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Table 2 Fe-normalized electrons transferred over 28 days relative to the redox state measured (a) directly after addition of HS or RHS, i.e. t = 0, in the HS or RHS magnetite sample and (b) t = 28 days bicarbonate control sample

From: Interactions between magnetite and humic substances: redox reactions and dissolution processes

Sample meq e Fe−1 a meq e Fe−1 b
Biogenic magnetite + HS 0.5 − 12.4
Biogenic magnetite + RHS − 47.7 − 67.5
13 nm magnetite + HS 17.9 − 6.3
13 nm magnetite + RHS 10.7 − 16.8
7 nm magnetite + HS 0.2 − 7.8
7 nm magnetite + RHS − 0.7 − 11.7
500 nm magnetite + HS 2.9 3.1
500 nm magnetite + RHS 2.0 2.6
  1. Positive numbers are net-oxidation reactions and negative numbers are net-reduction reactions with respect to Fe
  2. Using the values in Additional file 1: Table S5, the electrons transferred (z) were calculated as
  3. \(z = \frac{{\left( {\frac{{(Fe^{2 + } (\% )\,\, + \,\,Fe(II)(\% ))_{{_{ref.} }} - \,\,\,(Fe^{2 + } (\% ) + Fe(II)(\% ))_{{_{sample} }} }}{100}} \right) \times \left[ {Fe(II)} \right]\,_{tot.avg} }}{{\left[ {Fe} \right]\,\,_{tot.avg} }}\) where \(\left[ {Fe(II)} \right]_{tot.\,avg} = \frac{{[Fe(II)]_{tot.ref.} + [Fe(II)]_{tot.sample} }}{2}\) and \(\left[ {Fe} \right]\,_{tot.\,avg} = \frac{{\left[ {Fe_{tot} } \right]\,_{ref.} + \left[ {Fe_{tot} } \right]_{{_{sample} }} }}{2}\), Fe2+ represents dissolved Fe2+, Fe(II) represents solid phase Fe(II), [Fe(II)]tot is the sum of dissolved Fe2+ and solid phase Fe(II), [Fetot] is the total concentration of Fe (i.e. the sum of Fe2+, Fe(II), Fe3+ and Fe(III)) and ref. is (a) the t = 0 sample of the HS or RHS sample as indicated on the lines in the table or (b) the bicarbonate control at t = 28 days