How to Absorb Fluoride With Activated Alumina

Activated alumina demonstrates the ability to bind many of the common ions found in drinking water, such as chloride ions and fluoride ions. The alumina consists of small, porous particles of aluminum oxide. When ions such as fluoride contact the alumina, they tend to "stick" or bind to its surface. As such, activated alumina effectively acts as a fluoride filter. The extent to which activated alumina will remove fluoride from an aqueous solution depends on several factors, such as the pH of the solution and the identity and concentration of other ions that may be present.

Things You'll Need

• Dust mask
• 50-cc syringe
• Clamp
• Ring stand
• Cotton
• Distilled water
• 10 g activated alumina, 40-60 mesh size
• 2 small cups

Instructions

1. Remove the plunger and needle from a 50-cc syringe and secure the syringe in a clamp attached to a ring stand.

2. Place a small piece of cotton in the bottom of the syringe. Pack the cotton down with the eraser end of a pencil, if necessary.

3. Fill the syringe to about the 30-mL mark with activated alumina with a mesh size of 40 to 60. Shake the syringe back and forth to settle the powder in the syringe.

4. Place a cup under the alumina and wet the column by filling the syringe to the 50-cc mark with distilled water. Continue this process until water begins to flow out of the tip of the syringe. Plug the syringe by replacing the protective cap from the needle. Do not allow the liquid level in the syringe fall below the level of the alumina; doing so may form air pockets in the column and reduce its effectiveness.

5. Replace the collection cup below the syringe with a clean cup, then pour the fluoride-containing solution through the column in small increments. When finished, the cup will then contain defluoridated water.

Tips & Warnings

• For maximum fluoride removal, adjust the pH of the fluoride solution to 5.0 before pouring through the alumina-packed column.

• Alumina dust particles irritate the lungs. The use of a dust mask is recommended whenever handling powdered alumina.

References

• Scholar's Mine: "Colloids and Surfaces A"; Fluoride Adsorption onto Activated Alumina: Modeling the Effects of pH and Some Competing Ions; Y. Tang, et al.; 2008
• San Jose State University: Adsorption Principles
• "Evaluation of an Activated Alumina Sorption System for Removal of Fluoride from Water"; U.O. Onuoha; May 1983

Resources

• Mallinckrodt Baker, Inc.: Material Safety Data Sheet - Aluminum Oxide