Download Proposal for Research Project Mitigating Arsenic in Leachate Parties

Proposal for Research Project
Mitigating Arsenic in Leachate
Parties to the Research Project
Waste Corporation of America (WCA)
Derrick Standley
New Waste Concepts Inc. (NWC)
Milton F Knight, JD
Tonghua Zheng, PhD
Qi Wang, PhD
University of Central Florida (UCF)
Deborah Reinhart, PhD
Location of the Project:
WCA’s DeSoto County Landfill in Arcadia, Florida
Objective of Project:
The initial objective of this project is to field test and evaluate arsenic remediation
effectiveness of nanoscale zerovalent iron (ZVI)/aluminosilicate composite obtained
through hydrogen or NaBH4 reduction of red mud, an abundant aluminum manufacture
waste. Porous aluminosilicate matrix of red mud prevents aggregation of ZVI and ensures
high iron surface area for arsenic remediation. Nanoscale ZVI/aluminosilicate composite
will attract and lock up arsenic found in the leachate. A secondary objective of this study
is the development and creation of a low cost “funnel and gate” permeable reactive
barrier system designed to hold nanoscale ZVI/aluminosilicate composite and through
which the leachate is filtered and remediated before it enters either a holding pond or
tank. Silanol groups on aluminosilicate matrix make possible surface modification and
subsequent covalent binding of the composite to permeable reactive barriers, thereby
avoiding gradual loss of reactive ZVI over time.
Site specific objectives:
 Evaluate current arsenic levels at the Desoto County Landfill and reduce them to
below 10 μg/L.
 Dispose of barrier medium, including ZVI/aluminosilicate composite to which the
arsenic has attached in the landfill. Determine if this material could be used as an
ADC.
 Work to develop a low cost system that will make economic sense for deployment
as a method of locking up arsenic.
Research Participant Objectives:
New Waste Concepts:
New Waste Concepts team (NWC Team) objective is to do the field testing and
evaluation of the arsenic remediation process being proposed here. To the extent
necessary, the NWC team will work with the University of Central Florida to design and
Proposal for Research Project
Mitigating Arsenic in Leachate
create any prototype funnel-gate filtration structure necessary to carry out the objectives
of this research.
Waste Corporation of America:
Waste Corporation of America’s team (WCA’s Team) objective is to establish a
methodology that will help remove arsenic from the leachate waste water stream at
Desoto County Landfill. To the extent necessary, WCA will accept the sludge from any
processing of the liquid waste so long as the arsenic is locked up. WCA will also
determine whether this sludge is capable of being used as an alternative to daily soil
cover.
University of Central Florida:
The University of Central Florida (UCF) will further enhance and develop the permeable
reactive barriers necessary to avoid gradual loss of nanoscale ZVI/aluminosilicate
composite.
History and Background:
Arsenic is a contaminant of concerns for the environment. It is a well-known
carcinogen and prevalent in water and soil around the world. Because of its high toxicity,
the world health organization (WHO) and US environmental protection agency (EPA) set
strict arsenic concentration limit of less than 10 μg /L in drinking water. (1,2) However,
the lack of effective water treatment facilities in developing countries such as Bangladesh
and India makes such guideline unenforceable. Arsenic contaminated groundwater is
widely used as drinking and irrigation water source in these countries, leading to severe
health problems for their residents. Even in developed countries such as the US, many
locations in southwest states have arsenic concentration exceeding the required 10 μg/L
in drinking water. Worldwide, more than 137 million people in over 70 countries are
affected by arsenic contaminated water. (3) Remediation of arsenic in drinking water is of
utmost importance for health of the affected population.
Red mud is another environmental contaminant abundant around the world. It is a
waste from aluminum manufacture in the Bayer process, where hot sodium hydroxide is
used to leach alumina out of bauxite ore in which alumina, silica and iron oxide are the
major components. The remaining aluminosilicate and iron oxide of red mud are not
toxic inherently. However, sodium hydroxide used in the Bayer process leads to high pH
between 12 and 14 in the red mud leachate. Safe storage of these high pH materials has
proven to be challenging. A recent red mud spill in Hungary, where ten people were
killed in the accident, heightens the difficulty of safe handling of red mud. To make the
matter worse, for every ton of aluminum produced, 0.8 to 1.5 tons of red mud waste is
generated. Considering aluminum producers currently generate about 200 million tons of
red mud annually and a total of 3 billion tons of red mud has been accumulated during
140 years on-going aluminum manufacture, safe handling and reutilization of such a huge
amount of red mud is a daunting task. For years, aluminum industry has been searching
Proposal for Research Project
Mitigating Arsenic in Leachate
for technology to reutilize red mud waste to reduce its accumulation. For example, red
mud has found applications as the reinforcing filler for polymer and concrete. (4)
More recently, red mud is utilized as the sorbent for waste water heavy metal
contaminants. (5) The technology relies on the adsorption of contaminants such as
arsenic by iron oxide particle present in red mud. In comparison to current iron oxide
sorbent used in waste water treatment, aluminosilicate matrix of the red mud provides an
effective carrier to prevent iron oxide particle from aggregation and increases the
available surface area for adsorption. To be effective, sodium and other metal
components of red mud need to be first leached out by acid and iron oxide surface needs
to be activated by acid or sulfur. Application of red mud as sorbent for heavy metal
contaminants has the potential to reduce the accumulation of red mud waste as well as
remediate heavy metal contaminants. However, such adsorption process is pH sensitive
with the danger of desorption under undesirable conditions. (6,7)
Nanoscale zerovalent iron (ZVI) represents another promising approach for heavy
metal remediation. (8-10) In comparison to the adsorption mechanism of iron oxide,
nanoscale ZVI remediates heavy metal such as arsenic through both adsorption and redox
mechanism. Arsenic is first adsorbed by iron oxide on the partially oxidized surface of
nanoscale ZVI. Afterward, arsenic species such as arsenite [As (III)] and arsenate [As (V)]
are remediated mainly through a redox mechanism where As (III) and As (V) are reduced
to metallic arsenic [As (0)] and precipitated on ZVI particles. (11) Compared to iron
oxide sorbent, the redox mechanism of ZVI reduces the danger of desorption of arsenic,
enabling the construction of permeable reactive barriers using nanoscale ZVI for arsenic
remediation. At particle sizes exceeding 15 nm, however, nanoscale ZVI exhibits
ferromagnetism, leading to particle aggregation and a loss in surface area for adsorption
and redox reaction. (12) Additionally, it is hard to functionalize iron with organic
compound to attach to permeable reactive barrier, leading to loss of ZVI over time. The
particles by themselves are therefore inherently ineffective for permeable reactive barrier
construction. To prevent particle aggregation, nanoscale ZVI can be incorporated into
different matrix or carriers for environmental remediation. (14,15) However, these
technologies typically incur higher cost with the difficulty of functionalization of iron
surface.
The idea of this project came when an aluminum producer brought up the
challenge of red mud waste disposal and handling. The PI (T. Zheng) realized that iron
oxide in red mud can be reduced to nanoscale ZVI within red mud aluminosilicate matrix,
thus avoiding the costly ZVI aggregation prevention. The PI had previously developed
some unique technologies to incorporate nanoscale ZVI into silica matrix for
environmental remediation. (16,17) ZVI was successfully incorporated into silica matrix
through atomization of a precursor solution containing water, ferric chloride and silanes.
The resulting composite is effective for groundwater trichloroethylene (TCE) remediation.
The PI envisioned that using red mud instead of ferric chloride and silanes as the starting
material will lead to significant raw materials cost saving, making the nanoscale ZVI cost
competitive to current commercialized technology. Additionally, aluminum producer will
Proposal for Research Project
Mitigating Arsenic in Leachate
save waste disposal cost through reutilization of their industrial waste and reduce their
manufacturing impact on the environment. The PI has therefore started working in this
area with two technicians and Co-PIs (M. Knight and Q. Wang). The initial results are
highly promising and novel.
We now explain the technology we have developed.
Prior Technology Developed by the PI:
The PI had previously developed an efficient aerosol-assisted approach to make
nanoscale ZVI/silica composite using sol-gel chemistry. A typical silica sol-gel process
involve hydrolysis and condensation of alkoxysilane as shown by reaction (1) and (2),
where R is a non-hydrolysable ligand.
R3-Si-(OR) + H2O  R3-Si-(OH)+ ROH
R3-Si-(OH) + R3-Si-(OH)  R3-Si-O-Si-R3 + H2O
(1)
(2)
Organosilanes with one or more non-hydrolysable ligands R such as methyl, ethyl
and amino-propyl groups can be dispersed into silica matrix, resulting in the formation of
organic/inorganic composite. Ferric chloride can be incorporated into precursor, leading
to nanoscale ZVI/silica composite after iron reduction. Amino-propyl ligands provide the
sites for surface modification to covalently bind the composite to organic or polymeric
materials used in permeable reactive barriers.
An aerosol-assisted reactor were used to make iron/silica composite with organic
ligands as shown in Figure 1. Starting with a solution of ethyltriethoxlysilane (ETES),
tetraethyl orthosilicate (TEOS) and ferric chloride in water, the aerosol apparatus
atomizes the solution into droplets that undergo a drying and curing step generating
iron/silica composite nanoparticles that are collected by a filter. The iron species in the
nanoparticle were reduced by NaBH4 or hydrogen gas to nanoscale ZVI. The resulting
nanoscale ZVI/silica composites are effective for remediation of contaminants such as
TCE and arsenic.
(a)
Proposal for Research Project
Mitigating Arsenic in Leachate
(b)
Hydrolysis and
condensation
Solvent
evaporation
NaBH4
reduction
ETES
TEOS
FeCl3
Fe
(c)
Figure 1. (a) Structure of silica precursors used in the aerosol assisted process, (b)
Schematic of the aerosol reactor for particle synthesis and (c) Schematic of reactions
in an aerosol droplet.
Figure 2 show particle morphology of the synthesized materials. All the particles
are spherical with nanoscale ZVI inside. The particle with ethyl group reduced by NaBH4
(Figure 2(b), Fe(B)/ethyl-silica) are more porous due to the templating effect of organic
ethyl groups. Due to high temperature treatment during hydrogen gas reduction, the
particle reduced by hydrogen gas (Figure 2(c), Fe(H)/silica) are more crystalline than
particles reduced by NaBH4 (Figure 2(a), Fe(B)/silica).
Proposal for Research Project
Mitigating Arsenic in Leachate
Figure 2. TEM images of (a) Fe(B)/Silica reduced by NaBH4, (b) Fe(B)/Ethyl-Silica
reduced by NaBH4, (c) Fe(H)/Silica reduced by H2 and (d) electron diffraction
pattern of Fe(H)/Silica.
Figure 3 shows reaction characteristics of the nanoparticle for TCE remediation.
The presence of hydrophobic ethyl group in silica matrix clearly attract hydrophobic TCE
to particle surface as shown by fast decease of TCE concentration using Fe(B)/EthylSilica particles compared with Fe(B)/Silica particles within the first hour. TCE is
subsequently broken down through reacting with nanoscale ZVI in silica matrix. It is
noteworthy that addition of small amount of palladium (Pd/Fe(B)/Ethyl-Silica) results in
the remediation of 99% of TCE within an hour.
Proposal for Research Project
Mitigating Arsenic in Leachate
Figure 3. Reaction kinetics for Fe(B)/Ethyl-Silica (solid circles), Fe(B)/Silica (open
circles) and Pd/Fe(B)/Ethyl- Silica (solid triangles) over 8 hrs. M/M0 is the fraction
of TCE remaining in solution.
Our Recent Results:
While nanoscale ZVI/silica composite from the aerosol approach could be used
for arsenic remediation, red mud provides starting materials at almost no cost to us in
addition to lower red mud disposal cost for aluminum manufacturer. Figure 4 shows a
schematic for the synthesis route of nanoscale ZVI/aluminosilicate composite. Red mud
with iron oxide was first washed with HCl to remove soluble metal ions and activate iron
oxide surface. The activated iron oxide were reduced by sodium borohydride or hydrogen
gas to make nanoscale ZVI/aluminosilicate composite.
Proposal for Research Project
Mitigating Arsenic in Leachate
Figure 4. Schematic of acid leaching, iron oxide reduction to zerovalent iron in red mud
Figure 5.
SEM images of red mud (a) as-received, (b) after acid leaching (c) after
NaBH4 reduction and EDS spectra of red mud (d) as-received, (e) after acid leaching, (f)
after NaBH4 reduction
Surface morphology and element composition of the as-received red mud, acid
leached red mud and Fe/aluminosilicate after iron reduction by NaBH4 was characterized
using scanning electron microscopy (SEM) and energy dispersive X-way spectroscopy
(EDS). As seen in Figure 5(a), the red mud are irregular in shape with sizes in the micron
range. Leaching and activation of the red mud leads to a rougher surface morphology as
seen by Figure 5 (b). Acid leached red mud is more porous compared with as-received
red mud due to the voids left by leached metal ions, which originally occupy the space
within the matrix. Table 1 shows the elemental composition of as-received and acid
leached red mud. Leaching results in percentage weight loss of sodium from 10.09% to
0% and percentage weight increase of iron from 17.53% to 33.67%. Nanoscale
ZVI/aluminosilicate composite after NaBH4 reduction has similar morphology as acid
leached red mud. Sodium in EDS is the result of addition of NaBH4.
Proposal for Research Project
Mitigating Arsenic in Leachate
Table 1. Element composition of (a) as-received red mud, (b) acid leached red mud
and (c) nanoscale ZVI/aluminosilicate composite based on EDS spectra
Element
% weight (a)
% weight (b)
% weight (c)
Fe
17.53
33.67
32.75
Si
9.12
6.42
5.31
Ti
1.07
2.54
2.64
O
50.84
47.73
48.39
Na
10.09
0
1.25
Al
11.05
8.88
8.48
Ca
0.3
0
0
The adsorption and reaction of nanoscale ZVI/aluminosilicate composite with
arsenic was monitored through element analysis using an inductively coupled plasma
spectra (ICP) with arsenic detection limit of 0.1 μg /L. Adsorption and reaction
characteristics of systems containing ZVI/aluminosilicate are shown in Figures 6. The
arsenic concentration shows sharp reductions from 35.3 ppm to 17.5 ppm after the first
hour and from 17.5 ppm to 8.6 ppm after the second hour. This represents about 50%
arsenic concentration reduction every hour for the first two hours. The fast arsenic
concentration reduction is followed by a much slower rate (Fig 6). We explain the
apparent enhancement of arsenic remediation by ZVI/aluminosilicate as a consequence of
arsenic partitioning on iron oxide surface within aluminosilicate matrix. Nanoscale ZVI
typically has a layer of iron oxide on the surface due to its high reactivity. It has been
shown that arsenic has high affinity to iron oxide due to the abundance of surface charge
on iron oxide. The present of iron oxide on Fe/aluminosilicate enhances the adsorption of
arsenic on the composite. Subsequent redox reaction takes place between adsorbed
arsenic and zerovalent iron. After 2 hrs of adsorption and reaction, arsenic concentration
is reduced to below 10 ppm. After 3 hrs of adsorption and reaction, arsenic concentration
is reduced to below 6.8 ppm.
Figure 6.
composite.
Arsenic
remediation
kinetics
for
nanoscale
ZVI/Aluminosilicate
Proposal for Research Project
Mitigating Arsenic in Leachate
It is noteworthy that arsenic concentrations used in this experiment are much
higher than those found in the drinking water. Landfill leachate typically has higher
arsenic concentration than contaminated drinking water and we intentionally chose higher
concentration arsenic solutions to demonstrate iron/aluminosilicate’s effectiveness for
landfill leachate arsenic lockup. While red mud was used for its low cost, iron/silica
particles made by the aerosol process described earlier will be equally effective for
landfill leachate lockup. We envisioned a combination of iron/aluminosilicate and
iron/silica particles can be applied for permeable reactive barrier construction.
Proposed Studies:
The NWC Team will build a pilot scale hydrogen reduction chamber to make
nanoscale ZVI/aluminosilicate composite. While NaBH4 has been shown to be effective
in the lab for iron reduction. To make industrial scale nanoscale ZVI/aluminosilicate
composite, hydrogen reduction is more efficient. The PI has built a lab scale hydrogen
reduction chamber to make nanoscale ZVI/silica composite for TCE remediation (Figure
2c, Fe(H)/silica). The lab scale chamber can be scaled up to pilot and eventually
industrial scale to make nanoscale ZVI/aluminosilicate composite in the annual capacity
of more than 1000 tons to meet the demand of WCA for this project.
NWC Team will study the effect of pH on arsenic remediation efficiency of
nanoscale ZVI/aluminosilicate composite. It has been shown that arsenic desorption from
iron oxide limits the application of iron oxide particle in the construction of permeable
reactive barriers for arsenic remediation. We believe the redox mechanism of ZVI will
solve the desorption problems and would like to study pH impact on arsenic remediation
efficiency. Once we achieve the objective of making ZVI/aluminosilicate composite
though hydrogen reduction, we will use atomic adsorption spectrometer and ICP to
investigate the effectiveness of nanoscale ZVI/aluminosilicate composite for arsenic
remediation under varying pHs. The reactions will be done in cramp-sealed serum
bottles. Aliquots of the reaction samples will be recovered over time and analyzed to
determine arsenic concentration. Arsenic concentration change over time and different
pH will be monitored to determine the impact of pH on arsenic remediation. Iron/silica
particles can be used in place of ZVI/aluminosilicate to compare the difference of the two
materials. We envision there will be no desorption problem for both materials, but will
need to confirm before UCF team’s construction of a permeable reactive barriers.
The NWC Team will modify silica surface of nanoscale ZVI/aluminosilicate
composite or iron/silica particles to make possible the covalent binding of the composite
to permeable reactive barriers to prevent gradual loss of the composite over time.
Aluminosilicate surface can be modified via the reaction of surface silanol with
aminopropyltrimethylsilane (APTS). Hydrolysis of APTS (reaction 3) and subsequent
condensation with surface silanol will graft aminopropyl group to nanoscale
ZVI/aluminosilicate composite. The resulting amino functional group grafted on silica
matrix is reactive for acid groups to covalently bond with polymer matrix of the
permeable reactive barriers. For example, carboxylic acid or maleic anhydride groups of
Proposal for Research Project
Mitigating Arsenic in Leachate
the polymer can react with amino group of the composite. Such covalent binding of
composite to the barrier will avoid gradual loss of composite over time, thus increasing
remediation efficiency.
NH2CH2CH2CH2-Si-(OCH2CH3) 3 + H2O  NH2CH2CH2CH2-Si-(OH)3
(3)
The NWC team will work with the UCF team to build a permeable reactive
barrier with nanoscale ZVI/aluminosilicate composite and iron/silica particles as the
reagent and will collaborate with WCA to evaluate its effectiveness for arsenic leachate
remediation in Desoto County Landfill. WCA will facilitate evaluation of the arsenic
remediation efficiency on landfill site or at a suitable location nearby. The UCF team will
help on the construction of permeable reactive barrier and testing of arsenic concentration
during remediation. The NWC team will investigate if arsenic in the leachate can be
locked up by nanoscale ZVI/aluminosilicate composite in the barriers. If so, we will
determine the amount of nanoscale ZVI/aluminosilicate composite needed per thousand
gallon of leachate to be remediated. A cost benefit analysis will be conducted to evaluate
the competiveness of our technology vs. current commercialized technology. We will
also study leachate residence time and length of pathway in the barrier necessary to
reduce the arsenic concentration of the leachate to below 10 ppb.
Finally, The NWC Team will work with WCA Team to dispose the barrier
medium with nanoscale ZVI/aluminosilicate, iron/silica particles and the locked up
arsenic in the landfill. WCA’s equipment and expertise in this area will be relied upon to
ensure the safe handling of used barrier medium. The landfill will be monitored over time
to ensure no leakage of arsenic to the environment.
Funding and Term
The funding for this project will come from several sources. First, it is
intended to seek a grant from Environmental Research and Education Foundation.
Additionally, US EPA grants, in kind funding from NWC, and WCA, the Chinese
Government and such other sources can also be obtained.
The NWC team will be conducting research, both in the United States and
China. Funds have already been awarded in the amount of $200,000 to T. Zheng for
Proposal for Research Project
Mitigating Arsenic in Leachate
a project of equal stature in China by Chinese Bureau. We would hope to secure the
support of the World Bank and the US EPA on such a joint study between the US and
China.
The NWC team expects that this study will have a 3 year life before final
conclusions and reports will be done. Interim reports on the progress of the
research will be completed on a semi-annual basis or on a more frequent basis
depending upon the conditions of the grant.
Development of a Marketing Agreement for the Technology
The Parties will develop a Licensing Agreement providing New Waste Concepts
and Waste Corporation of America, parties to the Agreement, a development and
marketing license with regard to manufacturing and marketing the technology developed
hereunder.
The Licensing Agreement shall further provide for the patenting of the technology
to the extent that the technology is patentable in the United States with all costs of filing
and maintenance of the patents within the USA to be shared among all parties. To the
extent that one of the parties wishes to file for patent protection outside of the US, that
party shall be given a license to manufacture and sell outside of the US, the licensed
technology in consideration of the licensee paying for all costs associated with the
registration and maintenance of foreign patents.
The Agreement shall further create a method of compensation which shall be for
the benefit of the University of Central Florida. The amount of the funds to be
contributed will be an agreed upon percentage of sales from NWC to WCA. University
of Central Florida shall be the recipient of said funds or a stated designee which could be
either a UCF Foundation or the EREF for the benefit of Environmental Research to be
done at the University of Central Florida.
Patents shall be filed in the name of the contributing parties, and subsequently
assigned to their employer, to the extent there is an employer of the individual.
The Agreement shall further set forth a method of sharing the funds that are the
result of a sale of the patent to third party. Nothing in the Agreement shall prohibit one
of the parties of this Agreement from purchasing the interests of the other parties to the
Agreement.
Proposal for Research Project
Mitigating Arsenic in Leachate
Reference:
(1) US. Environmental Protection Agency, National Primary Drinking Water
Standards, 2003, EPA 816-F-03-016.
(2) World Health Organization. Guidelines for drinking water quality, Vol1:
Recommendations, 2nd ed.; World Health Organization: Geneva, Switzerland,
1993
(3) Ramos, M.; Yan, W.; Li, X.; Koel, B.; Zhang W. Simultaneous oxidation and
reduction of arsenic by aero-valent iron nanoparticles: understanding the
significance of the core-shell structure. J. Phys. Chem. C, 2009, 113, 1459114594
(4) Wagh, A.; Douse, V.; Silicate bonded unsintered ceramics of Bayer process
waste. J. Mater. Res., 1991, 6, 1094–1102.
(5) Gupta, V.; Gupta, M.; Sharma, S. Process development for the removal of lead
and chromium from aqueous using red mud—an aluminum industry waste,
Water Res. 2001, 35, 1125–1134.
(6) An, B.; Zhao, D. Immobilization of As(III) in soil and groundwater using a
new class of polysaccharide stabilized Fe–Mn oxide nanoparticles Journal of
Hazardous Materials, 2012, 211– 212, 332– 341
(7) Hu, H.; Goto, N.; Fujie, K. Effect of pH on the reduction of nitrite in water by
metallic iron. Water Res. 2001, 35, 2789-2793.
(8) Ponder, S.; Darab, J.; Mallouk, T. Remediation of Cr(VI) and Pb(II) aqueous
solutions using supported, nanoscale zero-valent iron. Environ. Sci. Technol.
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(9) Su, C.; Puls, R. In situ remediation of arsenic in simulated groundwater using
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(10) Astrup, T.; Stipp, S.; Christensen, T. Immobilization of chromate from coal
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(11) Yan, W; Ramos, M.; Koel, B.; Zhang, W. As(III) sequestration by iron
nanoparticles: study of solid-phase redox transformations with X-ray
photoelectron spectroscopy. J. Phys. Chem. C, 2012, 116, 5303-5311
(12) Phenrat, T.; Saleh, N.; Sirk, K.; Tilton, R.; Lowry, G. Aggregation and
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(13) Li, A.; Tai, C.; Zhao, Z.; Wang, Y.; Zhang, Q.; Jiang, G.; Hu, J.
Debromination of decabrominated diphenyl ether by resin-bound iron
nanoparticles. Environ. Sci. Technol. 2007, 41, 6841-6846.
(14) Saleh, N.; Phenrat, T.; Sirk, K.; Dufour, B.; Ok, J.; Sarbu, T.; Matyjaszewski,
K.; Tilton, R.; Lowry, G. Adsorbed triblock copolymers deliver reactive iron
nanoparticles to the oil/water interface. Nano Lett. 2005, 5, 2489-2494.
(15) He, F.; Zhao, D. Preparation and characterization of a new class of starchstabilized bimetallic nanoparticles for degradation of chlorinated
hydrocarbons in water. Environ. Sci. Technol. 2005, 39, 3314-3320
Proposal for Research Project
Mitigating Arsenic in Leachate
(16) Zheng, T.; Zhan, J.; He, J.; Day, C.; Lu, Y.; McPherson, G.; Piringer, G.;
John, V.T. Reactive characteristics of nanoscale zerovalent iron-silica
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