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Complex Reactions of Zinc With Organic Matter Extracted From Sewage Sludge¹

ABSTRACT

The organic fraction of sewage sludge, extracted with 0.1 N NaOH and separated into low and high molecular weight fulvic fractions by Sephadex G-50 gel filtration, was studied for its Zn-complexing capacity by the ion-exchange equilibrium method and infrared spectroscopy.

The number of moles of fulvic compounds complexed by 1 mole of Zn at pH 5.5 was low in the case of the high molecular weight fraction, but the low molecular weight fraction was complexed in amounts twice that stated for the high molecular weight compounds. By increasing the pH to 7.0 a 10-fold increase in amounts of low molecular weight fractions complexed by Zn was obtained. The stability constant also increased from 1.8 (pH 5.5) to 6.8 at pH 7.0 for the low molecular weight complex compounds.

The organic preparations had infrared characteristics similar to those reported earlier for polysaccharides. A shift in OH band from 3500 to 3200 cm^-1 and a sharp increase in carboxyl stretching vibration at 1650 and 1400 cm^-1, observed in the spectrograms of the Zn-complexes, indicated the formation of coordinate covalent bonds between OH groups and Zn and electrovalent linkages between COO^- and Zn, respectively.

Estimation of the free energy change (G_r) for Zn-complex reactions suggested at least two possibilities for stable Zn-complex formation.

¹ Journal Series Paper no. 898, Univ. of Georgia, College of Agr. Exp. Sta., College Station, Athens, Ga.

² Assistant Professor, Graduate Research Assistant, and Professor, respectively, Dept. of Agronomy, Univ. of Georgia, Athens, Ga. 30601.

Received for publication February 15, 1971. Accepted for publication May 13, 1971.