Professor Reeder's research focuses on geochemistry and mineralogy, with an emphasis on the mechanisms and processes operating at the mineral-water interface. A major goal of this work is to understand the role that mineral surfaces play in growth, dissolution, and the uptake of dissolved metals. Because of their reactive nature and their common occurrence in sediments, soils, and rocks, carbonate minerals are the focus for much of this work. Closely related research addresses crystal chemistry and structural phase transitions in minerals.

Mineral-Water Interface and Environmental Molecular Geochemistry
Structural and chemical properties of mineral surfaces provide some of the most fundamental constraints on reactions such as sorption, coprecipitation, crystal growth, and dissolution. Reeder's research program examines the structure and behavior of mineral surfaces in order to understand the mechanisms that control the fate of metals, including toxic species and radionuclides. A particular aspect of this work concerns the relationships among bulk crystal structure, surface structure, and metal uptake mechanisms. Various experimental techniques are used for examining surface structure and microtopography, including scanning probe microscopy and differential interference contrast microscopy, which provide direct evidence of growth mechanisms. Spectroscopic methods, such as X-ray absorption spectroscopy, provide direct characterization of metal coordination at mineral surfaces.

Trace elements coprecipitating with a mineral also act as sensitive "probes" of surface sites. Research by Reeder's group on the mechanisms of trace element incorporation in carbonates, phosphates, and silicates has revealed the manner in which differences in surface structure affect trace element uptake and incorporation. Experiments involve both synthetic and natural samples, and address both the partitioning behavior and incorporation mechanisms of geochemically and environmentally important trace metals among structurally distinct surface sites, as well as the local coordination of metals on mineral surfaces and in bulk minerals.

Reeder's group makes extensive use of the unique facilities at the National Synchrotron Light Source at nearby Brookhaven National Laboratory, and at ther synchrotron facilities throughout the US. Synchrotron X-ray absorption spectroscopy allows direct characterization of the local environment of heavy metal species, and synchrotron X-ray fluorescence microanalysis provides spatial distribution patterns for surface-controlled incorporation. This work has shown that the size and coordination geometry of sites as well as adsorption mechanisms are fundamental factors controlling element incorporation. The results of this work have been applied to trace element diagenetic studies of carbonate rocks and to studies of the uptake and mobility of toxic metals and radionuclides in environmentally sensitive areas.

Transmission Electron Microscopy
TEM and electron diffraction allow characterization of mineral crystals at scales ranging from nm to um, which complements both X-ray and optical methods. Reeder's research has shown that low-temperature carbonates commonly exhibit microstructures at this scale that contain information about their growth and diagenetic histories. Current studies address replacement mechanisms and the origin of compositional heterogeneities in calcite and dolomite. TEM is also used for characterizing domain microstructures that form in minerals undergoing structural phase transitions with changing temperature or pressure.

Crystal Chemistry of Carbonates
Related research pertains to structure and stability of minerals, particularly order-disorder and local structure in solid solutions in carbonates. This work combines single-crystal and powder X-ray diffraction with EXAFS spectroscopy. A particular problem is the nature of cation ordering in sedimentary dolomite. Low-temperature dolomite commonly contains excess calcium that is accommodated by complex cation ordering schemes, different from those in ideal dolomite. Differences of ordering and calcium content are primarily responsible for the variation in stability of sedimentary dolomite. Other work addresses structural relaxation and stability of solid solutions.

Selected Publications 

Hemming N.G., Reeder, R.J., and Hart, S.R. (1998) Growth-step-selective incorporation of boron on the calcite surface. Geochim. Cosmochim. Acta, 62, 2961-2968.

Zhang, J. and Reeder, R.J. (1999) Comparative compressibilities of calcite-structure carbonates: Deviations from empirical relations. Am. Mineral., 84, 861-870.

Reeder, R.J., Lamble, G.M., Northrup, P.A. (1999) XAFS study of the coordination and local relaxation around Co2+, Zn2+, Pb2+, and Ba2+ trace elements in calcite. Am. Mineral., 84, 1049-1060.

Navrotsky, A., Dooley, D., Reeder, R.J., and Brady, P. (1999) Calorimetric studies of the energetics of order-disorder in the system Mg1-xFexCa(CO3)2. Am. Mineral., 84, 1622-1626.

Reeder, R.J. (2000) Constraints on cation order in calcium-rich sedimentary dolomite. Aquatic Geochemistry, 6, 213-226.

Sanyal, A., Nugent, M., Reeder, R.J., and Bijma, J. (2000) Seawater pH control on the boron isotopic composition of calcite: Evidence from inorganic calcite precipitation experiments. Geochim. Cosmochim. Acta, 64, 1551-1555.

Reeder, R.J., Nugent, M., Lamble, G.M., Tait, C.D., and Morris, D.E. (2000) Uranyl incorporation into calcite and aragonite: XAFS and luminescence studies. Environ. Sci. Tech., 34, 638-644.

Michalopoulos, P., Aller, R.C., and Reeder, R.J. (2000) Conversion of diatoms to clays during early diagenesis in tropical, continental shelf muds. Geology, 28, 1095-1098.

Reeder, R.J., Nugent, M., Tait, C.D., Morris, D.E., Heald, S.M., Beck, K.M., Hess, W.P., and Lanzirotti, A. (2001) Coprecipitation of uranium(VI) with calcite: XAFS, micro-XAS, and luminescence characterization. Geochim. Cosmochim. Acta, 65, 3491-3503.

Reeder, R.J., Nugent, M. and Pabalan, R.T. (2001) Local structure of uranium(VI) sorbed on clinoptilolite and montmorillonite. In: Cidu, R. (ed.), Water-Rock Interaction, A.A. Balkema Publishers, Lisse, The Netherlands, 423-426.

Elzinga, E.J., Reeder, R.J., Withers, S.H., Peale, R.E., Mason, R.A., Beck, K.M., and Hess, W.P. (2002) EXAFS study of rare-earth element coordination in calcite. Geochim. Cosmochim. Acta, 66, 2875-2885.

Elzinga, E.J. and Reeder, R.J. (2002) X-ray absorption spectroscopy study of Cu2+ and Zn2+ adsorption complexes at the calcite surface: Implications for site-specific metal incorporation preferences during calcite crystal growth.  Geochim. Cosmochim. Acta, 66, 3943-3954

Rakovan, J., Reeder, R.J., Elzinga, E.J., Cherniak, D.J., Tait, C.D., and Morris, D.E. (2002) Characterization of U(VI) in the apatite structure by X-ray absorption spectroscopy. Env. Sci. Tech., 36, 3114-3117.

Lee, Y.J., Reeder, R.J., Wenskus, R.W., and Elzinga, E.J. (2002) Structural relaxation in the MnCO3-CaCO3 solid solution: a Mn K-edge EXAFS study. Phys. Chem. Minerals, 29, 585-594.

Withers, S.H., Peale, R.E., Schulte, A.F., Braunstein, G., Beck, K.M., Hess, W.P., and Reeder, R.J. (2003) Broad distribution of crystal-field environments for Nd3+ in calcite. Phys. Chem. Minerals, 30, 440-448.

Elzinga, E.J., Tait, C.D., Reeder, R.J., Rector, K.D., Donohoe, R.J., and Morris, D.E. (2004) Spectroscopic investigation of U(VI) sorption at the calcite-water interface. Geochim. Cosmochim. Acta 68, 2437-2448.

Rouff, A.A., Elzinga, E.J., Reeder, R.J., and Fisher, N.S. (2004) X-ray absorption spectroscopic evidence for the formation of Pb(II) inner-sphere adsorption complexes and precipitates at the calcite-water interface. Environ. Sci. Technol., 38, 1700-1707.

Reeder, R.J., Elzinga, E.J., Tait, C.D., Rector, K.D., Donohoe, R.J., and Morris, D.E. (2004) Site-specific incorporation of uranyl carbonate species at the calcite surface. Geochim. Cosmochim. Acta 68, 4799-4808.

Lee, Y.J., Elzinga, E.J, and Reeder, R.J. (2005) Cu(II) adsorption at the calcite-water interface in the presence of natural organic matter: kinetic studies and molecular-scale characterization. Geochim. Cosmochim. Acta 69, 49-61.

Lee, Y.J., Elzinga, E.J, and Reeder, R.J. (2005) Sorption mechanisms of zinc on hydroxyapatite: Systematic uptake studies and EXAFS spectroscopy analysis. Environ. Sci. Technol. 39, 4042-4048.

Phillips, B.L., Lee, Y.J., and Reeder, R.J. (2005) Organic coprecipitates with calcite: NMR spectroscopic evidence. Environ. Sci. Technol. 39, 4533-4539.

Rouff, A.A., Reeder, R.J., and Fisher, N.S. (2005) Electrolyte and pH effects on Pb(II)-calcite sorption processes: the role of the PbCO₃⁰(aq) complex. J. Colloid Interface Sci.,286, 61-67.

Chada, V.G.R., Hausner, D.B., Strongin, D.R., Rouff, A.A., and Reeder, R.J. (2005) Divalent Cd and Pb uptake on calcite {1014} cleavage faces: An XPS and AFM study. J. Colloid Interface Sci. 288, 35-360.

Rouff, A.A., Elzinga, E.J., Reeder, R.J., and Fisher, N.S. (2005) The Influence of pH on the kinetics, reversibility and mechanisms of Pb(II) sorption at the calcite-water interface. Geochim. Cosmochim. Acta 69, 5173-5186.

Rouff, A.A., Elzinga, E.J., Reeder, R.J., and Fisher, N.S. (2006) The effect of aging and pH on Pb(II) sorption processes at the calcite-water interface. Environ. Sci. Technol., 40, 1792-1798.

Lee, Y.J. and Reeder, R.J. (2006) The role of citrate and phthalate during Co(II) coprecipitation with calcite. Geochim. Cosmochim. Acta, 70, 2253-2263.

Elzinga, E.J., Rouff, A.A., and Reeder, R.J. (2006) The long-term fate of Cu²⁺, Zn²⁺, and Pb²⁺ adsorption complexes at the calcite surface: An X-ray absorption spectroscopy study. Geochim. Cosmochim. Acta, 70, 2715-2725.