Earth Scientist
Earth Scientist


Dr. Ravi Kukkadapu is an Earth scientist with the Biogeochemical Transformations team in PNNL’s Environmental Molecular Sciences Division and the Environmental Molecular Sciences Laboratory (EMSL) user program. He has brought international recognition to PNNL and EMSL, and its 57Fe-Mössbauer spectroscopy laboratory, as a premier capability for biogeochemical sciences involving Fe-oxides and Fe-containing clays that are ubiquitous in the subsurface. His expertise in the application of Mössbauer spectroscopy, coupled with electron microscopy, X-ray diffraction, and absorption techniques has resulted in many fruitful collaborations and numerous publications. He has applied these techniques to better understand the (bio)transformation of primary Fe(II)/(III)-oxides into secondary Fe(II)/(III)-minerals (carbonates, phosphates, and sulfides) and redox transformations of Fe-clays under various biological, geochemical, and hydrological conditions on attenuation or long-term stability of redox-sensitive contaminants. 

Currently, Kukkadapu is extensively involved in programmatic research funded by the U.S. Department of Energy’s (DOE) Biological and Environmental Research program’s Subsurface Biogeochemical Research and the Geosciences Division of DOE's Basic Energy Science program. He collaborates with numerous universities and other DOE laboratory investigators in subsurface biogeochemical research through EMSL user proposals. His research has direct implications to DOE's primary environmental mission, assisting in developing predictive biogeochemical transport models to better understand the fate and transport of radioactive and hazardous metal contaminants, such as uranium (U), technetium (Tc), plutonium (Pu), and mercury (Hg) in aquifers. 

Research Interest

Dr. Kukkadapu is recognized in the area of soil Fe minerals' role on soluble radionuclide attenuation in the subsurface. His current interests are: 

  • The interplay of organic matter-mineral-bacteria interactions in subsurface and floodplain/terrestrial-aquatic interfaces on stability of soil organic matter (effect on greenhouse gases), nutrient cycling, and metal contaminant remediation 

  • The role of (bio)transformation/redox cycling of Fe-(oxyhydr)oxides/Fe-clays/Fe-sulfides (and Mn-oxides and zero-valent Fe) in subsurface/floodplain/lake sediments on remediation of soluble metal contaminants( e.g., radionuclides), such as U, Tc, and Pu, and hazardous metals, such as, As, Cr, and Hg, and nitrate and phosphate nutrient cycling (water quality) 

  • The effect of soil organic matter on interfacial electron transfer between sorbed Fe(II) and clay Fe(III)/Fe-oxides 

  • The development of stable materials for safe disposal of nuclear materials (e.g., garnets) with large amounts of U loading 

  • Geological CO2 sequestration 

  • Reactive nano Fe phases 

  • Fe containing NH3-SCR catalysts 

  • The application of 57Fe (and 119Sn) Mössbauer spectroscopy in geosciences, material synthesis, and catalysis areas 


  • PhD in Chemistry, Indian Institutes of Technology 

  • MS in Chemistry, Osmania University 

Affiliations and Professional Service

  • American Chemistry Society 

  • American Geophysical Union 

  • The Clay Minerals Society 

  • Soil Science Society of America 

Awards and Recognitions

  • Co-Organizer, “Stability of Mineral-Organic Matter Interactions Under Varying Biogeochemical Conditions,” 2020 Clay Mineral Society, PNNL 

  • Co-Organizer, “Clays and Climate Change,” 2020 Clay Mineral Society, PNNL

  • Co-Organizer, “Emerging Methods in Soil Science,” 2020 Clay Mineral Society, PNNL 

  • Member, PhD Thesis Committee for Li Zhang, Miami University (2019) 

  • Member, PhD Thesis Committee for Elizabeth Wu, University of Delaware (2014) 

  • Member, PhD Thesis Committee for Wu Tao, University of Wisconsin (2014) 

  • Co-Organizer, The Sixth Nassau-Argonne International Mössbauer Symposium, Garden City (2011) 

  • Rising Star, Cover of Mössbauer Effect Reference and Data Journal (2010) 

  • Cover, Clays and Clay Minerals (2010) 

  • Associate Editor, Clays and Clay Minerals (2010) 

  • Keynote Speaker, Annual Meeting, Clay Minerals Group of the Mineralogical Society of United Kingdom, FuturoClay Symposium (2009) 

  • Outstanding Performance Award for bringing external visibility to EMSL’s Mössbauer capability, PNNL (2009) 

  • Emerging Scientist in the Mössbauer Spectroscopy Field, International Conference on the Applications of the Mössbauer Effect Conference (2009) 

  • Editor's Choice, "Reduction of Hg(II) to Hg(0) by Magnetite” in Environmental Science and Technology, Science Magazine (July 2009) 

  • Co-Organizer, Magnetic Resonance Spectroscopic Studies of Clay Minerals Session, 41st Annual Meeting of the Clay Minerals Society (2004) 

  • Best Poster Award, International Symposium on the Industrial Applications of Mössbauer Effect (2000) 

  • Postdoctoral Research Fellowship, Robert R. Welch Foundation, University of Houston (1987 – 1990)  


R. K. Kukkadapu and S. A. Boyd. 1996, 1997, 1998. “Method of Removing Organic Contaminants from Air and Water with Organophilic, Quaternary Phosphonium Ion-exchanged Smectite Clays.” 5,587,084 (1996), 5,630,075 (1997), and 5,747,403 (1998). 



Kenton AR, A. P Smith, Weinan Leng, Sean Colby, Ravi K. Kukkadapu, Mark Bowden, Odeta Qafoku, Wooyong Um, Michael F. Hochella, Jr, Vanessa L. Bailey, Ryan S. Renslow (2020) "Water dispersible nano-colloids and higher temperatures promote the release of carbon from riparian soil" Vadose Zone Journal  19 (1) 

Boglaienko, D., J. A. Soltis, R. K. Kukkadapu, Y. Du, L. E. Sweet, V. E. Holfeltz, G. B. Hall, E. C. Buck, C. U. Segre, H. P. Emerson, Y. Katsenovich, and T. G. Levitskaia. 2020. “Spontaneous Redox Continuum Reveals Sequestered Technetium Clusters and Retarded Mineral Transformation of Iron.” Communications Chemistry 3 (1).

Boiteau, R. M., R. Kukkadapu, J. B. Cliff, C. R. Smallwood, L. Kovarik, M. G. Wirth, M. H. Engelhard, T. Varga, A. Dohnalkova, D. E. Perea, T. Wietsma, J. J. Moran, and K. S. Hofmockel. 2020. “Calcareous Organic Matter Coatings Sequester Siderophores in Alkaline Soils.” Science of the Total Environment 724.

O'Connell, D. W., N. Ansems, R. K. Kukkadapu, D. Jaisi, D. M. Orihel, B. J. Cade-Menun, Y. Hu, J. Wiklund, R. I. Hall, H. Chessell, T. Behrends, and P. Van Cappellen. 2020. “Changes in Sedimentary Phosphorus Burial Following Artificial Eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada.” Journal of Geophysical Research: Biogeosciences 125 (8).

Zhao, Q., S. J. Callister, A. M. Thompson, R. K. Kukkadapu, M. M. Tfaily, L. M. Bramer, N. P. Qafoku, S. L. Bell, S. E. Hobbie, E. W. Seabloom, E. T. Borer, and K. S. Hofmockel. 2020. “Strong Mineralogic Control of Soil Organic Matter Composition in Response to Nutrient Addition across Diverse Grassland Sites.” Science of the Total Environment 736.

Zuo, H., R. Kukkadapu, Z. Zhu, S. Ni, L. Huang, Q. Zeng, C. Liu, and H. Dong. 2020. “Role of Clay-Associated Humic Substances in Catalyzing Bioreduction of Structural Fe(III) in Nontronite by Shewanella putrefaciens CN32.” Science of the Total Environment 741.


Garcia Arredondo, M., C. R. Lawrence, M. S. Schulz, M. M. Tfaily, R. Kukkadapu, M. E. Jones, K. Boye, and M. Keiluweit. 2019. “Root-Driven Weathering Impacts on Mineral-Organic Associations in Deep Soils over Pedogenic Time Scales.” Geochimica et Cosmochimica Acta 263: 68-84.

Ilgen, A. G., R. K. Kukkadapu, K. Leung, and R. E. Washington. 2019. “"Switching on" Iron in Clay Minerals.” Environmental Science: Nano 6 (6): 1704-1715.

Noël, V., K. Boye, R. K. Kukkadapu, Q. Li, and J. R. Bargar. 2019. “Uranium Storage Mechanisms in Wet-Dry Redox Cycled Sediments.” Water Research 152: 251-263.

Yuan, H., Q. Li, R. K. Kukkadapu, E. Liu, J. Yu, H. Fang, H. Li, and D. P. Jaisi. 2019. “Identifying Sources and Cycling of Phosphorus in the Sediment of a Shallow Freshwater Lake in China Using Phosphate Oxygen Isotopes.” Science of the Total Environment 676: 823-833.

Zhang, L., H. Dong, R. K. Kukkadapu, Q. Jin, and L. Kovarik. 2019. “Electron Transfer between Sorbed Fe(II) and Structural Fe(III) in Smectites and Its Effect on Nitrate-Dependent Iron Oxidation by Pseudogulbenkiania sp. Strain 2002.” Geochimica et Cosmochimica Acta 265: 132-147.


Bhattacharyya, A., A. N. Campbell, M. M. Tfaily, Y. Lin, R. K. Kukkadapu, W. L. Silver, P. S. Nico, and J. Pett-Ridge. 2018. “Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils.” Environmental Science and Technology 52 (24): 14129-14139.

Lawter, A. R., W. L. Garcia, R. K. Kukkadapu, O. Qafoku, M. E. Bowden, S. A. Saslow, and N. P. Qafoku. 2018. “Technetium and Iodine Aqueous Species Immobilization and Transformations in the Presence of Strong Reductants and Calcite-Forming Solutions: Remedial Action Implications.” Science of the Total Environment 636: 588-595.

Lawter, A. R., N. P. Qafoku, R. M. Asmussen, R. K. Kukkadapu, O. Qafoku, D. H. Bacon, and C. F. Brown. 2018. “Element Mobilization and Immobilization from Carbonate Rocks between CO2 Storage Reservoirs and the Overlying Aquifers During a Potential CO2 Leakage.” Chemosphere 197: 399-410.

Overman, N. R., X. Jiang, R. K. Kukkadapu, T. Clark, T. J. Roosendaal, G. Coffey, J. E. Shield, and S. N. Mathaudhu. 2018. “Physical and Electrical Properties of Melt-Spun Fe-Si (3–8 Wt.%) Soft Magnetic Ribbons.” Materials Characterization 136: 212-220.

Qafoku, O., E. S. Ilton, M. E. Bowden, L. Kovarik, X. Zhang, R. K. Kukkadapu, M. H. Engelhard, C. J. Thompson, H. T. Schaef, B. P. McGrail, K. M. Rosso, and J. S. Loring. 2018. “Synthesis of Nanometer-Sized Fayalite and Magnesium-Iron(II) Mixture Olivines.” Journal of Colloid and Interface Science 515: 129-138.

Wang, A., Y. Wang, E. D. Walter, R. K. Kukkadapu, Y. Guo, G. Lu, R. S. Weber, Y. Wang, C. H. F. Peden, and F. Gao. 2018. “Catalytic N2O Decomposition and Reduction by NH3 over Fe/Beta and Fe/SSZ-13 Catalysts.” Journal of Catalysis 358: 199-210.

Wu, Y., R. K. Kukkadapu, K. J. T. Livi, W. Xu, W. Li, and D. L. Sparks. 2018. “Iron and Arsenic Speciation During As(III) Oxidation by Manganese Oxides in the Presence of Fe(II): Molecular-Level Characterization Using XAFS, Mössbauer, and TEM Analysis.” ACS Earth and Space Chemistry 2 (3): 256-268.


Chen, C., R. K. Kukkadapu, O. Lazareva, and D. L. Sparks. 2017. “Solid-Phase Fe Speciation Along the Vertical Redox Gradients in Floodplains Using XAS and Mössbauer Spectroscopies.” Environmental Science and Technology 51 (14): 7903-7912.

Elsaidi, S. K., M. A. Sinnwell, D. Banerjee, A. Devaraj, R. K. Kukkadapu, T. C. Droubay, Z. Nie, L. Kovarik, M. Vijayakumar, S. Manandhar, M. Nandasiri, B. P. McGrail, and P. K. Thallapally. 2017. “Reduced Magnetism in Core-Shell Magnetite@MOF Composites.” Nano Letters 17 (11): 6968-6973.

Ilgen, A. G., R. K. Kukkadapu, D. R. Dunphy, K. Artyushkova, J. M. Cerrato, J. N. Kruichak, M. T. Janish, C. J. Sun, J. M. Argo, and R. E. Washington. 2017. “Synthesis and Characterization of Redox-Active Ferric Nontronite.” Chemical Geology 470: 1-12.

Kaur, M., J. S. McCloy, R. Kukkadapu, C. Pearce, J. Tucek, M. Bowden, M. Engelhard, E. Arenholz, and Y. Qiang. 2017. “Tetragonal-Like Phase in Core-Shell Iron Iron-Oxide Nanoclusters.” Journal of Physical Chemistry C 121 (21): 11794-11803.

Kovarik, L., N. M. Washton, R. Kukkadapu, A. Devaraj, A. Wang, Y. Wang, J. Szanyi, C. H. F. Peden, and F. Gao. 2017. “Transformation of Active Sites in Fe/Ssz-13 SCR Catalysts During Hydrothermal Aging: A Spectroscopic, Microscopic, and Kinetics Study.” ACS Catalysis 7 (4): 2458-2470.

Noël, V., K. Boye, R. K. Kukkadapu, S. Bone, J. S. Lezama Pacheco, E. Cardarelli, N. Janot, S. Fendorf, K. H. Williams, and J. R. Bargar. 2017. “Understanding Controls on Redox Processes in Floodplain Sediments of the Upper Colorado River Basin.” Science of the Total Environment 603-604: 663-675.

Wu, T., A. M. Griffin, C. A. Gorski, E. S. Shelobolina, H. Xu, R. K. Kukkadapu, and E. E. Roden. 2017. “Interactions between Fe(III)-Oxides and Fe(III)-Phyllosilicates During Microbial Reduction 2: Natural Subsurface Sediments.” Geomicrobiology Journal 34 (3): 231-241.

Xu, J., H. Veeramani, N. P. Qafoku, G. Singh, M. V. Riquelme, A. Pruden, R. K. Kukkadapu, B. N. Gartman, and M. F. Hochella, Jr. 2017. “Efficacy of Acetate-Amended Biostimulation for Uranium Sequestration: Combined Analysis of Sediment/Groundwater Geochemistry and Bacterial Community Structure.” Applied Geochemistry 78: 172-185.


Gao, F., Y. Zheng, R. K. Kukkadapu, Y. Wang, E. D. Walter, B. Schwenzer, J. Szanyi, and C. H. F. Peden. 2016. “Iron Loading Effects in Fe/SSZ-13 NH3-SCR Catalysts: Nature of the Fe Ions and Structure-Function Relationships.” ACS Catalysis 6 (5): 2939-2954.

Guo, X., A. Navrotsky, R. K. Kukkadapu, M. H. Engelhard, A. Lanzirotti, M. Newville, E. S. Ilton, S. R. Sutton, and H. Xu. 2016. “Structure and Thermodynamics of Uranium-Containing Iron Garnets.” Geochimica et Cosmochimica Acta 189: 269-281.

Guo, X., E. Tiferet, L. Qi, J. M. Solomon, A. Lanzirotti, M. Newville, M. H. Engelhard, R. K. Kukkadapu, D. Wu, E. S. Ilton, M. Asta, S. R. Sutton, H. Xu, and A. Navrotsky. 2016. “U(V) in Metal Uranates: A Combined Experimental and Theoretical Study of MgUO4, CrUO4, and FeUO4.” Dalton Transactions 45 (11): 4622-4632.

Kaplan, D. I., R. Kukkadapu, J. C. Seaman, B. W. Arey, A. C. Dohnalkova, S. Buettner, D. Li, T. Varga, K. G. Scheckel, and P. R. Jaffé. 2016. “Iron Mineralogy and Uranium-Binding Environment in the Rhizosphere of a Wetland Soil.” Science of the Total Environment 569-570: 53-64.

Long, G. J., F. Grandjean, X. Guo, A. Navrotsky, and R. K. Kukkadapu. 2016. “Mössbauer Spectral Properties of Yttrium Iron Garnet, Y3Fe5O12, and Its Isovalent and Nonisovalent Yttrium-Substituted Solid Solutions.” Inorganic Chemistry 55 (7): 3413-3418.

Nune, S. K., D. B. Lao, D. J. Heldebrant, J. Liu, M. J. Olszta, R. K. Kukkadapu, L. M. Gordon, M. I. Nandasiri, G. Whyatt, C. Clayton, D. W. Gotthold, M. H. Engelhard, and H. T. Schaef. 2016. “Anomalous Water Expulsion from Carbon-Based Rods at High Humidity.” Nature Nanotechnology 11 (9): 791-797.

Ruby C, Naille S, Ona-Nguema G, Morin G, Mallet M, Guerbois D, Barthelemy K, Etique M, Zegeye A, Zhang Y, Boumaiza H, Renard A, Noel V, Binda P, Hanna K, Despas C, Abdelmoula M, Kukkadapu R, Sarrias J, Albignac M, Rocklin P, Nauleau F, Hyvard N, and Genin JMR (2016) “Use of ferrihydrite-coated pouzzolana and biogenic green rust to purify waste water containing phosphate and nitrate” Green Rust and Related Iron Containing Compounds: Structure, Redox Properties and Environmental Applications” in Current Inorganic Chemistry, 6(2), 100-118. doi:10.2174/1877944106999160603125459 

Lao D, Kukkadapu RK, Kovarik L, Bruce W Arey, Heldebrant DJ, and Nune SK (2016) “Switchable Ionic Liquids: An Environmentally-friendly Medium to Synthesize Nanoparticulate Green Rust” Green Rust and Related Iron Containing Compounds: Structure, Redox Properties and Environmental Applications” in Current Inorganic Chemistry,  6(2), 92-99. 

Starcher, A. N., W. Li, R. K. Kukkadapu, E. J. Elzinga, and D. L. Sparks. 2016. “Fe(II) Sorption on Pyrophyllite: Effect of Structural Fe(III) (Impurity) in Pyrophyllite on Nature of Layered Double Hydroxide (LDH) Secondary Mineral Formation.” Chemical Geology 439: 152-160.

Wu, T., R. K. Kukkadapu, A. M. Griffin, C. A. Gorski, H. Konishi, H. Xu, and E. E. Roden. 2016. “Interactions between Fe(III)-Oxides and Fe(III)-Phyllosilicates During Microbial Reduction 1: Synthetic Sediments.” Geomicrobiology Journal 33 (9): 793-806.

Zhang, W., D. Banerjee, J. Liu, H. T. Schaef, J. V. Crum, C. A. Fernandez, R. K. Kukkadapu, Z. Nie, S. K. Nune, R. K. Motkuri, K. W. Chapman, M. H. Engelhard, J. C. Hayes, K. L. Silvers, R. Krishna, B. P. McGrail, J. Liu, and P. K. Thallapally. 2016. “Redox-Active Metal-Organic Composites for Highly Selective Oxygen Separation Applications.” Advanced Materials 28 (18): 3572-3577.


Abrecht, D. G., J. M. Schwantes, R. K. Kukkadapu, B. S. McDonald, G. C. Eiden, and L. E. Sweet. 2015. “Real-Time Noise Reduction for Mössbauer Spectroscopy through Online Implementation of a Modified Kalman Filter.” Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 773: 66-71.

Chen, C., R. Kukkadapu, and D. L. Sparks. 2015. “Influence of Coprecipitated Organic Matter on Fe2+(aq)-Catalyzed Transformation of Ferrihydrite: Implications for Carbon Dynamics.” Environmental Science and Technology 49 (18): 10927-10936.

Gao, F., M. Kollár, R. K. Kukkadapu, N. M. Washton, Y. Wang, J. Szanyi, and C. H. Peden. 2015. “Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study.” Applied Catalysis B: Environmental 164: 407-419.

Gartman, B. N., N. P. Qafoku, J. E. Szecsody, R. K. Kukkadapu, Z. Wang, D. M. Wellman, and M. J. Truex. 2015. “Uranium Fate in Hanford Sediment Altered by Simulated Acid Waste Solutions.” Applied Geochemistry 63: 1-9.

Guo, X., R. K. Kukkadapu, A. Lanzirotti, M. Newville, M. H. Engelhard, S. R. Sutton, and A. Navrotsky. 2015. “Charge-Coupled Substituted Garnets (Y3-xCa0.5xM0.5x)Fe5O12 (M = Ce, Th): Structure and Stability as Crystalline Nuclear Waste Forms.” Inorganic Chemistry 54 (8): 4156-4166.

Joshi, S. R., R. K. Kukkadapu, D. J. Burdige, M. E. Bowden, D. L. Sparks, and D. P. Jaisi. 2015. “Organic Matter Remineralization Predominates Phosphorus Cycling in the Mid-Bay Sediments in the Chesapeake Bay.” Environmental Science and Technology 49 (10): 5887-5896.

Liu, Y., C. Liu, R. K. Kukkadapu, J. P. McKinley, J. Zachara, A. E. Plymale, M. D. Miller, T. Varga, and C. T. Resch. 2015. “99Tc(VII) Retardation, Reduction, and Redox Rate Scaling in Naturally Reduced Sediments.” Environmental Science and Technology 49 (22): 13403-13412.

McCloy, J., N. Washton, P. Gassman, J. Marcial, J. Weaver, and R. Kukkadapu. 2015. “Nepheline Crystallization in Boron-Rich Alumino-Silicate Glasses as Investigated by Multi-Nuclear NMR, Raman, & Mössbauer Spectroscopies.” Journal of Non-Crystalline Solids 409: 149-165.

Zhao, L., H. Dong, R. K. Kukkadapu, Q. Zeng, R. E. Edelmann, M. Pentrák, and A. Agrawal. 2015. “Biological Redox Cycling of Iron in Nontronite and Its Potential Application in Nitrate Removal.” Environmental Science and Technology 49 (9): 5493-5501.


Fan, D., R. P. Anitori, B. M. Tebo, P. G. Tratnyek, J. S. Lezama Pacheco, R. K. Kukkadapu, L. Kovarik, M. H. Engelhard, and M. E. Bowden. 2014. “Oxidative Remobilization of Technetium Sequestered by Sulfide-Transformed Nano Zerovalent Iron.” Environmental Science and Technology 48 (13): 7409-7417.

Felmy, A. R., D. A. Moore, E. Buck, S. D. Conradson, R. Kukkadapu, L. Sweet, D. Abrecht, and E. S. Ilton. 2014. “The Solubility of 242PuO2 in the Presence of Aqueous Fe(II): The Impact of Precipitate Preparation.” Radiochimica Acta 102 (10): 861-874.

Guo, X., A. H. Tavakoli, S. Sutton, R. K. Kukkadapu, L. Qi, A. Lanzirotti, M. Newville, M. Asta, and A. Navrotsky. 2014. “Cerium Substitution in Yttrium Iron Garnet: Valence State, Structure, and Energetics.” Chemistry of Materials 26 (2): 1133-1143.

Qafoku, N. P., B. N. Gartman, R. K. Kukkadapu, B. W. Arey, K. H. Williams, P. J. Mouser, S. M. Heald, J. R. Bargar, N. Janot, S. Yabusaki, and P. E. Long. 2014. “Geochemical and Mineralogical Investigation of Uranium in Multi-Element Contaminated, Organic-Rich Subsurface Sediment.” Applied Geochemistry 42: 77-85.

Shah, M., C. C. Lin, R. Kukkadapu, M. H. Engelhard, X. Zhao, Y. Wang, T. Barkay, and N. Yee. 2014. “Syntrophic Effects in a Subsurface Clostridial Consortium on Fe(III)-(Oxyhydr)Oxide Reduction and Secondary Mineralization.” Geomicrobiology Journal 31 (2): 101-115.

Shao, H., R. K. Kukkadapu, E. J. Krogstad, M. K. Newburn, and K. J. Cantrell. 2014. “Mobilization of Metals from Eau Claire Siltstone and the Impact of Oxygen under Geological Carbon Dioxide Sequestration Conditions.” Geochimica et Cosmochimica Acta 141: 62-82.


Bi, Y., S. P. Hyun, R. Kukkadapu, and K. F. Hayes. 2013. “Oxidative Dissolution of UO2 in a Simulated Groundwater Containing Synthetic Nanocrystalline Mackinawite.” Geochimica et Cosmochimica Acta 102: 175-190.

Fan, D., R. P. Anitori, B. M. Tebo, P. G. Tratnyek, J. S. L. Pacheco, R. K. Kukkadapu, M. H. Engelhard, M. E. Bowden, L. Kovarik, and B. W. Arey. 2013. “Reductive Sequestration of Pertechnetate (99TcO4-) by Nano Zerovalent Iron (nZVI) Transformed by Abiotic Sulfide.” Environmental Science and Technology 47 (10): 5302-5310.

Fox, P. M., J. A. Davis, R. Kukkadapu, D. M. Singer, J. Bargar, and K. H. Williams. 2013. “Abiotic U(VI) Reduction by Sorbed Fe(II) on Natural Sediments.” Geochimica et Cosmochimica Acta 117: 266-282.

Veeramani, H., A. C. Scheinost, N. Monsegue, N. P. Qafoku, R. Kukkadapu, M. Newville, A. Lanzirotti, A. Pruden, M. Murayama, and M. F. Hochella. 2013. “Abiotic Reductive Immobilization of U(VI) by Biogenic Mackinawite.” Environmental Science and Technology 47 (5): 2361-2369.

Zhao, L., H. Dong, R. Kukkadapu, A. Agrawal, D. Liu, J. Zhang, and R. E. Edelmann. 2013. “Biological Oxidation of Fe(II) in Reduced Nontronite Coupled with Nitrate Reduction by Pseudogulbenkiania sp. Strain 2002.” Geochimica et Cosmochimica Acta 119: 231-247.


Campbell, K. M., R. K. Kukkadapu, N. P. Qafoku, A. D. Peacock, E. Lesher, K. H. Williams, J. R. Bargar, M. J. Wilkins, L. Figueroa, J. Ranville, J. A. Davis, and P. E. Long. 2012. “Geochemical, Mineralogical and Microbiological Characteristics of Sediment from a Naturally Reduced Zone in a Uranium-Contaminated Aquifer.” Applied Geochemistry 27 (8): 1499-1511.

Lee, J. H., J. K. Fredrickson, R. K. Kukkadapu, M. I. Boyanov, K. M. Kemner, X. Lin, D. W. Kennedy, B. N. Bjornstad, A. E. Konopka, D. A. Moore, C. T. Resch, and J. L. Phillips. 2012. “Microbial Reductive Transformation of Phyllosilicate Fe(III) and U(VI) in Fluvial Subsurface Sediments.” Environmental Science and Technology 46 (7): 3721-3730.

Pearce, C. I., O. Qafoku, J. Liu, E. Arenholz, S. M. Heald, R. K. Kukkadapu, C. A. Gorski, C. M. B. Henderson, and K. M. Rosso. 2012. “Synthesis and Properties of Titanomagnetite (Fe3-xTixO4) Nanoparticles: A Tunable Solid-State Fe(II/III) Redox System.” Journal of Colloid and Interface Science 387 (1): 24-38.

Peretyazhko, T. S., J. M. Zachara, R. K. Kukkadapu, S. M. Heald, I. V. Kutnyakov, C. T. Resch, B. W. Arey, C. M. Wang, L. Kovarik, J. L. Phillips, and D. A. Moore. 2012. “Pertechnetate (TcO4-) Reduction by Reactive Ferrous Iron Forms in Naturally Anoxic, Redox Transition Zone Sediments from the Hanford Site, USA.” Geochimica et Cosmochimica Acta 92: 48-66.

Qafoku, O., L. Kovarik, R. K. Kukkadapu, E. S. Ilton, B. W. Arey, J. Tucek, and A. R. Felmy. 2012. “Fayalite Dissolution and Siderite Formation in Water-Saturated Supercritical CO2.” Chemical Geology 332-333: 124-135.

Shelobolina, E., H. Xu, H. Konishi, R. Kukkadapu, T. Wu, M. Blöthe, and E. Roden. 2012. “Microbial Lithotrophic Oxidation of Structural Fe(II) in Biotite.” Applied and Environmental Microbiology 78 (16): 5746-5752.

Um, W., H. Chang, J. P. Icenhower, W. W. Lukens, R. Jeffrey Serne, N. Qafoku, R. K. Kukkadapu, and J. H. Westsik Jr. 2012. “Iron Oxide Waste Form for Stabilizing 99Tc.” Journal of Nuclear Materials 429 (1-3): 201-209.

Wu, T., E. Shelobolina, H. Xu, H. Konishi, R. Kukkadapu, and E. E. Roden. 2012. “Isolation and Microbial Reduction of Fe(III) Phyllosilicates from Subsurface Sediments.” Environmental Science and Technology 46 (21): 11618-11626.

Yang, J., R. K. Kukkadapu, H. Dong, E. S. Shelobolina, J. Zhang, and J. Kim. 2012. “Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium.” Chemical Geology 291: 206-216.


Bishop, M. E., H. Dong, R. K. Kukkadapu, C. Liu, and R. E. Edelmann. 2011. “Bioreduction of Fe-Bearing Clay Minerals and Their Reactivity toward Pertechnetate (Tc-99).” Geochimica et Cosmochimica Acta 75 (18): 5229-5246.

Campbell, K. M., J. A. Davis, J. Bargar, D. Giammar, R. Bernier-Latmani, R. Kukkadapu, K. H. Williams, H. Veramani, K. U. Ulrich, J. Stubbs, S. Yabusaki, L. Figueroa, E. Lesher, M. J. Wilkins, A. Peacock, and P. E. Long. 2011. “Composition, Stability, and Measurement of Reduced Uranium Phases for Groundwater Bioremediation at Old Rifle, CO.” Applied Geochemistry 26 (SUPPL.): S167-S169.

Jaisi, D. P., R. K. Kukkadapu, L. M. Stout, T. Varga, and R. E. Blake. 2011. “Biotic and Abiotic Pathways of Phosphorus Cycling in Minerals and Sediments: Insights from Oxygen Isotope Ratios in Phosphate.” Environmental Science and Technology 45 (15): 6254-6261.

McCloy, J., R. Kukkadapu, J. Crum, B. Johnson, and T. Droubay. 2011. “Size Effects on Gamma Radiation Response of Magnetic Properties of Barium Hexaferrite Powders.” Journal of Applied Physics 110 (11).

Zachara, J. M., R. K. Kukkadapu, T. Peretyazhko, M. Bowden, C. Wang, D. W. Kennedy, D. Moore, and B. Arey. 2011. “The Mineralogic Transformation of Ferrihydrite Induced by Heterogeneous Reaction with Bioreduced Anthraquinone Disulfonate (AQDS) and the Role of Phosphate.” Geochimica et Cosmochimica Acta 75 (21): 6330-6349.


Bishop, M. E., D. P. Jaisi, H. Dong, R. K. Kukkadapu, and J. Ji. 2010. “Bioavailability of Fe(III) in Loess Sediments: An Important Source of Electron Acceptors.” Clays and Clay Minerals 58 (4): 542-557.

Hixon, A. E., Y. J. Hu, D. I. Kaplan, R. K. Kukkadapu, H. Nitsche, O. Qafoku, and B. A. Powell. 2010. “Influence of Iron Redox Transformations on Plutonium Sorption to Sediments.” Radiochimica Acta 98 (9-11): 685-692.

Hu, Y. J., L. K. Schwaiger, C. H. Booth, R. K. Kukkadapu, E. Cristiano, D. Kaplan, and H. Nitsche. 2010. “Molecular Interactions of Plutonium(VI) with Synthetic Manganese- Substituted Goethite.” Radiochimica Acta 98 (9-11): 655-663.

Jaisi, D. P., R. E. Blake, and R. K. Kukkadapu. 2010. “Fractionation of Oxygen Isotopes in Phosphate During Its Interactions with Iron Oxides.” Geochimica et Cosmochimica Acta 74 (4): 1309-1319.

Moon, H. S., L. McGuinness, R. K. Kukkadapu, A. D. Peacock, J. Komlos, L. J. Kerkhof, P. E. Long, and P. R. Jaffé. 2010. “Microbial Reduction of Uranium under Iron- and Sulfate-Reducing Conditions: Effect of Amended Goethite on Microbial Community Composition and Dynamics.” Water Research 44 (14): 4015-4028.

Rastogi, G., S. Osman, R. Kukkadapu, M. Engelhard, P. A. Vaishampayan, G. L. Andersen, and R. K. Sani. 2010. “Microbial and Mineralogical Characterizations of Soils Collected from the Deep Biosphere of the Former Homestake Gold Mine, South Dakota.” Microbial Ecology 60 (3): 539-550.


Arey, B., R. K. Kukkadapu, J. P. McKinley, and C. Wang. 2009. “Microscopic Evidence of U Association with Fe-Minerals (Pyrite and Magnetite-Like Phases) in Naturally Bioreduced Sediment Cores Obtained from a U-Contaminated Aquifer.” Microscopy and Microanalysis 15 (SUPPL. 2): 912-913.

Qafoku, N. P., R. K. Kukkadapu, J. P. McKinley, B. W. Arey, S. D. Kelly, C. Wang, C. T. Resch, and P. E. Long. 2009. “Uranium in Framboidal Pyrite from a Naturally Bioreduced Alluvial Sediment.” Environmental Science and Technology 43 (22): 8528-8534.

Smith, S. C., M. Douglas, D. A. Moore, R. K. Kukkadapu, and B. W. Arey. 2009. “Uranium Extraction from Laboratory-Synthesized, Uranium-Doped Hydrous Ferric Oxides.” Environmental Science and Technology 43 (7): 2341-2347.

Wiatrowski, H. A., S. Das, R. Kukkadapu, E. S. Ilton, T. Barkay, and N. Yee. 2009. “Reduction of Hg(II) to Hg(0) by Magnetite.” Environmental Science and Technology 43 (14): 5307-5313.

Zhang, G., H. Dong, H. Jiang, R. K. Kukkadapu, J. Kim, D. Eberl, and Z. Xu. 2009. “Biomineralization Associated with Microbial Reduction of Fe3+ and Oxidation of Fe2+ in Solid Minerals.” American Mineralogist 94 (7): 1049-1058.


Bank, T. L., R. K. Kukkadapu, A. S. Madden, M. A. Ginder-Vogel, M. E. Baldwin, and P. M. Jardine. 2008. “Effects of Gamma-Sterilization on the Physico-Chemical Properties of Natural Sediments.” Chemical Geology 251 (1-4): 1-7.

Komlos, J., A. Peacock, R. K. Kukkadapu, and P. R. Jaffé. 2008. “Long-Term Dynamics of Uranium Reduction/Reoxidation under Low Sulfate Conditions.” Geochimica et Cosmochimica Acta 72 (15): 3603-3615.

Mohanty, S. R., B. Kollah, D. B. Hedrick, A. D. Peacock, R. K. Kukkadapu, and E. E. Roden. 2008. “Biogeochemical Processes in Ethanol Stimulated Uranium-Contaminated Subsurface Sediments.” Environmental Science and Technology 42 (12): 4384-4390.

Peretyazhko, T., J. M. Zachara, S. M. Heald, B. H. Jeon, R. K. Kukkadapu, C. Liu, D. Moore, and C. T. Resch. 2008. “Heterogeneous Reduction of Tc(VII) by Fe(II) at the Solid-Water Interface.” Geochimica et Cosmochimica Acta 72 (6): 1521-1539.

Peretyazhko, T., J. M. Zachara, S. M. Heald, R. K. Kukkadapu, C. Liu, A. E. Plymale, and C. T. Resch. 2008. “Reduction of Tc(VII) by Fe(II) Sorbed on Al (Hydr)Oxides.” Environmental Science and Technology 42 (15): 5499-5506.


Borch, T., Y. Masue, R. K. Kukkadapu, and S. Fendorf. 2007. “Phosphate Imposed Limitations on Biological Reduction and Alteration of Ferrihydrite.” Environmental Science and Technology 41 (1): 166-172.

Komlos, J., R. K. Kukkadapu, J. M. Zachara, and P. R. Jaffé. 2007. “Biostimulation of Iron Reduction and Subsequent Oxidation of Sediment Containing Fe-Silicates and Fe-Oxides: Effect of Redox Cycling on Fe(III) Bioreduction.” Water Research 41 (13): 2996-3004.

Zachara, J. M., S. M. Heald, B. H. Jeon, R. K. Kukkadapu, C. Liu, J. P. McKinley, A. C. Dohnalkova, and D. A. Moore. 2007. “Reduction of Pertechnetate [Tc(VII)] by Aqueous Fe(II) and the Nature of Solid Phase Redox Products.” Geochimica et Cosmochimica Acta 71 (9): 2137-2157.


Kukkadapu, R. K., J. M. Zachara, J. K. Fredrickson, J. P. McKinley, D. W. Kennedy, S. C. Smith, and H. Dong. 2006. “Reductive Biotransformation of Fe in Shale-Limestone Saprolite Containing Fe(III) Oxides and Fe(II)/Fe(III) Phyllosilicates.” Geochimica et Cosmochimica Acta 70 (14): 3662-3676.

Seabaugh, J. L., H. Dong, R. K. Kukkadapu, D. D. Eberl, J. P. Morton, and J. Kim. 2006. “Microbial Reduction of Fe(III) in the Fifthian and Muloorina Illites: Contrasting Extents and Rates of Bioreduction.” Clays and Clay Minerals 54 (1): 67-79.

Weber, K. A., M. M. Urrutia, P. F. Churchill, R. K. Kukkadapu, and E. E. Roden. 2006. “Anaerobic Redox Cycling of Iron by Freshwater Sediment Microorganisms.” Environmental Microbiology 8 (1): 100-113.


Cooper, D. C., A. L. Neal, R. K. Kukkadapu, D. Brewe, A. Coby, and F. W. Picardal. 2005. “Effects of Sediment Iron Mineral Composition on Microbially Mediated Changes in Divalent Metal Speciation: Importance of Ferrihydrite.” Geochimica et Cosmochimica Acta 69 (7): 1739-1754.

Jaisi, D. P., R. K. Kukkadapu, D. D. Eberl, and H. Dong. 2005. “Control of Fe(III) Site Occupancy on the Rate and Extent of Microbial Reduction of Fe(III) in Nontronite.” Geochimica et Cosmochimica Acta 69 (23): 5429-5440.

Kukkadapu, R. K., J. M. Zachara, J. K. Fredrickson, D. W. Kennedy, A. C. Dohnalkova, and D. E. McCready. 2005. “Ferrous Hydroxy Carbonate Is a Stable Transformation Product of Biogenic Magnetite.” American Mineralogist 90 (2-3): 510-515.

Liu, C., J. M. Zachara, L. Zhong, R. Kukkadupa, J. E. Szecsody, and D. W. Kennedy. 2005. “Influence of Sediment Bioreduction and Reoxidation on Uranium Sorption.” Environmental Science and Technology 39 (11): 4125-4133.

Punnoose, A., J. Hays, A. Thurber, M. H. Engelhard, R. K. Kukkadapu, C. Wang, V. Shutthanandan, and S. Thevuthasan. 2005. “Development of High-Temperature Ferromagnetism in SnO2 and Paramagnetism in SnO by Fe Doping.” Physical Review B - Condensed Matter and Materials Physics 72 (5).


Fredrickson, J. K., J. M. Zachara, D. W. Kennedy, R. K. Kukkadapu, J. P. McKinley, S. M. Heald, C. Liu, and A. E. Plymale. 2004. “Reduction of TcO4- by Sediment-Associated Biogenic Fe(II).” Geochimica et Cosmochimica Acta 68 (15): 3171-3187.

Kukkadapu, R. K., J. M. Zachara, J. K. Fredrickson, and D. W. Kennedy. 2004. “Biotransformation of Two-Line Silica-Ferrihydrite by a Dissimilatory Fe(III)-Reducing Bacterium: Formation of Carbonate Green Rust in the Presence of Phosphate.” Geochimica et Cosmochimica Acta 68 (13): 2799-2814.

Norberg, N. S., K. R. Kittilstved, J. E. Amonette, R. K. Kukkadapu, D. A. Schwartz, and D. R. Gamelin. 2004. “Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films.” Journal of the American Chemical Society 126 (30): 9387-9398.

Strawn, D. G., N. E. Palmer, L. J. Furnare, C. Goodell, J. E. Amonette, and R. K. Kukkadapu. 2004. “Copper Sorption Mechanisms on Smectites.” Clays and Clay Minerals 52 (3): 321-333.

Zachara, J. M., R. K. Kukkadapu, P. L. Gassman, A. Dohnalkova, J. K. Fredrickson, and T. Anderson. 2004. “Biogeochemical Transformation of Fe Minerals in a Petroleum-Contaminated Aquifer.” Geochimica et Cosmochimica Acta 68 (8): 1791-1805.


Amonette, J. E., R. K. Kukkadapu, E. E. Alp, W. Sturhahn, and T. S. Toellner. 2003. “Heterogeneous Electron-Transfer Kinetics with Synchrotron 57Fe Mössbauer Spectroscopy.” Geochimica et Cosmochimica Acta 67 (12): 2109-2116.

Dong, H., R. K. Kukkadapu, J. K. Fredrickson, J. M. Zachara, D. W. Kennedy, and H. M. Kostandarithes. 2003. “Microbial Reduction of Structural Fe(III) in Illite and Goethite.” Environmental Science and Technology 37 (7): 1268-1276.

Fredrickson, J. K., S. Kota, R. K. Kukkadapu, C. Liu, and J. M. Zachara. 2003. “Influence of Electron Donor/Acceptor Concentrations on Hydrous Ferric Oxide (HFO) Bioreduction.” Biodegradation 14 (2): 91-103.

Hansel, C. M., S. G. Benner, J. Neiss, A. Dohnalkova, R. K. Kukkadapu, and S. Fendorf. 2003. “Secondary Mineralization Pathways Induced by Dissimilatory Iron Reduction of Ferrihydrite under Advective Flow.” Geochimica et Cosmochimica Acta 67 (16): 2977-2992.

Kukkadapu, R. K., H. Li, G. L. Smith, J. D. Crum, J. S. Jeoung, W. H. Poisl, and M. C. Weinberg. 2003. “Mössbauer and Optical Spectroscopic Study of Temperature and Redox Effects on Iron Local Environments in a Fe-Doped (0.5 Mol% Fe2O3) 18Na2O-72SiO2 Glass.” Journal of Non-Crystalline Solids 317 (3): 301-318.

Kukkadapu, R. K., J. M. Zachara, J. K. Fredrickson, S. C. Smith, A. C. Dohnalkova, and C. K. Russell. 2003. “Transformation of 2-Line Ferrihydrite to 6-Line Ferrihydrite under Oxic and Anoxic Conditions.” American Mineralogist 88 (11-12 PART 2): 1903-1914.


Zachara, J. M., R. K. Kukkadapu, J. K. Fredrickson, Y. A. Gorby, and S. C. Smith. 2002. “Biomineralization of Poorly Crystalline Fe(III) Oxides by Dissimilatory Metal Reducing Bacteria (DMRB).” Geomicrobiology Journal 19 (2): 179-207.


Fredrickson, J. K., J. M. Zachara, R. K. Kukkadapu, Y. A. Gorby, S. C. Smith, and C. F. Brown. 2001. “Biotransformation of Ni-Substituted Hydrous Ferric Oxide by an Fe(III)-Reducing Bacterium.” Environmental Science and Technology 35 (4): 703-712.

Kukkadapu, R. K., J. M. Zachara, S. C. Smith, J. K. Fredrickson, and C. Liu. 2001. “Dissimilatory Bacterial Reduction of Al-Substituted Geothite in Subsurface Sediments.” Geochimica et Cosmochimica Acta 65 (17): 2913-2924.

Matocha, C. J., D. L. Sparks, J. E. Amonette, and R. K. Kukkadapu. 2001. “Kinetics and Mechanism of Birnessite Reduction by Catechol.” Soil Science Society of America Journal 65 (1): 58-66.

Wang, Z., R. C. Moore, A. R. Felmy, M. J. Mason, and R. K. Kukkadapu. 2001. “A Study of the Corrosion Products of Mild Steel in High Ionic Strength Brines.” Waste Management 21 (4): 335-341.


Dong, H., J. K. Fredrickson, D. W. Kennedy, J. M. Zachara, R. K. Kukkadapu, and T. C. Onstott. 2000. “Mineral Transformation Associated with the Microbial Reduction of Magnetite.” Chemical Geology 169 (3-4): 299-318.


Maxwell, R. S., R. K. Kukkadapu, J. E. Amonette, and H. Cho. 1999. “2H Solid-State NMR Investigation of Terephthalate Dynamics and Orientation in Mixed-Anion Hydrotalcite-Like Compounds.” Journal of Physical Chemistry B 103 (25): 5197-5203.


Lawrence, M. A. M., R. K. Kukkadapu, and S. A. Boyd. 1998. “Adsorption of Phenol and Chlorinated Phenols from Aqueous Solution by Tetramethylammonium- and Tetramethylphosphonium-Exchanged Montmorillonite.” Applied Clay Science 13 (1): 13-20.


Kukkadapu, R. K., M. S. Witkowski, and J. E. Amonette. 1997. “Synthesis of a Low-Carbonate High-Charge Hydrotalcite-Like Compound at Ambient Pressure and Atmosphere.” Chemistry of Materials 9 (2): 417-419.


Kukkadapu, R. K., and S. A. Boyd. 1995. “Tetramethylphosphonium- and Tetramethylammonium-Smectites as Adsorbents of Aromatic and Chlorinated Hydrocarbons: Effect of Water on Adsorption Efficiency.” Clays and Clay Minerals 43 (3): 318-323.