Water fluoridation is a double edged sword. In the U.S. fluoride has been added to most water streams in order to help prevent tooth decay. (I should mention fluoride naturally occurs in a lot of drinking water sources throughout the world). However fluoride can be damaging to bones at higher doses and it can even be fatal if you take in large quantities of it.
The desiccant activated alumina plays a very important role in reducing fluoride levels in water. By doing this activated alumina leaves enough fluoride in water for people to receive its potential health benefits while at the same time it makes sure that health damaging amounts of fluoride do not remain in drinking water.
In 1994 the World Health Organization recommended that fluoride levels in water should be contained from 0.5-1mg/L. Fluoride levels above 1mg should undergo defluoridation, which can be done three different ways: with chemicals and precipitation, with membrane based technologies, or with ion exchange and adsorption.
A lot of times these methods are used in combination. For example, when fluoride levels are above 15ppm using lime which falls under the chemicals and precipitation category should be used because they can handle the high levels of fluoride. Once that level is lowered using lime, activated alumina, which falls under the adsorption category, should be used to reduce to the fluoride content to below 1ppm since activated alumina can purify water up to 99%.
How does Activated Alumina work in removing fluoride from water?
Activated alumina adsorbs fluoride because fluoride is attracted to alumina. It wants to make aluminum fluoride which it does once it comes into contact with activated alumina. The alumina fluoride will remain stuck to the alumina beads so long as the pH level of the water remains below 6. If water’s pH remains lower than a 6 the effectiveness of activated alumina starts to be reduced. It can also allow aluminum to get in your water, although aluminum does not typically dissolve in water.
Note: Reverse osmosis is used to remove aluminum from water and so can certain distillers. Aluminum does not typically get into water because water has a difficult time dissolving it.
It’s recommended that you pre-treat activated alumina with aluminum sulfate before you use it in order to improve the first adsorption runs. After pretreatment it’s important to remember that adsorption reactions with activated alumina are flow-rate dependent. Although activated can handle high flow rates and still work, its adsorption capacity is reduced and this could lead to having to do additional cycles. Doubling the flow rate allowed 33% more fluoride through the activated alumina beds, thus reducing activated alumina effectiveness in adsorbing fluoride.
There is a possibility of other ions interfering with the adsorption process when working with activated alumina, this is due to water in the U.S. containing other ions. These ions are usually sodium chloride, sodium sulfate, and sodium bicarbonate. Sodium chloride and sodium sulfate do not interfere with the adsorption process, but sodium bicarbonate can reduce the capacity of activated alumina between 33% and 70%.
Activated alumina like most desiccants can be regenerated. Sodium hydroxide, aluminum sulfate, or sulfuric acid are applied to a lye solution with the activated alumina, allowing the adsorbent to be regenerated. Once regenerated activated alumina can continue to be re-used, and when used properly activated alumina can last years.
Activated alumina is essential in removing fluoride in water up to 99% and making water safe for people to drink.
Post time: Aug-05-2019