COMPLEXATION OF CADMIUM(II) WITH SOIL FULVIC-ACID

Cadmium(II) complexation by a well characterized soil fulvic acid (FA) from the Okchun Metamorphic Belt were studied at pH of 6.0 in 0.1 M NaClO4 using the ultrafiltration technique. The conditional stability constants thus obtained were log K=3.90+/-0.15 and 3.99+/-0.12 L.mol-1 at fulvic acid concentrations of 101 and 226 mg.L-1 respectively. When free cadmium ion concentration was measured directly using an ion selective electrode, log K of 4.12+/-0.03 L.mol-1 was obtained. These results show that fulvic acid forms predominately 1 : 1 complex with Cd2+ ions. The maximum binding ability of this polyelectrolyte material was 0.886 mmol Cd/g FA. The average gram formula weight of fulvic acid was estimated to be 1130 daltons.