Dye Adsorption on Expanding Three-Layer Clays - Green Chemistry for Dyes Removal from Wastewater - page 333

Table 9.1 ( Cont .)

Methods Advantages Disadvantages

Biodegradation Economically attractive,

publicly acceptable
treatment

Slow process; necessary
to create an optimal
favorable environment;
maintenance and nutri-
tion requirements

Biomass Low operating cost; good

efficiency and selectiv-
ity; no toxic effect on
microorganisms

Slow process; performance
depends on some external
factors (pH, salts); not
effective for all dyes

Anaerobic
textile-dye
bioremediation

Allows azo and other
water-soluble dyes to be
decolorized

Anaerobic breakdown yields
methane and hydrogen
sulfide

Coagulation
Flocculation

Simple; economically
feasible

High sludge production;
handling and disposal
problems

Membrane
separations

Remove all dye types;
produce a high-quality
treated effluent

High pressures; expensive;
incapable of treating large
volumes

Ion exchange No loss of sorbent on regen-

eration; effective

Not effective for all dyes,
especially disperse dye;
economic constraints

Irradiation Effective oxidation at lab scale Requires a lot of dissolved O 2

Adsorption on
activated carbons

The most effective adsor-
bent; great capacity;
produce a high-quality
treated effluent

Very expensive; ineffective
against disperse and vat
dyes; the regeneration
is expensive and results
in loss of the adsorbent;
nondestructive process

montmorillonite clay is cheaper than activated carbon, and it has a large
specific surface area and a high cation exchange capacity [14]. In addition,
clay minerals exhibit strong affinity for both cationic and anionic dyes.
However, the sorption capacity for basic dye is usually higher than for acid
dye because of the ionic charges on the dyes and clay. The adsorption of
dyes on clay minerals is mainly dominated by ion-exchange processes. This
means that the sorption capacity can vary strongly with pH.
This review presents (i) brief information on textile dyes; (ii) a criti-
cal analysis of natural and modified expanding three-layer clay minerals;
(iii) their characteristics, advantages and limitations; and (iv) discussion