New version of calculation of stability constant of metal–fulvate complexes on the example of zinc fulvate

  • G. MakharadzeEmail author
  • G. Supatashvili
  • T. Makharadze
Original Paper


Natural macromolecular organic substances—fulvic acids—take an active part in complex formation processes and stipulate migration forms of heavy metals in natural waters. In spite of researches, experimental data on stability constants of complex compounds of fulvic acids with heavy metals (among them zinc) are heterogenous and they differ in several lines from each other. One of the reasons of such condition is ignoring an average molecular weight of the associates of fulvic acids, which finally causes the wrong results. Complex formation process between zinc (II) and fulvic acids was studied by the solubility method at pH = 8.0. ZnO suspension was used as a solid phase. Fulvic acids were isolated from Paravani lake by the adsorption chromatographic method. This article shows that during the complex formation process, every 1/5 part of an associate of fulvic acids inculcates into zinc’s (II) inner coordination sphere, as an integral ligand. So it may assume that the average molecular weight of the associate of fulvic acids which takes part in complex formation process equals to 1252. This part of the associate of fulvic acids was conventionally called an “active associate.” The average molecular weight of the “active associate” was used for determining the composition of zinc fulvate complex, the concentration of free ligand and stability constant, which equals to \(1.6 \times 10^{4}\).


Active associate Average molecular weight Fulvic acids Natural water 



The work was done by supporting CRDF Global, Shota Rustaveli National Science Foundation (SRNSF) and Georgian Research and Development Foundation (GRDF) (Grant Number: 04/35).


  1. Beck MT, Nagypal I (1990) Chemistry of complex equilibria. Horwood, Chichester, New YorkGoogle Scholar
  2. Bertoli AC, Garcia JS, Trevisan MG, Ramalho TC, Freitas MP (2016) Interactions fulvate–metal (Zn2+, Cu2+ and Fe2+):theoretical investigation of thermodynamic, structural and spectroscopic properties. Biometals 29:275–285. doi: 10.1007/s10534-016-9914-8 CrossRefGoogle Scholar
  3. de Castro RT, da Cunha EFF, de Alencastro RB, Espínola A (2007) Differential complexation between Zn2+ and Cd2+ with fulvic acid: a computational chemistry study. Water Air Soil Pollut 183:467–472. doi: 10.1007/s11270-007-9364-6 CrossRefGoogle Scholar
  4. Ephraim J (1992) Heterogeneity as a concept in the interpretation of metal-ion binding by humic substances—the binding of zinc by an aquatic fulvic acid. Anal Chim Acta 267:39–45. doi: 10.1016/0003-2670(92)85004-P CrossRefGoogle Scholar
  5. Kirishima A, Ohnishi T, Sato N, Tochiyama O (2010) Simplified modeling of the complexation of humic substance for equilibrium calculations. J Nucl Sci Technol 47:1044–1054. doi: 10.1080/18811248.2010.9711669 CrossRefGoogle Scholar
  6. Linnik PN, Zhezherya VA, Linnik RP, YaS Ivanechko (2013) Influence of the component composition of organic matter on relationship between dissolved forms of metals in the surface waters. Hydrobiol J 49:91–108. doi: 10.1615/HydrobJ.v49.i1.90 CrossRefGoogle Scholar
  7. Revia R, Makharadze G (1999) Cloud-point preconcentration of fulvic and humic acids. Talanta 48:409–413. doi: 10.1016/S0039-9140(98)00262 CrossRefGoogle Scholar
  8. Rey-Castro C, Mongin S, Huidobro C, David C, Salvador J, Garces J, Galceran J, Mas F, Puy J (2009) Effective affinity distribution for the binding of metal ions to a generic fulvic acid in natural waters. Environ Sci Technol 43:7184–7191. doi: 10.1021/es803006p CrossRefGoogle Scholar
  9. Sasaki T, Yoshida H, Kobayashi T, Takagi I, Moriyama H (2012) Determination of apparent formation constants of Eu(III) with humic substances by ion selective liquid membrane electrode. Am J Anal Chem 3:462–469. doi: 10.4236/ajac.2012.37061 CrossRefGoogle Scholar
  10. Schnitzer M, Skinner SIM (1966) Organo-metallic interactions in soils: 5. stability constants of Cu ++-, Fe ++-, and Zn ++-fulvic acid complexes. Soil Sci 102:361–365. doi: 10.1097/00010694-196612000-00002 CrossRefGoogle Scholar
  11. Shizuko H (1981) Stability constants for the complexes of transition-metal ions with fulvic and humic acids in sediments measured by gel-filtration. Talanta 28:809–815. doi: 10.1016/0039-9140(81)80022-7 CrossRefGoogle Scholar
  12. Tochiyama O, Nibbori Y, Tanaka K, Yoshino H, Kubota T, Kirishima A, Setiawan B (2004) Modeling of the complex formation of metal ions with humic acids. Radiochim Acta 92:559–565. doi: 10.1524/ract.92.9.559.54996 CrossRefGoogle Scholar
  13. Town RM, Van Leeuwen HP, Buffle J (2012) Chemodynamics of soft nanoparticulate complexes: Cu(II) and Ni(II) complexes with fulvic acids and aquatic humic acids. Environ Sci Technol 46:10487–10498. doi: 10.1021/es3018013 CrossRefGoogle Scholar
  14. Varshal GM(1994) Migration forms of fulvic acids and metals in natural waters. Dissertation. Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academу of SciencesGoogle Scholar
  15. Wang J, Lü C, He J, Zhao B (2016) Binding characteristics of Pb2 + to natural fulvic acids extracted from the sediments in Lake Wuliangsuhai, Inner Mongolia plateau, P.R. China. Environ Earth Sci 75:768–779. doi: 10.1007/s12665-016-5608-3 CrossRefGoogle Scholar

Copyright information

© Islamic Azad University (IAU) 2017

Authors and Affiliations

  1. 1.Department of ChemistryIvane Javakhishvili Tbilisi State UniversityTbilisiGeorgia

Personalised recommendations