JNC TN8400 99-011 JP9955327 42 Thermodynamic Data for the Speciation and Solubility of Pd, Pb, Sn, Sb, Nb and Bi in Aqueous Solution January, 1999 33002936. JAPAN NUCLEAR CYCLE DEVELOPMENT INSTITUTE 3 1-09 319-1194 Inquiries about copyright and reproduction should be addressed to : Techinical Information Section Administration Division Tokai Works Japan Nuclear Cycle Development Institute 4-33 Muramatsu, Naka-gun, Ibaraki 319-1194, Japan. JNC TN8400 99-011 January,1999 Thermodynamic Data for the Speciation and Solubility of Pd, Pb, Sn, Sb, Nb and Bi in Aqueous Solution Barbara Lothenbach**, Michael Ochs**, Hans Wanner*** and Mikazu Yui* Abstract This report provides thermodynamic data for predicting concentrations of palladium Pd, lead Pb, tin Sn, antimony Sb, niobium Nb and bismuth Bi in geologic environments, and contributes to an integration of the JNC chemical thermodynamic database, JNC-TDB (previously PNC-TDB), for the performance analysis of geological isolation system of high-level radioactive wastes. Besides treating hydrolysis in detail, this report focuses on the formation of complexes or compounds with chloride, fluoride, carbonate, nitrate, sulfate and phosphate. Other important inorganic ligands (sulfide for lead and antimony, ammonia for palladium) are also included. In this study, the specific ion interaction theory (SIT) approach is used to extrapolate thermodynamic constants to zero ionic strength at 25 °C. *: Waste Isolation Research Division, Tokai works, Japan Nuclear Cycle Development Institute (JNC) **: BMG ENGINEERING Ltd., Switzerland **: HSK, Switzerland JNC TN8400 99-011 1999 £fU£ Pd, Pb,Sn,Sb, Bi Barbara Lothenbach**, Michael Ochs**, Hans Wanner***, M#HfP* (10 PNC-TDB) ^fO—lit LtilL/:, £&(Pb), ^X(Sn), , - * 7* (Nb) iJ «t O* H'X-7^ m tzo ttz, & r{i, SIT (specific ion interaction theory ) , 25°C, -< 0 Hi3tt£-*libtf>!tftfc L > ^ - **: BMG ENGINEERING Ltd. (X -f 7,) ***: HSK (X-fX) JNC TN8400 99-011 Preface The PNC-TDB project was initiated by PNC in 1996 with the aim to establish, by March 31, 1998, an internationally acknowledged equilibrium database for 20 elements that were defined as potentially important by PNC for the safety of a nuclear waste repository. I accepted to coordinate the project at an international level, and Dr. Dhanpat Rai (Battelle PNNL, Richland) as well as Dr. Gregory Choppin (Florida State University, Tallahassee) accepted to participate as experts. Their task was the setting-up of an equilibrium database on the actinide elements. The tedious job of administrative project management, including the contracting business with all participants was assumed by Dr. Michael Ochs (BMG Engineering, Schlieren, Zurich). In the 2nd year of this project, he and his colleague Dr. Barbara Lothenbach also were put in charge to develop the chemical thermodynamics of some non-actinide elements. The kick-off meeting was held at Tokai-mura, May 27-30, 1996, in the presence of the Japanese experts: Dr. O. Tochiyama, Dr. H. Moriyama, Dr. S. Nakayama and Dr. T. Yamaguchi. Nevertheless, the various contracts were not in place until October 1996. A second meeting involving only PNC, BMG and myself was held at BMG, Zurich, November 18 - 20, a third meeting was held at Richland, Washington, May 27 - 29, 1997, without participation of the Japanese experts, and a fourth one on October 29, 1997, on the occasion of the Migration '97 conference at Sendai, again with the presence of the Japanese experts. It was clear from the beginning, and stated explicitly at the kick-off meeting, that the timescale of the project (1.5 years) was extremely ambitious. Obviously, it was impossible to achieve, for the final product, a quality level that would be comparable to that of the NEA-TDB. We nevertheless decided to choose a procedure that resembles the one of NEA-TDB at least in the basic principles. This will allow immediate improvements of the pre-selected data in a possible follow-up project. PNC decided from the start to accept different procedures for the establishment of the actinide database on one hand, and of the non-actinide databases on the other hand. For the actinide compounds and complexes of the +III and +IV oxidation states PNC preferred the establishment of a complete Pitzer model to the adoption of the NEA database. Less weight was put on the development of databases for penta- and hexavalent actinide species. The motivation behind this decision was PNC's conviction that only the +III and +IV oxidation states of the actinides will be relevant in their performance assessment analyses due to their choice of near- field components and geological sites. For the non-actinide elements, PNC preferred initially to have its own staff perform a review of the available literature and establish selected data sets, while the members of the expert team should review these data sets and make constructive comments in such a way that the PNC staff could then implement the improvements and thus accomplish the various data sets according to international standards. The state-of-the-art analysis of the project during the second meeting in November 1996 revealed that this procedure was unlikely to result in satisfactory data sets by the final deadline of March 31, 1998. It was then decided to split the non-actinide elements up into two sets, one to be treated by BMG according to the guidelines of the NEA-TDB, the other to be treated by PNC staff according to their own procedures. in JNC TN8400 99-011 The tasks that had to be accomplished by the PNC-TDB project team were the following: D. Rai/PNNL Database on actinide compounds and complexes in the +III and +IV oxidation states G. Choppin/FSU Database on actinide compounds and complexes in the +V and +VI oxidation states, plus the actinide redox potentials M. Ochs/BMG Database on the elements Bi, Nb, Pb, Pd, Sb and Sn As I have indicated above, the data sets presented in this report cannot be considered to correspond to the quality level of the NEA-TDB due to the reasons outlined below. However, I consider them as an excellent, partly high-quality basis that will require some quality-checking with independent experimental literature in the case of the actinide models, and a more detailed review of some of the reported literature in the other cases. My personal assessment of the quality of the database presented in this report and the reports by D. Rai, G. Choppin and co-workers, and of the improvements and refinements that may be required to obtain ,,final", high-quality data sets, is briefly summarized below: Actinide elements: The actinide +III model is based on the extensive experimental experience of D. Rai with the chemical behavior of lanthanides and actinides. The evidence for analogous treatment of the +III oxidation states is compelling and convincing. A complete Pitzer parameter set is provided. It is important that the Pitzer parameters be used in modeling studies, because in some cases (e.g., the sulfate complexes) complex formation is expressed by Pitzer parameters rather than equilibrium constants. This data set has, to my knowledge, not yet been checked against independent experimental studies from other laboratories. This task, which was not part of the present project but would improve the credibility of the data set, is strongly recommended for the near future. For the +IV oxidation state of the actinides, the analogy concept is less evident than for the +III oxidation state. The recommendation to cross-check the data against independent experiments is also valid here. The reason why the +V and +VI oxidation states of the actinides have been treated in a less sophisticated way is due to the low weight PNC has assigned to them. Without expressing any criticism of the selected values themselves, I feel that the review procedure here is not sufficiently transparent to cope with international standards. These data are based on expert judgment rather than on detailed analysis of the available experimental papers. The same comment applies to the redox potentials. However, due to the low weight PNC had assigned to this part of the project, the corresponding budget was quite limited, and a detailed analysis of these chemical systems could not be carried out. Non-actinide elements (Bi, Nb, Pb, Pd, Sb and Sn): For these elements all the experimental data have been compiled from the available literature. Detailed reviews of the experimental papers have in general not been performed due to time and IV JNC TN8400 99-011 budget constraints, an exception being the hydrolysis papers of the palladium review. The procedure chosen is consistent with the guidelines of the NEA-TDB: Experimental data are used to perform SIT plots (SIT = Specific Ion Interaction Theory, cf. NEA-TDB). In cases where the experimental data from different sources show satisfactory agreement on the SIT plot, an extrapolation to zero ionic strength may provide confidence in the resulting thermodynamic constants. It will nevertheless be necessary to review the experimental papers in detail in order to achieve international quality standards for the selected data sets. In addition, important gaps have been identified in many cases, and experimental programs should be performed to provide the information required for credible predictive modeling. As a conclusion, I believe that the objectives of the PNC-TDB project, as defined at the kick-off meeting and re-defined at the second meeting in June 1997, have been reached. It is somewhat unfortunate that part of the database comes with complete Pitzer parameter sets, others with SIT parameter sets, and yet others with no ion interaction parameters at all. However, as I have mentioned in the beginning of this Preface, the procedure that unavoidably had to lead to this difference in activity factor treatment was consciously chosen by PNC.