Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 362

capacities using values of the monolayer capacity obtained from batch
studies are compiled and discussed.

10.2 Activated Carbons from Solid Wastes

Adsorption and ion-exchange processes from aqueous solutions are impor-
tant processes in water purification and wastewater decontamination.
Amongst all the adsorbent materials proposed, activated carbon (AC) is
the more popular adsorbent for the removal of pollutants from wastewater
[2,14-16]. However, the use of carbons based on relatively expensive start-
ing materials is unjustified for most pollution control applications [17].
This has led many workers to search for more economic carbon-based
adsorbents from non-conventional resources. Indeed, certain waste prod-
ucts from industrial and agricultural operations, including wood byprod-
ucts, represent potentially economical alternative materials to prepare AC.
These waste materials have little or no economic value and often present
a disposal problem. Therefore, there is a need to valorize these low-cost
byproducts. So, their conversion into AC would add economic value, help
reduce the cost of waste disposal, and most importantly provide a poten-
tially inexpensive alternative to the existing commercial activated carbons.
A wide variety of carbons have been prepared from agricultural
and wood wastes such as bagasse, coir pith, banana pith, date pits, sago
waste, silk cotton hull, corn cob, maize cob, straw, rice husk, rice hulls,
fruit stones, nutshells, pinewood, sawdust, coconut tree sawdust, bam-
boo, and cassava peel. Many of them have been tested and proposed for
dye removal (Table 10.1). The excellent ability and economic promise of
the activated carbons prepared from agricultural byproducts have been
presented and described in a comprehensive and interesting review by
Oliveira and Franca [18]. There are also several reports on the produc-
tion of AC from various city wastes and industrial byproducts such as
waste PET bottles, waste tires, refuse-derived fuel, wastes generated during
lactic acid fermentation from garbage, sewage sludges, waste newspaper,
waste carbon slurries and blast furnace slag. These non-conventional ACs
exhibited high adsorption properties as shown in Table 10.1. However, it
should be point out that the adsorption capacities of a non-conventional
carbon depend on the different sources of raw materials, the history of its
preparation and treatment conditions such as pyrolysis temperature and
activation time. Many other factors can also affect the adsorption capacity
in the same adsorption conditions such as surface chemistry (heteroatom
content), surface charge and pore structure. The adsorption mechanisms