Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 375

studying the adsorption of Reactive Blue 19 onto a waste metal hydrox-
ide sludge. Another industrial byproduct shown to adsorb dyes is fly ash,
the major solid waste byproduct from coal-fired power plants. Although it
may contain some hazardous substances, such as heavy metals, it is widely
utilized in industry in many countries [149]. Gupta et al. [150] showed
that bagasse fly ash generated in the sugar industry does not contain large
amounts of toxic metals and could be used efficiently for adsorption of
dyes. Numerous other studies reported that fly ash has interesting adsorp-
tion properties [151,152,16,153]. However, although fly ash is a waste mate-
rial originating in great amounts in combustion processes, its properties
are extremely variable and depend strongly on their origin [151,149,154].
Another abundant industrial byproduct is red mud [155-157]. Red mud
emerges as a waste byproduct during the alkaline leaching of bauxite in
the Bayer process, and causes serious environmental problems due to its
high alkalinity and large amount. Owing to its high aluminum, iron and
calcium content, red mud has been able to remove many types of pollut-
ants. Waste red mud is a bauxite processing residue discarded in alumina
production. Namasivayam and Arasi [156] proposed red mud as adsorbent
for the removal of Congo red. The maximum capacity was 4.05 mg g -1 .
Wa n g et al. [155] showed that physical and chemical treatment can sig-
nificantly change the adsorption capacity. The industrial tanning of leather
produces considerable amounts of chromium-containing solid wastes and
liquid effluents [158,159]. Oliveira et al. [158] proposed the use of these
solid wastes as complexing materials for textile dye removal. Their results
showed that no chromium lixiviation from chromium-containing leather
waste occurs during the adsorption experiments. However, the adsorption
mechanisms are not clearly identified [158].
10.8 Peat
Peat is porous and rather complex soil material with organic matter in vari-
ous stages of decomposition. This natural material is a plentiful, relatively
inexpensive and widely available biosorbent, which has adsorption capa-
bilities for a variety of pollutants [8,171]. It is a heterogeneous material
with some hydrophobic fractions (such as aromatic and aliphatic moieties
contained in humic substances) having natural affinity with hydrophobic
molecules in aqueous solution. Raw peat contains lignin, cellulose, fulvic
and humic acid as major constituents. These constituents, especially lig-
nin and humic acid, bear polar functional groups such as alcohols, alde-
hydes, ketones, carboxylic acids, phenolic hydroxides and ethers that can