Stability Constants of Fe(III) and Cr(III) Complexes with dl-2-(2-Carboxymethyl)nitrilotriacetic Acid (GLDA) and 3-Hydroxy-2,2′-iminodisuccinic acid (HIDS) in Aqueous Solution

Abstract

The complex formation equilibria of Cr3+ and Fe3+ ions in aqueous solution with two biodegradable aminopolycarboxylate chelants (dl-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2′-iminodisuccinic acid (HIDS)) were investigated. The potentiometric data obtained at the constant ionic strengths (I) of (0.1 and 1.0) mol·dm–3 KCl and at (25 ± 0.1) °C was processed with the aid of the computer program HYPERQUAD 2008. The formation constants of the proton–chelant and metal–chelant (log KML) species (M = Fe3+ or Cr3+; L = GLDA or HIDS) were determined, and the concentration distributions of complex species in solution were evaluated for both metal ions. In various pH conditions, the interaction between the chelants (L = GLDA or HIDS) and the metal ions (M = Fe3+ or Cr3+) leads to the formation of different complexes formulated as MH2L+, MHL, ML–, M(OH)L2–, and M(OH)2L3–. The log KML values at I = 0.1 mol·dm–3 KCl (T = (25 ± 0.1) °C) were 15.27 (log KFe–GLDA), 14.96 (log KFe–HIDS), 13.77 (log KC...