Complexation kinetics in humic colloidal systems

Complexation kinetics in humic colloidal systems

Paper in proceedings (conference paper)

The binding of metal ions by humic acids (HA) is one of the most important environmental qualities of these substances. They determine the pH buffering capacity and cation exchange capabilities in natural waters and soils. Metal-organic interactions, including complexation reactions of metal ions and HA are increasingly becoming recognized as important factor in many natural systems. Metal binding can generally occur as complexation with carboxylic and phenolic groups therefore H+ ions are produced during this process. In this contribution, complexation of metal ions with HA in form of colloidal dispersions (sol, gel) is studied. There are similar problems in the description of reactivity as in the case of adsorption processes on solid HA particles however the situation in these colloidal systems is even more complicated. HA can be dissolved using basic solutions (usually NaOH or KOH) and Na- or K- humates are formed. But alkaline medium may cause the precipitation of metals in form of their hydroxides. This problem can be solved by using of humic colloidal systems. To prepare humic colloidal solution (sol) the equivalent amount of hydrochloric acid is added to humate up to pH = 7. The influence of ionic strength on complexation has to be taken into consideration in this case. Other possibility is re-precipitation of HA from humate by HCl adding up to pH = 1-2. The formed humic gel is repeatedly washed and centrifuged to prepare "pure" humic gel composed only from HA and water. In previous works, kinetics and mechanism of interaction of copper(II) ions with HA in these two system was studied. In this contribution, experimental data obtained for other metals (cobalt, nickel) are compared with previous ones and possible mechanism of humic complexation is discussed.

The binding of metal ions by humic acids (HA) is one of the most important environmental qualities of these substances. They determine the pH buffering capacity and cation exchange capabilities in natural waters and soils. Metal-organic interactions, including complexation reactions of metal ions and HA are increasingly becoming recognized as important factor in many natural systems. Metal binding can generally occur as complexation with carboxylic and phenolic groups therefore H+ ions are produced during this process. In this contribution, complexation of metal ions with HA in form of colloidal dispersions (sol, gel) is studied. There are similar problems in the description of reactivity as in the case of adsorption processes on solid HA particles however the situation in these colloidal systems is even more complicated. HA can be dissolved using basic solutions (usually NaOH or KOH) and Na- or K- humates are formed. But alkaline medium may cause the precipitation of metals in form of their hydroxides. This problem can be solved by using of humic colloidal systems. To prepare humic colloidal solution (sol) the equivalent amount of hydrochloric acid is added to humate up to pH = 7. The influence of ionic strength on complexation has to be taken into consideration in this case. Other possibility is re-precipitation of HA from humate by HCl adding up to pH = 1-2. The formed humic gel is repeatedly washed and centrifuged to prepare "pure" humic gel composed only from HA and water. In previous works, kinetics and mechanism of interaction of copper(II) ions with HA in these two system was studied. In this contribution, experimental data obtained for other metals (cobalt, nickel) are compared with previous ones and possible mechanism of humic complexation is discussed.

humic acids, complexation, kinetics

humic acids, complexation, kinetics

KLUČÁKOVÁ, M.; ŽBÁNKOVÁ, P.; PEKAŘ, M.

16.02.2005

Boston

Humic Science & Technology. Aggregation and Physiological Effects

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