Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 376

be involved in chemical bonding. Brown et al. [172] reported that the pre-
cise composition of peat formed depends on the nature of the vegetation,
regional climate, acidity of the water and the degree of metamorphosis.
Peat is known to have excellent ion exchange properties similar to nat-
ural zeolites. Indeed, because of its polar character andcellular structure,
peat can effectively remove dyes from solution [173-177,131,178,179,16].
Peat is shown to be a particularly effective adsorbent for basic dyes but
has a lower capacity for acid dyes. Peat adsorption capacities are reported
in Table 10.7. Adsorption of a cationic dye generally increases with an
increase in pH consistent with a mechanism of adsorption by cation
exchange with acidic functional groups. There are then more adsorption
sites for cation uptake from solution. Similarly a decrease in pH produces
more competition for adsorption between cations and the increased H +
presence, and as a result of this, cations will be desorbed. For the acid and
basic dye, the removal performance was comparable with that of activated
carbon, while for the disperse dyes, the performance was much better. Peat
tends to have a high cation exchange capacity, and is a very effective adsor-
bent for decolorization purposes. The adsorption was strongly dependent
on electrical charge density on the surface because the interactions, for
example, between the dye molecules and carboxylic groups of the peat,
could be either electrostatic or non-electrostatic. This was dependent on
each dye structure.
When raw peat is directly used as an adsorbent, there are possible limi-
tations because natural peat has a low mechanical strength, a high affinity
for water, a poor chemical stability, a tendency to shrink and/or swell, and
to leach fulvic acid [180,181]. Chemical pretreatment and the development
of immobilized biomass beads can produce a more robust media. As with

Table 10.7 Reported adso rption capacities q m (mg g -1 ) for peat (selected papers).
Biosorbent Dye q max Reference

Magellanic peat Acid Black 1 33.7 [183]

Magellanic peat Basic Blue 3 33.1 [183]

Peat Basic Blue 69 195 [184]

Peat Basic Blue 9 190 [173]

Peat Astrazone Blue 26.32 [185]

Peat Acid Blue 25 12.7 [184]

Peat Reactive Black 5 7 [186]

Treated peat Basic Violet 14 400 [179]

Treated peat Basic Green 4 350 [179]