Activated alumina is manufactured from aluminium hydroxide by dehydroxylating
it in a way that produces a highly porous material; this material can have
a surface area significantly over 200 m²/g. The compound is used as a
desiccant and as a filter of fluoride, arsenic and selenium in drinking water.
It is made of aluminium oxide, the same chemical substance as sapphire and ruby.
It has a very high surface-area-to-weight ratio, due to the
many "tunnel like" pores that it has. Uses
= Catalyst applications = Activated alumina is used for a wide
range of adsorbent and catalyst applications including the adsorption of
catalysts in polyethylene production, in hydrogen peroxide production, as a
selective adsorbent for many chemicals including arsenic, fluoride, in sulphur
removal from gas streams. = Desiccant =
Used as a desiccant, it works by a process called adsorption. The water in
the air actually sticks to the alumina itself in between the tiny passages as
the air passes through them. The water molecules become trapped so that the air
is dried out as it passes through the filter. This process is reversible. If
the alumina desiccant is heated to ~200°C, it will release the trapped
water. This process is called regenerating the desiccant.
= 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 Jaipur
region of India, there is enough fluoride in the water to cause
fluorosis. Activated alumina filters can easily reduce fluoride levels from 0.5
ppm to less than 0.1 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
are filtered more effectively too. Ideal pH for treatment is 5.5, which allows
for up to a 95% removal rate. Activated alumina, when used as a
fluoride filter, can be regenerated by a solution of lye, sulphuric acid, or
alum2). The fluoride uptake capacity of activated alumina can be up to 5000
mg/kg. The FUC can be determined as follows:
V.K.Chhabra’s method: 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 produce 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. = Vacuum systems =
In high vacuum applications, activated alumina is used as a charge material in
fore-line traps to prevent oil generated by rotary vane pumps from back streaming
into the system. = Biomaterial =
Its mechanical properties and non-reactivity in the biological
environment allow it to be a suitable material used to cover surfaces in
friction in body prostheses. See also
Activated carbon Silica gel
Synthetic Magnesium Silicate References
^ Ronald Vane. "Reducing Oil Back streaming in Electron Microscopes".
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