Polarographic study of the removal of cadmium(II) and lead(II) from dilute aqueous solution by a synthetic flocculant. Comparison with copper(II) and nickel(II)

The aim of this work was to assess the possible removal of cadmium(II) or lead(II) from dilute aqueous solution by a synthetic flocculant used in the water treatment field. The cadmium(II) or lead(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 lead(II) at pH 6.0 was estimated to be 6.3 mmol Pb(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/lead(II) complex species was determined using the method proposed by Ruzic [(1982) Anal. Chim. Acta 140, 99–113] assuming that only the 1:1 complex species was formed: log K′=5.3±0.2 at pH 6.0. Both values decreased with the pH of the aqueous medium. The results were compared to those previously obtained in the same conditions with copper(II) and nickel(II) [(2000) Wat. Res. 34, 455–462]. It appeared that the binding properties of PAA 3×106 increased in the following order, depending on the metal ion: Ni(II)