Experimental Investigation of Arsenic Removal by Using Fe Nano Particles in Batch Experiment

Introduction
Toxic and dangerous pollution in groundwater is enormous. This assenic pollution is concentrated more than
its permissible limits. It can be observed in different countries like India, Nepa l,Bangladesh, Pakistan, Taiwan,
Thailand, Vietnam, Argentina, Brazil, Chili and Mexico. In some places in Iran like Hashtgerd and Kordestan
the arsenic pollution has been observed more than the permissible concentration. As the arsenic pollution is
increasing, many studies have been done to find different treatment options. Due to rapid removing of the As (V)
and As (III) by using Iron Nano particles, this method have recently been considered useful.
In this paper arsenic removal process was investigated by using nanoparticles. Based on batch
experiments, the influence of Zero-valent iron nanoparticles concentration, tem perature, pH, time, and
arsenic initial concentration were observed in arsenic removal process. The results of this study
indicated that the Iron nanoparticles have high performance in arsenic pollution removal.
Experimental Method
The purpose of the current experimental study was to investigate the arsenic remediation process by using iron
nanoparticles in batch experiment. Specific concentration of iron nanoparticles produced by PNF Corporation
along with the arsenite sodium salt was used. Specification of iron nanoparticle and arsenic has been shown in
table 1 and 2.
Table 1. Arsenic proportions in arsenic sodium salt
Element Valance Percent % gr/ 1000ppm
Na 23 0.18 0.31
As 74.9 0.58 1
O2 32 0.25 0.43
NaAsO2 129.9 1 1.73
Table 2. Specifications of iron nanoparticles
Actual density
(gr/Cm3)
Bulk density
(gr/Cm3)
Specific surface
(Cm2/gr)
Purity
(%)
99.9 8-6 0.25-0.1 7.9
Firstly, the polluted arsenic solutionw as put on shaker with a speed of around 250 rpm . Then
specific concentration of iron nanoparticles were added to the solution and the test was begun. The
arsenic reducing process was investigated with sampling, conducted during the experiments. Samples
were kept in dark glassetos prevent the arsenic oxidation. It should be m entioned that iron
nanoparticles were separated from samples by filtering papers S&S with the size of 11􀂗m. Arsenic
was measured by coupling VGA and atomic adsorption machineries and the results were finally
analyzed.
In batch experiments, the effect of five parameters, i.e. time, pH, temperature, initial concentration
of arsenic and injection concentration of nanoparticles were investigated. Specifications of the
experiment have been showed in Table 3.
Table 3. Specifications of experimental
Time
(min)
Iron nanoparticles
concentration (gr/lit)
Arsenic initial
concentration (ppm)
Specifications
Experimental
Time 0.5 1 2,5,10,15,30,60,90,120
Iron nanoparticles concentration 0.5 0.5, 2 30,60,90,120
Arsenic initial concentration 0.5, 5 1, 2 30,60,90,120
Temperature 0.5 1 15,30,45,60
pH 0.5 1 30,60,90,120
In the first test, the solution containing 0.5 gr/lit arsenic and 1 gr/lit nanoparticles reacted after 1
hour and the results showed that arsenic concentration reduced to below the allowable concentration
by using Fe nanoparticles in this time interval (Fig. 1 and 2). In pH test, alkaline, acidic and natural
environments were investigated and the result indicated that the reaction rate increased with
decreasing of pH. The results also indicated that pH increased during the test (Fig4) and this result was
one reason for decreasing reaction rate with time. For studying the temperature effect, two similar tests
were done in 60􀁱C and 30􀁱C temperatures. In these tests, the reaction rate increased with increasing
the temperature. Initial arsenic concentration and injection iron concentration affected the reaction rate
significantly. Consequently, the experiments were conducted by considering different concentration of
iron nanoparticles and arsenic thawt ere for arsenic concentration 5 and 0.5 ppm and for iron
nanoparticles of 2 and o.5 gr/lit (Table 3). After that, the results indicated that the reaction rate
increased with increasing the arsenic or iron nanoparticles concentration (Fig. 3) because of the
increase in the contact between arsenic pollution and iron nanoparticles as reactive. Finally, the results
revealed that iron nanoparticles could effectively been used to eliminate the arsenic pollution.
Conclusion
Nowadays, arsenic remediation as a toxic and widespread pollution is important in groundwater studies. One of
the methods for the arsenic remediation is using the iron nano particles. This method involves lower costs with
high performance and can be used for in-site pollutant remediation in aquifers. The result of this investigation
indicated that the reaction between iron nanoparticles and arsenic lasts only about several minutes. Increase in
the temperature and decrease in pH reduced the reaction rate. Investigation of arsenic concentration com pared
with iron nanoparticles injection concentration revealed that the arsenic removal rate is increased by an increase
in the ratio of nanoparticles to arsenic. For removing 500 ppb of arsenic concentration by using 1 gr/lit of iron
nanoparticles, an exponential decreasing process was observed so that the arsenic concentration was reached to
less than the arsenic permissible concentration during two hours. Finally it can be concluded that the capability
of the Zero-valent Fe nanoparticles is a useful tool for removing the arsenic pollution in the groundwater.