Abstract
Fulvic acid is a water-soluble humic material that occurs widely in soils and waters and that tends to form water-soluble and water-insoluble complexes with a variety of metal ions, some of which are toxic. This paper presents information on the conditions under which the different types of FA-metal complexes are formed.
The solubility in water, separately and after mixing, of FA (2 to 30 mg/100 ml) and eleven metal ions (Fe(III), Al, Cr(III), Pb, Cu, Hg(II), Zn, Ni, Co, Cd and Mn; 1 × 10−5 moles of each metal ion) was investigated over the pH range 4 to 9. After mixing, the solubility of the components was significantly affected by pH only when less than 20 mg of FA was present. As the systems became richer in FA (22 to 30 mg), most of the metal ions remained in the aqueous phase, likely due to the formation of FA-metal complexes, inhibiting the formation of metal hydroxides.
The order in which the eleven metal ions tended to form water-insoluble FA-metal complexes depended on the pH. At pH 6 it was: Fe = Cr = Al > Pb = Cu > Hg > Zn = Ni = Co = Cd = Mn. This order appeared to correlate with the valence, 1st hydrolysis constants and effective hydrated ionic diameters of the metal ions. In general, FA/metals weight ratios of > 2 favored the formation of water-soluble FA-metal complexes; at lower ratios, water-insoluble complexes, which could accumulate in soils and sediments, were formed.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Chen, Y., Senesi, N., and Schnitzer, M.: 1978, Geoderma 20, 87.
Geological Survey, 1974, Handbook of thermodynamic data. PB-226 722, US Dept. of Commerce, pp. 196–236.
Gjessing, E. T.: 1976, Physical and Chemical Characteristics of Aquatic Humus, Ann Arbor Science, p. 33.
Khan, S. U.: 1969, Soil Sci. Soc. Am. Proc. 33, 851.
Klotz, I. M. and Rosenberg, R. M.: 1972, Chemical Thermodynamics, W. A. Benjamin Inc., p. 344.
Malaiyandi, M. and Barette, J.: 1970, Anal. Lett. 3, 579.
McKeague, J. A., Ross, G. J., and Gamble, D. S.: 1978, In W. C. Mahaney (ed.) Quaternary Soils, Geo Abstracts, Norwich, 27–60.
Ong, H. L. and Bisque, R. E.: 1968, Soil Sci. 106, 220.
Orlov, D. S. and Grindel, N. M.: 1967, Soviet Soil Sci. (Engl. transl.), 94. Schnitzer, M.: 1978, In M. Schnitzer and S. U. Khan (eds.), Soil Organic Matter, Elsevier, pp. 1–64.
Schnitzer, M. and Gupta, U. C.: 1965, Soil Sci. Soc. Am. Proc. 29, 274.
Schnitzer, M. and Hansen, E. H.: 1970, Soil Sci. 109, 333.
Wright, J. R. and Schnitzer, M.: 1963, Soil Sci. Soc. Am. Proc. 27, 171.
Author information
Authors and Affiliations
Additional information
Visiting scientist from the Institute of Geosciences, University of Mainz, Mainz, W. Germany. Contribution No. 1183.
Rights and permissions
About this article
Cite this article
Schnitzer, M., Kerndorff, H. Reactions of fulvic acid with metal ions. Water Air Soil Pollut 15, 97–108 (1981). https://doi.org/10.1007/BF00285536
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00285536