The process of removing excess
naturally occurring fluoride(>4 ppm) from drinking water to reduce the
prevalence and severity of health issues including skeletal fluorosis causing
bone fractures, dental fluorosis or even cancer, employs various methods of
defluoridation. One of the effective means is by dispersion of odorless and non
toxic activated alumina balls produced by heating aluminum oxide at high
temperature to function as a selective adsorbent in fluoride filters.
It is a potent fluoride filter with tunnel like pores that
aids large surface area against water thereby removing fluoride content in
excess. Activated alumina filters can
effectively reduce fluoride levels from .5 ppm to less than .1 ppm with a
fluoride uptake capacity of about 5000mg/kg. It requires an ideal pH of up to
5.5 for treatment but independent of temperature changes in order to which
approximately 95% removal rate.
The bed can be
regenerated with a solution of 2% sodium hydroxide, 5% sodium chloride and
sulphuric acid. The removal capacity of the medium has been found
around 800 mg/L of fluoride/L of Alumina. The ability of activated alumina and
efficiency of filter beds depends on many factors such as chemistry of water,
its hardness, presence of silica or boron, etc.
Activated alumina
serves many advantages such as better adsorption, strong catalytic activity, maximum
porosity, high dispersion rate and large specific surface. It can be put into
multiple roles as an absorbent, desiccant and catalyst carrier. Activated alumina defluoridates simply by behaving as the anion exchange resin. It has
wide range of applications in ethylene and propylene, hydrogen-generation,
separation of air, air drying of instruments and fluorine water treatment along
with its action in absorbing pollutant material like sulphides, HF and paraffin
in the waste gas, especially in the drinking water defluoridation.
The
fluoride coats the surface of the alumina and with time the cartridge needs to
be replaced at least once a year. The use of activated alumina in alumina filter system is an
economical and most recommended method.
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