmed by the detection of antimony after its destruction by acid in this part of the electropherogram strip (Fig. 6).

The presence of complex compounds of antimony with organic matter in natural waters was also found when electrophoresis was carried out on natural water with an antimony content of 400 µg/l and \(C_{\mathrm{org}}\) of 7.4 mg/l. Electrophoresis was carried out in acidic and alkaline media. In both cases, the presence of antimony is detected in the anodic and cathodic parts of the electropherogram only after destruction of the antimony humate complexes; moreover, considerably more antimony is present in the form of negatively charged complexes.

To determine the sign of the charge of antimony–organic compounds, we carried out electrodialysis of aqueous solutions obtained by leaching antimonite, with separate addition to them of 50 mg/l (sodium humate and fulvate). The results of electrodialysis are presented in Table 1. It is evident from the table that in water with separate presence of humic and fulvic acids, respectively, in a neutral medium, antimony humates with a neutral charge, occurring in the precipitate, predominate, and

Table 1

Results of electrodialysis of water at different pH values in the presence of humic and fulvic acids in an amount of 50 mg/l

antimony fulvates with a negative sign, which are mainly water-soluble. In an acidic medium, organo-antimony complexes of both acids with a positive charge predominate. In an alkaline medium, recharging of the complexes occurs, and antimony humates acquire mainly a negative charge. Consequently, depending on conditions, antimony may occur in natural waters in the form of negatively and positively charged complexes; the possibility of simultaneous occurrence of these complexes is also not excluded.

Conclusions

1. In analyzing the data obtained, a certain regularity was found in the increase in antimony content with an increase in organic matter in surface waters; in waters of zones of rupture disturbances this is not observed, while fissure waters occupy an intermediate position between them.

2. Humus-type organic matter participates in the processes of enrichment of natural waters with antimony, with the formation of complex antimony-organic compounds.

3. Depending on conditions, antimony may occur in natural waters in the form of negatively and positively charged complexes; the possibility of simultaneous occurrence of these complexes in natural waters is also not excluded. In waters having a mainly neutral medium, a predominance of negatively charged complexes is observed.

References

1. S. M. Manskaya, T. V. Drozdova. Geochemistry of Organic Matter. Moscow, Nauka Publishing House, 1964.

2. P. A. Ulodov, N. M. Rasskazov, R. S. Solodovnikova, G. N. Tkachik, E. S. Lisovik. Some results of the development of a hydrogeochemical method for prospecting ore deposits. In: Results of Research in Geology and Geography over 50 Years, 1917–1967. Tomsk, Tomsk State University Publishing House, 1968.

3. G. A. Levashkevich. Interaction of humic acids with ionic forms of iron and aluminum. In: Geology and Geochemistry of Weathering Crusts. Moscow, Nauka Publishing House, Academy of Sciences of the USSR, 1968.

4. A. A. Reznikov, E. P. Mulikovskaya, I. Yu. Sokolov. Methods for the Analysis of Natural Waters. Moscow, Publishing House for Literature on Geology and Subsoil Protection, 1963.

5. I. V. Tyurin. Soil Organic Matter and Its Role in Fertility. Moscow, Nauka Publishing House, 1965.