Page 361 - Industrial Wastewater Treatment, Recycling and Reuse

Phenolic Wastewater Treatment: Development and Applications of New Adsorbent Materials 333

The activating agents such as H 3 PO 4 , ZnCl 2 , KOH, H 2 O 2 , NaOH, and
MnO 2 can influence the modification and consequently the performance of
the adsorbents. In the following discussion, the activated adsorbents were
prepared by chemical activation with orthophosphoric acid. Phosphoric
acid is a proven effective activating agent for many lignocellulosic materials.
It produces adsorbents with high surface area and iodine adsorption value

(Patnukao and Pavasant, 2008). Phosphoric acid is preferred over ZnCl 2
because of the environmental disadvantage associated with the latter. Phos-
phoric acid activation has also been applied to a wide variety of cellulose
precursors such as coconut shell. The use of chemical reagents also promotes
cross linking, resulting in a product that is less prone to volume contraction
and volatile loss upon heating.
Different newer adsorbents, such as those derived from BP, TW, acti-
vated egg shell (AES), and neem leaf (NL) can be used for phenol adsorption.
The preparation of untreated adsorbents from BP and TW involves exten-
sive washing to remove any particulates, cutting into small pieces, drying in
sunlight, sizing, and sieving through a 1 mm size before its use in adsorption
experiments without any further treatment. Similarly, TW-based adsorbent
materials are prepared by removing hydrolysable tannins and other soluble
and colored components from the crushed TWs by washing with hot water

(80 C) for 6 h periods until a colorless solution of TW is observed at room

temperature, drying the decolorized and cleaned TW in an oven at 105 C,
and sizing to 60–170 mesh particles. In the present chapter, we report
another newer material: chicken egg shells. The egg shells were collected
and dried for 2 h in an oven after properly washing and treated them with
phosphoric acid in 1:1 ratio at 373 K for 2 h followed by heat treatment at
773 K for 2 h in a muffle furnace and subsequent washing with double dis-
tilled water to remove any free acids that might have been present on the
adsorbent surface until the pH reaches nearly 7. The final product was then
kept in an oven for 12 h, maintained at a temperature of 373 K to remove
the excess moisture trapped inside the pores of the adsorbent. The adsorbent
so prepared is named AESs.

8.2.3 Synthetic Adsorbents

The use of mixtures of metal oxides as catalysts has been known for years.
Here, we report on the binary mixed oxide of iron and aluminum for its
efficiency as an adsorbent for the removal of phenolic compounds. Prepa-
ration of Fe-Al mixed oxide was envisioned with the view that alumina