Diffusivity of Cu(II) ions in humic gels – influence of reactive functional groups of humic acids

Abstract

Abstract The reactivity and transport properties of metal ions in humic systems are important for understanding the role of humic substances in both natural systems and human-driven applications. This work is focused on the transport and immobilization of Cu(II) ions in hydrogels based on several humic acids differing in the raw materials in which they were present and in the conditions in which they were isolated. The prepared humic hydrogels contained different amounts of reactive functional groups (with different affinities to metal ions) in order to study the effect of the structure and properties of humic acids and the selective blocking of carboxylic groups (by methylation) on the mobility and immobilization of Cu(II) ions in the hydrogel structure. An experimental arrangement was selected in order to facilitate an instantaneous planar source method for data processing based on the determination of the concentration distribution of Cu(II) ions in hydrogels. The resulting values of the effective diffusion coefficient include both the effect of hydrogel structure and the effect of the reaction between Cu(II) ions and humic acids. The blocking of functional groups was reflected in lower values of diffusivity in comparison to hydrogels prepared from unmodified humic acids. The isolation procedure for humic acids as well as their properties were also confirmed to have an effect on the diffusivity of Cu(II) ions in hydrogels.