The FeSe2(cr) solubility determined by solubility experiments of Se co-existing with Fe

Abstract

To determine the equilibrium constant for ferroselite (FeSe2(cr)) dissolution reaction, FeSe2(cr) solubility experiments were performed at 298 ± 1 K from both the over- and under-saturation directions with Fe–Se precipitates that were aged at 348 K. X-ray diffraction (XRD) analysis detected only FeSe2(cr) as the Se solid phase in the equilibrated precipitates. The Eh values of the equilibrated suspensions ranged from −188.6 to −4.9 mV vs. standard hydrogen electrode (SHE) and the pH values ranged from 6.00 to 8.76. Based on the available thermodynamic data, Se42− and Fe2+ are thermodynamically stable within this Eh–pH range. Agreement between the solubility data obtained from the over- and under-saturation directions lends credence to the attainment of equilibrium at 298 ± 1 K. The thermodynamic interpretations using the specific ion interaction theory (SIT) model showed that Eh values and the concentrations of Se and Fe are well represented by the 2FeSe2(cr) solubility reaction (2FeSe2(cr) ⇌ 2Fe2+ + Se42− + 2e−) with log10K○ = −17.09 ± 0.28. The obtained log10K○ value falls within the uncertainty limits of the log10K○ value calculated from the available thermodynamic data.