INTERACTION OF MERCURY(II) WITH HUMIC SUBSTANCES FROM THE RIO-NEGRO (AMAZONAS STATE, BRAZIL) BY MEANS OF AN ION-EXCHANGE PROCEDURE

The aquatic humic substances (HS) investigated in this study with resp ect to their binding capability towards mercury(II) were isolated from the river Rio Negro, Amazonas State - Brazil, by means of the adsorbe nt XAD 8. Labile/inert fractions of inorganic Hg(II) complexes formed with these HS were characterized using an ion-exchange batch and colum n technique, respectively, based on Chelite S. This collector exhibits high Hg(II) distribution coefficients, K-d, up to the order of 10(4) decreasing, however, in the case of small Hg(II)/HS ratios (< 0.1 mu g Hg(II) / mg HS). The influence of different complexation parameters ( ratio of Hg(II)/HS, pH, contact time, complexing time) relevant for Hg (II) binding in aquatic environments was assessed. The Hg(II) lability in dissolved HS is mainly influenced by the mass ratio of Hg(II)/HS a nd the ageing of Hg(II)-HS species formed. This is particularly obviou s in the case of low Hg(II) loading of HS where slow transformation pr ocesses of freshly formed Hg(II)-HS species significantly decrease the ir lability, leading to incomplete recoveries (< 20%) of the total Hg( II) bound to HS.