Environmental Engineering Reference
In-Depth Information
precipitation) play an important role. Most iron oxides are i ne powders
that are dii cult to separate from solution at erwards. h erefore, the EPA
has proposed iron oxide-coated sand i ltration as an emerging technol-
ogy for arsenic removal at small water facilities [103, 104]. Granular fer-
ric hydroxide (GFH) was investigated for arsenic removal from natural
water [105]. h e application of GFH in test adsorbers demonstrated high
treatment capacity of 30,000-40,000 bed volumes before an arsenic con-
centration of 10 g/L was exceeded in the adsorber el uent. h e sorp-
tion capacity was 8.5 g/kg. Badruzzaman
et al.
[106] evaluated porous
granular ferric hydroxide for arsenic removal in potable water systems.
Granular ferric hydroxide (GFH) is a highly porous (micropore volume
∼
0.0394 cm
3
/g, mesopore volume
∼
0.10 cm
3
/g) adsorbent with a BET
surface area of
235 m
2
/g. h e pseudo-equilibrium (18 days of contact)
arsenate adsorption capacity at pH 7 was 8 gAs/mg dry GFH at a liquid
phase arsenate concentration of 10 gAs/L. Adsorption and desorp-
tion of methyl arsenic acid [CH
3
AsO(OH)
2
], methyl arsonous acid
[CH
3
As(OH)
2
], dimethylarsinic acid [(CH
3
)
2
AsO(OH)], dimethylars-
inous acid [(CH
3
)
2
AsOH], arsenate [AsO(OH)
3
], and arsenite [As(OH)
3
]
on iron oxide minerals (goethite and 2-line ferrihydrite) were studied
by Laf erty and Loeppert [107]. Akaganeite [Fe(III)7.6 Ni (0.4) O (6.4)
OH (9.7) C(11.3)] in either i ne powder (nanocrystals) or granular forms
can also be used to remove As(V) from water [108, 109]. Akaganeite
powder was prepared by FeCl
3
hydrolysis in aqueous solutions and pre-
cipitation using ammonium carbonate. Removal of As(V) by akaganeite
β-FeO(OH) nanocrystals was also reported [110]. Arsenic removal
increased with increasing temperature and the Langmuir adsorption
capacities were compared and the results are tabulated in Table 3.7.
∼
3.1.5.10 Biosorbents
Biosorption is capable of removing traces of heavy metals and other ele-
ments from dilute aqueous solutions. Algae, fungi and bacteria are exam-
ples of biomass-derived sorbents for several metals. Such sorbents have
produced encouraging results. h ere has been a review of how bacteria,
fungi and algae take up toxic metal ions [111, 112]. It is important to dif-
ferentiate biosorption or sorption from bioaccumulation. Biosorption
(or bioadsorption) is a passive immobilization of metals by biomass.
Mechanisms of cell surface sorption are independent of cell metabolism;
they are based upon physicochemical interactions between metal and
functional groups of the cell wall.
Search WWH ::
Custom Search