Caption: 
Relative distribution of ferric (Fig. a) and ferrous (Fig. b) species as a function of pH, calculated using the equilibrium constant values from Panias et al. [298] and Pozdnyakov et al. [313]. The pH at $c_{\mathrm{H_2C_2O_4}}=0.19\,$mol/L is calculated assuming the dissociation constants $\mathrm{pKa_1} = 1.25$ and $\mathrm{pKa_2} = 4.21$ at 25$^\circ$C [299]. The data points represent the measured fraction of total dissolved iron as a function of pH at $c_{\mathrm{H_2C_2O_4}}=0.19\,$mol/L, obtained from Lee et al. [227]. Reproduced with permission from Elsevier.

Notes: 
[227] Lee, S. O., Tran, T., Jung, B. H., Kim, S. J., & Kim, M. J. (2007). Dissolution
of iron oxide using oxalic acid. Hydrometallurgy, 87(3):91–99. DOI: https:
//doi.org/10.1016/j.hydromet.2007.02.005.

[298] Panias, D., Taxiarchou, M., Douni, I., Paspaliaris, I., & Kontopoulos, A.
(1996a). Thermodynamic analysis of the reactions of iron oxides: Dissolution
in oxalic acid. Canadian Metallurgical Quarterly, 35(4):363–373. DOI: https:
//doi.org/10.1016/S0008-4433(96)00018-3.

[299] Panias, D., Taxiarchou, M., Paspaliaris, I., & Kontopoulos, A. (1996b). Mechanisms of dissolution of iron oxides in aqueous oxalic acid solutions. Hydrometallurgy, 42(2):257–265. DOI: https://doi.org/10.1016/0304-386X(95)00104-O.

[313] Pozdnyakov, I. P., Kel, O. V., Plyusnin, V. F., Grivin, V. P., & Bazhin,
N. M. (2008). New insight into photochemistry of ferrioxalate. The Journal
of Physical Chemistry A, 112(36):8316–8322. PMID: 18707071. DOI: https:
//doi.org/10.1021/jp8040583.

Plot data:
plot_0: 30 min [227]
plot_1: 60 min [227]

