Adsorption of lead (II) on mercury electrodes from chloride-bromide mixtures of high ionic strength

✍ Scribed by Marina Zelić; Marko Branica

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 550 KB
• Volume: 4
• Category: Article
• ISSN: 1040-0397
• DOI: 10.1002/elan.1140040604

✦ Synopsis

The adsorption of lead (11) from chloride-bromide mixtures of a high ionic strength (I=4 mol/L) to mercury electrodes was studied using square wave voltammetry, differential, and normal pulse polarography. The presence of excess chloride ions in the solution prevents additional surface complexation of PbBr, with previously adsorbed free bromide ions and the formation of PbBr; at the mercury drop. Adsorption effects are highly pronounced, even when PbRr," makes less than 1% of dissolved metal, indicating that a mixed-ligand species could be attached to the electrode. It is possible to explain nearly all experimental results by the surface activity of both PbBr, and a mixed-ligand complex PbBr,Cl;: m y WORDS: Lead, speciation, adsorption.

IATRODUCl7ON

Tn the early sixties, while studying the absorption spectra of lead (II), Spiro and Hume [l] managed to obtain clearcut evidence of the presence of mixed chloride-bromide complexes in solution. Ten years later, Fedorov and coworkers [21 determined stability constants of all lead (11) species, simple and mixed, appearing in corresponding chloride-bromide mixtures at different ionic strengths up to I = 4 mol/L. Their results, based on potentiometric measurements, together with those obtained later by Byrne and Young [31 from W absorbance observations, indicate that formation constants pa, of all PbCl,Br, species are in good agreement with statistically expected values [41 except p 11, which is slightly higher.

Corresponding polarographic/voltammetric results are lacking. It is not surprising if complications caused by lead (TI) adsorption on mercury electrodes are taken into account. PbCl; [5, 61 is "extracted" from chloride 'To whom correspondence should be addressed.