Characterization of Humin-Metal Complexes in a Buried Volcanic Ash Soil Profile and a Peat Soil

概要

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Humin was prepared from samples of a buried humic volcanic ash soil profile and a peat soil by the HF/HCl treatment method as well as by the DMSO extraction method. Recovery of humic carbon was 35-86% by HF/HCl treatment and 9-22% by DMSO extraction. With respect to the elementary composition, DMSO-humin was characterized by higher H/C and N/C ratios and a lower degree of unsaturation compared with HF-humin. The elementary composition of the humin from the peat soil was similar to that of lignin. Both HF-humin and DMSO-humin contained a large amount of ash. In HF-humin aluminum was the predominant metal accompanied by small amounts of magnesium and calcium. In DMSO-humin, iron was the predominant metal accompanied by a small amount of titanium. Other elements were contained in trace amounts in both humin preparations. Though both HF-humin and DMSO-humin were insoluble in aqueous alkaline solution, a large part of them could be solubilized in alkaline solution by treatment with Chelex 100, a chelating resin, which suggested that HF-humin occurred as a complex with aluminum while DMSO-humin with iron. Only HF-humin from the peat soil was hardly soluble in alkaline solution after treatment with Chelex 100 presumably because the humin in the peat soil occurred as a hardly soluble polymer like lignin and not as a metal complex.
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