Отправлено: 18.08.08 05:10. Заголовок: Volume 324, Issues 1-2, Pages 1-260 (August 2008)

Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: Effect of citric acid
Pages 85-91
Weibing Gan, Qi Liu


Abstract
Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca2+ and Mg2+ on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing of Ca2+, Mg2+ and Fe3+ with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of Ca2+ and Mg2+ cations at pH10, and at pH8 for Fe3+. It was found that hydrolyzable metal cations enhanced bitumen–kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal–citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.
Article Outline
1. Introduction
2. Materials and methods
2.1. Minerals and chemicals
2.2. Experimental methods
2.2.1. Preparation of stock suspensions for zeta potential measurement
2.2.2. Bitumen–kaolinite coagulation
2.2.3. Zeta potential measurement
2.2.4. Adsorption of multivalent metal ions on kaolinite
3. Results and discussion
3.1. Coagulation of bitumen with kaolinite
3.1.1. In the presence of Ca2+, Mg2+ and Fe3+
3.1.2. In the co-presence of the metal cations and citric acid
3.2. Zeta potentials of kaolinite and bitumen
3.2.1. Effect of multivalent metal cations
3.2.2. Effect of citric acid
3.3. Adsorption of Ca2+ and Mg2+ on kaolinite
3.4. Total potential energy of interaction between bitumen and kaolinite
4. Conclusions
Acknowledgements
References

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