New Generation Material for the Removal of Arsenic from Water - Advanced Materials for Agriculture, Food and Environmental Safety - page 65

3.1.5 Adsorption Process

Adsorption is evolving as a frontline of defense. It takes stuf (arsenic) out
of water and puts it onto a solid adsorbent with micro and macro pores.
Adsorption removes contaminants from water by attaching them onto the
surface of a porous solid adsorbent. In physical adsorption, the process is
low energy consuming and reversible, while the chemical adsorption pro-
cess requires high energy and is irreversible.

3.1.5.1 Commercial Activated Carbons

In 1998, Allen and Whitten reviewed the production and characterization
of activated carbon from many carbonaceous sources. Recently, the science
and technology of charcoal production was reviewed [52]. Commercial
activated carbons have been extensively used for As(III) and As(V) adsorp-
tion from water [53-56].

3.1.5.2 Synthetic Activated Carbons

Activated carbons are produced by carbonization employing slow substrate
heating in the absence of air below 600 C. h is removes volatiles. h en chem-

ical or physical activation follows. Treatment with oxidizing agents (steam,
carbon dioxide, or oxygen) at elevated temperature or with chemical activates
(ZnCl 2 , H 2 PO 4 , H 2 SO 4 , KOH, K2S, KCNS, etc.) completes the activation [57,
58]. Huang and Fu [59] examined the As(V) capacity of 15 brands of acti-
vated carbon over a wide pH range. h e carbon type, total As(V) concentra-
tion and pH were major factors controlling As(V) removal. Manju et al. [60]
prepared a coconut husk carbon (CHC) by carbonizing one part coconut husk
with 1.8 parts by weight of sulphuric acid (18 M) at 150

°

C for 24 h. Recently,
arsenic(III) was removed from aqueous solution (concentration range of 5-20
mg/L) by activated carbons developed from olive stones and solvent-extracted
olive pulp [61]. Oat concentrations from 5 to 20 mg/L were also tested as
adsorbent. Dif erent parameters of activated carbons are given in Table 3.2.

°

3.1.5.3 Chars and Coals

A mixture of synthetic hydroxyapatite and barite, or bone char, has been
used for arsenic(v) removal from water. Although the hydroxyapatite
and barite mixture had a small inl uence on arsenic concentrations, bone
char was found to be a very ef ective adsorbing agent for As(V) in the
pH range of 2-5 [62]. Biochar byproducts from fast wood/bark pyroly-
sis, were investigated as adsorbents for the removal of As(III), Cd(II), and
Pb(II) from water [63]. Oak bark, pine bark, oak wood, and pine wood