97
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 93-103
Song & Song,
Kinetics and influential factors of nanoscale iron-facilitated nitrate-nitrogen removal
ISSN 2007-2422
•
nitrogen concentration (C) to the initial nitrate
nitrogen concentration (C
0
) of the solution
increased gradually as the pH increased. In
addition, the maximum removal efficiency oc-
curred when the pH of the solution was 2.0. As
the pH increased, the removal rate also gradu-
ally increased. After achieving equilibrium, the
highest nitrate-nitrogen removal rate was only
approximately 20%. This was attributed to the
conversion of zero-valent iron to iron ions. The
reaction equation can be expressed as:
Fe
0
+ 2H
2
O
→
Fe
2+
+ H
2
+ 2OH
-
(2)
As shown in the following equation, the
zero-valent iron also reacted with the nitrate
nitrogen:
5Fe
0
+ 2NO
3
-
+ 6H
2
O
→
5Fe
2+
+ N
2
+ 12OH
-
(3)
Furthermore, under acidic conditions, the
zero-valent iron reduced the nitrate nitrogen
according to the following reaction equation:
Fe
0
+ NO
3
-
+ 2H
+
→
Fe
2+
+ H
2
O + NO
2
-
(4)
In an alkaline environment, Fe
0
is easily con-
verted into Fe(OH)
2
, Fe(OH)
3
, and several fer-
rous hydroxide complexions, such as [Fe(OH)]
+
,
[Fe(OH)
3
]
-
, [Fe(OH)
4
]
2-
, and [Fe(OH)
4
]
2+
. These
changes significantly reduce the ability of iron to
absorb nitrate nitrogen (Martin
et al
., 2008; Yang
& Lee, 2005). Due to the dual role of adsorption
and reduction during nanoscale iron-facilitated
nitrate-nitrogen removal, the pH of the solution
significantly impacted the reactions. Since the
acidity of water in practical engineering applica-
tions varies, adjusting the pH of water could
allow for improved nitrate-nitrogen removal.
Influence of temperature and kinetic analysis
of the removal of nitrate-nitrogen
In the experiment, 0.5 g of nanoscale iron was
added to water containing 50 mg/l of nitrate-
nitrogen. Then, the nitrate nitrogen content was
measured at 25, 30, 35, 40, 45, and 50 ˚C. The
Figure 2. Influence of different initial concentrations on removal efficiency (at a constant temperature of 25 °C, 0.5 g o
f nanoscale iron was added to water containing 10, 50 and 100 mg/l of nitrate-nitrogen).
