University of Southern California Undergraduate Research Symposium for Creative
and Scholarly Work,
April 9-11, 2012
Removal of Radioactive Uranium from
Groundwater
using Nanoparticle Technology and
Adsorption Mechanisms
Student Researchers: Hannah Gray and Aditi Yokota-Joshi
Faulty Advisor: Professor Massoud Pirbazari; Research Scientist: Dr. Varadarajan Ravindran
Doctoral Student Advisors: Ryan Thacher and Kuo-Hsun Tsai
Lab Coordinator: Erick Hernandez
Sonny Astani Department of Civil and Environmental Engineering, Viterbi School of Engineering, University of Southern
California
Work sponsored by Women in Science and Engineering (WiSE) Grant
Introduction to Uranium
 Uranium is a radioactive element that can be released
into groundwater through anthropogenic and natural
sources, including leaching from uranium mill tailing,
hydraulic fracturing, and accidents in nuclear reactors.
Radioactive uranium is toxic to humans and can increase
risk of cancer, kidney disease, neurological damage, and
birth defects.
 Uranium exists in two valence states:
 Soluble, mobile hexavalent U(VI)
 Insoluble, immobile tetravalent U(IV).
 This difference in solubility can be exploited to remove
dissolved uranium from contaminated groundwater.
Figure 1. Uranium tailing ponds, Colorado Figure 2. Fukushima nuclear power plant accident
Figure 3. Uranium-related health effects and birth defects.
Goals of Research
 Conventional removal techniques are invasive
and chemical-intensive. The primary goal of this
research is to develop alternative means of
uranium removal by:
 Simulate U(VI) behavior in groundwater systems by
investigating adsorption of U(VI) to common soils
 Assess the use of nZVI for removal of U(VI) from
groundwater
 Investigating microbial remediation through biocatalyzed reduction of U(VI)
Materials
 The Beckman 6000 Liquid Scintillation Counter (LSC) was
used to measure radionuclide activity. The liquid
scintillation counting technique detects photons
released during radioactive decay events, and uses
photon counts to determine Disintegrations per Minute
(DPM). Sample preparation for the LSC included
addition of a scintillation cocktail and 0.2 N HNO3 to
reduce loss of counts from interferences.
 Rate studies and adsorption tests were performed on a
shaker unit to ensure uniform mixing within bottles, and
pH was controlled through a phosphate buffer addition.
Methods
 Sand adsorption experiments were performed with
glass bottles of 20g sand and 0 to 1000 ug/L uranium.
The samples were mixed continuously for 72 hrs and
then analyzed for U(VI) by liquid scintillation counting.
 Removal of U(VI) by nZVI was investigated under oxic
and anoxic conditions in 100 mL batch reactors,
containing 0.1 g/L nZVI and 5-100 mg/L U(VI), resulting
in a ratio of nZVI to U(VI) of between 20:1 and 1:1.
Adsorption experiments were handled in a nitrogen
glove box to prevent iron oxidation. For anaerobic
testing, the uranium solutions were purged with
nitrogen and placed in anaerobic glass jars to prevent
any oxidation.
nZVI Adsorption Isotherm Determination
 Zero-valent iron nanoparticles (nZVI) have a very high
specific surface area, are highly mobile, and have been
found effective in the removal of heavy metals and
chlorinated compounds by an adsorption-reduction
reaction. nZVI reduces soluble U(VI) to insoluble U(IV)
via adsorption and precipitation of uranyl ions onto the
nZVI particles.
 Four key isotherm models were developed - oxic and
anoxic adsorption models, and humic acid oxic and
anoxic adsorption models. Humic acid, in 30 mg/L
concentration, reflects the naturally present humic acid
in groundwater.
Sorption
Fe0
 U(VI)  UO2(CH3COO)2·2H2O
Figure 4. TEM Micrograph and diagram to illustrate adsorption of uranium oxide nodules on sand.
U(IV)
Fe0
Reduction
UO2(CH3COO)2·2H2O
 U(VI)
Sorption
Figure 5. TEM Micrograph and diagram to illustrate reduction and adsorption of uranium nodules
on zero-valent iron nanoparticles.
Langmuir Isotherm – U(VI) with sand
0.120
1/qe (g sand/mg U(VI))
0.100
0.080
y = 1.3846x + 0.0094
R² = 0.9732
0.060
0.040
0.020
0.000
0.00
0.01
0.02
0.03
0.04
0.05
1/Ce (L/mg U(VI))
0.06
0.07
0.08
Langmuir Isotherm for uranium and sand
 Adsorption of uranium on sand was found to follow the Langmuir
isotherm, indicating that the organic layer on the sand media was capab
of uranium removal. This result was further supported by the humic acid
adsorption isotherm.
Add nZVI
Filtration
Figure 5. The removal of Uranium contamination by nZVI reduction and filtration. The
rate of this process was studied to develop the isotherm models for nZVI and U(VI)
shown below.
Langmuir Isotherm - Anaerobic U(VI) with nZVI
0.1
1/qe (g nZVI/mg U(VI))
0.08
y = 0.3853x - 0.0132
R² = 0.9588
0.06
0.04
0.02
0
0
0.05
0.1
0.15
-0.02
1/Ce (L/mg U(VI))
0.2
0.25
0.3
Langmuir Isotherm - Anaerobic U(VI) with nZVI
0.1
1/qe (g nZVI/mg U(VI))
0.08
y = 0.3853x - 0.0132
R² = 0.9588
0.06
0.04
0.02
0
0
0.05
0.1
0.15
-0.02
1/Ce (L/mg U(VI))
0.2
0.25
0.3
Langmuir Isotherm for uranium and nZVI
The nZVI-U(VI) equilibrium data fit a Langmuir
isotherm model, representing the behavior of nZVI
in the presence of U(VI) aerobically and
anaerobically. Below, further testing with humic
acid verified these findings, while also reflecting
groundwater’s natural characteristics.
Langmuir Isotherm - Aerobic U(VI) with Humic Acid and nZVI
0.03
1/qe (g nZVI/mg U(VI))
0.025
y = 0.0232x + 0.0017
R² = 0.9664
0.02
0.015
0.01
0.005
0
0
0.2
0.4
0.6
1/Ce (L/mg U(VI))
0.8
1
1.2
Summary of Results
 nZVI successfully reduces U(VI) to U(IV), enabling
adsorption and removal, up to 93% removal in some cases.
 The data suggests the adsorption of uranium onto nZVI
follows a Langmuir isotherm model.
 Aerobic adsorption works more effectively for U238 removal
than anaerobic adsorption, with a adsorption capacity of
 Humic acid positively impacts the aerobic adsorption of
U238 onto nZVI, by both an increase in the rate of
adsorption and in the total quantity adsorbed.
 Humic acid negatively impacts the anaerobic adsorption of
U238 onto nZVI, by reducing the total quantity of uranium
adsorbed.
Conclusions
 The Langmuir isotherm model describes a relation
between the maximum adsorption capacity and the net
enthalpy of adsorption. For nZVI, adsorption capacity is:




17.45 mg U(VI)/g nZVI for aerobic nZVI
588.23 mg U(VI)/g nZVI for aerobic nZVI with humic acid
*** (TBD) mg U(VI)/g nZVI for anaerobic nZVI
*** (TBD) mg U(VI)/g nZVI for anaerobic nZVI with humic acid
 The increased adsorption with the aerobic addition of
humic acid might suggest ***. Additionally, aerobic
groundwater with naturally occurring humic acid would
result in effective removal of uranium by nZVI.
Future Work
 Future work will include
 Developing isotherm models for U(VI)-nZVI
adsorption with additional organic materials present.
 Comparing the removal of uranium by sulfur-reducing
bacteria (SRB) versus the nZVI technology to
evaluated the best treatment option for uraniumcontaminated groundwater.
 Performing dynamic sand column isotherm tests,
integrated with both SRB and nZVI, thus maximizing
U(VI) reduction to U(IV).
 Applying bioremediation columns as an in-situ or exsitu treatment for contaminated sites.
Acknowledgements
Special thanks to Professor Donal Manahan of the USC College
Department of Biological Sciences and the USC Women in Science and
Engineering for their assistance in this research project.
Works Cited


Fact Sheet on Uranium Mill Tailings. http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/milltailings.html
Luna-Velasco, Antonia, Reyes Sierra-Alvarez, Beatriz Castro, and Jim A. Field. “Removal of Nitrate and
Hexavalent Uranium from Groundwater by Sequential Treatment in Bioreactors Packed with Elemental
Sulfur and Zero-Valent Iron.” Biotechnology and Bioengineering 107.6 (2010): 933-936.

Ramos, Mauricio A. V., Weile Yan, Xiao-qin Li, Bruce E. Koel, and Wei-xian Zhang. "Simultaneous Oxidation
and Reduction of Arsenic by Zero-Valent Iron Nanoparticles: Understanding the Significance of the




Core−Shell Structure." The Journal of Physical Chemistry C 113.33 (2009): 14591-4594. Print.
Riba, Olga, Thomas B. Scott, K. Vala Ragnarsdottir, Geoffrey C. Allen. “Reaction mechanism of uranyl in
the presence of zero-valent iron nanoparticles.” Geochimica et Cosmochimica Acta, 72.16 (2008): 40474057.
Seyrig, Gregoire. “Uranium bioremediation: current knowledge and trends.” MMG 445 Basic
Biotechnology (2010) 6:19-24.
Suzuki, Yohey, Shelly D. Kelly, Kenneth M. Kemner, Jillian F. Banfield. “Microbial Populations Stimulated for
Hexavalent Uranium Reduction in Uranium Mine Sediment.” Applied and Environmental Microbiology.
69.3 (2003): 1337-1346.
“What Happened at Fukushima.” http://environment-clean-generations.blogspot.com/2011/06/whathappened-at-fukushima.html