Comment on “Hydrolysis of neptunium(V) at variable temperatures (10-85 °C)” by L. Rao, T.G. Srinivasan, A.Yu. Garnov, P. Zanonato, P. Di Bernardo, and A. Bismondo

In a recent study [Rao, L., Srinivasan, T.G., Garnov, A.Yu., Zanonato, P., Di Bernardo, P., Bismondo, A., 2004. Hydrolysis of neptunium(V) at variable temperatures (10-85 °C). Geochim. Cosmochim. Acta68, 4821-4830.] the hydrolysis of Np(V) was investigated at 10-85 °C by absorption spectroscopy, potentiometry, and microcalorimetry along the titration of Np(V) solutions with tetramethylammonium hydroxide up to pH 10. However, there is strong evidence that the precautions to avoid competing reactions with carbonate were not sufficient and that the measured effects are not caused by the formation of Np(V) hydroxide complexes but primarily by the formation of Np(V) carbonate complexes. The reported equilibrium constants, enthalpies, entropies, and heat capacities for the complexes NpO₂OH(aq) and are severely in error and must not be used for the geochemical modeling of neptunium. If the hydrolysis constants reported by Rao et al. [Rao, L., Srinivasan, T.G., Garnov, A.Yu., Zanonato, P., Di Bernardo, P., Bismondo, A., 2004. Hydrolysis of neptunium(V) at variable temperatures (10-85 °C). Geochim. Cosmochim. Acta68, 4821-4830] are used to calculate neptunium solubilities in alkaline solutions relevant for nuclear waste repositories, the Np(V) concentrations are overestimated by orders of magnitude.     

Reply to comments by R. Von Herzen, E.E. Davis, A.T. Fisher, C.A. Stein and H.N. Pollack on “Earth's heat flux revised and linked to chemistry”

The lengthy comment by Von Herzen et al. does not address the most important conclusions of the paper by Hofmeister and Criss [Hofmeister, A.M., Criss, R.E., 2005, Earth's heat flux revisited and linked to chemistry. Tectonophys. 395, 159–177.]. These are 1) that actual measurements better describe the Earth than do simplistic models with demonstrably unrealistic boundary conditions that diverge markedly from the data; and 2) that the models are unconstrained, resulting in a series of papers proposing values for the global flux that have become increasingly disparate from the growing data base over time (Fig. 3 in our paper). We disagree strongly with penultimate concluding statement of Von Herzen et al., “that it is preferable to base surface heat flow analysis not only on the extensive measurements but also on well understood processes that are known to bias the values and statistics of the measurements,” as our Fig. 3 demonstrates that no consistent magnitude has been assigned to the alleged advective flux, so that neither the processes nor the correction are “well understood”. We do not deny the existence of submarine hydrothermal systems, but we disagree strongly with the scales over which they are alleged to operate, and with the large Rayleigh and Nusselt numbers Von Herzen et al. assign to them.