Antimony and arsenic partitioning during Fe 2þ -induced transformation of jarosite under acidic conditions Niloofar Karimian * , Scott G. Johnston, Edward D. Burton Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia highlights graphical abstract  At pH 4.0, the addition of Fe 2þ (aq) resulted in no significant trans- formation in jarosite.  At pH 5.5, 60 min was sufficient for partial transformation of jarosite to green rust.  Formation of green rust and goethite under pH 5.5, sequestered dissolved antimony.  Arsenic was mostly repartitioned to the surface of green rust and goethite. article info Article history: Available online 27 December 2017 Keywords: Antimony Arsenic Jarosite Fe 2þ Green rust pH abstract Jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ] is considered a potent scavenger for arsenic (As) and antimony (Sb) under oxidizing conditions. Fluctuations in water levels in re-flooded acid sulfate soils (ASS) can lead to high Fe 2þ (aq) concentrations (~10e20 mM) in the soil solution under acidic to circumneutral pH conditions. This may create favorable conditions for the Fe 2þ -induced transformation of jarosite. In this study, synthetic arsenate [As(V)]/antimonate [Sb(V)]-bearing jarosite was subjected to Fe 2þ (aq) (20 mM) at pH 4.0 and 5.5 for 24 h to simulate the pH and Fe 2þ (aq) conditions of re-flooded freshwater ASS/acid mine drainage (AMD)-affected environments at early and mid-stages of remediation, respectively. The addi- tion of Fe 2þ at pH 5.5 resulted in the formation of a metastable green rust sulfate (GR- SO 4 ) phase within ~60 min, which was replaced by goethite within 24 h. In contrast, at pH 4.0, jarosite underwent no significant mineralogical transformation. Although the addition of Fe 2þ (aq) induced the dissolution/ transformation of jarosite at pH 5.5 and increased the mobility of Sb during the initial stages of the experiment (Sb (aq) ¼ ~0.05 mmol L 1 ), formation of metastable green rust (GR-SO 4 ) and subsequent transformation to goethite effectively sequestered dissolved Sb. Aqueous concentrations of As remained negligible in both pH treatments, with As being mostly repartitioned to the labile (~10%) and poorly crystalline Fe(III)-associated phases (~10e30%). The results imply that, under moderately acidic condi- tions (i.e. pH 5.5), reaction of Fe 2þ (aq) with jarosite can drive the dissolution of jarosite and increase Sb mobility prior to the formation of GR-SO 4 and goethite. In addition, repartitioning of As to the labile * Corresponding author. E-mail address: niloofar.karimian@scu.edu.au (N. Karimian). Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere https://doi.org/10.1016/j.chemosphere.2017.12.106 0045-6535/© 2017 Elsevier Ltd. All rights reserved. Chemosphere 195 (2018) 515e523