Complexation of Cadmium() with Soil Fulvic Acid : Effect of pH and Fulvic Acid Concentration

摘要

The complexation of cadmium(￥±) with a well characterized local soil fulvic acid was investigated at different solution pH and fulvic acid concentration using ion selective electrode. The stability constants were determined using a continuous distribution model based on Scatchard Plot; this model takes into consideration the diversitv of cation binding sites on a naturally occurring organic macromolecules even if the nature of the binding sites may not be known. The mean value of logKi(￥ì) was found to increase at higher pH(pH 4.0: ￥ì=3.79??0.74 l mol-1; pH 6.0: ￥ì=4.51??0.78 l mol-1), and in more dilute fulvic acid concentration([FA] = 50 mgl-1: ￥ì=4.16??0.60 l mol-1; [FA]=151 mgl-1: ￥ì= 3.75??0.56 l mol-1). The intrinsic constant(logKint) for binding at the strongest site was measured to be around 4.72 l mol-1 at both pH4.0 and 5.0, but was found to be increased to 6.03 l mol-1 when pH was 6.0.