Gamma-ray irradiation impact of humic substances on apparent formation constants with Cu(II)

Abstract

ABSTRACT Aqueous solution samples of humic acid and fulvic acid were irradiated with gamma-rays in the dose range of 0–500 kGy at two dose rates, 0.1 and 1 kGy/h. The brownish solutions discolored with 500 kGy irradiation indicating degradation by radiolysis, and the index of degree of humification (as the absorbance ratio at 400 nm and 600 nm) was studied using UV-Visible spectroscopy. Apparent formation constants of Cu(II) with humic substances (HSs) in 0.1 M NaClO4 were determined at 298 K by potentiometric titration using Cu ion selective electrode (ISE), and the effect of gamma irradiation on the constants is herein discussed. To calculate formation constants, the acid dissociation constants of HSs were also measured by potentiometric titration and used as the degree of dissociation. Though the concentration of carboxylic groups decreased drastically with high radiation exposure, no significant change in apparent formation constants was found.