Studies in the system PbSNaClH 2SH 2O: Stability of lead(II) thiocomplexes at 90°C

Abstract

The solubility of PbS in 1.0 m and 3.0 m NaClHC1H 2O solutions saturated with H 2S has been determined at 90°C. When plotted against the solution pH, the saturation curves define troughs. The left limb of each trough represents the acid solubility, due mainly to the formation of chloride complexes. The flat portions and the right limbs of the troughs have been interpreted in terms of the formation of PbS 2H 2S and Pb(HS) − 3 complexes respectively. The following constants were derived for the formation reactions at 90°C: PbS+2 H 2 S= PbS 2 H 2 S Log K= −2.1±0.3 and: PbS+ H 2 S+ HS −= Pb( HS) − 3 Log K = −2.5 These constants show that at 90°C, the thiocomplexes are potential ore carriers, moving more than 10 p.p.m. of lead in neutral to slightly acid NaCl solutions with total sulfur contents as low as 0.2 molal.