The complexing capacities of humic substances isolated from Baltic sediments and their molecular weight fraction towards copper [II] and iron [III]

Humic substances were isolated from sediments collected from the Gdansk Deep, separated into humic acids and fulvic acids, and further separated into molec­ ular weight fractions by ultrafiltration. The respective complexing capacities of the fractions towards copper(II) and iron(III) lie in the 0.067-0.240 pgmg-1 and 0.094-0.240 fig mg-1 ranges. The complexing capacity increased with decreasing molecular weight of the fractions. Examination of the IR spectra of humic sub­ stances and their precipitates obtained after addition of excess metals revealed that the absorption band at 1710 cm-1 (carbonyl of carboxylic groups) had shifted to 1600 cm-1 (carboxylate ions), indicating the participation of carboxyl groups in the bonding of metal ions. The decreasing intensity of the DTG peak at 365°C supported this conclusion. * This work was supported financially by the Committee of Scientific Research (grant no. 739/6/90) and the Foundation for the Scientific Research in Poland (grant no. 102/43/92).

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