Fractal Dimension of Humic Acids as Influenced by Complex Formation

Abstract

Among the tools available to explain the conformation of humic acids (HA), the fractal dimension (D) seems to be one of the most adequate. The aim of this study was to determine the conformational modifications of the HA particles in the absence and presence of Zn2+ and Cd2+, with the determination of the D value. The adsorption experiments were carried out with a commercial HA (Fukla AG) and HA extracted from SPODOSOL soils. The HA were characterized for their total C, H, and N content, E4/E6 ratios, IR-FTIR, and ash content. The metal concentration of Zn2+ and Cd2+ in the suspension was determined through atomic absorption spectrophotometer. The HA particles in diluted aqueous suspension were analyzed using turbidimetry, under varied experimental conditions, to calculate D. The addition of metals to the HA suspensions induced a decrease in the standard-deviation between replications and an increase of D values, revealing stabilization of the suspensions and a collapse of the HA structure during the formation of metal-organic complex. The results showed that the D values were able to represent the conformational changes of the HA-metal complexes.