Fluoride adsorbent
Activated alumina is also widely used to remove fluoride from drinking water. In the US, there are widespread programs to fluoridate drinking water. However, in certain regions, such as the Rajasthan region of India, there is enough fluoride in the water to cause fluorosis. A study from the Harvard school of Public Health found exposure to high levels of fluoride as a child correlated with lower IQ.[1]
Activated alumina filters can easily reduce fluoride levels from 10 ppm to less than 1 ppm. The amount of fluoride leached from the water being filtered depends on how long the water is actually touching the alumina filter media. Basically, the more alumina in the filter, the less fluoride will be in the final, filtered water. Lower temperature water, and lower pH water (acidic water) are filtered more effectively too. Ideal pH for treatment is 5.5, which allows for up to a 95% removal rate.
As per researches conducted by V.K.Chhabra, Chief Chemist (retd.) P.H.E.D. Rajasthan, activated alumina, when used as a fluoride filter, under field conditions can best be regenerated by a solution of lye (sodium hydroxide; NaOH), sulfuric acid (H2SO4).
The fluoride uptake capacity (FUC) of commertial activated alumina can be up to 700 mg/kg. The FUC using V.K. Chhabra's method can be determined as follows:
Fluoride solution: Dissolve 22.1 g anhydrous NaF in distilled water and dilute to 1,000 mL.
1 mL = 10 mg fluoride.
10 mL/L = 100 mg/L fluoride.
Procedure:
To one litre of simulated distilled water containing 100 mg/L of fluoride, agitate at 100 rpm using the jar test machine. Add 10 g of the AA under test. After one hour, switch off the machine and take out the solution. After 5 minutes, carefully decant the supernatant solution and determine the fluoride. Calculate the difference between the original and treated water fluoride concentration. Multiply the difference by 100 to give the fluoride uptake capacity of AA in mg/kg.