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 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 47, 2016 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Angelo Chianese, Luca Di Palma, Elisabetta Petrucci, Marco Stoller
Copyright © 2016, AIDIC Servizi S.r.l., 
ISBN 978-88-95608-38-9; ISSN 2283-9216 

Application of Iron Based Nanoparticles as Adsorbents for 
Arsenic Removal from Water 

Agostina Chiavola*a, Emilio D’Amatoa, Marco Stollerb, Angelo Chianeseb, Maria 
Rosaria Bonia 

a
Department of Civil Building and Environmental Engineering, Sapienza University of Rome, Via Eudossiana, 18, Rome 

00184, Italy 
b
Department of Chemical Materials Environmental Engineering, Sapienza University of Rome, Via Eudossiana, 18, Rome, 

00184, Italy 
agostina.chiavola@uniroma1.it 

Arsenic contaminations of groundwater in several parts of the world are the results of natural and/or 
anthropogenic sources, and have a large impact on human health. Millions of people rely on groundwater for 
drinking water supply; therefore, contamination of these sources represents a strong limitation to their civil and 
urban development. Due to the toxicity and potential carcinogen effect, in 2001 the World Health Organization 
has reduced the maximum allowable concentration of arsenic in drinking water to 10 g/L. This new limit has 
been then adopted by numerous countries, such as Italy.  
Among the methods used to reduce arsenic concentration, the adsorption process has often proved to be the 
most suitable in the case of drinking water sources. Adsorption efficiency strongly depends on the type of 
adsorbents. In the case of arsenic contaminated groundwater, a number of media have been tested so far 
(alumina, iron-based), some of which providing good removal. However, there is still an high interest in new 
media capable of providing better performances, i.e. longer duration of the column plants where the 
adsorption process is usually implemented at the full-scale. Recently there has been increasing interest on the 
application of nanoparticles and nanostructured materials as efficient and viable alternatives to conventional 
adsorbents in the removal of metals from water. Due to their small size, they possess a large surface area and 
a high surface area to volume ratio. These characteristics improve the adsorption capacity of the nanoparticles 
and make them potentially suitable for the application where higher removal efficiency are required. 
The present work investigates the application of a new nano-adsorbent for arsenic removal from water. The 
media was produced in laboratory and made by magnetite nanoparticles. These iron-based nanoparticles, 
characterized by a very small size (9 nm), showed high removal rate, providing a specific adsorption capacity 
at equilibrium of about 8.25 [mg As/g ads]. Among the investigated models, the pseudo-second order best 
fitted the experimental data of the kinetic tests. Comparisons made with the performance provided by 
commercial adsorbents and other materials confirms the use of magnetite nanoparticles for the removal of 
arsenic as a promising technique. 

1. Introduction 

Arsenic is a widely diffused metalloid, commonly found in all the environmental matrices. High levels of 
arsenic have been measured in many groundwaters worldwide as a consequence of either natural or 
anthropogenic sources. Since it has been recognized toxic and potentially carcinogen, the World Health 
Organization (WHO, 2004) reduced the arsenic maximum contaminant level (MCL) in drinking water from 50 
to 10 μg/L (Sharma and Sohn, 2009). This new limit has been then adopted by numerous countries, such as 
Italy. Thus treatment of As contaminated water with improved or completely new technologies to provide safe 
drinking water to the community is an urgent issue at present. 
Several physico-chemical techniques have been developed to this purpose (Ng et al., 2004). The most 
commonly used technologies are: oxidation, co-precipitation followed by adsorption onto coagulated flocks, 
lime treatment, ion exchange, adsorption onto various solid media and membrane filtration (Choong et al., 

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1647055

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Chiavola A., D Amato E., Stoller M., Chianese A., Boni M.R., 2016, Application of iron-based nanoparticles as 
adsorbents for arsenic removal from water, Chemical Engineering Transactions, 47, 325-330  DOI: 10.3303/CET1647055

325



2007). Among them, precipitation usually requires high chemical dosages and produces high volumes of 
sludge which need proper treatment and disposal. Furthermore, the addition of chemicals to the water may 
negatively alter its quality in view of the use as drinking water source. Ion exchange is highly efficient, 
provided that interfering ions are absent or at very low concentration. Membrane filtration, although capable of 
producing a very high quality permeate, it recovers only a fraction of the treated water volume while the 
remaining fraction is wasted as concentrate stream. This represents a severe drawback in the case of drinking 
water sources.  
The above limitations have frequently made the adsorption process to be preferable with respect to the 
alternative technologies. It is capable of reducing arsenic concentration below the MCL without the need of 
chemical addition; total treated volume of water is recovered and no sludge are being generated. However, its 
efficiency is strongly dependent on the type of adsorbent (Mohan and Pittman, 2007). Extensive studies have 
been performed to determine performances and optimal operating conditions of numerous natural or 
commercial media. For instance, activated carbons  
Among all the tested adsorbents, iron and activated alumina based adsorption have been more widely used 
for treatment of As contaminated groundwater. Activated alumina (AA) was the first adsorptive medium to be 
successfully applied for the removal of arsenic from water supplies. The reported adsorption capacity of AA 
ranges from 0.003 to 0.112 g of arsenic per gram of AA. It is available in different mesh sizes and its particle 
size affects contaminant removal efficiency. Several different studies have established the optimum pH range 
as 5.5-6.0, and demonstrated greater than 98% arsenic removal under these conditions (Jain and Singh, 
2012). 
Adsorption on iron-based (IB) is a more recent treatment technique for arsenic removal, but it is considered to 
be one of the most promising solution. This has led to the development of a great number of products, such as 
granular ferric hydroxide, zero valent iron, iron coated sand, modified iron and iron oxide based adsorbents. 
The studies conducted with IB media have revealed that the affinity of this media for arsenic is strong under 
natural pH conditions, relative to AA. This feature allows IBS to treat much higher bed volumes without the 
need for pH adjustment, as compared to AA (Jain and Singh, 2012). 
Recent advances in nanoscience and nanotechnology have led to the development of a number of 
nanoparticles for the environmental remediation of various contaminants from groundwater (Zhang, 2003). 
Due to their high specific surface area and reactivity, nanoparticles are considered as a suitable option for fast 
removal of contaminants from aqueous solution (Huber, 2005). Nanostructured metal oxides such as 
mesoporous alumina (Kim et al., 2004), titanium oxide (Pena et al., 2006), nanocomposites comprised of 
aluminiumoxide nanoparticles (AluNPs) incorporated in macroporous polyacrylamide-based cryogels (Önnby 
et al., 2014), iron oxide (Tang et al., 2011), hydrous cerium oxide (Li et al., 2012) have attracted the attention 
of researchers due to their great capability of arsenic removal. Nevertheless, the study of other nanomaterials 
is still of a wide interest (Tsynedov et al., 2014). 
The main purpose of this preliminary work was to investigate the adsorption characteristics of magnetite 
nanoparticles for arsenic removal from water at high contamination level. Magnetite nanoparticles were 
chosen since have large specific surface area with a strong tunneling effect and a small size of the border 
effect which might be useful for the adsorption process; furthermore, they possess the general properties of 
ordinary iron and therefore potentially a high affinity to arsenic.  
Magnetite is a naturally occurring mineral, but can be also easily prepared in the laboratory from solutions 
containing ferric and ferrous ions. The iron nanoparticles are widely used in radar absorbers, magnetic 
recording devices, heat resistant alloys, powder metallurgy, injection molding, a variety of additives, water 
treatment and many other areas. They have an uniform particle size, high purity and low contents of carbon, 
nitrogen, oxygen, sulfur, phosphorus and other harmful elements. 
The experimental activity was conducted through batch tests, investigating both the adsorption kinetics and 
equilibrium. 

2. Materials and methods 

2.1 Adsorbents 

The magnetite nanoparticles were produced in laboratory by following the procedure reported in detail in 
Ruzmanova et al. (2013). Briefly explained, a FeCl3 solution in 2M of HCl and 1M of Na2SO3 is mixed to a 
0.85M ammonia solution on a spinning disk reactor.  
Due to the excellent micromixing conditions achieved by this device, the magnetite nanoparticles precipitate 
immediately and are washed by distilled water using a centrifuge (De Caprariis et al., 2012) (Figure 1).  
The resulting model size of the pure magnetite nanoparticles was 9 nm (Figure 2). 
 

326



 
Figure 1: Scheme of the spinning disc reactor 

2.2 Chemical solutions 

Arsenic aqueous solutions at various concentrations were obtained by adding arsenic solution (99% in As (V)) 
in 0.5 N nitric acid), supplied by CHEBIOS, to deionized water. Arsenic was always maintained in the 
pentavalent form by adding 100 μL H2O2 (30% v/v) to the solutions. All chemical were of analytical grade and 
were used without a further purification.  

2.3 Analytical methods 

Arsenic concentration in aqueous solutions was measured by using an Atomic Absorption Spectrophotometer 
(Agilent Technologies 240Z AA supplied with the GTA 120 Zeeman graphite tube atomizer) at the wavelength 
of 193.5 nm, following the 3113 B. Electrothermal Atomic Absorption Spectrometric Method (APHA, 2005). 
Standard solutions of arsenate were used for calibration. The As(V) detection accuracy was 0.22 µg/L.  
pH values were continuously monitored during the batch tests by using the standard probe HI8418 by HANNA 
Instruments.  
All the experiments were repeated three times and the data were averaged.  
 

 

Figure 2: Particle Size Distribution of the used nanoparticles of magnetite 

327



2.4 Adsorption kinetics 

Kinetics of the adsorption process on magnetite nanoparticles were determined by means of batch 
experiments, performed in a jar –tester (Velp Scientifica, Italy), stirred at a constant rate of 120 rpm. The batch 
duration was 24 h, found to be enough to reach equilibrium conditions. 
The initial arsenic concentration in solution (at time t=0 of the test), C0, was posed equal to 10 mg/L: such a 
value, which is significantly higher than the concentrations usually found in naturally contaminated 
groundwater, was chosen based on the need to ensure reproducible data since it was the first time this 
adsorbent was tested. The solid to liquid (S/L) ratio was fixed to 5 g/L.  
Periodical sampling of the liquid solution was performed until the mass transfer process reached equilibrium 
conditions. Each sample was then filtered by using a syringe equipped with a 45 m PV filter and the filtrate 
was analyzed to determine the residual arsenic concentration in solution.  
The amount of the arsenic adsorbed onto the media was calculated based on the mass balance of arsenic 
between solid and liquid phases. The adsorption capacity of the adsorbent at equilibrium, Qads, which 
represents the mass of arsenic adsorbed per unit mass of adsorbent, was calculated by applying the following 
equation: 

 
m

CCV
Q e0ads


    (1) 

where C0 and Ce are the initial and final (at equilibrium) arsenic concentration in solution, respectively, V is the 
solution volume and m is the mass of the adsorbent material.  

2.5 Kinetics modeling 

The best fitting of the experimental data by the following models was found based on the value of the 
correlation coefficient (R2): zero, first, second, saturation, pseudo-first-, pseudo-second-order, Weber-Morris 
and Bangham.  
The linear forms of the model equations shown below was used to determine the best agreement between the 
experimental and the predicted data. 

Zero order 
  tkCtC 00     (2) 

First order 
  tkClntlnC 10     (3) 

Second order 

 
tk

C

1

tC

1
2

0
    (4) 

Pseudo-first-order 
  tk'lnQQ(t)Qln 1adsads     (5) 

Pseudo-second-order 

  ads2ads2 Q
t

Qk'

1

tQ

t



    (6) 

Saturation 

 
 

ss K

k

t

tCC

K

1

tC

C
ln

t

1



 00    (7) 

Weber-Morris 

  qtktQ wm  2
1

   (8) 

Bangham 

 
tln

V

mK
ln

mtQC

C
lnln 







 























0

0

0    (9) 

328



where C(t) and Q(t) stand for the concentration in solution and the amount of arsenic adsorbed per unit weight 
of adsorbent, respectively, at time t; k0, k1, k2,  k’1, k’2 represent the rate constants of the zero, first, second, 
pseudo-first and pseudo-second order model, respectively; Ks and k indicate the semi-saturation and the rate 
constants, respectively, of the saturation model; kwm and q are the Weber-Morris rate constant and constant, 
while K0 and  are the Bangham constants. 

3. Results  

Table 1 shows the values of concentration, removal percentage, pH and adsorption capacity calculated at the 
different times during the kinetic tests. 

Table 1:  Experimental results of the kinetic tests 

Time (min)  0 5 10 15 30 60 90 120 150 180 240 300 360 420 

C(t) (mg/L) 10.2 5.9 3.9 3.2 2.1 1.0 1.2 0.7 0.4 0.4 0.3 0.1 0.1 0.0 
Removal (%) - 42.2 61.8 68.6 79.4 90.2 88.2 93.1 96.1 96.1 97.1 99.02 99.02 100.0
pH (unit) 6.0 4.0 3.8 3.7 3.6 3.5 3.5 3.5 3.4 3.4 3.4 3.4 3.4 3.4 
Q(t) (mg/g) 0.0 0.9 1.3 1.4 1.6 1.8 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.0 

The mass transfer process by adsorption of arsenic onto magnetite was very rapid, as can be seen in Figure 
3, representing the solution concentration time-profile. After about 3 h, the equilibrium conditions were likely to 
be established: indeed, the following variations of arsenic concentration in solution were negligible.  
It is interesting to notice that all the As in the sample was adsorbed by the nanoparticles within 420 min, 
whereas the limit of As for potable water in Italy, equal to 0.1 mg/L, was reached within 300 min. At this point, 
a purification from As of the sample equal to 99% was achieved. 
 

 
Figure 3: Arsenic concentration time-profile during the kinetic test 
 
The best fitting of the kinetic data was obtained by the pseudo-second order model (R2=0.9944): the 
corresponding fitting line had the following equation 
 

 
0.5618t1.344

tQ

t
  

 
Based on the above equation, it was possible to calculate the equilibrium adsorption capacity, Qads, and the 
rate constant, k’2. The following values were obtained: Qads=1.8 (mg/g), k’2=0.03 (g/mg min). 

4. Conclusions 

Based on this preliminary study, the use of nanomagnetite particles for the removal of arsenic from water 
appears to be promising: a very high rate of adsorption was observed, with the limit of As concentration for 
drinking water achieved after only 300 min. However, the specific adsorption capacity at equilibrium was very 
low as compared to the values reported by the literature using other media (Jain and Singh, 2012). 
Nonetheless, it must be taken into account that the initial contaminant load adopted in the present study was 
very high as compared to the more common cases of natural contamination. Therefore, further experiments 

0

2

4

6

8

10

12

0 40 80 120 160 200 240 280 320 360 400

C
(t

) 
(m

g
/L

)

Time (min)

329



will be carried out for investigating the removal capability of nanomagnetite particles at lower arsenic 
concentration.  
It is noteworthy that magnetic particles offer the possibility of easy recovery (and possibly reuse) by means of 
a magnetic trap: this suggests the need of a deeper understanding of this kind of adsorbent.  
To this purpose, the following studies will also address a detailed characterization of the media and the effects 
of pH on the removal rate. 

Acknowledgments 

The work was performed in the framework of the TEMPUS ECONANO project (FP7), here gratefully 
acknowledged.  

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