Environmental Engineering Reference
In-Depth Information
of adsorption mechanisms involved. The adsorption mechanisms, capaci-
ties, thermodynamics, and kinetics are given as text or tables. It should
be remembered that comparisons in these tables are necessarily limited
because of differences in surface area, pore structure, functional groups,
modification processes, and experimental conditions. Therefore, the reader
is encouraged to refer to original articles for more detailed information.
9.2
Classification of Dyes
Textile dyes represent a category of organic compounds and are mainly
classified in two different ways: (1) based on their application character-
istics (i.e., C.I. Generic Name such as acidic, basic, direct, disperse, mor-
dant, reactive, sulphur dye, pigment, vat, azo insoluble), and (2) based on
their chemical structure (i.e., C.I. Constitution Number such as nitro, azo,
carotenoid, diphenylmethane, xanthene, acridine, quinoline, indamine,
sulphur, amino and hydroxy ketone, anthraquinone, indigoid, phthalo-
cyanine, inorganic pigment, etc.). Table 9.2 shows the characteristics of
textile dyes. They are also classified as anionic, cationic, and nonionic dyes
[5,7,15]. Cationic dyes are basic dyes, while the anionic dyes include direct,
acid, and reactive dyes [16,17]. The literature on adsorption of cationic and
anionic dyes by natural and modified clays has recently been expanding.
9.2.1 Anionic Dye
Anionic dyes are used with silk, wool, polyamide, modified acrylic and
polypropylene fibers, and are the most varied class of dyes. Examples are
azoic, anthraquinone, triphenylmethan and nitro dyes. They possess com-
mon features of being water-soluble, having ionic substituents, possessing
a negative charge, and having harmful effects on humans [21,22]. Some of
the adsorption studies by clay minerals include: the removal of acid fuch-
sin (AF) by sodium montmorillonite [23], acid green B and direct pink 3B
by organophilic montmorillonite [24]; Congo red (CR) by natural, thermal
activated, and acid activated bentonite [25]; and Acid scarlet, Acid tur-
quoise blue, and Indigo carmine by organo-bentonite [26].
9.2.2 Cationic Dyes
Cationic dyes are used in acrylic, wool, nylon and silk dyeing, have a posi-
tive charge, and are known as basic dyes. Examples are azo and methane
dyes, anthraquinone, di- and tri-arylcarbenium and phthalocyanine dyes,
and various polycarbocyclic and solvent dyes [21]. Depending on aromatic
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