Precipitation kinetics and carbon isotope partitioning of inorganic siderite at 25°C and 1 atm
CONCEPCION JIMENEZ-LOPEZ1, and CHRISTOPHER S. ROMANEK1,2
l
1Savannah River Ecology Laboratory, Drawer E,
Aiken SC, 29802 USA
2Department of Geology, University of Georgia, Athens, GA 30602
USA
(Received May 22, 2002;.accepted in revised,form June 24, 2003)
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were withdrawn at different time intervals during time course experiments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 (103ln) averaged
8.5 ± 0.2 (l0'; n = 4) for the siderite-CO2(g) system
and 0.5 ± 0.2 (lu; 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.
