Reductive dissolution of Pb-Zn jarosite under near-neutral conditions

Abstract

Jarosite, an oxyhydroxysulfate secondary mineral, exists widely in mining areas, typically in association with heavy metals, such as Pb or Zn. Replacement by heavy metals at different sites within the jarosite crystal structure may lead to change in its dissolution behavior. Fe(II) can significantly catalyze jarosite dissolution–recrystallization under near-neutral conditions in reductive soil or sediment systems. However, it has been unclear whether the reductive dissolution characteristics, and the end products of bimetallic–replaced Pb-Zn jarosite, were similar to those of other jarosite–type minerals (such as As(V)–bearing jarosite). In this study, the dynamics of aqueous and solid parameters were combined to analyze liberation of Pb2+, Zn2+ and SO42− from Pb-Zn jarosite, in 0, 1, and 10 mM Fe(II) systems. We found that in all the systems, the Pb2+, Zn2+, and SO₄2− release percentages exhibited two liberation stages, which appeared to be mainly due to the formation of secondary phases. In the fast stage, which occurred within 1 d, the Pb2+, Zn2+, and SO₄2−, liberation speeds ranked in the order of SO42− > Pb2+ > Zn2+, while in slower liberation stage, which occurred after 1 d, the liberation speeds ranked in the order of Pb2+ > Zn2+ > SO42−, and on the whole, the liberation priority ranked in the order of SO42− > Pb2+ > Zn2+. Examination using X–ray powder diffraction, Raman spectroscopy, scanning electron microscopy, and X–ray photoelectron spectroscopy revealed that lepidocrocite was the only detectable secondary product in the low Fe(II) system, while lepidocrocite and goethite, together with amorphous anglesite, formed in the high Fe(II) system. The author considers that this study sheds light on predicting the environmental fates of trace elements associated with acid mine drainage environments, while providing a basic concept, together with useful information, for heavy metal remediation in mining areas.