Sulfur reduction distillation of sulfides and verification of the effect of sulfur isotopic fractionation during pretreatment

Abstract

Toxic gases can be emitted when sulfides form compounds with heavy metals; thus, a series of pretreatments are required prior to the analysis of sulfur isotope ratios to remove unnecessary elements. In addition, it is necessary to verify the effect of sulfur isotope fractionation caused by the plurality of sulfides comprising different sulfide species during the pretreatment process. In this study, H2S(gas) was extracted from mixed sulfides comprising pyrite and galena and reacted with mixed acids (i.e., HCl + HI + H3PO2) at 200 °C, in sealed conditions filled with N2. Subsequently, CdS(s) was precipitated from the reaction with H2S(gas) in a trap filled with Cd(CH3COO)2(aq). CdS(s) was then ionized to SO42−(aq) after reacting with H2O2(l), followed by the addition of BaCl2(l) to precipitate BaSO4(s). The sulfur isotope values of the products (barite: av. 5.9‰) were lower than those of the reactants (sulfides: av. 6.9‰); this is attributed to the preferential fractionation of galena with a low isotope ratio when converting sulfide to H2S(gas). Therefore, in the pretreatment process for the sulfur isotope analysis of a sample composed of a sulfide mixture, the effect of isotope fractionation between sulfur species should be considered.