Uncertainty and Sensitivity Analysis of Solubility Calculations at Elevated Temperatures

Abstract

Computer simulations are commonly used in many areas to obtain information about a system. It is, however, important to remember that the indata to these models are encumbered with errors of varying magnitude. To investigate the effect of these errors, a sensitivityuncertainty (s/u) analysis is often made.This paper focuses on how the solubility of a solid phase is affected by uncertainties in the enthalpy of reaction for the species present in the solvent. Usually, thermodynamic data are given for a temperature of 25°C, but calculations are not made at this temperature for many practical applications. It is interesting to know which enthalpies are important and how much given uncertainties in these enthalpies affect the calculated solubility of a solid phase.The solubility calculations were performed by the thermodynamic equilibrium program PHREEQE and the statistical evaluations with a modified version of the SENVAR program.The solubility of e.g. UO3-2H2O at 80°C was investigated. The conclusion was that the solubility ranged from lE-05 to 4.5E-06 when the enthalpies of reaction for the interesting species were changed within a four kcal/mole wide interval. The maximum solubility, based on an arbitrary distribution, was found to be no greater than 9E-05 with 95% confidence.

Determining Stability Constants Using the AKUFVE Technique

“…It was not until the middle of the 1990s that stability constants determined by solvent extraction first received a thorough uncertainty analysis. [14][15][16] The extraction system consists of two almost immiscible liquid phases and, in many cases, an extraction reagent. There exist several kinds of extraction reagents, e.g.…”