Influence of trace level As or Ni on pyrite formation kinetics at low temperature

Pyrite formation at low temperature during early diagenesis in (sub-)surface sediments is an essential step of Fe and S biogeochemical cycles the presence this ubiquitous mineral surface environments often used as indicator paleo-redox conditions. Pathways pyrite are usually discussed environmental settings by involving a variety nanosized Fe-S mineralogical precursors function local geochemical However, influence trace element impurities such Ni As solution time has been poorly studied, whereas specific chemical signatures elements commonly observed sedimentary pyrites. A better understanding impact incorporation levels on to help refining use these indicators evaluate role sink regulating cycle potentially toxic elements. In study, we have performed syntheses via polysulfide pathway using aqueous Fe(III) H2S amounts Ni(II) (0.001 mol%Fe) As(III) mol%Fe). Analysis solids collected different steps over course experiments X-Ray absorption spectroscopy both K-edges shows that starts precipitate within 5 days 32 As(III), while control experiment showed intermediate precipitation rate 14 days. Shell-by-shell analysis K-edge EXAFS data initial same all correspond poorly-crystalline FeS (3.0 ± 0.1 [email protected] Å; 1.7 0.2 Å). addition, XANES qualitative suggests small precursors. Synchrotron-based XRD WAXS-PDF starting show addition S(0), continuum particles ranges from tetragonal nanocrystalline (a = 3.70(2) Å, c 5.24(7) MCDab 41 4 Å MCDc 21 2 Å) cluster-type (MCDabc < 8.4 4.3 We propose type interaction with precursors, resulting respectively increase decrease nucleation. While would incorporate structure interact (poly)sulfides form thio-As, possibly binding or precipitating onto surfaces thus slowing transformation FeS2. Given were introduced our experiments, results suggest occurrence could strong kinetics natural pore-scale microenvironments. emphasizing importance persistence mobile colloidal species anoxic conditions, present study also point considering actual nature when composition for ancient past climates reconstruction.