95
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
•
volume of 1.0 mol/l FeCl
3
solution; during this
process, a magnetic stirrer was used to stir the
mixture. Then after ten minutes of reaction, we
obtained the nanoscale iron particles needed for
the experiment. According to reaction equation
(1), this process resulted in the reduction of Fe
3+
to nanoscale iron (Zhang, Wang, & Lien, 1998):
4Fe
3+
+ 3BH
4
-
+ 9H
2
O
→
4Fe
0
↓
+ 3H
2
BO
3
-
+ 12H
+
+ 6H
2
↑
(1)
The black iron grains obtained via the above
method have washed a minimum of three times
with de-ionized water and absolute alcohol and
then dried for 4 hours at 100-105 ˚C. The samples
were then preserved in the dry container. All of
these processes were conducted under nitrogen
protection conditions.
The specific surface area and porosity ana-
lyzer were used to measure the specific surface
area of the nanoscale iron particles via the nitro-
gen adsorption method. The X-ray diffractom-
eter was used to perform a phase analysis of the
nanometer particles with Cu as the target, Ka as
the ray, and 100 mA as the current flow rate. The
scanning transmission electron microscope was
used to observe the features of the particles, and
the nitrogen adsorption surface area tester was
used to determine the specific surface areas of
the particles.
Water sample analysis method
The methods adopted in the water sample
analysis experiments included the nitrate ni-
trogen test method (UV spectrophotometry),
the sub-nitrate nitrogen test method (N-(1-
naphthyl)-ethylenediamine photometry), and
the ammonia nitrogen test method (Nessler
reagent spectrophotometry).
Nitrate nitrogen removal method
First, 5 ml of nitrate nitrogen solution with a
known concentration and nanoscale iron were
added to a 250-ml conical flask and allowed to
react in the water-bathing constant temperature
vibrator at a rotation speed of 150 rpm. The
water-bathing constant temperature vibrator
was used to control the reaction temperature.
Next, after time sampling, each sample was
filtered using a 0.45-μm membrane. Then, the
concentration of each sample was measured.
Results and discussion
Characterization analysis results
According to the results, the diameter of the
nano-iron particles ranged from 20 nm to 60 nm.
In addition, the synthesized particles primarily
existed in the granular and linear states with nu-
merous gaps, indicating that the absolute alco-
hol controlled the accumulation of the nanoscale
iron parcels during the synthesis process. There-
fore, the absolute alcohol significantly increased
the specific surface area of the nanoscale iron
particles (Wang, Jin, Li, Zhang, & Gao, 2006).
The average specific surface area of the synthe-
sized nanoscale iron parcels was approximately
41.16 m
2
/g, 1 to 2 orders of magnitude higher
than that of the micro iron particles available
for purchase. The results obtained via the X-ray
diffractometer (figure 1) indicated that when the
scanned diffraction angle (2θ) ranged from 30°
to 100°, the synthesized nanoscale iron exhibited
diffraction peaks at 44.58, 64.03, 81, and 89°,
corresponding to the diffraction peaks of the
body-centered cubic a-Fe (110). Furthermore,
diffraction peaks approximate to those of the
body-centered cubic a-Fe (200) and a-Fe (211)
were observed (figure 1), indicating that the
particles prepared through these experiments
were comprised of iron rather than iron oxide.
Influence of the initial nitrate nitrogen
concentration on the removal efficiency
At a constant temperature of 25 °C, 0.5 g of
nanoscale iron was added to water containing
10, 50, and 100 mg/l of nitrate nitrogen. Then,
the nitrate nitrogen concentrations at different
reactions were measured with the spectropho-
tometer. The reaction time was used as the
