Spectroscopic investigation of soil humic substances from Okchun basin and complexation study with Eu(Ⅲ) and Cm(Ⅲ)

Abstract

Three humic acids (HA) and one fulvic acid (FA) are extracted from soils of the Okchun Basin (Koyesan, Yungkwang and Taejon), and are purified and characterized using chemical (element analysis, total acidity, molecular size distribution) and spectroscopic ($^{1}H$, $^{13}C$ NMR, and IR) methods. The results are compared with one another. The IR, and $^1H$ and $^{13}C$ NMR spectral features are found to be nearly identical, suggesting that humic substances formed in the Okchun Basin have quite similar chemical properties. These humic substances from Okchun Basin soils have undergone low degree of aromatic condensation and have high contents of aliphatic functionalities including carbohydrates. The soil humic acid (Koyesan-HA) was subdivided into four subfractions by molecular size (F1 > 100.000 dalton; F2 < 100.000 dalton; F3 < 10.000 dalton; F4 < 2.000 dalton) using MP-dual hollow fiber ultrafiltration system. The characterization using IR and $^{13}C$ NMR spectroscopy, showed similar spectroscopic features of HA, demonstrating that the bulk properties of HA subfraction are very similar to one another. IR spectral data also showed a decrease in polysaccharides contents and increase in carboxylate functionality as molecular weight become smaller. The $CH_n$ (n = 0-3) subspectra separated by carbon multiplicity of Koyesan-HA and Koyesan-FA are obtained using distortionless enhancement by polarization transfer (DEPT) pulse sequence, together with the quaternary-only carbon spectra (QUAT). The assignment of the structural moieties was facilitated by the use of a set of DEPT/QUAT subspectra of HA and FA, obtained by under quantitative conditions. The spectral and other information obtained thus are used to proposal of an "average" structure of soil fulvic acid (Koyesan-FA): This was carried out by modifying one of the structural model proposed for Suwannee river fulvic acids, IHSS (International Humic Substances Society) reference sample. This information enable us...