FN Archimer Export Format
PT J
TI Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions
BT 
AF Neubeck, Anna
   Hemmingsson, Christoffer
   Boosman, Arjen
   Rouxel, Olivier
   Bohlin, Madeleine
AS 1:1;2:2;3:3;4:4;5:1;
FF 1:;2:;3:;4:PDG-REM-GM;5:;
C1 Department of Earth Sciences, Uppsala University, Sweden
   Department of Geological Sciences, Stockholm University, Sweden
   Department of Earth Sciences, Utrecht University, The Netherlands
   Ifremer, Unit of Marine Geosciences, Brest, France
C2 UNIV UPPSALA, SWEDEN
   UNIV STOCKHOLM, SWEDEN
   UNIV UTRECHT, NETHERLANDS
   IFREMER, FRANCE
SI BREST
SE PDG-REM-GM
IN WOS Ifremer UPR
   copubli-europe
IF 4.127
TC 5
UR https://archimer.ifremer.fr/doc/00661/77275/78710.pdf
LA English
DT Article
DE ;Stable Ni isotopes;Ferrihydrite precipitation;Co-precipitation experiment;Banded iron formation;Silica
AB The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 ± 0.17‰). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5‰. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the δ60Ni values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry. 
PY 2021
PD APR
SO Geochemistry
SN 0009-2819
PU Elsevier BV
VL 81
IS 1
UT 000645660900018
DI 10.1016/j.chemer.2020.125714
ID 77275
ER

EF