New Generation Material for the Removal of Arsenic from Water - Advanced Materials for Agriculture, Food and Environmental Safety - page 72

Table 3.7 Oxi des with dif erent parameters.

Adsorbent pH Concentration

range

Capacity (mg/g)
As III)

Ref.

As(V)

AA 7.6 1 mg/L 0.180 - [96, 97]

Iron
hydroxide
coated
alumina

6.62-6.74 As(III)
7.15-7.2 AS(V)

0.1-1.8 mmol/L 7.64 36.64 [98]

OH group. h e pH of the isoelectric points for these adsorbents (pHiep)
were 6.1 for As(III) and 8.0 for As(V) [98] and the remaining parameters
are given in Table 3.7.

3.1.5.9.3 Titanium Dioxide
h e ability of nanocrystalline titanium dioxide (TiO 2 ) to remove arsenate
and arsenite and to photocatalytically oxidize As(III) was evaluated [99].
Adsorption of As(V) and As(III) on commercially available TiO 2 suspen-
sions (Hombikat UV100 and Degussa P25) was investigated versus pH
and initial adsorbate concentration [100]. Bang et al. [101] studied a novel
granular titanium dioxide for groundwater arsenic removal. More arsenate
was adsorbed than arsenite on TiO2 at pH 7.0. h e adsorption capacities
for As(V) and As(III) were 41.4 and 32.4 mg/g TiO 2 , respectively.
3.1.5.9.4 Lanthanum Hydroxide
Lanthanum hydroxide (LH), lanthanum carbonate (LC), and basic lantha-
num carbonate (BLC) remove As(V) from aqueous solutions [102]. h ese
lanthanum compounds were ef ective at a concentration of < 0.001 mM.
Dissolution was appreciable at initial pH values < 4.3, < 4.3, and < 4.0 for
LH, LC and BLC, respectively.
Arsenic removal followed i rst-order kinetics in the neutral pH range,
and the order of the rate constants was LH > LC > BLC. h e optimum pH
range was 3-8 for LH, 4-7 for LC, and 2-4 for BLC. Two arsenic uptake
mechanisms were proposed: (i) adsorption by the exchange of and/or OH
groups with arsenic ions in neutral to alkaline pH where La does not dis-
solve, and (ii) precipitation of insoluble lanthanum arsenate, LaAsO4, in
acidic pHs.

3.1.5.9.5 Ferrihydrite/Iron Hydroxide/Iron Oxides
Amorphous Fe(O)OH has the highest adsorption capability since it has
the highest surface area. Surface area is not the only criterion for high
removal capacities of metal ions and other mechanisms (ion exchange,