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Monatshefte für Chemie - Chemical Monthly

, Volume 149, Issue 2, pp 423–429 | Cite as

Speciation and equilibria in the H+–Al3+ - polyacrylic acid system

  • Johannes LützenkirchenEmail author
  • Staffan Sjöberg
Original Paper
  • 102 Downloads

Abstract

Equilibria between Al3+ and the polyelectrolyte polyacrylic acid (PAA) were studied in 0.1 M NaCl medium at 25 °C (M = mol dm−3). The measurements were performed as precise potentiometric titrations in which OH was in most cases generated coulometrically. The total concentration of Al(III) and PAA varied within the limits 6.23 × 10−5–2.01 × 10−4 M and 7.20 × 10−4–1.12 × 10−3 M, resp., with a 4–18 fold excess of ligand. The value of − log{[H+]/mol dm−3} varied between 3 and 5–7, the upper limit set by drifting EMF potentials caused by the onset of a precipitation reaction. The constant capacitance model was utilized to model the experimental data. With the objective of finding a model as simple as possible that gives an acceptable fit to data, the two species AlPAA2+ and Al(OH)2PAA are postulated. The polyelectrolyte effect resulting in pH-dependent formation constants is demonstrated. Furthermore a comparison between the stability constant of the 1:1 complexes of Al3+ with acrylate and PAA, respectively, shows the logK value of the latter to be five units higher and is ascribed to particular properties of the polyelectrolyte.

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Keywords

Stability constants Carboxylic acids Acidity Potentiometric titrations Surface complexation modelling Constant capacitance model 

Notes

Acknowledgements

The contributions of Heinz Gamsjäger to surface complexation were early, but  will be lasting. We are grateful for the various possibilities to meet Heinz over the years and will continue to remember him as the successful scientist and friendly and sociable person he was.

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Copyright information

© Springer-Verlag GmbH Austria, part of Springer Nature 2017

Authors and Affiliations

  1. 1.Institut für Nukleare EntsorgungKarlsruhe Institute of TechnologyKarlsruheGermany
  2. 2.Department of ChemistryUmeå UniversityUmeåSweden

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