Technical Report NTB 99-03
Solubility Products of M(II)-Carbonates
The geochemical behaviour of elements of importance plays an important role in safety assessments of radioactive waste repositories. Carbonate, hydroxide and oxide anions form perhaps the most important complexants and concentration-limiting solids among a large variety of relevant compounds. In many cases, complexes and solids including these anions form the backbone of the thermodynamic data bases used in geochemical modelling. Therefore, defensible and reliable thermodynamic data for these compounds are of key importance in waste management.
All his life, Professor Rolf Grauer maintained a strong interest in the chemistry of transition metal carbonates and published many studies on this topic. However, being a chemist of the old school, he was very much disturbed by the many inconsistencies in the solubility data for transition metal carbonates which he found even in "critical" data compilations. He finished the present critical comments on theses findings very shortly before his unexpected demise in September 1994. Unfortunately, he was not granted the privilege of presenting this, his very last work, to a broader audience, because it was only provisionally issued as a PSI internal report written in German (TM-44-94-05).
The aim of an update of the PSI geochemical data base which was recently begun is not only to improve the quality of data sets for individual elements, but also to provide a comprehensive picture, with chemical consistency among the various elements. Previous studies have shown that chemical consistency is just as important as the numerical precision of individual equilibria.
This critical review by Rolf Grauer represents an essential cornerstone of this particular scientific area. It analyses and quantifies the solubility data available for transition metal carbonates with meticulous attention to detail. Frequently, thermodynamic data compiled in tables are not sufficiently well documented and commented upon. Therefore, the author traces them back to the original publications, judges the experimental methods applied, and discusses the solid phases used in the experiments. In addition, he gives appropriate weight to the conversion of experimental results to standard conditions, as well as to error limits. In his summary, Rolf Grauer presents a new, chemically consistent and comprehensively supported picture of the solubility of transition metal carbonates.
Because of my conviction that this study deserves special attention from experts in this field, I decided to prepare an English translation to open it a broader audience. Along with the scientific facts and terms, the translation also tries to capture the expressive style of Rolf Grauer's original German text. Therefore, very few clarifications and supplementary comments were added.
PSI, December 1998
Translation of original summary: Many solubility data for M(II) carbonates commonly compiled in tables are contradictory and sometimes obviously wrong. The quality of such data has been evaluated based on the original publications and reliable solubility constants have been selected for the carbonates of Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb with the help of cross-comparisons.