Evaluation of thermodynamic data of hydroxide and chloride species for lead

Lead-210, which continuously releases from a decay chain of 4n+2 series of radionuclides with long half-lives, is one of the important elements for performance assessment of geological disposal of high-level radioactive waste. Equilibrium constants of lead species and compounds are required to estimate their migration behavior in the geological disposal system. The Japan Nuclear Cycle Development Institute (JNC) developed thermodynamic data for lead species and compounds in the JNC's thermodynamic database (JNC-TDB) published in 1999. In the present paper we reviewed latest literatures after publishing the JNC-TDB, and confirmed the reliability of their experimental values and obtained equilibrium constants for Pb(OH)n2-n and PbCln2-n (n=1-3). Furthermore, we re-evaluated the equilibrium constants at zero ionic strength for Pb(OH)n2-n and PbCln2-n (n=1-3) using the presently reviewed data and the previously confirmed literature data as shown below. We improved the reliability of thermodynamic data for these species. Pb2+ + H2O=PbOH+ + H+, logK=-6.91 ±0.36, Pb2+ + 2H2O=Pb(OH)2(aq) + 2H+, logK=-16.11 ±0.71, Pb2+ + 3H2O=Pb(OH)3- + 3H+, logK=-26.27 ±1.18, Pb2+ + Cl-=PbCl+, logK=1.48 ±0.10, Pb2+ + 2Cl-=PbCl2(aq), logK=2.07 ±0.17, Pb2+ + 3Cl-=PbCl3-, logK=1.80 ±0.32. (author)