Chemical Structure of Humic Acids in Colloidal Systems

Chemical Structure of Humic Acids in Colloidal Systems

Paper in proceedings (conference paper)

Humic acids play important role in natural soil and water chemistry. They can form stable complexes with heavy metals which influences their toxicity in environment. Because humic acids are not a chemical individuum but mixture of various compounds their structure is very complex. The acidity of humic substances is caused mainly by carboxylic and phenolic groups. The total acidity (including all acidic functional groups) is often considered as binding capacity of humic acid in chemical interaction with metal ions. Titration methods are usually utilized for determination of content of various functional groups. Several samples of humic acids were used in this contribution: IHSS Leonardite, commercial Fluka and three samples with various ash contents (extracted from South-Moravian lignite). In determination of total acidity the local minima were observed on some titration curves. Results obtained for individual samples are compared and possible explanation of observed local minima is discussed. Because standard titration methods are carried out with suspension of humic acids, they were modified to determine total acidity in humic sols and gels. The influence of humic colloidal form on total acidity is also discussed.

Humic acids play important role in natural soil and water chemistry. They can form stable complexes with heavy metals which influences their toxicity in environment. Because humic acids are not a chemical individuum but mixture of various compounds their structure is very complex. The acidity of humic substances is caused mainly by carboxylic and phenolic groups. The total acidity (including all acidic functional groups) is often considered as binding capacity of humic acid in chemical interaction with metal ions. Titration methods are usually utilized for determination of content of various functional groups. Several samples of humic acids were used in this contribution: IHSS Leonardite, commercial Fluka and three samples with various ash contents (extracted from South-Moravian lignite). In determination of total acidity the local minima were observed on some titration curves. Results obtained for individual samples are compared and possible explanation of observed local minima is discussed. Because standard titration methods are carried out with suspension of humic acids, they were modified to determine total acidity in humic sols and gels. The influence of humic colloidal form on total acidity is also discussed.

humic acids, complexation, model

humic acids, complexation, model

KLUČÁKOVÁ, M.; VÁLKOVÁ, D.

01.01.2006

Edičné stredisko VÚPOP Bratislava

Bratislava

80-89128-16-5

Humic Substances in Ecosystems 6

81

83

3

http://hdl.handle.net/