Project Details Critical Evaluation of Metal-Sulfate Equilibrium Data

Project No.: 
Start Date: 
27 November 2019
End Date: 


Metal-sulfate complexes are widely encountered in the environment (freshwaters, wastewaters, seawater, aerosols) and in many industries (extractive metallurgy, fertilizer, etc). Reliable quantitative knowledge of the equilibrium data (stability constants, enthalpies, etc) for such complexes is required to inform the chemical speciation computer models that are being used increasingly on a global basis to monitor, optimize and control chemical processes. This project aims to assemble all of the thermodynamic data (currently spread throughout the literature) on these complexes, to critically evaluate them, and to recommend reliable values to the potential users.


Metal-Ion/sulfate equilibria dominate chemical behaviour in many environmental, biochemical and industrial contexts. This project involves the collection and critical evaluation of all experimental thermodynamic data (stability constants, enthalpies, entropies and heat capacities) pertaining to these equilibria in aqueous solution. Vast amounts of such data are spread throughout the literature, often in obscure journals, reports and databases. Many of these data are in poor agreement or are flatly contradictory. This makes it difficult (if not impossible) for the non-expert to distinguish between good and bad (not to mention just plain ugly) data. This in turn compromises the reliability of the chemical speciation calculations based upon such data. Such failures can have important impacts on decision making, for example, in dealing with nuclear waste depositories.

Most of the required data have already been compiled by the task group members. Following a completeness cross-check, the TGMs will then abstract the numerical values from the literature and enter them into appropriate tables. Critical evaluation of the data will be based on the criteria outlined in previous IUPAC publications (eg, Powell et al., PAC 85 (2013) 2249;


Feb 2022 update – Progress on this project has continued at a much reduced rate due to COVID lockdowns, etc. Literature searching continues and files have been updated. Detailed analysis of the important proton-sulfate interaction has commenced.

Page last update 2 Feb 2022