Humic acids

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Example structure of a humic acid. This can contain different chemical components such as quinone , phenol , sugar or peptide components, which are linked to one another for example via phenolic bridges.

Humic acids are naturally in humus , peat and lignite occurring humic substances . The group of different acids is formed by the partial breakdown of remains of dead organisms in the soil. In humus soils, they fulfill an important function as a bioeffector and store for basic nitrogen compounds. They were first described by the German chemist Franz Carl Achard . Their salts are called humates.


Humic acids are high-molecular chemical compounds which, along with other humic substances, are formed during the degradation process of biological material through "humification". The molar mass range of humic acids is between 2000 and 300,000 Dalton . They mainly consist of partially degraded vegetable lignin and cellulose , to which proteins and carbohydrates are often attached. Easily degradable substances such as sugar are end- oxidized , whereas poorly degradable substances such as lignin, waxes and fat and protein components remain in the soil for a long time and thus ensure the preservation of biological components such as wood, leather, plant fibers, pollen, etc. archeology is important, but on the other hand, due to the high degree of acidity, the lime in bones dissolves quickly.

So humus represents a mostly dark mass of organic, not easily degradable substances that are converted into chemically not clearly defined polymeric substances by bacteria, fungi and protozoa . In the soil, the humic acids play an important role as natural ion exchangers that bind basic nitrogen compounds and release them again in exchange for metallic cations.

In addition to the acid groups , humic acids also have other functional groups . In water they dissociate into an electrically highly charged poly anion and a corresponding number of cations . During water treatment, humic acids are removed with activated carbon filters , special ion exchange filters ( scavenger filters ) or membrane processes ( reverse osmosis ), as the water would otherwise be colored yellow or downstream ion exchange resins would be damaged by “fouling” .

Composition / fractionation

Depending on the different solubility , humic substances can be fractionated (chemically divided). According to FJ Stevenson, a distinction is made between water-soluble fulvic acids (molar mass <3000 Da) and water-insoluble, but alkali-soluble humic acids and water- and alkali- insoluble humins . From the humic acids may be obtained by dissolution with alcohol the Hymatomelansäuren separate. In addition, special separation processes enable the humic acids to be separated into gray and brown human acids. Humic acids can be precipitated from their alkaline solutions with dilute mineral acids .

The International Humic Substances Society (IHSS, German: Internationale Huminstoffgesellschaft) deals with the chemistry, properties and application of humic acids, especially in the environment, water management and agriculture, while the International Moor and Peat Society (IMTG) deals primarily with the Research and application of humic and fulvic acids from peat in agriculture ( horticulture ) but also in medicine ( balneology ).

Individual evidence

  1. ^ FJ Stevenson: Humus Chemistry. Genesis, Composition, Reactions . 2nd Edition. John Wiley and Sons, New York NY et al. 1994, ISBN 0-471-59474-1 , p. 289.
  2. a b c Wissenschaft-Online-Lexika: Entry on “Humic Acids” in the Lexikon der Chemie, accessed on April 6, 2010.


  • FJ Stevenson: Humus Chemistry. Genesis, Composition, Reactions . 2nd Edition. John Wiley and Sons, New York NY et al. 1994, ISBN 0-471-59474-1 .

Web links

Wiktionary: Humic acid  - explanations of meanings, word origins, synonyms, translations