Adsorption of dissolved aluminum on sapphire-c and kaolinite: implications for points of zero charge of clay minerals

Geochemical Transactions

Research Article

Rohan Weerasooriya¹  Johannes Lützenkirchen²  Volker Metz²  Remi Marsac²  Frank Heberling²  Ahmed Abdelmonem³ 

[1] Department of Soil Science, University of Peradeniya, Peradeniya, Sri Lanka;Karlsruhe Institute of Technology (KIT) Institut für Nukleare Entsorgung, INE Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany;Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research - Atmospheric Aerosol Research – (IMKAAF), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany;

关键词: Isoelectric point;    Streaming potential;    Second harmonic generation;    Electrophoretic mobility;    Kaolinite;    Sapphire;    Alumina;   

DOI  :  10.1186/1467-4866-15-9

 received in 2013-12-12, accepted in 2014-06-12,  发布年份 2014

来源: Springer

【 摘 要 】

We have studied the impact of dissolved aluminum on interfacial properties of two aluminum bearing minerals, corundum and kaolinite. The effect of intentionally adding dissolved aluminum on electrokinetic potential of basal plane surfaces of sapphire was studied by streaming potential measurements as a function of pH and was complemented by a second harmonic generation (SHG) study at pH 6. The electrokinetic data show a similar trend as the SHG data, suggesting that the SHG electric field correlates to zeta-potential. A comparable study was carried out on kaolinite particles. In this case electrophoretic mobility was measured as a function of pH. In both systems the addition of dissolved aluminum caused significant changes in the charging behavior. The isoelectric point consistently shifted to higher pH values, the extent of the shift depending on the amount of aluminum present or added. The experimental results imply that published isoelectric points of clay minerals may have been affected by this phenomenon. The presence of dissolved aluminum in experimental studies may be caused by particular pre-treatment methods (such as washing in acids and subsequent adsorption of dissolved aluminum) or even simply by starting a series of measurements from extreme pH (causing dissolution), and subsequently varying the pH in the very same batch. This results in interactions of dissolved aluminum with the target surface.A possible interpretation of the experimental results could be that at low aluminum concentrations adatoms of aluminum (we will refer to adsorbed mineral constituents as adatoms) can form at the sapphire basal plane, which can be rather easily removed. Simultaneously, once the surface has been exposed to sufficiently high aluminum concentration, a visible change of the surface is seen by AFM which is attributed to a surface precipitate that cannot be removed under the conditions employed in the current study.In conclusion, whenever pre-treatment or the starting point of an experiment favor the dissolution of aluminum, dissolved Al may remain in the experimental system and interact with the target surfaces. The systems are then no longer pristine and points of zero charge or sorption data are those of aluminum-bearing systems.

【 授权许可】

CC BY   
© Lützenkirchen et al.; licensee BioMed Central Ltd. 2014. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.