Complex formation of nickel(II) ions with citric acid in aqueous solution: a potentiometric and spectroscopic study

Abstract

From a potentiometric and visible spectrophotometric study of the nickel(II)-citric acid (H3L) system in the pH range 3-6, four complexes, NiL-, NiHL, NiH2L+ and NiL24-, have been characterized. Stability constants for the formation of these complexes have been determined at 25°C in 0.1 mol dm-3 KCl. The results suggest that the hydroxy group of citric acid is coordinated in the nickel-citrate complexes.

Stripping chronopotentiometry at scanned deposition potential (SSCP). Part 6: Features of irreversible complex systems

“…8 shows a typical set of curves: for a citrate concentration of 2.9 · 10 À5 mol dm À3 , the measured limiting s ratio, s NiL /s Ni , is 0.3. This compares very well with the calculated value for the lability criterion, L, of 0.4 (with k a = 4.05 · 10 5 dm 3 mol À1 s À1 , K = 10 5.35 dm 3 mol À1 [35], D M = D ML = 6.9 · 10 À10 [17], d = 2 · 10 À5 m). The slope of the SSCP wave is not changed in the presence of ligand, but as noted above, at this degree of irreversibility this observation is no indicator of an invariant charge transfer rate.…”

Microbially enhanced chemisorption of nickel into biologically synthesized hydrogen uranyl phosphate: A novel system for the removal and recovery of metals from aqueous solutions

“…The composition of uranyl-citrate complexes was studied by 1 H-and 13 C-nuclear magnetic resonance (NMR) spectroscopy and the existence of the different types of complexes at different pH, as reflected in Rajan and Martell's scheme (Rajan and Martell, 1965), was confirmed (Bramley et al, 1965;Nunes and Gil, 1987). Nickel-citrate complexes were studied by potentiometric and spectroscopic methods (Hedwig et al, 1980;Still and Wikberg, 1980), but formation of polymeric complexes, analogous to those of uranyl-citrate, was not observed. These differences in the pH-related stability of the Ni-citrate and U-citrate complexes, respectively, explain the selective removal of Ni from the Ni/HUP-loaded columns, under the conditions used.…”

Simultaneous biodegradation of Ni–citrate complexes and removal of nickel from solutions by Pseudomonas alcaliphila

“…In the pH range 5-8, Ni and citrate are present predominantly as a mononuclear bidentate [NiCit] À complex (Hedwig et al, 1980). Above pH 8, the complex exists in a tridentate form involving the hydroxyl group of citrate, and above pH 9, it exists in a polymeric form [Ni 4 (OH)Cit 3 ] 5À (Still and Wikberg, 1980;Strouse et al, 1977 complex can be biodegraded by bacteria; however, the tridentate and polymeric Ni-citrate complexes are recalcitrant to biodegradation (Francis et al, 1996).…”