The removal of copper (II) and nickel (II) from dilute aqueous solution by a synthetic flocculant: a polarographic study of the complexation with a high molecular weight poly(acrylic acid) for different pH values

The aim of this work was to assess the possible removal of copper (II) or nickel (II) from dilute aqueous solution by a synthetic flocculant used in the water treatment field. The copper (II) or nickel (II) complex formation with the 3×106 g mol−1 average molecular weight poly(acrylic acid) (PAA 3×106) was examined at pH 6.0, 5.0 and 4.0 successively using differential pulse polarography as an investigation mean. The complexing capacity Cc of the polyacid towards copper (II) at pH 6.0 was estimated to be 5.8 mmol Cu (II)/g PAA 3×106 in the operative conditions considered here (NaNO3 0.1 mol l−1; 25°C). The conditional stability constant of the PAA 3×106/copper (II) complex species was determined using the method proposed by Ruzic (1982) assuming that only the 1:1 complex species was formed: log K′=5.2± 0.2 at pH 6.0. Both values decreased with the pH of the aqueous medium. Whatever the pH considered, all the values of Cc and log K′ obtained with nickel (II) were significantly lower than those obtained with copper (II); this confirmed the conclusions of the previous potentiometric study of the PAA 3×106 complexation properties (Morlay et al., 1998).