Kinetic studies of carbonation reactions using radioactive tracers

In this study a radioactive tracer technique was used to determine the kinetic reaction rate constants in the CO 2 NaHCO 3 Na 2 CO 3 H 2 O system at temperatures of 32, 50, and 68°F., and at various values of p H ranging from 5.6 to 7.6. By operating with this system at chemical equilibrium but at isotopic disequilibrium, it was possible to divorce the influence of the diffusion of CO 2 into and out of the aqueous solution from the kinetic effects of the chemical reaction. Radioactive carbon‐14 in the form of CO 2 was analyzed by means of the Bernstein‐Ballentine technique in order to measure the rates of reaction. By this treatment, without using intricate equipment, reaction rate constants were computed from simple, integrated first‐order equations. Results showed that values for the forward rate constant of the reaction CO 2 + H 2 O ⇌ HCO 3 − + H + agreed well with the values published by previous investigators. On the other hand, the forward rate constants of the reaction CO 2 + OH − ⇌ HCO 3 − were about 100 times as large as previously reported values. This difference is believed due to the complete elimination of any mass transfer effects in this study. In addition, values for the rate constants of the reverse reactions were measured for the first time, and the calculated values of the equilibrium constants for the two reactions agreed within 6% on the average with those given by Harned and Owen. The technique used, with its variations, is expected to have numerous applications in the study of the kinetics of heterogeneous systems.