Dispersion of Colloidal Alumina using a Rhamnolipid Biosurfactant

Dispersability of colloidal alumina in water has been studied using a rhamnolipid containing biosurfactant. Zeta potential measurements revealed that the surface charge of alumina was altered due to adsorption of the biosurfactant and the iso‐electric‐point of alumina shifted from pH 9 to 6.3. Sedimentation tests indicated that the alumina suspension was completely dispersed for 3–5 hours in the presence of biosurfactant after which some settling was observed. Stability of the suspension in the time period studied was found to be independent of pH. Capillary suction time measurements showed that the alumina suspension was dispersed in the presence of the biosurfactant and varied with pH. Maximum dispersion is obtained in the pH range of 3.5–5 and 7–11 while a minimum is obtained around pH 6. This behavior is consistent with the changes in zeta potential in the presence of the biosurfactant and thus capillary suction time measurements appeared to be more reliable than the sedimentation tests. Optimization studies showed that about 60 mg/g of biosurfactant was necessary for best dispersion and dispersion could be done up to 40% solids. The application of a natural biosurfactant for dispersing colloidal alumina has been demonstrated.

Keywords:

• Alumina
• biosurfactant
• rhamnolipid
• dispersion
• capillary suction time
• zeta potential

Acknowledgments

The author wishes to acknowledge the help of Ms. Mohini Acharya and Ms. N. Shyamala in carrying out some of the experiments. Thanks to Sasol North America, Inc., R. T. Vanderbilt Company, Inc., and Jeneil Biosurfactant Co., for donating the alumina, APMA, and biosurfactant, respectively, used in this work. The work also was partially funded by a research grant from the Council of Scientific and Industrial Research, New Delhi, India.