engleski

Characterization of acid-base properties of two gibbsite samples by a multidisciplinary experimental approach

Two different gibbsite samples, one commercial and one synthetized, were studied in an interlaboratory comparison with respect to their superficial acid-base properties. In addition to a thorough characterization of the solids, several methods were used for the determination of the pH dependant surface charge: potentiometric titrations, zeta-potential measurements, and Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) for the measurement of nitrate counter-ions. Isoelectric points of 9-10 and 11.3 were found for the commercial sample and synthesized sample, respectively. Results showed large differences in the charging behavior and in the titration kinetics for the two samples. A detailed literature review also showed such a large disparity. The amount of titrant added in each aliquot has a large influence on the titration curves, while the waiting time is not a major experimental feature determining the experimental surface charge. However, a number of open questions and contradictions remain. We suggest a number of processes, which can explain the observed behavior.

Gibbsite; surface charge; zeta-potential; acid-base titration; mass titration; MUSIC model; surface complexation; ATR-FTIR

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