DIVISION OF ENVIRONMENTAL CHEMISTRY PREPRINTS OF EXTENDED ABSTRACTS: VOL. 40(2) AUGUST 2000

Temperature - fC] Sedimentation Rate - [10^ m min'Fe - [pM]

Figure 2. Measured temperature, calculated dispersion coefficient, sedimentation rates for colloidal and particulate Fe, andpredicted (lines) and experimental (symbols) distribution of Fe(ll), Felllc, Felllp in July 1995.

The temperature measured, the calculated dispersion coefficient and sedimentation rates of colloids (0.2 |jm) and particles (1jjm), and the iron speciation calculated with the model and measured in the field are presented for one season in Fig. 2.Generally, the model can fit experimental data quite well, suggesting that the reaction mechanisms assumed in the model canreasonably predict the distribution of iron in the water column. Not surprisingly, it is found that the transport has an importantinfluence on the distribution of iron in the water column. In addition, side reactions can also explain discrepancies betweenthe modeled and experimental data. Although particulate lead is close to detection limit, the distribution of lead can bereasonably modeled with the mechanism presented.

R e f e r e n c e s

Baccini, P., and Joller, T. 1981. Schweiz. Zeit. Hydrol., 43,176.Balistrieri, L.S., Murray, J.W. and Paul, B. 1994. Geochim. Cosmochim. Acta, 58, 3993.Millero, F.J., Sotolango, S. and Izaguirre, M. 1987. Geochim. Cosmochim. Acta, 51, 793.Mortimer, C.H. 1941. J. Ecol., 29, 280.Pyzik, A.J. and Sommer, S.E. 1981. Geochim. Cosmochim. Acta, 45, 687.Sigg, L. 1985. In Chemical Processes in lakes, J. Wiley, New York, p. 283.Stumm, W. and Morgan J.J. 1981. Wiley & Sons, NY, pp. 756.Sung, W. and Morgan, J.J, 1980. Environ. Sci. Techno!., 14, 561.Suter, D., Siffert, C. Sulzberger, B., and Stumm, W. 1988. Natunviss., 75, 571.Taillefert M., Rose E., and Gaillard J-F. 1997. Coli. INRA, 85, 289.Taillefert, M., Lienemann, C-P., Gaillard, J-F., Perret, D. 2000. Geochim. Cosmochim. Acta, 64, 169.Tessier, A. 1992. In Environmental particles, Vol. I., Lewis, Boca Raton, p.425.Zinder, B., FurrerG. and Stumm, W. 1986. Geochim. Cosmochim. Acta, 50, 1861.

ROLE OF TRIVALENT Mn IN OXIDATION OF ORGANIC MATTER

Christopher J. Matocha and D.L. SparksDept. of Agronomy, University of Kentucky, Lexington, KY 40546-0091

Dept. of Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303

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DIVISION OF ENVIRONMENTAL CHEMISTRY PREPRINTS OF EXTENDED ABSTRACTS: VOL. 40(2) AUGUST 2000

I N T R O D U C T I O NManganese(ll) and Mn(IV) have received the most attention in aquatic chemistry until recently, where solid Mn(lll) oxides andsoluble Mn(lll) complexes have been shown to be environmentally significant oxidants '. Solid Mn(lll,IV) (hydr) oxide minerals are powerful oxidants in soils and geochemical environments because of the vacant orbitals of sigma symmetry thatimpart significant surface reactivity®. Manganese(lll) solid phases would be expected to be more kinetically reactive thanMn(IV) minerals, however, no detailed studies have been conducted. This study was undertaken to test the hypothesis thatthe lability of Mn(lll) predicted by frontier molecular orbital theory in solution affects the reductive dissolution kinetics ofnaturally occurring solid Mn(lll,IV) (hydr) oxide minerals by comparing several phases with varying levels of structural Mn(lll)in their reactivity with catechol, a model organic ligand of soil organic matter

M AT E R I A L S A N D M E T H O D S

Reactivity studies of solid Mn(lll,IV) (hydr) oxide minerals with catechol were followed In situ using electron paramagneticresonance (EPR) spectroscopy and diffuse reflectance spectroscopy (DRS). Micromolar concentrations of Mn(lll)-pyrophos-phate complexes were measured in the UV region at 210 and 260 nm and mM concentrations at 480 nm as described previously'. Initial rates of pyrophosphate-extractable Mn(lll) from solid phase Mn minerals were used as an operationally definedmeasure of available Mn(lli).

R E S U L T SNo correlation existed between the initial reductive dissolution rates of solid Mn(lll,IV) (hydr) oxides by catechol and surfacearea or thermodynamic driving force. In contrast, the reductive dissolution rates were linearly related to initial rates ofpyrophosphate-extractable IVIn(lll), defined as available Mn(lll) (Figure 1). The positions of the Mn(lll) ligand field bandsderived from DRS analyses suggested different coordination environments for structural Mn(lll) in manganite and birnessite,which explained the different levels of availability. Therefore, the role of Mn(lll) in different coordination environments meritsspecial attention In abiotic cycling of soil organic matter and Mn.

R E F E R E N C E S1. Morgan, J.J. (1967) /n S.D. Faust and J.V. Hunter (ed.) Principles and applications of water chemistry, p. 561-626.

Wiley, New York.2. Stone, A.T., and Morgan, J.J. (1984) Environ. Sci. Techno!. 18:450-456.3. Kostka, J.E., Luther, G.W., III, and Nealson, K.H. (1995) Geochim.

Cosmochim. Acta 59:885-894.4. Klewlcki, J.K., and Morgan, J.J. (1998) Environ. Sci. Techno!.

3 2 : 2 9 1 6 - 2 9 2 2 .5. Luther, G.W. Ill, Ruppel, D.T., and Burkhard, C. (1998) In D.L.

Sparks and T.J. Grundl (ed.) Mineral-water interfacial reactions:Kinetics and mechanisms, p. 265-280. ACS Symposium Ser. No.715, Washington, DC.

6. Luther, G.W. III. (1990) In W. Stumm (ed.) Aquatic chemical kinetics: Reaction rates of processes in natural water, p. 173-198.Wiley-lnterscience, New York.

7. Evanko, C.R., and Dzombak, D.A. (1998) Environ. Sci. Technol.32: 2846-2855.

Figure 1. Relationship between the initial rate of Mn(lll) extraction bypyrophosphate (r) and the reductive dissolution rate by catechol (R).

THE EFFECT OF BIOLOGY ON THE pH-DEPENDENT REACTIVITIESOF Fe AND Mn OXYHYDROXIDES IN AQUATIC ENVIRONMENTS

Y a r r o w M . N e l s o nDept. of Civil and Environmental Engineering, California Polytechnic State University, San Luis Obispo, CA 93407

Alyson R. Wilson and Leonard W. LionSchool of Civil and Environmental Engineering,Cornell University, Ithaca, NY 14853

Adsorption to Fe and Mn oxides has long been known to control trace metal transport in aquatic environments Qenne 1968),but the relative magnitudes of the reactivities of these oxides in aquatic environments have been poorly understood becauseof the complexity of interrelated biological and chemical factors affecting them. The relative roles of Fe and Mn oxides Incontrolling trace metal adsorption were elucidated by examining the effects of biological Mn oxidation on Pb adsorption over a

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