Experimental determination of solubilities of lead oxalate (PbC2O4(cr)) in a NaCl medium to high ionic strengths, and the importance of lead oxalate in low temperature environments

In this study, the solubility product constant (log10Kso) for crystalline lead oxalate (PbC2O4(cr)) pertaining to Reaction (I), and the formation constant of PbC2O4(aq) (log10β1o) pertaining to Reaction (II),equation(I)PbC2O4(cr)=Pb2++C2O42–PbC2O4cr=Pb2++C2O42–equation(II)Pb2++C2O42–=PbC2O4(aq)Pb2++C2O42–=PbC2O4aqat infinite dilution, 298.15 K and 0.1 MPa, are determined as − 11.13 ± 0.15 (2σ) and 5.85 ± 0.10 (2σ), respectively, based on solubility data for PbC2O4(cr) in NaCl solutions up to 3.2 mol·kg− 1 (molal) evaluated using the Pitzer model. The above solubility product constant determined in this study is lower than the value of − 10.27 ± 0.30 (2σ) for log10Kso evaluated from the literature data. The above log10β1o agrees within the quoted uncertainties with the value of 5.44 ± 0.38 (2σ) derived in this study based on the literature data using the Brønsted–Guggenheim–Scatchard specific interaction theory (SIT) model.In addition, based on solubility data for PbC2O4(cr) in NaCl solutions with 4.4 and 5.0 mol·kg− 1 produced in this work and in a K2C2O4 medium up to 0.51 mol·kg− 1 at 298.15 ± 2 K from the literature, this study also evaluates log10β2o for the following reaction by using the Pitzer model,equation(III)Pb2++2C2O42–=Pb(C2O4)22–Pb2++2C2O42–=PbC2O422–as 8.05 ± 0.15 (2σ).The new parameters presented in this study would enable researchers to accurately predict solubilities of PbC2O4(cr) to high ionic strengths, up to 5.0 mol·kg− 1.

► New solubility data of lead oxalate in NaCl solutions up to 5.0 m are presented.
► New log Kso for PbC2O4(cr), log β1o for PbC2O4(aq), and log β2o are obtained.
► New constants with the Pitzer and SIT parameters are valid to high ionic strengths.
► Lead oxalate would be a source-term phase for lead in low temperature environments.