Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 368

Table 10.3 Reported adsorption capacities q max (mg g -1 ) for siliceous materials
and silica gel (selected papers) .

Adsorbent Dye q max Reference

Alunite (Turkey) Reactive yellow 64 5 [94]

Alunite (Turkey) Reactive Blue 114 2.92 [94]

Alunite (Turkey) Reactive Red 124 2.85 [94]

Calcined alunite (Turkey) Acid Red 88 832.81 [102]

Calcined alunite (Turkey) Reactive Red 124 153 [94]

Calcined alunite (Turkey) Acid Yellow 17 151.5 [93]

Glass powder Acid Red 4 4.03 [59]

Modified silica Acid Blue 25 45.8 [99]

Perlite (Turkey) Basic Blue 9 162.3 [89]

Silica (Taiwan) Basic Blue 9 11.21 [98]

with uptake using a commercial carbon indicating the adsorption by the
dolomite char was greater than that of carbon and untreated dolomite.
Indeed charred dolomite has a higher equilibrium capacity for reactive dye
removal than CAC, with a capacity of 950 mg g -1 of adsorbent for dolomite
compared to 650 mg dye adsorbed per g of adsorbent for carbon. However,
the mechanism was not clear (probably a combination of precipitation and
adsorption).
The use of perlite as a low-cost adsorbent for the removal of dyes has
been investigated for the first time by Alkan and co-workers [88-92].
Perlite is a glassy volcanic rock with a rhyolithic composition which can
be processed into an expanded form for cellular structure formation. The
expansion takes place due to the presence of water in perlite when it is
heated to high temperature. Perlite has high silica content, usually greater
than 70% and this material is inexpensive and easily available in many
countries. Interesting adsorption performances were obtained and it was
suggested that dye molecules were physically adsorbed onto the surface
material. However, perlite of different types (expanded and unexpanded)
and of different origin have different properties because of the differences
in composition. Alunite is one of the minerals of the jarosite group and
contains approximately 50% SiO 2 . This material is so cheap that regenera-
tion was not necessary. Its surface charge and the pH play a significant role
in influencing the capacity of alunite towards dyes. However, Özacar and
Sengil [93,94] showed that untreated alunite does not have good adsorbent
properties, but after a suitable process, alunite-type layered compounds