Competition of Ca(II) and Mg(II) with Ni(II) for Binding by a Well-Characterized Fulvic Acid in Model Solutions

Abstract

Competition of Ca(II) and Mg(II) with Ni(II) ions for binding sites of a well-characterized fulvic acid (FA) in model solutions at constant pH and ionic strength was investigated. The Competing Ligand Exchange Method with Chelex-100 and dimethyl glyoxime as the competing ligands was employed to measure the rate of free Ni2+ ion release using graphite furnace atomic absorption spectrometry and adsorptive cathodic stripping voltammetry, respectively. The Windermere Humic Aqueous Model was used to predict the effect of competition of Ca(II) and Mg(II) on the binding of Ni(II) by the FA. The results show that the presence of high concentrations of Ca(II) and Mg(II) in model solutions has considerable effects on the binding of Ni(II) by the FA. Since the concentrations of Ca(II) and Mg(II) used are 4 orders of magnitude higher than those of Ni(II), Ca(II) and Mg(II) can outcompete Ni(II) for sites where electrostatic interactions dominate, resulting in Ni(II) forming weak Ni(II)−FA complexes that are labile. The significance is that in freshwaters containing humic substances and trace quantities of nickel and major cations, Ca2+ and Mg2+, the competition of Ca2+ and Mg2+ with Ni2+ for binding sites of humic substances produces weak Ni(II)−humate complexes that are labile, releasing free Ni2+ ions.

Ecological impacts of lead mining on Ozark streams: Toxicity of sediment and pore water

“…The strong association of toxicity with Ni concentrations reflects the occurrence of high Ni concentrations in the highly toxic sediment (and pore water) from Strother Creek. carbonates (Lee et al, 2005) and due to competitive displacement of Ni 2+ from strong binding sites on organic ligands by high concentrations of calcium and magnesium (Mandal et al, 2000). Mandal et al (2002) reported that free Ni 2+ predominated in waters draining another mining area (Sudbury, Canada) that has similar calcium-and magnesium-rich geology.…”

Speciation of nickel in surface waters measured with the Donnan membrane technique

“…In earlier studies slow dissociation kinetics 80 of natural Ni-DOM complexes have been demonstrated [6,10,[13][14][15][16], however no data were 81 found on association kinetics. We used the Donnan speciation technique [17], a method which 82 minimizes the disturbance of the equilibrium composition in the test solution and which does 83 not rely on a priori knowledge of the conditional stability constant of a competing ligand.…”

Competitive effect of iron(III) on metal complexation by humic substances: Characterisation of ageing processes

“…Pertinent studies hitherto published were mostly concerned with the displacement of divalent trace metals (Ni, Cu, Zn, Cd, Pb) by calcium or magnesium (e.g., Buffle et al, 1980;Hering and Morel, 1988;Cabaniss and Shuman, 1988;Cao et al, 1995;Van den Hoop et al, 1995;Mandal et al, 2000), several papers dealt with the competitive effect of aluminium (e. g., Susetyo et al, 1990;Pinheiro et al, 2000;Lippold et al, 2005). There are only few investigations on the influence of iron(III), although it is the most abundant trivalent electrolyte in terrestrial waters, and expected to be very effective in out competing other metals.…”