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Experimental observations on carbon isotope exchange in carbonate-water systems
Authors:AA Mozeto  P Fritz  EJ Reardon
Institution:1. Departamento de Quimica, Universidade Federal de São Carlos, 13560 São Carlos, S.P., Brasil;2. Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
Abstract:This study presents data from experiments investigating carbon isotope exchange between carbonate solution and solid calcite using carbon-13 as a tracer. All experiments were done with calcite saturated solutions and results show that a two-step adsorption-recrystallization reaction takes place. Isotope effects are caused by exchange by carbonate on the solid surface with carbon in the aqueous phase. Adsorption reactions are characterized by a maximum isotopic exchange capacity (IEC) on crystal surfaces of about 1011 reaction sites per cm2, following a second order rate law with respect to 13C concentration in solution (constant kex ? 106 cm5 mole?1 s?1 and half-life t12 = 700 s). The adsorption reaction was followed by a first order recrystallization which is characterized by a rate constant of the order of 10?8 s?1 and a t12 of 107 s. Negative isotopic gradient experiments and runs with calcite crystals in Mg2+ spiked solutions provided the preliminary basis for the characterization of the mechanisms of both proposed reactions.
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