In-situ Pb2+ remediation using nano iron particles
© Tehrani et al.; licensee BioMed Central. 2015
Received: 19 June 2014
Accepted: 6 January 2015
Published: 21 January 2015
Originally, application of nano zero valent iron (nZVI) particles for the removal of lead (Pb2+) in porous media was studied. At first, stabilized nZVI (S-nZVI) was prepared and characterized, then used in batch and continuous systems. Based on the batch experiments, corresponding reaction kinetics well fitted with the pseudo-first-order adsorption model, and reaction rate ranged from 0.01 to 0.04 g/mg/min depend on solution pH and the molar ratio between Fe and Pb. In batch tests, optimal condition with more than 90% removal efficiency at 60 min was observed at a pH range of 4 to 6 and Fe/Pb ratio more than 2.5. Continuous experiments exposed that Pb2+ remediation was as well influenced by seepage velocity, grain size, and type of porous media. The maximum Pb2+ removal efficiency in batch and bench-scale systems were 97% and 81%, correspondingly. The results have shown the ability of S-nZVI to use in permeable reactive barriers, as an efficient adsorbent for Pb2+, because of its excellent stability, high reducing power, and a large surface area.
KeywordsnZVI in-situ Remediation Lead Bench-scale
During the last two decades, presence of heavy metal ions in the environment, especially in water sources, was becoming a major concern due to their non-biodegradability, toxicity, wide-spread presence, and tendency to accumulate in living organisms . Lead, a main concern metal pollutant, is widely used in battery manufacturing, electroplating industry, painting and printing processes, plumbing and the combustion of automobile petrol . The U.S. Environmental Protection Agency (U.S.EPA) has set a permissible limit of 0.015 mg/L in drinking water and has placed it on top of the priority list of toxic pollutants . Lead pollution can cause nervous system damage, renal kidney disease, mental retardation, cancer, and anemia in humans . Chemical reduction, ion exchange, chemical precipitation, mineral adsorption, membrane separation, and bio-sorption are the most frequently used treatment technologies for Pb2+ removal  which are ex-situ techniques. Most of these methods are only suitable for the removal of Pb2+ in low concentrations and often require extensive processing as well as being too expensive.
Recently, in-situ techniques such as permeable reactive barriers (PRB) have become promising alternatives to ex-situ methods owing to their lower operating costs . Nano zero valent iron particles could be used as reducing agents in PRBs for removing the wide range of pollutions that promises to be significantly more effective than granular iron, the reaction rates are 25 to 30 times faster, and the sorption capacity is much higher compared with granular iron .
The high reactivity of nZVI is the consequence of greater total surface area, higher density of reactive sites on the particle surface, and/or more intrinsic reactivity of the surface sites . Iron nano particles have been extensively studied to remediate pollutants such as chlorinated compounds and metal ions , nitrate , carbon tetrachloride, benzoquinone , metalloids such as arsenic , and organic compounds . However, there are many uncertainties regarding to the features of nZVI-based remediation technologies, which have made it difficult to engineer applications for optimal performance or to assess the risk to human or ecological health. In this study, application of surface modified nZVI (S-nZVI) for Pb2+ remediation in porous media was experimented that consists of following steps: (1) synthesis, stabilization, and characterization of S-nZVI; (2) determination of kinetics of Pb2+ removal by nZVI and the key factors affecting the reaction; (3) investigation of the effects of flow characteristics on the removal rate; (4) bench-scale modeling of lead remediation under natural conditions.
Lead nitrate (Pb(NO3)2), used as the source of Pb2+ in all experiments, and other chemical reagents, including FeCl3.6H2O, NaBH4, and NiCl2.6H2O, were supplied by Merck, Germany. The concentration of lead, divalent and total, was determined using an atomic absorption spectrometer (Varian SpectrAA 220, Germany).
The black precipitates were filtered by vacuum filtration through 0.45 μm filter papers and then washed with DI water and ethanol three times.
Previous researches have indicated that nZVI particles aggregate quickly, after decreasing surface area for reaction and limiting mobility. To control nano particle agglomeration, various particle stabilizing strategies have been reported that surface modification with surfactant is one of the most important approaches . Surfactants, such as starch, could be coated on existing nZVI particles in a post-synthesis process; or synthesizing nZVI in the presence of polymer in a pre-synthesis process. The post-synthesis stabilization approach has been shown to decrease reactivity whereas the pre-synthesis approach has improved reactivity and significantly increased surface area . In the present study, nZVI was stabilized by starch in a pre-synthesis process, according to He and Zhao method , which is termed here as S-nZVI.
Experimental design in present study* all experiments were conducted in ambient temperature 15–20 °C
S-nZVI: 0.5 g/L, Co: 200 mg/L
Initial Pb2+ (mg/L)
S-nZVI: 0.5 g/L, pH: 4.0
Co: 200 mg/L, pH: 4.0
Seepage velocity (m/d)
Co = 200 mg/L, pH: 4, Seepage velocity: 10 m/d
S-nZVI loading (g)
nZVI: 5 g, pH: 4, Co = 200 mg/L
Seepage velocity (m/d)
nZVI: 15 g, pH: 4, Co = 200 mg/L
Prior to each run, in the first system, glass beads were soaked in hydrogen peroxide solution for 10 hr, washed with de-ionized water, and finally baked at 105°C for 24 hr . For the continuous system, sands were prepared by baking at 500°C for 24 hr to eliminate adsorbed organic matter. In this set of experiments, the pH of the solution was adjusted to 4 ± 0.2 using 0.1 N HCl.
The effects of some flow parameters were investigated by transparent column model, including seepage velocity and S-nZVI loading. Seepage velocity tests, consisted of 5, 10, 20, and 40 m/d, were conducted by distilled water with initial Pb2+ concentrations of 200 mg/L, and 5 g S-nZVI injection. S-nZVI loading tests were experimented by initial Pb2+ concentrations of 200 mg/L, seepage velocity of 10 m/d, and frequent 5, 10, and 15 g S-nZVI injection.
The bench-scale experiments were planned based on the results of the batch and transparent column tests. The S-nZVI injected into the bottom center of the column forms a permeable reactive zone which reduced inlet pb2+. This configuration is applicable to study the effects of groundwater ionic strength, porous media type, seepage velocity, initial concentration of pb2+ and nano particle loading, at the same time. Three treatments, consisted of 5, 10, and 15 g initial S-nZVI loading, were carried out in the bench-scale model. Other conditions were kept as seepage velocity 10 m/d, pH 4, and were used wastewater with initial Pb2+ concentration of 200 mg/L.
Results and discussion
Characteristics of S-nZVI
a. Effect of solution pH
b. Effect of initial Pb 2+ concentration
c. Effect of S-nZVI concentration
As shown in Figure 4c, the Pb2+ removal efficiency improved as the S-nZVI concentration increased. The removal efficiency of Pb2+ was about 50% using S-nZVI at 0.1 g/L for 60 min, but was nearly 95% when the S-nZVI concentration was higher than 1 g/L. In the same conditions, Kobs raised as the S-nZVI concentration increased. These phenomena can be attributed to the increase in available active sites resulting from the increase in S-nZVI concentration, where the lead reduction occurred. Additionally, lead ions removal sharply enhanced by increasing contact time for the first 60 min, and then gradually approached equilibrium after approximately 120 min.
d. Kinetics of the Pb 2+ reduction
The adsorption kinetics of Pb2+ ions was studied to determine the required time to achieve equilibrium adsorption of lead ions on the adsorbents. It was reported that nZVI can remove metal ions from aqueous solutions by various mechanisms, including electrostatic adsorption, complex formation, reduction, and precipitation . It seems that when nZVI was used, the nano particles captured aqueous lead ions easily and rapidly because of their large surface areas and high reactivity.
where C o and C are the concentration of Pb2+ (mg/g) at initial and time t (min), respectively. K obs (min−1) is the equilibrium rate constant for first order adsorption. Therefore, by plotting ln(C/C o ) against t, the values of K obs can be found from the slope of the revealed plots.
Pseudo first-order adsorption kinetics constants for Pb 2+ removal by S-nZVI
Fixed conditions: Initial Pb2+ 200 mg/L, S-nZVI 0.5 g/L
Initial Pb 2 + : 100 mg/ L
Fixed conditions: S-nZVI 0.5 g/L, pH 4.0,
S-nZVI:0.1 g/ L
Fixed conditions: Initial Pb2+ 200 mg/L, pH 4.0,
e. Adsorption isotherms
Experimental data were modeled using the well known adsorption models described by the Freundlich and Langmuir equations to study the ability of Pb2+ ions to adsorb on S-nZVI .
Freundlich and Langmuir adsorption isotherms constants for Pb 2+ removal by S-nZVI
Fixed conditions: Initial Pb2+ 200 mg/L, S-nZVI 0.2 g/L
Initial Pb 2+: 100 mg/L
Fixed conditions: S-nZVI 0.2 g/L, pH 4.0,
Fixed conditions: Initial Pb2+ 200 mg/L, pH 4.0,
a. Effect of seepage velocity
The results of seepage velocity tests are shown in Figure 4c. It was observed that a seepage velocity of 10 m/d yielded the maximum removal rate. Furthermore, any variation, increasing or decreasing of this velocity, had a negative effect on the Pb2+ removal. Higher seepage velocities enhanced the mobility of nano particles through porous media and reduced the contact time and as a result, reduced the remediation efficiency.
b. Effect of S-nZVI loading
As shown in Figure 4e, when S-nZVI loading rose from 1 to 10 g, the Pb2+ removal efficiency within 60 min increased from about 50% to 80%. It is found out that when further amount of S-nZVI was injected, the Pb2+ removal has been improved.
The results of bench-scale experiments, illustrated in Figure 4f, indicated that the removal efficiency through sand materials were higher than glass beads. In addition, increasing seepage velocity had a decreasing effect on the Pb2+ remediation. Through bench-scale experiments, the best Pb2+ remediation efficiency was achieved, i.e. about 81%. In pH of 4, initial concentration of 200 mg/L, and 15 g S-nZVI injection, finally 31 L of treated water with Pb2+ concentration less than 20 mg/L was acquired. Therefore, it could be proposed that the capacity of S-nZVI for in-situ lead removal is about 300 mg Pb2+/g S-nZVI.
Findings of this study indicated that starched nZVI has a good feasibility for in-situ lead remediation in contaminated water. Batch experiments proved that pH of solution was an important parameter while kinetics coefficients were directly related to pH with correlation coefficients R2 > 0.90. In addition, increasing of S-nZVI dosage or decreasing Pb2+ initial concentration, both lead to enhancement in removal efficiency. It means that if mass-ratio between nZVI and Pb is kept constant, i.e. about 2.5, the removal rate would be invariable.
Transparent column experiments revealed that Pb2+ remediation also was mostly influenced by seepage velocity, grain size, and type of porous media. Bench-scale results confirmed the batch and transparent column outcomes. As a final point, because of the fast reaction kinetics and high Pb2+ removal capacity, S-nZVI has the fine potential to become an effective remedial agent in PRB for in-situ immobilization of lead in polluted groundwater resources.
nano Zero Valent Iron particles
Stabilized nano Zero Valent Iron particles
U.S. Environmental Protection Agency
Permeable Reactive Barriers
X-Ray powder Diffraction
Scanning Electron Microscopy
Dynamic light scattering
This work was supported by the Institute of Biotechnology and Environment (IBE) in Sharif University of Technology, Tehran, Iran.
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