Formation and stability of binary complexes of divalent ecotoxic ions (Ni, Cu, Zn, Cd, Pb) with biodegradable aminopolycarboxylate chelants (dl-2-(2-carboxymethyl)nitrilotriacetic acid, GLDA, and 3-hydroxy-2,2′- iminodisuccinic acid, HIDS) in aqueous solutions

摘要

The protonation and complex formation equilibria of two biodegradable aminopolycarboxylate chelants {dl-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2′-iminodisuccinic acid (HIDS)} with Ni 2+, Cu2+, Zn2+, Cd2+ and Pb 2+ ions were investigated using the potentiometric method at a constant ionic strength of I = 0.10 mol·dm-3 (KCl) in aqueous solutions at 25 ± 0.1 C. The stability constants of the proton-chelant and metal-chelant species for each metal ion were determined, and the concentration distributions of various complex species in solution were evaluated for each ion. The stability constants (log10 K ML) of the complexes containing Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ ions followed the identical order of log10 K CuL > log10 K NiL > log10 K PbL > log10 K ZnL > log10 K CdL for either GLDA (13.03 > 12.74 > 11.60 > 11.52 > 10.31) or HIDS (12.63 > 11.30 > 10.21 > 9.76 > 7.58). In each case, the constants obtained for metal-GLDA complexes were larger than the corresponding constants for metal-HIDS complexes. The conditional stability constants (log10 $$ K-{\text{ML}}^{'} $$) of the metal-chelant complexes containing GLDA and HIDS were calculated in terms of pH, and compared with the stability constants for EDTA and other biodegradable chelants. © 2012 Springer Science+Business Media New York.