Utilization of fractional extraction for characterization of the interactions between humic acids and metals

- Diffusion experiments were combined with selective extraction of copper(II) ions.
- As a diffusion medium the humic hydrogel was used.
- Utilized extractants: water, 1 M MgCl2, 1 M HCl
- Classification of the interactions: mobile, ion-exchangeable and strongly bound
- Distribution of copper into the fractions was constant after some initial period.

Diffusion experiments in humic hydrogels provide valuable findings on reactivity of humic matrices. This article concentrates on the study of interactions between humic acids and copper(II) ions in diffusion experiments. The diffusion experiments were supplemented with selective extraction of the diffused copper(II) ions. For this purpose, the leaching agents with increasing affinity towards copper(II) ions were used. The presented results showed that several different forms of the diffused ions exist in the humic gel, which is given by the strength of bonds towards humic acids. Distribution of copper into these forms becomes constant after some initial period, which indicates local equilibration of interactions between the ions and the humic content of the gel during the transport process. The proposed experimental method seems promising in order to shed new light on the effects of humic acids reactivity on mobility of important compounds in nature.