Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 371

imperfections on the surface [105,106]. However, it is recognized that like
clay, the adsorption properties of zeolites result mainly from their ion-
exchange capabilities.

10.6 Agricultural Solid Wastes

The byproducts from the agricultural and forest industries could be
assumed as low-cost adsorbents since they are abundant in nature, inex-
pensive, require little processing and are effective materials. Agricultural
solid wastes from cheap and readily available resources such as date pits
[31], pith, corncob, barley husk, wheat straw, wood chips and orange peel
have been successfully employed for the removal of dyes from an aqueous
solution (Table 10.5). There have been numerous studies on the use of these
agricultural solid wastes for dye removal and recent information about
the most important features of these wastes can be found in the recent
review by Rangabhashiyam et al. [112]. In this excellent review, the authors
comprehensively discussed the sequestration of dye from textile industry
wastewater using agricultural waste products as non-conventional adsor-
bents. Sawdust and bark have also been the subject of numerous studies.
These low-cost materials are available in large quantities and may have
potential as adsorbents due to their physicochemical characteristics and
adsorption properties. Sawdust contains various organic compounds (lig-
nin, cellulose, and hemicellulose) with polyphenolic groups that might be
useful for binding dyes through different mechanisms. Shukla et al. [113]
have reviewed the role of sawdust materials in the removal of pollut-
ants from aqueous solutions. Baouab et al. [114], Garg et al. [115,116]
and Özacar and Sengil [117] demonstrated that sawdust is a promising
effective material for the removal of dyes from wastewaters. Examples of
sawdust adsorption capacities are reported in Table 10.5. The adsorption
mechanisms can be explained by the presence of several interactions such
as complexation, ion-exchange due to a surface ionization, and hydrogen
bonds. One problem with sawdust materials is that the adsorption results
are strongly pH-dependent and in general, the adsorption capacity of basic
dye is much higher than acid dye because of the ionic charges on the dyes
and the ionic character of sawdust. Garg et al. [115,116,118] and Batzias
and Sidiras [119] proposed chemical pretreatment of sawdust in order to
improve the adsorption capacity and to enhance the efficiency of sawdust
adsorption. Another waste product from the timber industry is bark, a
polyphenol-rich material. Bark is an abundant forest residue which has
been found to be effective in removing dyes from water solutions. Because