Kinetic investigation of galvanic dissolution of ZnS and PbS with FeS2 from hydrothermal sulfides in seawater

Sulfide mineral dissolution is an important reaction controlling geochemical and environmental chemical processes in aqueous environments. In this study, we quantitatively evaluated the kinetic influence of galvanic interactions between different sulfide minerals on their dissolution in seawater. Four hydrothermal sulfides with different amounts of Fe disulfide minerals (pyrite) were reacted with artificial seawater for 144 h, and the dissolution rates of Zn and Pb were determined by an extraction method. The Zn dissolution rates from samples with high Fe/Zn molar ratios ( 0.26) were 1.3-1.5 x 10-10 mol m- 2 s- 1; approximately one order of magnitude higher than those of samples with low Fe/Zn molar ratios (<0.002; 1.6-1.8 x 10-11 mol m- 2 s- 1). The Pb dissolution rates from a sample with high Fe disulfide were approximately nine orders of magnitude higher (8.4x 10-10 mol m- 2 s- 1) than reference data of the single galena dissolution rate (8.9 x 10-19 mol m- 2 s- 1). The higher solubility of PbSO4 than PbS and PbCO3 could explain the intense release of Pb from the other samples. These results and mineralogical observations with X-ray diffraction, X-ray photoelectron spectroscopy, and electron probe micro-analysis of sulfide mineral particulates provide evidence for the selective dissolution of anodic sulfide minerals (e.g., sphalerite and galena) at a higher reaction rate than cathodic sulfide minerals of Fe disulfide (e.g., pyrite).