Specialized
activated alumina were designed for the
purification of the bark and needles of Pacific
Yew trees harvested for taxane compounds
clinically important in the treatment of breast
and ovarian tumors. Taxanes include paclitaxel (Taxol)
and docetaxel (Paclitaxel). In order to obtain
maximum yield of the taxane drugs, it was
necessary to remove the color pigments.
Therefore, modifications were made to the pore
size, the particle distribution and the pH of
this designed alumina. Through extensive trial
the best activated alumina for taxane isolation
and purification was found to be a wide pore
material with an average dp50 particle
distribution of 50 microns.
The result has
been that this same specialized activated
alumina, originally developed for purifying
taxane materials used for the treatment of
cancer provides the textile industry with a
superior decolorizing agent for the removal of
dyes and other colored waste materials in water
effluents. Dyes are chemicals, which on binding
provide materials with color. Dyes are ionic,
aromatic organic compounds with structures
including aryl rings possessing delocalized
electron systems. Dyes used by the textile
industry are largely synthetic and are derived
from coal, tar and petroleum based intermediates.
The color of a dye is provided by the presence
of a chromophore group, which is a radical
configuration consisting of conjugated double
bonds containing delocalized electrons.
The primary
classification of dyes is based on the fibers to
which they can be applied and the chemical
nature of each dye determines the fibers for
which the dye has affinity. Acid dyes are water
soluble anionic compounds applied to nylon,
wool, silk and some modified acrylic textiles in
an acidic medium. They have one or more sulfonic
or carboxylic acid groups in their molecular
structure. The dye fiber affinity is the result
of ionic bonds between the sulfonic acid part of
the dye and the basic amino groups in the wool,
silk and nylon fibers. There are more than
100,000 commercially available dyes, with over 7
x 105 tons of dyes produced annually. The
release of large quantities of dyes into water
by textile industries is a major environmental
waste issue. It has been estimated that about 9%
of the total amount (450,000 tons) of dyestuffs
produced in the world are discharged in textile
wastewater. Untreated or partially treated
effluents from other industries such as paper,
plastic leather, cosmetic, woolen and carpet
industries also contribute a heavy pollution
burden.
Reactive dyes
are water soluble, anionic dyes requiring
relatively simple dyeing methods. Reactive dyes
have largely replaced direct, azoic and vat dyes
and are the largest dye class in the United
States. The most common class of dyes and
pigments are azo and anthraquinone colorants,
and represent about 90% of all organic
colorants. The dyes form covalent bonds with the
fiber and become part of the fiber.
The greatest
environmental impact from discharged dyes lies
in their adsorption and reflection of sunlight.
Dyes placed into wastewater effluent interfere
with the growth of bacteria which biologically
degrade the dyes, and then hinder photosynthesis
in aquatic plants. Furthermore, the anaerobic
breakdown of some dyes leads to the production
of toxic amines. Add to this the fact that at
concentrations as low as 0.005 parts per million
dyes can be visible in water and one has a major
environmental problem. Indeed it is the presence
of color which is the telltale sign alerting to
this environmental issue.
Adsorption has
become the most effective method for the
decolorization of textile wastewater.
Traditionally, activated carbon was the most
commonly used adsorbent. Activated alumina has a
major advantage over carbon, in that it can be
reactivated at a temperature of 400 C and
reused. As such activated alumina has recently
become the adsorbent of choice for the textile
industry.
Variables which
can affect the degree of adsorption include the
molecular volume of the dye, its planarity and
its ability to bind to the adsorbent. The
mechanism of color removal can be described in
four steps
-
migration
of the dye molecules from the solution to
the film around the particle
-
diffusion
through the liquid film to the surface
-
intraparticle diffusion
-
adsorption
on an active site
The adsorption
of dyes is influenced by many factors including
the dye/adsorbent interaction, initial dye
concentration, sorbent surface area, particle
size, temperature, pH and contact time.
Physical
adsorption occurs when weak interparticle bonds
exist between the adsorbate and adsorbent. Such
bonds include van de Wall, hydrogen and
dipole-dipole forces. Chemical adsorption is
based upon strong interparticle bonds which
occur due to the exchange of electrons such as
with covalent and ionic bonds.
The advantage
for using activated alumina to bind and
decolorize dyes lies in the amphoteric
properties of alumina. Both acid and basic dyes
are able to bind onto the same particle. This
unique property of our decolorization alumina
provides a benefit which makes this special
activated alumina unheralded in its ability to
decolorize materials.
The use of this
activated decolorization alumina and adsorption
for decolorization of dyes and cleanup of
textile wastewater discharge has in a very short
time moved from curiosity to manufacturing
guideline.
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