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Table 1 Precipitate synthesis, composition, and structure

From: Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions

Label Synthesis solutiona Precipitateb Structurec
Cation P/Fe (−) Si/Fe (−) As/Fe (−) P/Fe (−) Si/Fe (−) As/Fe (−)
Ca-00-00 Ca 0.014 0.013 100% pcLp
Ca-01-00 Ca 0.09 0.013 0.09 0.013 21% HFO; 79% pcLp
Ca-02-00 Ca 0.20 0.014 0.20 0.014 15% CaFeP, 26% HFO, 59% pcLp
Ca-05-00 Ca 0.53 0.016 0.53 0.016 59% CaFeP, 16% HFO, 25% pcLp
Ca-15-00 Ca 1.49 0.014 1.04 0.007 100% CaFeP
Na-15-00 Na 1.46 0.014 0.60 0.005 100% FeP
Ca-02-05 Ca 0.21 0.48 0.014 0.21 0.06 0.014 (25% CaFeP, 75% Fh-lowSi)
Ca-02-10 Ca 0.20 0.96 0.014 0.21 0.11 0.014 25% CaFeP, 75% Fh-Si
Ca-00-10 Ca 0.96 0.014 0.13 0.014 100% Fh-Si
2L-Fhd Ca 2L-Fh
  1. aInitial Fe(II) concentration 0.5 mM; pH 7.0 adjusted with CO2 in 4 mM CaCO3 (Ca) or 8 mM NaHCO3 (Na)
  2. bMolar P/Fe and Si/Fe of precipitates calculated from difference between initial total and final dissolved P, Si and Fe concentrations measured by ICP-MS; values are average of triplicate samples (duplicate for Ca-00-00)
  3. cStructure based on Fe K-edge EXAFS analysis of dried samples from Ref. [20] (pcLp poorly crystalline lepidocrocite, HFO hydrous ferric oxide, CaFeP amorphous Ca–Fe(III)-phosphate, FeP amorphous Fe(III)-phosphate), Fh-Si silicate-containing ferrihydrite. Precipitate Ca-02-05 has not been examined by EXAFS spectroscopy and the indicated structural composition is tentative (see text)
  4. d2-line ferrihydrite synthesized by neutralization of 0.2 M Fe(NO3)3 × 9H2O with 1 M KOH [31]. Freshly prepared 2L-Fh was suspended in Ca electrolyte and wet and dry precipitates were prepared as for other Fe(III)-precipitates
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