SREL Reprint #2740

 

 

 

Precipitation kinetics and carbon isotope partitioning of inorganic siderite at 25°C and 1 atm

Concepción Jimenez-Lopez1, and Christopher S. Romanek1,2

1Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA
2Department of Geology, University of Georgia, Athens, GA 30602 USA

Abstract: Siderite was precipitated from NaHCO3 and Fe(CIO4)2 solutions under anaerobic conditions at 25°C and 1 atm total pressure using a modified version of the chemo-stat technique and the free-drift technique. Samples of solution and solid were withdrawn at different time intervals during time course experiments to determine the bulk and isotope composition of the solution and solid, and the morphology and mineralogy of the solid. A series of metastable precursors precipitated and dissolved sequentially, culminating in well-crystallized siderite rhombohedra having an average edge of ~2µm and a limited size distribution. Siderite precipitation rate ranged from 100.23 to 102.44 µmol·m-2·h-1 for saturation states (with respect to siderite) ranging from near equilibrium to 103.53. Calculated carbon isotope fractionation factors (103lnα) averaged 8.5 ± 0.2 (lσ; n = 4) for the siderite-CO2(g) system and 0.5 ± 0.2 (lσ; n = 4) for the siderite-HCO3-(aq) system.

SREL Reprint #2740

Jimenez-Lopez, C. and C. S. Romanek. 2004. Precipitation kinetics and carbon isotope partitioning of inorganic siderite at 25°C and 1 atm. Geochimica et Cosmochimica Acta 68:557-571.

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