Fulvic acid

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Fulvic acids are a family of organic acids, natural compounds, and components of the humus (which is a fraction of soil organic matter).[1] They are similar to humic acids, with differences being their carbon and oxygen contents, acidity (pKa value), degree of polymerization, molecular weight, and color.[2]

Fulvic and humic acids are extracted at high pH by treating soil humus with a solution of NaOH. Their dissolution is favored by the dissociation and the ionization of their carboxylic and phenolic groups at high pH. The insoluble fraction of humus remaining after its leaching by NaOH is humin. After alkaline extraction, fulvic and humic acids are then separated by further acidification of the obtained leachate. The small molecular weight fulvic acids remain in solution after precipitation of the high molecular weight humic acids by acidification at pH = 1.[3][4]

Fulvic acids are produced by microbial degradation of plant matter in a soil with sufficient oxygen.[5]

Fulvic acids cannot be readily synthesized[6] because of their extremely complex nature, although lignosulfonates from the pulp and paper industry can appear similar to fulvic acids in certain tests.[7]

In soil chemistry, or in paper pulp effluent treatment, the main problem is not the extraction, but the subsequent purification and characterization of fulvic acids.

When fulvic acids and humic acids, or lignin derivatives, react with molecular chlorine used for bleaching wood pulp they can also form toxic organochlorine compounds.

Undesirable small molecular weight organochlorine compounds such as dichloroacetonitrile (CHCl
2
CN
) can also be formed at the trace level (a few ppb, or µg/L) by chlorinating dissolved humic and fulvic aquatic substances in drinking water purification plant.[8]

References[edit]

  1. ^ Bremner, J. M. (January 1951). "A Review of Recent Work on Soil Organic Matter Part I". Journal of Soil Science. 2 (1): 67–82. doi:10.1111/j.1365-2389.1951.tb00591.x. ISSN 1365-2389. Retrieved April 28, 2021 – via Wiley Online Library.
  2. ^ "Properties of humic substances". Archived from the original on February 15, 2020. Retrieved April 28, 2021.
  3. ^ Aiken, G.R.; McKnight, D.M.; Thorn, K.A.; Thurman, E.M. (July 1992). "Isolation of hydrophilic organic acids from water using nonionic macroporous resins". Organic Geochemistry. 18 (4): 567–573. doi:10.1016/0146-6380(92)90119-I. Retrieved April 28, 2021 – via Elsevier Science Direct.
  4. ^ Chefetz, Benny; Chen, Yona; Hadar, Yitzhak; Hatcher, Patrick (1998-03-01). "Characterization of Dissolved Organic Matter Extracted from Composted Municipal Solid Waste". Soil Science Society of America Journal. 62 (2): 326–332. doi:10.2136/sssaj1998.03615995006200020005x. ISSN 0361-5995. Retrieved April 28, 2021 – via Wiley Online Library.
  5. ^ Schnitzer, M. (1977). "Recent findings on the characterization of humic substances extracted from soils from widely differing climatic zones" (PDF). Proceedings of the Symposium on Soil Organic Matter Studies. Environment with adeequate oxygen. Braunsweig: 117–131. Archived from the original (PDF) on April 28, 2021. Retrieved April 28, 2021.
  6. ^ Murray, K.; Linder, P. W. (September 1983). "Fulvic acids: structure and metal binding. I. A random molecular model". European Journal of Soil Science. 34 (3): 511–523. doi:10.1111/j.1365-2389.1983.tb01052.x. Retrieved April 28, 2021 – via Wiley Online Library.
  7. ^ Senesi, N.; Chen, Y.; Schnitzer, M. (1977). "The role of humic acids in extracellular electron transport and chemical determination of pH in natural waters". Soil Biology and Biochemistry. 9: 397–403. doi:10.1016/0038-0717(77)90018-9.
  8. ^ Oliver, Barry G. (February 1, 1983). "Dihaloacetonitriles in drinking water: algae and fulvic acid as precursors". Environmental Science & Technology. 17 (2): 80–83. doi:10.1021/es00108a003. PMID 22295957 – via ACS Publications.

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