Interaction between selenium derivatives and heavy metal ions: Cu2+ and Pb2+

The interaction between selenium derivatives (sodium selenate, sodium selenite, selenourea, and DL-selenomethionine) and heavy metal ions (Cu2+ and Pb2+) was studied by polarography in aqueous solutions. Selenate does not interact with the selected ions; while selenite form a 1:1 soluble complex with Pb2+ (Kf = 4.9 x 10(4)) and a poorly soluble salt with Cu2+ (K-ps = 3.8 X 10(-9)). DL-Selenomethionine forms a colloidal complex with Cu2+ (K-f = 1.4 X 10(4)), while does not interact with Pb2+. Pb2+ ions also display a poor affinity for selenourea: the system is not stable, because oxidation and hydrolysis of selenourea and precipitation of lead (II) selenide can occur. In the presence of Cu2+, selenourea forms a complex. The potential for the oxidation of selenourea and the reduction of Cu2+ ions originated mixed currents (cathanodic wave). For comparison also systems containing thiourea and methionine were considered. (C) 1997 Academic Press.