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WO2007115189A2 - Restauration in situ visant la neutralisation de contaminants inorganiques au moyen de nanoparticules de fer à valence zéro stabilisées - Google Patents

Restauration in situ visant la neutralisation de contaminants inorganiques au moyen de nanoparticules de fer à valence zéro stabilisées Download PDF

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WO2007115189A2
WO2007115189A2 PCT/US2007/065664 US2007065664W WO2007115189A2 WO 2007115189 A2 WO2007115189 A2 WO 2007115189A2 US 2007065664 W US2007065664 W US 2007065664W WO 2007115189 A2 WO2007115189 A2 WO 2007115189A2
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nanoparticles
nitrate
perchlorate
stabilized
iron
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WO2007115189A3 (fr
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Dongye Zhao
Yinhui Xu
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Auburn University
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Auburn University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/08—Reclamation of contaminated soil chemically
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation

Definitions

  • the present invention relates to mitigating the toxic effect of inorganic contaminants in contaminated sites, and more particularly, to using stabilized zero-valent iron nanoparticles for the in situ immobilization and/or remediation of toxic inorganic contaminants such as chromate (CrO 4 2" ), perchlorate (ClO 4 ' ), nitrate (NO 3 ' ), and arsenate (AsO 4 3" ) in water, brine, and soil.
  • Chromium has been widely detected in groundwater and soils, particularly at sites associated with metal plating, wood processing, leather tanning, metal corrosion inhibition, and pigment production. From 1987 to 1993, releases of various chromium compounds to land and water in the U.S.
  • MCL maximum contaminant level
  • ZVI particles and non-stabilized or agglomerated nanoparticles has been investigated in a number of laboratory and field studies.
  • permeable reactive barriers (PRBs) with commercially available ZVI powder have elicited great interest for in situ treatment of groundwater contaminated with various redox active compounds including Cr(VI).
  • PRBs permeable reactive barriers
  • a field-scale PRB using granular ZVI particles to remove Cr(VI) from groundwater was installed at the U.S. Coast Guard Support Center in North Carolina in June of 1996. After eight years of operation, the PRB remained effective for reducing more than 1,500 ⁇ g/L of Cr(VI) to less than 1 ⁇ g/L.
  • ZVI nanoparticles prepared using traditional methods tend to either agglomerate rapidly or react quickly with the surrounding media (e.g. dissolved oxygen or water), resulting in rapid loss in soil mobility as well as reactivity. Because agglomerated ZVI particles are often in the range of micron scale, they are essentially not transportable or deliverable in soils, and thus, cannot be used for in situ applications.
  • the surrounding media e.g. dissolved oxygen or water
  • Perchlorate (ClO 4 ' ) has been primarily used in solid rocket fuels. It is also widely used in firework powder, roadside flares, airbag inflators, and fertilizers imported from Chile. Past massive application of perchlorate has left a contamination legacy. Perchlorate has been detected at about 400 sites in groundwater, surface water, soil or public drinking water in more than 35 states across the United States with concentrations ranging from 4 ⁇ g-L '1 to more than 3.7 million ⁇ g-L "1 . Perchlorate has been also detected in milk and bottled water.
  • perchlorate When ingested, perchlorate can alter the endocrine function by blocking iodide from entering a person's thyroid gland, thereby reducing the production of thyroid hormones.
  • the adverse health effects are reported to be more profound for newborns, children, and pregnant women.
  • a study from the U.S. Centers for Disease Control (CDC) found that of the 36 percent of U.S. women with low iodine intake, almost any amount of perchlorate exposure was linked to a significant change in levels of thyroid hormones.
  • the US EPA adopted a Drinking Water Equivalent Level (DWEL) of 24.5 ⁇ g-L '1 .
  • DWEL Drinking Water Equivalent Level
  • Perchlorate is highly water-soluble, non-complexing, non-volatile, and chemically stable. For its unique chemistry, it has been highly challenging to remove perchlorate from water by traditional water treatment approaches.
  • IX has been considered as one of the best available technologies for perchlorate removal. While many commercial IX resins can offer high perchlorate sorption capacity, regeneration efficiency of the IX resins has been found prohibitively poor. As a result, current IX processes are often used on a disposable basis (i.e. the resin is disposed of after only one service run) or, when resin regeneration is practiced, it will result in large volumes of spent regenerant brine.
  • the spent regenerant is often characterized with high salinity (e.g.
  • ZVI zero-valent iron
  • Nitrate contamination of groundwater is also a widespread environmental problem, and has been associated with agricultural land runoff, leaching of nitrogen fertilizers, concentrated animal feeding operations, food processing, and industrial waste effluent discharge. Each year, about 11.5 million tons of nitrogen is applied as fertilizer in agricultural areas of the United States. Commercial fertilizer uses in the United States increased by a factor of 20 between 1945 and 1985. Manure produced yearly by farm animals in the United States contributes an estimated 6.5 million tons of nitrogen. The National Research Council (NRC, 1994) reported that there were approximately 300 - 400 thousands of nitrate-contaminated sites in the United States. [0016] Ingestion of nitrate in drinking water by infants can cause dangerously low oxygen levels in the blood.
  • Nitrate-N concentrations of 4 mg/L or more in rural drinking water supplies have been associated with increased risk of non-Hodgkin's lymphoma.
  • the US EPA has established a maximum contaminant level (MCL) of 10 mg/L nitrate as N (US EPA, 1995).
  • MCL maximum contaminant level
  • nitrate concentration in natural groundwater is generally less than 2 mg/L, it is common for ground water in 10% - 25% of the water-supply wells in large regions of the U.S. to exceed the MCL for nitrate.
  • Biological denitrification has been a rather mature technology for nitrate removal from municipal wastewater. However, it has not gained popularity in drinking water treatment for its slow kinetics under typical drinking water conditions, pH sensitivity, and unfavorable byproducts including taste and odor in the treated water.
  • Thermal nitrate destruction requires an anaerobic condition at temperatures of 200 - 350 0 C and pressures of 600 - 2800 psig and at pH 13 with the presence of reducing agents, such as ammonia, formate, urea, glucose, methane, and hydrogen.
  • Eqn (3) was proposed by Alowitz and Scherer (2002) using iron powers (18 - 35 mesh) and Fisher Scientific iron fillings (40 mesh) under controlled solution p ⁇ (5.5 - 9.0).
  • Eqn (4) was proposed by Huang et al. (1998) by assuming nitrite is one of the intermediate products of nitrate reduction.
  • Eqn(5) was suggested to be the main nitrate reduction pathway when nanoscale zero-valent iron (BET specific surface area to mass ratio equal to 31.4 m 2 /g) was used in anaerobic system under ambient conditions with no pH control (Choe et al., 2000). [0019] Studies have demonstrated that solution pH plays an important role in nitrate reduction by Fe 0 .
  • Nitrate reduction by iron powder at near-neutral pH was negligible in an unbuffered system, but it was greatly enhanced in the presence of a pH buffer (Zhang and Huang, 2005; Cheng et al., 1997).
  • Ruangchainikom et al. (2006) used a CO 2 -bubbled system to create an acidic environment favorable to nitrate reduction and found that the bubbling of CO 2 flow rate at 200 mL/min was sufficient for supplying H + to these reactions.
  • ZVI including 1) iron surface pretreatment; 2) addition of selected cations; 3) deposition of a second metal on iron surface; 4) presence of ultraviolet (UV) light and hydrogen peroxide (H 2 O 2 ); and 5) increasing ZVI surface area by preparing nanoscale ZVI.
  • He and Zhao developed a new class of Fe-Pd bimetallic nanoparticles by modifying the conventional preparation approach by using an environment-friendly and low-cost starch and a food-grade cellulose (known as sodium carboxymethyl cellulose, NaCMC) as a stabilizer.
  • the stabilized nanoparticles displayed both superior physical stability and much faster reactivity than their non-stabilized counterparts when used for degradation of chlorinated hydrocarbons (He and Zhao, 2005; 2006).
  • Arsenic is ranked the second most common inorganic pollutant in the U.S. superfund sites. Arsenic-contaminated soils, sediments and waste slurry are major sources of arsenic in food and water. To mitigate the toxic effect on human health, the maximum contaminant level (MCL) for arsenic in drinking water was lowered from the previous 50 ppb to 10 ppb, effective in January 2006. [0024] Arsenic is a redox active element, with As(V) or (III) being the two most common stable oxidation states in soils.
  • inorganic arsenic is more toxic than organic arsenic, and arsenic in soils is less bioavailable and less bioaccessible than As in water due to soil adsorption effect.
  • Arsenate can strongly interact with soils, especially, iron
  • Bioaccessibility is quantified by a physiologically based extraction test (PBET), which mimics the conditions in human stomach and essentially reflects an in vivo accessibility of As (Ruby et al. 1999).
  • PBET physiologically based extraction test
  • TCLP is an EPA-defined standard method for measuring extractability of various chemicals from solid wastes. Earlier, a number of researchers (Akhter et al. 2000; Jing et al. 2005; Miller et al. 2000) used TCLP tests to evaluate the leachability of As in contaminated soils.
  • the present invention provides a method for preparing highly stabilized and dispersible zero valent iron nanoparticles and using the nanoparticles as a remediation technology against inorganic chemical toxins in contaminated sites.
  • the method employs a composition containing select polysaccharides (starch or cellulose) as a stabilizer for the iron nanoparticles in a liquid carrier, and results in suspensions of iron nanoparticles of desired size and mobility in water (surface water, ground water or fresh water), brine (especially from ion exchange processes), soils or sediments.
  • the stabilizer facilitates controlling the dispersibility of the iron nanoparticles in the liquid carrier.
  • the step of delivering the iron nanoparticle suspension to a contaminated site preferably comprises injecting, spraying or just mixing the nanoparticles into the contaminated site, which is typically a contaminated surface or subsurface zone or location, and which may comprise soil, sediment, ground water, solid wastes, brine, or surface water in order to promote the remediation of the inorganic chemical toxin.
  • the iron nanoparticles react with the inorganic chemical toxin to transform, degrade or immobilize the toxin to a less toxic form.
  • These zero valent iron nanoparticles can be easily delivered, e.g. sprayed, mixed and/or injected, to surface or sub-surface contaminated sites or zones.
  • the nanoparticles can thus be applied in situ and are an especially effective method to completely transform and degrade inorganic chemical toxins in both fresh water and brine residue from ion exchange regeneration.
  • the relatively high surface area, relatively high reactivity, and the ability to diffuse and disperse in water, soil, brine and sediment makes the stabilized iron nanoparticles disclosed herein ideally suited for the present method.
  • the iron nanoparticles typically have a particle size ranging from about 1 nm to about 200 nm.
  • the composition includes about >80% by weight zero valent iron nanoparticles, preferably >95% by weight.
  • the composition also includes about ⁇ 20% by weight stabilizer.
  • the iron nanoparticles are prepared in a water solution at a concentration ranging from 0.2 to 10 g/L.
  • the preferred stabilizers are selected from the group consisting of water soluble starch, carboxymethyl starch, thiolated starch, aminated starch, sodium carboxymethyl cellulose, carboxymethyl chitosan, and mixtures thereof.
  • the desired iron nanoparticles can be prepared with the aid of select low cost and environmentally friendly starch or cellulose as a stabilizer.
  • the stabilized iron nanoparticles can be directly injected, mixed or dispersed into contaminated sites such as ground water, surface water, fresh water, brine, soils or sediments, and the size, growth rate, and dispersibility of the nanoparticles can be controlled by manipulating the types and concentration of the stabilizer used.
  • the application of the nanoparticles will not pose any harmful effect on the local environment.
  • Figure 1 is a graph illustrating reduction of Cr(VI) in water over time by CMC-stabilized Fe nanoparticles.
  • Figure 2 is a graph illustrating Cr(VI) reduction as a function of dosage in the presence of CMC, borohydride, and various concentration of CMC- stabilized Fe nanoparticles.
  • Figure 7 is a graph illustrating Fe breakthrough curve as 0.06 g/L ZVI nanoparticles was passed through a sandy loam soil bed.
  • Figure 8 is a TEM image of fresh 2 g L "1 Fe(O) nanoparticles stabilized with 0.9% (w/w) NaCMC wherein the dark spherical dots are Fe(O) nanoparticles.
  • Figure 9 is a graph illustrating perchlorate reduction by NaCMC- stabilized Fe(O) nanoparticles at various temperatures without pH control.
  • Figure 10 is a graph illustrating the pseudo- first-order model fitted perchlorate reduction by Fe(O) nanoparticles at various temperatures.
  • Figure 11 is a graph illustrating an arrhenius plot of the natural logarithm of the estimated first-order rate constant (k) against 1/T for perchlorate reduction by NaCMC-stabilized Fe(O) nanoparticles.
  • Figure 12 is a graph illustrating the chlorine mass balance of perchlorate reduction by NaCMC-stabilized Fe(O) nanoparticles.
  • Figure 13 is a graph illustrating the perchlorate reduction by various
  • FIG. 14 is a graph illustrating the perchlorate reduction by NaCMC- stabilized Fe(O) nanoparticles in the presence of various background chloride concentration at 95 0 C.
  • Initial [ClO 4 " ] 10 mg L "1
  • Fe(O) dose 1.8 g L "1
  • NaCMC 0.9% (w/w).
  • Figure 15 is a graph illustrating the effect of pH on perchlorate reduction by NaCMC-stabilized Fe(O) nanoparticles in the presence of 6% NaCl (w/w) at 95 0 C.
  • Figure 16 is a TEM image of 0.9% NaCMC-stablized Fe 0 nanoparticles (1 g/L).
  • Figure 17 is a graph illustrating degradation of nitrate in fresh water by various ZVI particles.
  • Fe 0 was prepared with 0.9% NaCMC. Solution pH was controlled at 7.0 to about 7.5 by adding 0.05 M HEPES buffer.
  • Figure 18 is a graph illustrating the effect of Fe/Nitrate molar ratio on nitrate removal.
  • Fe 0 was prepared with 0.9% NaCMC.
  • Solution pH was controlled at 7.0 to about 7.5 by adding 0.05 M HEPES buffer.
  • Figure 19 is a graph illustrating nitrate reduction by different kind of
  • Figure 22 is a graph illustrating nitrate removal by stabilized Fe 0 in the presence of different concentration of NaCl.
  • Fe 0 was prepared with 0.9% NaCMC. Solution pH was controlled at 7.1 to about 7.5 by adding 0.05 M HEPES buffer.
  • Fe 0 was prepared with 0.9% NaCMC.
  • Solution pH was controlled at 7.1 to about 7.5 by adding 0.05 M HEPES buffer.
  • Figure 24 is a graph illustrating a comparison of arsenic (As) bioaccessability (PBET) of WAOS soil sample by different Fe/As ratio iron based nanoparticles treatment.
  • As arsenic
  • Figure 25 is a graph illustrating a comparison of As bioaccessability
  • PBET As-spiking soil sample by different Fe/As ratio iron based nanoparticles treatment.
  • Figure 26 is a graph illustration a comparison of As TCLP leachability of WAOS soil samples by series Fe/As ratio iron based nanoparticles treatment.
  • Figure 27 is a graph illustrating a comparison of As TCLP leachability of As-spiking soil samples by series Fe/As ratio iron based nanoparticles treatment.
  • Figure 28 is a graph illustrating a comparison of As bioaccessability of WAOS soil samples for 3 and 7 days treatment by different iron based nanoparticles.
  • Figure 29 is a graph illustrating a comparison of As leachability of
  • WAOS soil samples for 3 and 7 days treatment by different iron based nanoparticles WAOS soil samples for 3 and 7 days treatment by different iron based nanoparticles.
  • Figure 30 is a graph illustrating a comparison of As bioaccessability of As-spiking soil samples for 3 and 7 days treatment by different iron based nanoparticles.
  • Figure 31 is a graph illustrating a comparison of As leachability of
  • the present invention provides a method for preparing novel stabilized zero valent iron (ZVI) nanoparticles of controlled size, and using the iron nanoparticles as a remediation technology for immobilizing and/or degrading inorganic chemical toxins such as arsenates, nitrates, chromates or perchlorates in contaminated sites.
  • the technology employs zero valent iron nanoparticles dispersed in a liquid carrier (water) and utilizes a stabilizer to control the dispersibility of the iron nanoparticles in the liquid carrier and in the targeted media (soils, sediments, water, brine, or solid and hazardous wastes).
  • the nanoparticles are particularly advantageous because they have high surface area, are highly reactive with the inorganic chemical toxins to be remediated, and are readily able to be delivered in soils, sediments, brine and water to reach the contaminated sites or zones.
  • the nanoparticles can be easily delivered, e.g. mixed, sprayed or injected, to surface or subsurface sites of contaminated solid wastes, soils, sediments, brine, ground water or surface water.
  • the composition can be used in- situ to remediate the contaminated site.
  • the preferred metal nanoparticles useful in the present invention are zero valent iron (Fe 0 ) nanoparticles.
  • Zero valent iron nanoparticles are highly stable, extremely insoluble in water, unavailable to biota, innocuous to the environment and extremely reactive with arsenates, nitrates, chromates and perchlorates.
  • the preparation of the nanoparticles involves a water-based approach. In general, the zero valent iron nanoparticles are prepared in three steps. The first step is to prepare a dilute aqueous solution of a stabilizer, such as a water soluble cellulose or starch containing about 0.001% to about 1.0% (w/w/) of the stabilizer (preferably sodium carboxymethyl cellulose; i.e.
  • NaCMC with a molecular weight from 5,000 to 500,000
  • nitrogen purged deionized water while also preparing an aqueous solution containing 0.05 to 1 g/L as Fe OfFe 2+ containing 0.1 to 1.0 M Fe 2+ and/or OfFe 3+ containing 0.1 to 1.0 M Fe 3+ , and adjusting the pH of the solutions between 6 and 7 with, for example, sodium hydroxide (NaOH).
  • the Fe 2+ solution may, for example, be obtained by preparing an aqueous solution of Fe SO 4 • 7H 2 O.
  • the second step is to mix the two solutions together, and vary the stabilizer-to-Fe molar ration and/or types of stabilizer for preparing nanoparticles of desired concentration, size and dispersibility.
  • the third step is to add stoichiometric amounts of an electron donor (BH " 4 ) such as a sodium borohydride (NaBH 4 ) solution into the mixture of step 2 and allow for reaction for about 20 minutes under vacuum and at room temperature. Non-magnetic stirring should be employed during both steps 2 and 3.
  • BH " 4 ) such as a sodium borohydride (NaBH 4 ) solution
  • NaBH 4 sodium borohydride
  • Step 3 Fe 3+ /Fe 2+ is reduced to Fe(O) with 1 to about 1.3 times stoichiometric amounts of sodium borohydride (NaBH 4 ).
  • the reactor system is operated under vacuum.
  • the type and concentration of the stabilizer can be varied to optimize the preparation.
  • the optimal nanoparticles will be determined based on: 1) reactivity for perchlorate and nitrate reduction in the target media; 2) cost; and 3) environmental friendliness.
  • a novel stabilizer should possess the following essential attributes: 1) it can effectively facilitate dispersion of the nanoparticles; 2) it must not cause any harmful environmental effect; 3) it will not alter the conductivity of soils or sediments; and 4) it must be cost-effective.
  • Starch and cellulose are the most abundant polysaccharide members.
  • the physical-chemical characteristics of nanoparticles are governed by four major factors, including a) particle size, b) surface properties, c) particle- solvent interactions, and d) particle-particle interactions. Accordingly, the present invention's strategy for preparing the "smart" nanoparticles is geared toward controlling the particle size and growth/agglomeration rate with the aid of select starch or cellulose as a capping agent or surface modifier.
  • Agglomeration of zero valent iron nanoparticles is a thermodynamically favorable process and can take place in a number of fashions, including a) Oswald ripening (i.e.
  • a capping or dispersing/stabilizing agent can regulate the size growth of nanoparticles through: a) electrostatic interactions (adsorption of charged stabilizer molecules to the metal core, resulting in an electrical double layer and Coulombic repulsion between capped particles), and/or b) steric stabilization (coating metal core with sterically bulky agents such as polymers impedes particle agglomeration).
  • the physical-chemical characteristics of the resultant nanoparticles can be affected by: a) the physical-chemical properties of the capping agents (e.g. molecular weight, structural orientation, and functionalities); b) concentration of the stabilizers (i.e., stabilizer: metal molar ratio); c) solution chemistry (pH and ionic strength); and d) temperature.
  • solution chemistry and temperature should be compatible with the brine, subsurface and groundwater conditions. Therefore, the greatest flexibility in preparing the desired nanoparticles comes from the diverse choices of available starch or cellulose (e.g. the molecular weight for starch/cellulose ranges from a few thousands to 1 million).
  • Starch and cellulose are the most abundant polysaccharide members.
  • Water soluble starch and water soluble cellulose are the most preferred capping agents for preparing the nanoparticles.
  • NaCMC water soluble cellulose
  • Table 10 shows a list of useful polysaccharides for use as stabilizers or capping agents.
  • Table 10 A list of polysaccharides for modifying/capping nanoparticles.
  • a capping agent a) molecular weight, size and their distribution; b) molecular structure (linear vs. globular); c) functional groups; d) degree of functionalization/substitution; e) viscosity; and f) water solubility.
  • Molecular weight of the coating polymer plays a crucial role in stabilization of nanoparticles. For example, low-molecular-weight stabilizers may form coatings too thin to screen van der Waals forces, while high-molecular-weight stabilizers may bridge between particles to form floes. It appears that the carboxy methyl groups in NaCMC facilitate sorption of the stabilizer to Fe(O) nanoparticles, resulting in improved stabilization.
  • Table 10 is not intended to be exhaustive, nor is every compound necessarily a suitable agent for all of the nanoparticles. Where comparable functional stabilizers are not commercially available, functionalization of select starch and cellulose can be carried out in a laboratory following the well- established procedures used for preparing various food-grade functionalized starch or cellulose derivatives.
  • 0.001% to about 1.0% by weight (w/w) of the stabilizer should be incorporated into a composition containing the nanoparticles.
  • the preferred amounts will typically be between about 0.001% to about 0.5% (w/w), and the most preferred amounts between about 0.001% to about 0.2% (w/w).
  • the composition containing the nanoparticles and stabilizer will also include from about 95% to about 99.9% (w/w) of a liquid carrier in which the nanoparticles are dispersed by the stabilizer.
  • the liquid carrier is preferably water so that the composition is an aqueous solution, but other liquids could be employed so long as the liquid carrier is compatible with the stabilizer and nanoparticles, is environmentally friendly, and is relatively inexpensive.
  • the present invention provides a method for degrading a perchlorate in spent ion exchange (IX) brine and/or water (ground water, surface water and fresh water). Measuring the production rates of the intermediates and final chloride will provide direct evidence of the perchlorate degradation rates and completeness. Moderate heating to between about 5O 0 C and
  • the present invention provides a method for degrading a nitrate in spent ion exchange (IX) brine and/or water
  • the present invention provides a method for in situ reductive immobilization of a chromate and/or arsenate in soils, water or other industrial wastes.
  • Stabilized zero valent iron nanoparticles can reduce leachability of chromates and arsenates in soils by 90%, depending on the particle size and concentration used.
  • arsenate refers to a salt or ester of an arsenic acid. Typically examples include lithium arsenate, sodium arsenate, potassium arsenate, magnesium arsenate, calcium arsenate, ammonium arsenate, lead arsenate, and mixtures thereof.
  • nitrate refers to a salt or ester of nitric acid. Typical examples include lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, ammonium nitrate, lead nitrate, and mixtures thereof.
  • chromate refers to a salt or ester of chromic acid. Typical examples include lithium chromate, sodium chromate, potassium chromate, magnesium chromate, calcium chromate, ammonium chromate, lead chromate, and mixtures thereof.
  • perchlorate refers to a salt or ester of perchloric acid. Typical examples include lithium perchlorate, sodium perchlorate, potassium perchlorate, magnesium perchlorate, calcium perchlorate, ammonium perchlorate, lead perchlorate, and mixtures thereof.
  • the present invention provides for the recycling and reuse of brine treated with zero valent iron nanoparticles for regeneration of perchlorate and/or nitrate exhausted ion exchange (IX) resins. For the case of perchlorate brine, the nanoparticle treatment converts all perchlorate to chloride.
  • the resultant Cl " is not only innocuous, but also compensates the chloride loss in the brine upon regeneration uses.
  • the ferrous ions are fully soluble and will not interfere with the regeneration runs. Therefore, the treated brine can be reused for regeneration.
  • the brine will contain both ClO 4 " and Fe 2+ ions.
  • This new brine can be treated following the same concept.
  • the Fe 0 nanoparticles in this case will be produced by reducing the Fe 2+ ions in the spent brine with stoichiometric amounts of sodium borohydride in a sealed vessel.
  • the resultant nanoparticles then destroy the perchlorate (note: despite the strong reducing power, sodium borohydride cannot reduce perchlorate).
  • the treated brine is then reused for regeneration, and the loop goes on. Consequently, the process results in minimal amounts of waste residuals.
  • the schematic of the proposed brine treatment and reuse process is as follows:
  • both Fe 2+ and NH 4 + ions are present in the treated brine. Again, both cations do not affect the regeneration of nitrate, and thus, the treated brine can be reused for regenerating nitrate-laden resin.
  • Fe 2+ can be reduced by borohydride to form the Fe 0 nanoparticles in-situ in the same manner as for perchlorate.
  • the Fe 0 nanoparticles then reduce nitrate to ammonium.
  • the ammonium in the brine is further concentrated. The concentrated ammonium can then be removed from the brine via the following reaction:
  • Fe 0 nanoparticles for rapid and complete destruction of perchlorate and nitrate in spent IX brine or saline water.
  • the most distinctive innovation of this technology includes: First, it employs a new class of starch- or cellulose-stabilized Fe 0 nanoparticles.
  • the nanoparticle stabilizing technique represents a substantial advancement in preparing Fe 0 nanoparticles suitable for various environmental cleanup uses, and can prevent the Fe 0 "nanoparticles" from agglomerating to larger "floes” and thereby preserve the maximum reactivity of the nanoparticles.
  • this proposed technology offers some key advantages, including a) it degrades perchlorate or nitrate much faster and completely, and thus, requires a much smaller reactor size and results in no harmful intermediate by-products, b) it does not produce any process wastes, c) it is more viable and stable, and d) it requires no sophisticated operation and maintenance.
  • the overall goal of this experiment was to test the feasibility of using the CMC-stabilized ZVI nanoparticles developed by He et al. (2006) for in situ reductive immobilization of Cr(VI) in contaminated soils.
  • the specific objectives of this work were to: (1) test the CMC-stabilized nanoparticles for reducing and removing Cr(VI) in water and in a sandy loam soil slurry under various experimental conditions, and (2) test the stabilized nanoparticles for reductive immobilization of Cr(VI) in a contaminated sandy loam through fixed-bed column elution experiments. 1. Materials and Methods
  • a sandy loam soil obtained from a local farm in Auburn AL, was used in this study. Before use, the raw soil was sieved with a 2 mm standard sieve. The soil contains 0.43% of organic matter and was initially free of chromium. Cr(VI) was loaded to the soil by equilibrating 1 L of a solution containing 315 mg/L Cr(VI) (in Na 2 CrO 4 ⁇ H 2 O) with 180 g of an air-dried soil sample in a batch reactor at pH 6.5 (pH was maintained at pH 6.5 by intermittent adjusting using 1 N HCl or 1 N NaOH solution), which resulted in a 83 mg/kg Cr(VI) uptake in the air- dried soil.
  • the stabilized ZVI nanoparticles were prepared in water by reducing
  • the supernatant was then analyzed for total Cr as well as Cr(VI) , and the Cr(VI) reduction rate was calculated based on mass balance calculations.
  • the initial and final pH was measured.
  • a control test was conducted in parallel with DI water and under otherwise identical conditions. All the experimental points were duplicated to assure data quality.
  • the flow rate was kept constant at 0.15 mL/min, which translates into an empty bed contact time (EBCT) of 21 minutes and a superficial velocity (SLV) of 4.2 X 10 "5 m/s.
  • EBCT empty bed contact time
  • SLV superficial velocity
  • a control column test was also performed in parallel but using deionized water and CMC at pH 5.6 as the influent.
  • the concentration of total Cr and Cr(VI) in the effluent was then followed.
  • the concentration of total Fe in the influent and effluent was also analyzed and compared.
  • the effectiveness of the stabilized ZVI nanoparticles for Cr immobilization was quantified by comparing the teachability of Cr in the soil before and after the nanoparticle treatment.
  • the teachability was determined following the EPA TCLP method (EPA method 1311) as well as the California Waste Extraction Test (WET, California HML Method 910).
  • WET California Waste Extraction Test
  • Fluid #1 was used as the extractant.
  • air-dried soil samples were mixed with the TCLP fluid at a solid-to-solution ratio of 1 g to 20 mL. The mixtures were then rotated on an end-to-end rotator at 30 rpm and at room temperature (21 ⁇ 1 C) for 19 hours and then centrifuged at 500 g-force for 20 min.
  • the supernatant was then collected and filtered with 0.45 pm membranes.
  • the filtrate was then acidified to pH ⁇ 2.0 with 1 N HNO3 and analyzed for Cr concentration.
  • air-dried soil samples were extracted with a stronger citric acid solution for 48 hours at a solid-to-solution ratio of 1 g to 10 mL on a rotating shaker.
  • the mixtures were then centrifuged at 5,000 g-force for 20 min, and the supernatants filtered with 0.45 ⁇ m membranes.
  • the filtrate was then acidified with 5% (v/v) nitric acid, and analyzed for Cr.
  • Total Cr was analyzed using a graphite atomic absorption spectrophotometer (GF-AA, Perkin Elmer 3110). Cr(VI) was analyzed following the standard 3500-CrB. Colorimetric Method (Clesceri et al. 1998), which employed a UV- Visible spectrophotometer (HP 8453) operated at 540 nm wavelength.
  • Total Fe was analyzed using a flame atomic-absorption spectrophotometer (FLAA, Varian model 220FS).
  • Fig. 1 shows the batch kinetic data during reduction of Cr(VI) by
  • the resultant Cr(OH)3 is a sparingly soluble precipitate (K sp 6.3 x 10 "31 ), and thus, can be easily separated from water.
  • Cr(III) can also be precipitated via the formation Of Fe(III)-Cr(III) hydroxide according to Eqn (8)
  • the CMC molecules in the system not only stabilize the Fe nanoparticles, they can also complex with the resultant Cr 3+ and Fe 3+ ions and their metal hydroxide precipitates.
  • the initial pH of the solution in the batch tests was about 9.0, and the final pH was increased to 9.2 to about 9.4, which was high enough to precipitate Cr(OH) 3 (K sp of 6.3 X 10 '31 ) and Fe(OH) 3 (K sp of 4 X 10 " ). However, no precipitation was observed during the reaction.
  • the stabilized nanoparticles can reduce over 90% Cr(VI) under ambient conditions, i.e. one gram of the stabilized ZVI nanoparticles can reduce 252 mg Cr(VI) in water. This number is 20 times greater than that observed by Ponder et al. (2000) who reported that one gram of resin-supported ZVI nanoparticles reduced only 12.6 mg Cr(VI) at an Fe dosage of >8 times the stoichiometric amount for 8 days.
  • Cao and Zhang (2006) reported that one gram of non-stabilized Fe nanoparticles was able to reduce 84.4-109 mg Cr(VI) in the groundwater.
  • Fig. 3 shows the transient release of total Cr or Cr(VI) when 1.5 g of a Cr(VI)-laden soil sample was mixed with 15 mL of the nanoparticle suspension containing 0.08 g/L Fe and at an initial pH of 9.0.
  • Cr(VI) desorption kinetic data in DI water at pH 9.0 are also superimposed in the Fig. 3.
  • Fig. 5 (a) shows that the Fe nanoparticle suspension essentially eluted no chromate, i.e. the Fe nanoparticles converted all of the 4.9% Cr(VI) eluted from the soil bed to Cr(III) during the treatment.
  • the WET Compared to the TCLP fluid, the WET employs a much more aggressive extracting agent (citric acid for WET vs. acetic acid for TCLP). As a result, the leached Cr in the WET extractant was 1.2 mg/L for the same untreated soil (3 times greater than in the TCLP fluid). Upon the brief nanoparticle treatment, the WET-leached Cr concentration was reduced to 0.28 mg/L, a reduction of about 76%.
  • the extracted Cr in both TCLP and WET tests was far below the regulated TCLP or WET limit (5 mg/L), which is commonly applied to classifying hazardous wastes in the U.S.
  • the stabilized nanoparticles may also be applied to treat Cr(VI)-laden solid wastes, which may greatly minimize Cr(VI) leachability and cut down the handling and disposal cost of hazardous materials.
  • the nanoparticles are expected to be highly mobile in soil to ensure delivery of the nanoparticles to the targeted locations.
  • Fig. 7 shows that more than 81 % of Fe introduced broke through rapidly in less than one BV, indicating that the stabilized ZVI nanoparticles were highly mobile through the soil bed Fig. 7 also showed that about 19% of Fe introduced was stuck in the soil bed.
  • a number of processes can be held responsible for retaining Fe in the soil bed. For example, some Fe larger particles may be intercepted by the soil via the classical filtration mechanisms; in addition, because of the high reactivity, a fraction of zero-valent Fe is oxidized to iron oxides or hydroxides, which can precipitate or be sorbed in the soil pores. After 3 BVs, the effluent Fe concentration dropped gradually, indicating more Fe was retained in the soil. Results in Fig.
  • the stabilized Fe nanoparticles will be completely converted to iron minerals in a month or so. These innocuous minerals are likely much less mobile in soils, especially when CMC molecules are degraded, and eventually incorporated in the ambient geo-media. From environmental remediation aspect, the retained Fe minerals can offer added sorption capacity for a number of toxic chemicals including, chromate. 3. Summary and conclusions
  • This present experiment aims to test the feasibility of using the CMC- or starch- stabilized ZVI nanoparticles for perchlorate destruction in fresh water or in typical spent IX regenerant brine or contaminated saline water.
  • the specific objectives are to: 1) determine the rate and extent of perchlorate reduction by stabilized ZVI nanoparticles; and 2) characterize the influences of temperature, salinity, and pH on the reaction rate. 1. Materials and methods
  • HEPES 1-piperazineethane ethanesulfonic acid
  • Al chloride A1C1 3 « 6H 2 O) (Fisher); cobalt chloride (CoCl 2 ⁇ H 2 O) (Fisher); cupric chloride (CuCl 2 -2H 2 O) (Fisher); ferrous sulfate (FeSO 4 » 7H 2 O) (Acros Organics, Morris Plains, NJ, USA); methyltrioxorhenium (VII) (MeReO 3 , 98%) (Strem Chemicals, Newburyport, MA, USA); nickel chloride (NiCl 2 -OH 2 O) (Fisher); potassium hexachloropalladate (K 2 PdCl 6 , 99%) (Acros Organics); sodium borohydride (NaBH 4 ) (MP Biomedicals, Aurora, OH, USA); sodium carb
  • Stabilized ZVI nanoparticles were prepared following a procedure reported previously (He and Zhao, 2005; He et al. 2007). In brief, the preparation was carried out in a 500 mL flask attached to a vacuum line. A solution containing 1% (w/w) starch or 1% CMC was prepared by dissolving a waster soluble starch or CMC with deionized (DI) water and then the solutions were purged with purified N 2 for half an hour to remove dissolved oxygen (DO). Stock solutions of 0.1-0.2 M FeSO 4 » 7H 2 O were also prepared with degassed DI water.
  • DI deionized
  • a FeSO 4 » 7H 2 O stock solution was added to the starch or CMC solution through a burette to yield a desired concentration of iron and the stabilizer.
  • the mixture was purged with N 2 for half an hour to remove DO and to mix the solution.
  • Fe(II) ions were then reduced to Fe(O) nanoparticles by adding a stoichiometric amount of sodium borohydride to the mixture.
  • the reactor system was operated under inert conditions through continuously vacuuming. The flask was hand-shaken intermittently during the preparation. When gas (hydrogen) evolution ceased (after 15 min), the ZVI nanoparticles were ready for use.
  • TEM and DLS characterization [00128] Transmission electron micrograph (TEM) images were obtained using a Zeiss EMlO transmission electron microscope (Zeiss, Thornwood, NJ) operated at 25 and 40 kV. The TEM image was analyzed using a specialty image processing software (ImageJ, give sources) to obtain the particle size. Detailed procedures on sample preparation were reported elsewhere (He and Zhao, 2005).
  • Fig. 8 shows the transmission electron microscope image of the ZVI nanoparticles prepared at 2 g-L "1 Fe and stabilized with 0.9% CMC. The stabilized ZVI nanoparticles appeared as discrete nanoparticles and remained dispersed in water for more than one week.
  • Fig. 9 shows the perchlorate reduction kinetics using 1.8 g-L "1 ZVI nanoparticles stabilized with 0.9% NaCMC (w/w) at temperatures ranging from 25 0 C to 1 10 0 C.
  • the initial pH was about 6.5 and the final ph was increased to 7.5-7.8 after 6 hours.
  • the degradation proceeded slowly with only 23% of perchlorate reduced in 6 hours.
  • the temperature was raised to 50 0 C, 80 0 C, 95 0 C, and 1 10 0 C, respectively, the reaction was accelerated progressively.
  • [ClO 4 ' ] is the perchlorate concentration (mg-L " ) in water at time t (min)
  • k SA is the specific reaction rate constant based on surface area of the nanoparticles (L # min ⁇ '*m 2 )
  • ⁇ s is the specific surface area of the nanoparticles (m 2# g "1 )
  • p m is the mass concentration of the nanoparticles (g'L “1 )
  • k obs is the observed pseudo- first-order rate constant (min "1 ). Because the model describes only reactive degradation of perchlorate, it is only used for the degradation data after perchlorate concentration was recovered from the sorption/desorption perturbation step. [00137] Fig.
  • k is the reaction rate coefficient (min “1 )
  • A is a constant
  • E a is the activation energy (kJ ⁇ mol “1 )
  • R is the universal gas constant (8.314 J* IC 1 TnOl “1 )
  • T is the absolute temperature (K).
  • Fig. 1 1 shows the Arrhenius plot of the first-order rate constant (k obs ) against (1/T) in accord with Eq. (13), which results in an activation energy (E a ) of 52.59 ⁇ 8.41 kJ-mol "1 and an A value of 194,075.
  • E a activation energy
  • Gu et al. (2003) reported an activation energy of 120 ⁇ 5 kJ ⁇ mol "1 when ferrous iron was used to reduce a perchlorate waste residual containing ferric chloride and hydrochloric acid at elevated temperatures (up to 200 0 C) and/or pressure (about 20 atm).
  • Cao et al. (2005) reported an activation energy of 79.02 ⁇ 7.75 kJ'mol "1 for perchlorate reduction by non- stabilized ZVI nanoparticles.
  • Fig. 13 compares the perchlorate degradation rates for various particles at 110 0 C under otherwise identical conditions. Again, Eq. (13) is used to interpret the experimental data, and Table 2 gives the fitted model parameters. Based on the k ObS values, starch- and CMC-stabilized ZVI nanoparticles degraded perchlorate 1.8 and 5.5 times, respectively, faster than non-stabilized ZVI particles. Based on the surface-area normalized rate constant ks A , starch- and CMC-stabilized ZVI nanoparticles degraded perchlorate 1.8 and 3.3 times, respectively, faster than non-stabilized ZVI particles.
  • ks A values suggest that stabilizers not only increased the surface area of the nanoparticles (because of the much smaller particle size), but also resulted in much more reactive particle surface.
  • the k $A value for CMC-stabilized ZVI nanoparticles is more than 2 orders of magnitude greater than that for a cast iron reported by Oh et al. (2006a).
  • the k obs and k SA for CMC-stabilized nanoparticles are 3.0 and 1.8 times, respectively, higher than for starch-stabilized nanoparticles. This observation indicate that CMC is a more efficient stabilizer than starch, i.e. CMC gives not only smaller but also more reactive ZVI nanoparticles.
  • the perchlorate reduction rate drop for Fe-Pd nanoparticles can be attributed to 1) physical shielding of the Fe(O) surface by the coated metal, 2) loss of Fe(O) via reaction of Eq. (16), and more importantly 3) the metal catalysts were catalyzing the corrosion reaction of ZVI (Eq. 10), rendering significant loss in perchlorate reducing power of the ZVI nanoparticles.
  • Cao et al. (2005) reported that addition of Pd or Ag to non-stabilized ZVI particles showed no performance enhancement.
  • Rhenium has been well recognized to be able to catalyze perchlorate reduction through an oxygen transfer reaction (Cai and Espenson, 2005; Abu-Omar et al., 2000; 2006).
  • a recent study reported that perchlorate was reduced completely to chloride within 24 hours by hydrogen (40 psig) in the presence of methyltrioxorhenium (MeReO 3 , 0.5 mM) and palladium (0.5 mM) as catalysts (Hurley and Shapley, 2006).
  • MeReO 3 0.5 mM
  • Pd 0.5 mM
  • This reaction enhancement by chloride can be attributed to three factors.
  • the passive oxide layers formed on the iron surface can be broken apart in the presence of chloride. It has been reported that hard Lewis bases (such as Cl “ , Br “ , I " ) are especially aggressive toward passivating oxide layers because they diffuse readily into the passivation film and form strong complex with iron centers (Gotpagar et al., 1999; Johnson et al., 1998). When the passivation oxide layers are broken by these diffusing anions, more Fe(O) surface are available for perchlorate reduction, which resulted in a improved perchlorate degradation rate.
  • Fig. 15 shows the perchlorate reduction using 1.8 g-L "1 CMC- stabilized ZVI nanoparticles in the presence of 6% (w/w) NaCl at 95 0 C and at various solution pH.
  • red precipitate was observed in the filter when the reacted Fe(O) solution was filtered through 0.22 ⁇ m membrane filter.
  • Perchlorate is a widespread contaminant in groundwater and surface water. Although it is in the highest oxidation level (+7) of chlorine, perchlorate is hard to be reduced due to the high activation energy barrier. Stabilized Fe(O) nanoparticles were used in this study to reduce perchlorate in both fresh water and simulated ion-exchange regenerant brine. The main conclusions from this study include:
  • R 2 is the linear regression coefficient for plots of ln(C/Co') aj gainst reaction time (min) as shown in Fig. 3.
  • Table 2 The estimated perchlorate reduction rate constants for various iron nanoparticles at 110 0 C.
  • the surface area of NaCMC-stabilized Pd/Fe was used as the same of NaCMC- stabilized Fe.
  • the overall goal of this experiment is to test the effectiveness of using the CMC-stabilized Fe 0 nanoparticles for rapid degradation of nitrate in water.
  • the specific objectives are to: 1) prepare CMC-stabilized Fe 0 nanoparticles following the approach by He and Zhao (2005); 2) determine the rate and extent of nitrate reduction by the stabilized Fe 0 nanoparticles; 3) characterize the influences of pH, salinity and a metal catalyst on the nitrate reaction rate; and 4) test the effectiveness of using stabilized Fe 0 for degradation of nitrate in saline water.
  • Materials and Methods 1.1. Chemicals.
  • Stabilized Fe 0 nanoparticles were prepared in a 250 mL flask attached to a vacuum line. Before use, deionized (DI) water and NaCMC solution were purged with purified N 2 for 30 minutes to remove dissolved oxygen (DO).
  • DI deionized
  • NaCMC NaCMC
  • FeSO 4 -7H 2 O stock solution (0.1M) was prepared freshly before use with degassed DI water. In a typical preparation, FeSO 4 -7H 2 O stock solution was added to the NaCMC solution to yield a desired concentration of Fe (1 g/L) and NaCMC (0.9%, w/w) (give concentrations of Fe and NaCMC you used, how about starch? Strach has not been tried in this study).
  • Fe2+ ions were then reduced to FeO by adding a stoichiometric amount of sodium borohydride into the mixture under shaking. .
  • Ferrous iron was reduced following the reaction stoichiometry:
  • TEM Zeiss EMlO transmission electron microscope
  • PSS Nicomp 380 Submicron Particle Sizer
  • the freshly prepared 1 g/L Fe 0 was diluted to 0.1 g/L with nitrogen-purged 0.2 % NaCMC solution before DLS measurement.
  • Solution viscosities (2.74 cp for 0.2 % NaCMC solution) were measured by a Gilmont falling ball viscometer, then used to correct for the influence of viscosity on particle mobility. All samples were placed in the machine for 5 minutes prior to start of measurements to eliminate temperature differences between the sample and the machine. Three cycles of 20 minutes of data collection time each were run. The instrument parameters were set as follows: automatic choice of channel width; number weighting; and minimum diameter of 1 nm. The DLS data were processed with a software package CW380 to yield the number- weighted size distributions.
  • Nitrate and nitrite were analyzed using a Dionex Ion Chromatography (DX- 120) equipped with an AS 14 column, an AG 14 guard column, and a 100 ⁇ L sample loop. A solution containing 3.5 mM sodium carbonate and 1.0 raM sodium bicarbonate was used as the eluent. The detection limits for nitrate and nitrite are 0.01 mg/L and 0.008 mg/L, respectively. Ammonium was measured by adding Nessler reagent to the samples. After allowing 10 minutes for yellow color development, the U V- Vis adsorption was measured by an HP 8453 UV- Visible spectrophotometer at a wavelength of 425 nm. The detection limit for ammonium is 0.4 mg/L. 2.0 Results and Discussion
  • Figure 16 shows a representative transmission electron microscope (TEM) image of freshly-prepared NaCMC-stabilized Fe 0 nanoparticles. Unlike non-stabilized Fe 0 particles, the stabilize nanoparticles appear as well dispersed, nanoscale particles. Dynamic Light Scattering (DLS) tests were also carried out to determine the particle size distribution. The mean size of the freshly prepared 0.9% NaCMC stabilized Fe 0 nanoparticles was measured to be 7.4 nm with a standard deviation of 1.2 nm. A surface area of about 103.02 m 2 /g was calculated by following the method described by He and Zhao (2005) and based on a diameter of 7.4 nm.
  • TEM transmission electron microscope
  • Figure 17 compares nitrate degradation rates for non-stabilized Fe 0 , CMC-stabilized Fe 0 , and CMC-stabilized Fe-Pd nanoparticles under otherwise identical conditions.
  • solution pH was controlled at 7.0-7.5 during the reaction with 0.05 M of an HEPES buffer.
  • HEPES buffer At a dosage of 0.7 g/L Fe, both stabilized Fe and Fe-Pd nanoparticles displayed much improved kinetics and reactivity.
  • the stabilized nanoparticles degraded 96.2% of nitrate, whereas non-stabilized particles degraded only 77.1%.
  • ⁇ -k ohs C (20) where C is the nitrate concentration (mg/L) at time t; t is the time (minute); k O b S is the pseudo-first order rate constant (min "1 ). Because of the labile nature of the nanoparticles and the complexity of the system, only early stage ( ⁇ 60 minutes) data were fitted. Thus, the resultant k o b s only reflects an operationally defined initial rate constant, which has been commonly used to facilitate reaction rate comparison.
  • Table 3 gives the best-fitted values of k obs . Based on the observed k o b s values, stabililzed Fe 0 nanoparticles offered a 5.2 times greater reaction kinetics over the non-stabilized counterparts. The observed rate constant can be converted to the surface- area-based reaction rate constant (/C SA ) via eqn (21),
  • ⁇ 1 MA (21) where k O bs is the pseudo-first order rate constant (min "1 ); ksA is the specific reaction rate constant based on surface area of the nanoparticles (L/min-m 2 ); a s is the specific surface area of the nanoparticles (m 2 /g); p m is the mass concentration of the nanoparticles (g/L).
  • the k SA is calculated to be 1.73 ⁇ lO "3 L/min-m 2 for CMC-stabilized Fe and 1.04 ⁇ l0 "3 L/min-m 2 for non-stabilized Fe.
  • the marked enhancement in nitrate degradation rate for stabilized Fe nanoparticles is attributed to the increased Fe 0 surface area and surface activity.
  • Fe 0 nanoparticles can react with nitrate and H + ions. Based on the nitrate reduction stoichiometry given in eqns (5) and (6), it takes a minimum Fe/NO 3 " of 2.5 to reduce nitrate to N 2 and a Fe/NO 3 ' of 4 to reach ammonium. [00176]
  • Figure 18 compares the nitrate reduction kinetics at an Fe/NO 3 ' molar ratio of 2.5, 3.9 and 5.3, respectively. Note that the FeZNO 3 " of 2.5 corresponds to the reaction stoichiometry of eq (6), whereas the ratio of 3.9 conforms to the mechanism of eq (5).
  • the pH of the solution was controlled at neutral by adding 0.05 M HEPES buffer.
  • Fe/NO 3 ' of 5.3 (i.e. 33% above the highest possible stoichiometry)
  • 100% of 150 mg/L nitrate was rapidly degraded within 50 minutes.
  • the Error! Not a valid link was reduced to 3.9 (the stoichiometric quantity of eq (5))
  • about 95.5 of 200 mg/L nitrate was destroyed within 120 minutes.
  • the Error! Not a valid link was reduced to 2.5 (the stoichiometric quantity of eq (6))
  • a steady state conversion of 83% of 310 mg/L nitrate was observed within 50 minutes.
  • Figure 19 shows the nitrate removal by Fe 0 nanoparticles which were stabilized with varying NaCMC concentrations.
  • Fe 0 nanoparticles 0%, 0.2%, 0.5%, 0.9% NaCMC were used to stabilize 1 or 0.724 g/L Fe 0 (iron was prepared as 1 g/L, but it was diluted to 0.724g/L after adding nitrate and pH buffer).
  • the kinetics of nitrate reduction with 0.9% NaCMC stabilized Fe 0 was so fast that all nitrate was removed within 60 minutes while nitrate was reduced relatively slowly when 0.2% NaCMC stabilized Fe 0 or non-stabilized Fe 0 was used.
  • the reaction rate constants (k obs ) were calculated to be 0.3018 min "1 (#9 in Table 3), 0.2597 min '1 (#14 in Table 3), 0.1981 min “1 (#13 in Table 3), 0.0391 mm “1 (#12 in Table 3) for 0.9% NaCMC stabilized Fe 0 , 0.5% NaCMC stabilized Fe 0 , 0.2% NaCMC stabilized Fe 0 , non-stabilized Fe 0 , respectively.
  • the results suggest that higher concentration of stabilizer can result in faster nitrate reduction kinetics. The reason for this result is that higher dose of stabilizer provide better stabilized Fe 0 nanoparticles which have more surface area for nitrate reduction.
  • reaction rate k obs 0.0015 min '1 (#7 in Table 3) was calculated and the pH increased from 6.80 to 8.51 in 5 minutes and moved up slowly to 8.58 in 120 minutes.
  • This difference in reaction rates between stabilized and non-stabilized Fe 0 without pH adjustment is consistent with early discussion that stabilized Fe 0 provides more surface area for nitrate reduction.
  • a lower initial pH was used to speed up this reaction by spiking the pH to 2.50 with 1 M HCl. This increased acidity improved moderately the nitrate reduction kinetics.
  • a reaction rate k obs 0.01 13 min "1 (#5 in Table 3) was calculated and the pH jumped to 8.05 in 5 minutes and increased slowly to 8.60 in 120 minutes.
  • HEPES neutral pH buffer
  • Ion exchange is a widely used process for nitrate removal.
  • Some nitrate-selective resins have been developed and used.
  • nitrate is concentrated in the regeneration residue after the exhausted resins are regenerated with an eluent, such as 4% to about 12% (w/w) NaCl.
  • eluent such as 4% to about 12% (w/w) NaCl.
  • Disposal of used regenerant containing high level of nitrate and sodium chloride is an important issue in the application of ion exchange process for nitrate removal.
  • Figure 22 shows the nitrate removal by stabilized Fe 0 nanoparticles in the presence of varying concentration of NaCl. Tests were conducted with 0.72 g/L Fe 0 and 150 mg/L NO 3 " to yield a Fe°/NO 3 " molar ratio of 5.34. The solution pH was control at 7.1 to about 7.5 by adding 0.05M HEPES buffer. 1% or 6% (w/w) NaCl were added to the solution. As shown in Figure 19, nitrate reduction by Fe 0 nanoparticles was inhibited by chloride. With increasing NaCl concentration, the nitrate reduction rate (k obs ) was reduced.
  • Figure 23 shows the mass balance of nitrogenous species during the denitrification by stabilized Fe 0 nanoparticles. 5.34 mol-Fe°/mol-NO 3 ⁇ (0.724 g/L Fe 0 and 150 mg/L NO 3 " ) was used in this test and 6% NaCl was present in the system. Nitrite was detected before 80 minutes and it disappeared at 120 minutes. The nitrite concentration was very low and it accounted for 0.25% to about 0.39% of total nitrogenous species during the reaction. This indicates that nitrite is one of the intermediate products from nitrate reduction by stabilized Fe 0 nanoparticles, but it was further reduced quickly to other nitrogen form. And the reaction step from nitrate to nitrite may be the rate-limiting step.
  • nanoscale ZVI size: 1 - 20 nm; surface area: 25.4 m 2 /g
  • eqn (3) and eqn (5) are the main reaction pathways for nitrate reduction by stabilized Fe 0 nanoparticles. Nitrate can be reduced to ammonium either directly through eqn (3) or indirectly through a pathway consisting eqn (4) and the following eqn (23), which is evidenced by the detection of nitrite. 3.0. Conclusions
  • a stabilized Fe 0 nanoparticles was prepared with a "green” and low- cost cellulose (sodium carboxymethyl cellulose) for nitrate removal.
  • the particle size of the stabilized Fe 0 nanoparticles was about 7.4 nm with a standard deviation of 1.2 nm and the specific surface area was 103.02 m 2 /g. Batch tests proved that Fe 0 nanoparticles are efficient for nitrate reduction.
  • the first order reaction model was used to fit the reaction.
  • a first- order reaction rate constant (k ObS - 0.3018 min "1 ) was calculated.
  • Pd a stands for the weight of Pd used in the tests.
  • the objective of this experiment was to test the effectiveness of stabilized nanoparticles for reducing the bioaccessibility and TCLP leachability of arsenic in soils.
  • Three types (ZVI, FeS, and Fe 3 O 4 ) of stabilized nanoparticles were prepared using a water-soluble starch as a stabilizer, and then used for treating two representative soils in batch experiments. Effects of the Fe-Xo-As molar ratio and treatment time on the treatment effectiveness were examined.
  • An ⁇ s-contaminated sandy soil (As concentration: 315 mg/kg and denoted as WAOS) was collected from Washington Orchard, an orchard contaminated from application of As-based pesticides.
  • WAOS As-based pesticides
  • a relatively clean red soil was collected near a small police fire range in east-central, Alabama, USA. Both soils were first fractionated using standard sieves, and soil fractions of ⁇ 250 ⁇ m were used in all experiments.
  • the WAOS soil has an iron content of nearly 5.24% and a soil pH of 6.75.
  • the range soil has a higher iron content (12.2%) and a soil pH of 4.83.
  • the range soil was first spiked with arsenic following the procedures by Yang et al. (2002), resulting in an arsenic concentration of 89 mg/Kg.
  • a water-soluble starch (Alfa Aesar, Wall Hill, MA) was used as a stabilizer in the preparation.
  • the preparation was carried out in a 250 mL flask. Before use, deionized (DI) water and starch solution were purged with N 2 for 2 h to remove dissolved oxygen (DO).
  • DI deionized
  • DO dissolved oxygen
  • FeCl 3 stock solution was added to a starch solution (2.4%) through a buret, to give a final Fe concentration of 2.35 g/L and a starch concentration of 1.2%. The final pH was 8.1. Then, Fe 3+ was reduced to Fe 0 using stoichiometric amounts of sodium borohydride (equation 25).
  • control tests were carried out in parallel with 2 g of a soil with 4 mL and 10 mL, respectively, of 1.2% starch solution. After the mixtures were shaken thoroughly for 5 minutes, the tubes were placed on a rotator for 3 days or 7 days. After the treatments, all samples were centrifuged with 6000 g force (Fisher, Accuspri 400 centrifuger). Arsenic and iron concentrations in the supernatants were monitored after centrifuging. Upon removal of the supernatant, each soil sample was oven-dried at 70 0 C for one day. The, 0.1 g of treated soils was sampled and used for PBET, 0.5 g for TCLP tests, and 1.0 g for soil pH measurements. To ensure data quality, all tests were performed in duplicates.
  • PBET extraction solution was made using a 0.4 M glycine solution adjusted to a pH of 1.5 using HCl solution.
  • 0.1 gram of a soil sample is mixed with 10 mL of the extraction solution, i.e. a solid-to-solution ratio of 1 : 100.
  • water temperature was maintained at body temperature (37 ⁇ 2 0 C) with a water bath. After the extraction, the samples were centrifuged at 1000 g force.
  • the supernatant was then filtered using 0.45 ⁇ m filter (Fisher, DISPNR 25mm 0.45 ⁇ m filter), and then analyzed for arsenic extracted. To ensure QA/QC, NIST soil samples were also subjected to the same procedure.
  • TCLP tests were performed to evaluate the leaching potential of arsenic in the untreated and treated As-contaminated soils following the US. EPA protocol (Method SW-846).
  • 0.5 g of an air-dried soil sample was mixed with the TCLP extraction solution at a solid-to-liquid ratio of 1 :20.
  • the mixtures were placed on a rotating shaker operated at 30 rpm. After 18 hours of extraction, the samples were centrifuged at 1000 g force, and the supernatants were separated by 0.45 ⁇ m filter.
  • the soluble arsenic concentration in the filtrate was analyzed with AAS.
  • Aqueous samples were diluted as necessary and analyzed for aqueous As and Fe concentrations.
  • a graphite-furnace atomic absorption spectrometer (GFAA) was used to analyze As concentration.
  • Aqueous Fe concentrations in samples were analyzed using a flame atomic adsorption spectrometer (FLAA).
  • TCLP leachability is the As percent in the leachate vs. the total As content.
  • the initial TCLP leachability for the untreated range soil was 0.51 % and 3.28% for the untreated WAOS soil. This result was in accord with those reported by Akhter et al. (2000), they studied As-contaminated soil from industrial sites. No TCLP leachates showed arsenic concentrations as high as 5 mg/L, which is the EPA benchmark value for a hazardous waste.
  • Figure 28-31 compares the TCLP and PBET results when the soils were treated for 3 days and 7 days. From these figures, the bioaccessibility and leachability of As for 100: 1 Fe/ As molar ratio by 3 or 7 days treatment are comparable. A student t-test revealed no significant difference between the results from the two treatment times. Earlier, Subacz (2004) observed that the bioaccessibility of contaminated soils when amended with FeCl 3 for 3 days and 7days differed significantly. These results suggest that the stabilized nanoparticles offer rather fast mass transfer and reaction kinetics. Most of adsorption of arsenate occurred in one hour for nano zero valent iron groundwater treatments (Kanel et al. 2006). And the As adsorption reaction on nanoscale NVI were more quick than on micron ZVI.
  • Nanoscale zero-valent iron has a structure which 19% were in zero valent state with a coat of 81% iron oxides (Kanel et al. 2006). Kanel et al. also confirmed that nanoscale zero-valent iron and arsenate forms an inner-sphere surface complexation, 99% arsenate was adsorbed by nanoscale zero- valent iron in one hour. Bang et al. (2005) claimed that arsenic can also be removed by Fe 0 through reducing arsenite and arsenate to zerovalent arsenic, which is insoluble in water.
  • Arsenic concentrations typically decrease under anoxic conditions by sulfide minerals (Bostick et al. 2004). Arsenic sorption on FeS was studied by (Bostick and Fendorf 2003) with X-ray absorption spectroscopy. They proposed eqn (37) as the main reaction for arsenite removal by FeS, which was supported by their XRD results. Nanoscale FeS particles have greater surface area, the sorption of arsenic on FeS nanoparticles can explain the immobilization of arsenic. 3FeS + H 3 AsO 3 ⁇ FeS 2 +FeAsS +Fe(OH) 3 (37)
  • the bioaccessibility of As decreased from an initial 71.3 ⁇ 3.1% to 29.8 ⁇ 3.1%, 30.9 ⁇ 3.2%, 37.6 ⁇ 1.2% for Fe/As ratio 100: 1 Fe 3 O 4 , NVI, FeS nanoparticles, respectively, and for the 100 Fe/As ratio, the teachability of arsenic of in a range soil decreased from an initial 0.51 ⁇ 0.11% to 0.17 ⁇ 0.04%, 0.24 ⁇ 0.03%, 0.27 ⁇ 0.04% by Fe 3 O 4 , NVI, FeS Nanoparticles, respectively. Fe 3 O 4 nanoparticles worked better than the other two nanoparticles in reducing the bioaccessibility and leachability. No significant difference in the effectiveness was evident between 3 days and 7 days treatments.

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  • Treatment Of Water By Oxidation Or Reduction (AREA)

Abstract

L'invention concerne un procédé qui permet de préparer des nanoparticules de fer à valence zéro fortement stabilisées et dispersables, et d'utiliser ces nanoparticules comme technologie de restauration visant les toxines chimiques inorganiques sur des sites contaminés. Ce procédé fait intervenir une composition qui renferme des polysaccharides (amidon ou cellulose) choisis comme stabilisant des nanoparticules de fer dans un support liquide, et permet d'obtenir des suspensions de nanoparticules de fer de taille et de mobilité recherchées dans l'eau, la saumure, les sols ou les sédiments. Par ailleurs, le stabilisant permet d'agir aisément sur la dispersibilité des nanoparticules de fer dans le support liquide. Une quantité efficace de la composition est libérée sur le site contaminé de sorte que les nanoparticules de fer à valence zéro neutralisent une ou plusieurs toxines telles que l'arséniate, le nitrate, le chromate ou le perchlorate sur le site contaminé.
PCT/US2007/065664 2006-03-30 2007-03-30 Restauration in situ visant la neutralisation de contaminants inorganiques au moyen de nanoparticules de fer à valence zéro stabilisées Ceased WO2007115189A2 (fr)

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US78762106P 2006-03-30 2006-03-30
US60/787,621 2006-03-30
US87261606P 2006-12-01 2006-12-01
US60/872,616 2006-12-01

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