Anodic stripping voltammetric study of the lability of Cd, Pb, Cu ions sorbed on humic acid particles

Abstract

The sorption of Cd, Pb and Cu by humic acid particles has been studied at μg l −1 levels using A.S.V. on a Hg film electrode as the measuring technique. The variables examined included amount of solid present (0.01–0.2% w/v), initial metal ion concn (10–100 μg l −1), systems pH (5.3, 6.35, 8.15) and base electrolyte composition. The calculated capacity for specific adsorption of the metal ions was a few mmol M 2+ kg −1, or less. The apparent lability of part of the sorbed material was examined by analysing the base solution before and after filtering, and by adding Chelex 100 particles to the suspension. Some sorbed Cd 2+ was A.S.V. labile, another fraction transferred to the resin. The effect of solution reactions on uptake was studied by making the 1 M CH 3COONa base solution 0.2 M in a range of Na + salts (8 different anions), or in carboxylic acid content (5 acids) or in compounds having S-type bonding groups. Formation of complex ions in solution altered the extent of metal ion uptake, and in the case of Cu A.S.V. peak size, shape and position were varied. It is suggested that natural waters containing suspended matter should be analysed by A.S.V. “as received”, as well as after filtration since response differences provide guidance in respect to the lability of sorbed ions.