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Abstract
The complexation of mixed ligand solutions with Cu(II) and Ca(II) is studied. The systems contain fulvic acids as natural ligand, and a phosphonic acid (nitrilotris(methylenephosphonic acid), ATMP, or 1-hydroxyethane-1, 1′-diphosphonic acid, HEDP) as anthropogenic ligand. The two cations were chosen for their high environmental interest and their extreme complexation behaviors with the two phosphonic acids. Complexation properties are determined with pH titration data in the natural water pH-range (5 to 9), and with Ionic Selective Electrode experiments at pH 5. First, fulvic acids protometric and complexing properties are studied. Fulvic acids/copper complexation constants are determined whereas calcium complexation constants are too low to be calculated with the methods used. The mixed ligand solutions are studied to determine their complexing properties with each cation. The protometric properties of the two kinds of ligand (natural and anthropogenic) do not interfere. We observe only a weak interaction between their binding properties with copper, under our experimental conditions, similar to those encountered in the environment. Electric charges beared by the complexed species might explain this slight synergy.