Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 370

studied zeolite in the world is clinoptilolite, a mineral of the heulandite
group (chemical formula: (K 2 , Na 2 , Ca) 3 Al 6 Si 30 O 72 .21H 2 O). In its structure,
three independent components are found: the aluminosilicate framework,
exchangeable cations, and zeolitic water. It has been intensively studied
recently because of its applicability in removing trace quantities of pollut-
ants such as cations including heavy metals, and organics including phe-
nols and dyes, thanks to its cage-like structures suitable for ion exchange.
High ion exchange capacity and relatively high specific surface areas,
and more importantly their relatively cheap prices, make zeolites attractive
adsorbents for dye removal [104,103]. Another advantage of zeolites over
resins is their ion selectivities generated by their rigid porous structures.
Several studies have been conducted on the adsorbent behavior of natu-
ral zeolites (Table 10.4). These literature data shows natural zeolites were
effective for cationic dye adsorption mainly due to their cation-exchange
characteristic, while they exhibited low capacity in anionic dyes. Another
problem of zeolites is their low permeability which requires an artifi-
cial support when used in column operations. However, in their excel-
lent review, Wang and Peng [104] concluded that application of natural
or modified zeolites for water and wastewater treatment is a promising
technique in environmental cleaning processes. The adsorption mecha-
nism on zeolite particles is also complex because of their porous structure,
inner and outer charged surfaces, mineralogical heterogeneity, and other

Table 10.4 Reported adsorption capacities q max (mg g -1 ) for zeolites (selected
papers).

Adsorbent Dye q max Reference

Modified zeolite Congo Red 69.94 [107]

Modified zeolite Basic Blue 9 42.7 [108]

Modified zeolite Basic Blue 9 15.68 [109]

Zeolite (Turkey) Reactive Red 239 111.1 [60]

Zeolite (Turkey) Reactive Yellow 176 88.5 [60]

Zeolite (Turkey) Methyl Violet 75.25 [110]

Zeolite (Turkey) Basic Blue 9 70.42 [89]

Zeolite (Turkey) Basic Blue 9 28.6 [108]

Zeolite (Algeria) Basic Blue 9 22 [79]

Zeolite (China) Basic Blue 9 8.67 [109]

Zeolite (Turkey) Reactive Black 5 60.5 [60]

Zeolite (Macedonia) Basic Dye 55.86 [111]