The Use of Nano Zero Valent Iron in Remediation of Contaminated Soil and Groundwater

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1 International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(7), pp , 2013 Available online at ISSN: ; 2013 IJSRPUB Review Paper The Use of Nano Zero Valent Iron in Remediation of Contaminated Soil and Groundwater Maryam Taghizadeh 1, Daryoush Yousefi Kebria 2 *, Golamreza Darvishi 1, Farshad Golbabaei Kootenaei 3 1 Department of Civil and Environmental Engineering, Babol Noshirvani University of Technology, Iran 2 Assistant Professor in Civil Engineering, Babol University of Technology, P.O. Box: 484, Babol, Iran. 3 Young Researchers Club, Islamic Azad University, Qaemshahr Branch, Qaemshahr, Iran *Corresponding Author: Dy.kebria@nit.ac.ir Received 22 April 2013; Accepted 27 May 2013 Abstract. Environmental contaminants have been known to be present in many hazardous waste sites, which made an enormous impact on the quality of groundwater, soil and associated ecosystems. Remediation of these contaminated sites is an important challenge for the scientific and technical community. Nanotechnology is a broad and interdisciplinary field dealing with structures and particles at the nanoscale. Nano Zero Valent Iron (nzvi) is emerging as a new option for the treatment of contaminated soil and groundwater. Due to the small size, the particles are more reactive than granular iron which is conventionally applied in reactive barriers and can be used for in situ treatment. NZVI effectively reduces chlorinated organic contaminants (e.g. PCB, TCE, PCE, TCA, pesticides, solvents) and also inorganic anions (perchlorate). This present research gives an overview over the characteristics and application of nano zero valent iron in general and summarizes its use in groundwater remediation. Key words: Nanotechnology, Groundwater, Nano Zero Valent Iron (nzvi), Remediation, soil 1. INTRODUCTION Maintaining and restoring the quality of air, water and soil is one of the great challenges of our time. Most countries face serious environmental problems, such as the availability of drinking water, the treatment of waste and wastewater, air pollution and the contamination of soil and groundwater. Enormous effort has been made to find efficient and effective ways to remediate petroleum contamination in soil and groundwater (Rickerby et al., 2007). Petroleum compounds and its derivatives cause contamination of groundwater and soil, whatever petroleum compounds penetrated to a greater depth from the soil, decontamination will be more difficult. Many remediation technologies have been developed to treat contaminated soil, such as soil washing, bioremediation, thermal adsorption and chemical oxidation. Thousands of sites exist in the United States and worldwide where subsurface soils and groundwater have been contaminated with a wide range of toxic organic compounds and heavy metals. In particular, halogenated organic contaminants, such as Pentachlorophenol, Trichloroethylene, Trichloroethane, Dinitrotoulene, and Trinitrotoluene, are present at several sites, and these contaminants are listed as priority pollutants by the United States Environmental Protection Agency (USEPA) due to 152 their toxicity and carcinogenicity. These contaminants are persistent in the environment and they are transformed or degraded extremely slowly by natural processes (Vogel et al., 1987). The conventional methods of treating these contaminants include soil washing/ flushing, thermal desorption, vitrification, and bioremediation; however, these methods are relatively expensive, slow, or limited by the production of secondary waste streams that require subsequent disposal or treatment (Sharma et al. 2004). Nanotechnology is a branch of applied sciences that can be defined as particles of size ranging from one to hundred nanometers (nm) in any dimension. The size of nano particles is of several times smaller than even the red blood cells (Breytenbach, 2005). A nanoparticles is a microscopic particles whose size is measured in nanometers (nm). It defined as a particles with atleast one dimention < 100 nm. Nanotechnology is expected to bring a fundamental chang in manufacturing in the next few years, and will have an enormous impact on Environmental science for detection, monitoring and remediation of pollutants as well as life sciences including dry delivery, diagnostics, nutraceuticals and production af biomaterials Engineered nanoparticles NP (<100nm) are an important tool to realize a number of these applications (Bhawana and Fulekar, 2012). Andreta showed that nanotechnology is the actions and reactions that occur at the atomic level; a more

2 Taghizadeh et al. The Use of Nano Zero Valent Iron in Remediation of Contaminated Soil and Groundwater accurate interpretation nanotechnology is new revolution for all science in the future. This technology can improve methods of assessment, management and reduce risks for the environment and provide opportunities for new products (Andreta, 2003). Laboratory research has established that nanoscale metallic iron is very effective in destroying a wide variety of common contaminants such as chlorinated methanes, brominated methanes, trihalomethanes, chlorinated etenes, chlorinated benzenes, other polychlorinated hydrocarbons, pesticides and dyes. The basis for the reaction is the corrosion of zerovalent iron in the environment. Contaminants such as tetrachloroethene cn readly accept the electros from iron oxidation and be reduced to ethane (Bhawana and Fulekar, 2012). Nanoscale iron particles represent a new generation of environmental remediation technologies that could provide cost-effective solutions to some of the most challenging environmental cleanup problems. Nanoparticles show a higher catalytic activity because of their small size ( nm) and their large specific area. Nanoscale zero valent Iron (nzvi) promises to be significantly more effective than granular iron: The reaction rates are times faster and the sorption capacity is much higher compared with granular iron. This is due to the large reactive surface area with 2-5 nm particles giving approximately 142 m2/g. Nano zero valent iron particles have surface areas up to 30 times greater than larger size powders or granular iron. Thus nzvi is times more reactive (Müller and Nowack 2010). 2. ENVIRONMENTAL APPLICATIONS OF NANOTECHNOLOGY Nanotechnology provides the possibility of producing product of high quality and low cost. One of the important areas of application of nanotechnology in the environment is removal or cleanup of chemical contaminants such as chemical pesticides, or converts them to substances that have less risk of toxicity. For example, nano zero valent iron can be used for the cleanup of soil and groundwater for a variety of chemical contaminants. These nanoparticles as a catalyst can accelerate the oxidation process and cause the organic pollutants such as chemical pesticides to brake down into smaller carbon compounds that have less toxicity. The same projects about removal of microbial and chemical contaminants of water, soil and air is in progress in nanotechnologies centers at various countries around the world that represent the capabilities of nanotechnology in this field. 153 There are different methods for improvement and cleanup of soil and groundwater, for example in pump and treat method, which is one of the conventional methods, groundwater pumped and after filtration and removal of contaminants, groundwater aquifers are returned again, this method is very costly and take a long time. Iron was first recognized and patented in 1972 as a chlorinated pesticide degrader. In 1981, Sweeny utilized iron powders to degrade various hydrocarbons, such as trichloroethylene (Sweeny, 1972). Additional suggestions for using zero valent iron to degrade trichloroethylene and trichloroethane were made in the late 1980s (Senzaki, 1988). In 1993 a patent was lodged by the University of Waterloo for using zero valent iron for treating contaminated groundwater in-situ, demonstrating the identification of zero valent iron as a remediation constituent. Nanoscale zero valent iron (nzvi) is more effective at reaching deep zones of contamination, and is more effective at contaminant degradation than iron of larger size. Nano zero valent iron can induce greater rates of reaction because of its greater specific surface area, which allows a greater exposure of the iron particle to the contaminant per unit weight of iron than other larger particles. Additionally, as particle size decreases and tend towards 10 nm, thermodynamic properties, such as work-function and free energy can increase reactivity. Gavaskar has found that nzvi is significantly more reactive than granular iron, and it can remediate a plume in a much shorter time scale (Gavaskar et al., 2005). Henry states that nanoscale zero iron has a superior pore penetration ability when compared to larger particulate zero valent iron (Henry, 2003). Zero valent iron has been shown to react and degrade with many types of chemicals (Gavaskar et al., 2005), including halogenated aliphatics, polyhalogenated aromatics and nitrates and trichloroethene (Henry et al., 2003; zawaideh et al., 1997). The standard half reaction for zero valent iron reacting to yield a ferrous cation and 2 electrons is: Fe 0 Fe e - (1) This reaction has a standard reduction potential of V (Atkins, 1998). Alkyl halides have a typical half reaction as such, where RX indicates a halogenated hydrocarbon, and X- represents a halogen anion: RX + 2e - + H + RH + X- (2)

3 International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(7), pp , 2013 These types of half reactions have reduction potentials ranging from +0.5 V to +1.5V at ph 7 (Matheson et al. 1994), the variation is attributed to the wide range of alkyl halides that this reaction applies to. When combined, these two half reactions yield a thermodynamically spontaneous reaction: Fe 0 +RX+H + Fe 2+ + RH+X - (3) This constitutes the most basic mechanism for halogenated hydrocarbon degradation by zero valent iron, yielding a ferrous cation, an aliphatic hydrocarbon and a halogen anion (Matheson et al. 1994). A second mechanism for degradation of halogenated hydrocarbon by zero valent iron is the oxidation of zero valent iron to a ferrous cation by water (Matheson et al. 1994). The ferrous ion then further oxidizes to a ferric cation by the following half equation: Fe 2+ Fe 3+ + e - (4) This oxidation reaction can be coupled with the reduction half equation to reduce the alkyl halide shown above to yield: Fe 2+ + RX + H + Fe 3+ + RH + X - (5) This is a second mechanism for the degradation of an alkyl halide (Matheson et al. 1994) by zero valent iron. Matheson describes a third mechanism, which involves the zero valent iron reacting with water to yield the ferrous cation, the hydroxyl anion and hydrogen gas (H 2 ) (Matheson et al. 1994). It is combination of the two following half reaction: Fe 0 Fe 2+ +2e - (6) H 2 O+ e - H 2 + OH - (7) Fe 0 + 2H 2 O Fe 2+ 2H 2 +2OH - (8) The H 2 gas generated can then continue to react with an alkyl halide in a reaction known as addition reaction to yield a dehalogenated aliphatic, a halogen anion and a proton in the following manner: RX+ H 2 RX + X - (9) It is important to note that H 2 can only react with the alkyl halide if a suitable catalyst is present. 3. ADVANTAGES OF ZERO VALENT IRON NANOPARTICLES Using zero valent iron as a remediation technology has the following advantages: (Zawaideh et al. 1997) I. It is relatively inexpensive. II. It is non-toxic. III. It degrades certain chemical faster than other techniques of remediation, such as biotic remediation IV. It has high energy effectiveness. A widely used technique to treat contaminated groundwater in situ is by utilizing Passive Reactive Barriers (PRB). The location of the PRB must first be ascertained, then the existing soil must be excavated and the void space filled with the reactive medium with relatively high hydraulic conductivity. Some of the initial field testing of PRBs was done using zero valent elemental iron filings (Gillham et al. 1993, Gillham et al. 1994). Incorrect understanding of the frequently complex hydrogeology of various contamination sites can lead to incorrect barrier wall placement, which can leave contaminated zones outside of the barriers untreated. Passive Reactive Barrier has proven to be effective at treating a great number of contaminated groundwater plumes; however, they have certain limitations (Pankow et al. 1996): I. They only target contaminant plume, and not the source of contamination. They, therefore, have to wait for the contaminant to be leached into or advected with the groundwater before treatment can be initiated. II. They are unfeasible solutions in certain situations of complex hydro geological conditions, such as fractured rock. III. Most Passive Reactive Barriers have been installed to a depth of approximately 15 meters, although there have been instances of depths up to 35 meters (Henry et al. 2003). Barriers cannot penetrate deep into the soil, rendering them wholly ineffective with deep plumes, as they cannot reach the target zone. A comprehensive understanding of the hydrogeological conditions at the contamination site is required for this technology to work, as the positioning of PRB is of utmost importance. 4. SOIL AND GROUNDWATER REMEDIATION WITH NANOPARTICLES Environmental remediation methods can be classified as adsorptive and reactive and as in situ or ex situ (Tratnyek et al., 2006; Hodson, 2010). The use of nanomaterial in all scenarios has been investigation. In soil and groundwater remediation, for in situ treatment, it is necessary to create either an in 154

4 Taghizadeh et al. The Use of Nano Zero Valent Iron in Remediation of Contaminated Soil and Groundwater situ reactive zone with relatively immobile nanoparticles or a reactive nanoparticles plume that migrates to contaminated zones. There are two ways to use nzvi in groundwater and soil remediation (Tratnyek et al., 2006; Nowack, 2007): nzvi is injected to form a reactive barrier of iron particles. nzvi is injected in surface- modified form to establish a plume of reactive iron, which destroys any organic contaminants within the aqueous phase Several studies have shown that nzvi as a reactive barrier is very effective in the reductive degradation of halogenated solvents, such as chlorinated methane, brominated methane, trihalomethane, chlorinated ethene, chlorinated benzenes and other polychlorinated hydrocarbons, in groundwater (Zhang, 2003; Mueller et al., 2010). nzvi has also been shown to be effective against pesticides and dyes (Zhang, 2003). Efficient removal by nzvi of polycyclic aromatic hydrocarbons (PAHs) adsorbed to soils has been reported at room temperature (Chang et al., 2005; Chang et al., 2007), while under the same conditions only 38% of the polychlorinated biphenyls (PCBs) were destroyed because of the very strong sorption of PCBs to the soil matrix (Varanasi et al., 2007). Krishna investigated electrokinetic delivery of nanoscale iron particles for remediation of pentachlorophenol in clay soil. The results showed that 80 to 98% pentachlorophenol (PCP) was removed from the soil within an hour, but PCP reduction increased from 50 to 78% in 1h to 40 to 90% in 24h reaction time period for different nanoscale iron particles (NIP) concentrations. There was no significant effect of NIPs concentration on the PCP removal, but the amount of PCP reduction increased with increase in concentration of NIP. According to Tratnyek and Johnson (2006), nzvi used in real- world groundwater remediation has a particle size larger than 100 nm and is strictly speaking outside the standard definition of NP size. These authors also state that the mobility of nzvi is less than a few meters under almost all relevant conditions as nzvi tends to aggregate, producing clusters that may approach several micrometers in size and thus be easily removed from the water (Tratnyek et al. 2006). Companies are therefore producing new nzvi particles to stop them from aggregating, for example, with surfactants or polymers. Other approaches combine the nzvi with carbon plateles or embed the nzvi in oil droplets to facilitate particle delivery into the contaminated area (Mueller et al. 2010). In the United States, it is common to combine the nzvi with other metals, such as palladium, to increase the reactivity. In Europe such bimetallic 155 particles are not used due to their possible toxicity and the limited additional benefit (Mueller et al., 2010). Tratnyek and Johnson (2006) state that high reactivity tends to correlate with low selectivity. For this reason, remediation with nzvi may be inefficient because nzvi particles may react with non-target substances, including dissolved oxygen, sulphate, nitrate and water. This also implies that nzvi will have a limited lifetime in porous media and reinjection of nzvi may be necessary, which makes the treatment more costly (Tratnyek et al., 2006). 5. CONCLUSION Emergence of nanotechnology, particularly synthesis of nanoscale iron particles, has provided opportunities to develop innovative site remediation technologies. The small particles have great sorption capacity. However, technical challenges, such as the delivery of the particles to the target area, have to be solved. The reaction pathways of NIP with target halogenated organic contaminants are similar to that of zero-valent iron (iron filings) commonly used in a permeable reactive barrier technology. However, due to their infinitesimally small size, NIP can be highly reactive due to their high surface to volume ratio and greater number of reactive sites and higher intrinsic reactivity on reactive sites. In addition, NIP can be injected directly into the contaminated zones, making the in-situ remediation faster and effective. Due to their small size, the particles are very reactive (more reactive than granular iron which is conventionally applied in reactive barriers) and can be used for in situ treatment. Nano zero valent iron effectively reduces chlorinated organic contaminants (e.g. Perchlorobenzen, Tetrachloroethylene, Perchloroethylene, pesticides, solvents) and also inorganic anions (perchlorate). It can even be used to recover/remove dissolved metals from solution (e.g. Cr (VI), U (VI)). Also nanoscale zero valent iron is more effective at reaching deep zones of contamination, and is more effective at contaminant degradation than iron of larger size. REFERENCES Andreta E (2003). Nanosciences and Nanotechnologies: What Future for Research. rfuture Conference and Expo, Chiba- shi, Chiba, Tokyo, Japan. Atkins P (1998). Physical Chemistry. 6th. Oxford University Press, Oxford, Melbourne, Tokyo. Breytenbach JH (2005). The Metris of vaccination international poultry production. Savian Influenza Control, 13(4):

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6 Taghizadeh et al. The Use of Nano Zero Valent Iron in Remediation of Contaminated Soil and Groundwater Maryam Taghizadeh has MSC in Civil Engineering-Environment Science from Babol Noshirvani university of Technology (Iran).Currently; she works in the Islamic Azad University of Behshahr. She has more than 5 articles in the international conference and Journal. Daryoush Yousefi Kebria has PHD in civil engineering-environment Science from Tarbiat modares University (Tehran-Iran).Currently; he is Assistant Professor in Civil Engineering, Babol University of Technology. He has more than 7 articles in the international conference and Journal. Gholamreza Darvishi has MSC in civil engineering-environment Science from Babol Noshirvani university of Technology (Iran). Currently, he works in the Islamic Azad University of Qaemshahr. He has more 3 articles in the international conference and Journals. Farshad Golbabaei Kootenaei is a PhD student in Environmental Engineering-Water and wastewater in Graduate faculty of Environment of Tehran University (Tehran-Iran). He has 6 articles in the international conference and Journals. 157