In-Situ Chemical Reduction (ISCR) of Cr(VI)
          “A Belgian Case Study”
                  Samuel Van Herreweghe,
    ...
Site characteristics

   • Chrome plating facility near
     Brussels

   • Several overfillings of chromium
     baths <1...
Project phases

        • Characterization study
              – plume delineation (monitoring wells)
              – risk...
Characterization Study
        •   Source zone: <200 m2; 350 mg/l Cr(VI)
        •   Plume: 4.000 m2; +/- 350 µg/l Cr(VI)
...
Geochemical context

    •        Speciation of chromium
         –      Cr(VI): toxic & mobile
         –      Cr(III): l...
MinteqA2 modelling
    – Cr(III) dominant if thermodynamic equilibrium
    – Cr2O3 supersaturated (Saturation-index=12,5)
...
MinteqA2 modelling

   Cr2O3 will finally precipitate (~ spontaneous attenuation)




                                    ...
Bench-scale lab test

    • In-situ redox manipulation (ISRM) is necessary

    • Lab test:
         – biological
        ...
Dithionite
    • dithionite creates a progressing plume of soluble Fe(II) by reducing
      native iron oxides
      6Fe(O...
Remediation concept

                                         > 1%
                                         MnO2
         ...
Pilot-scale test
                       In situ chemical reduction (ISCR)

   Fe(II)-dithionite (FeSO4-Na2S2O4) pilot test...
pilot-scale test
   • setting up monitoring scheme
        –   installing new monitoring wells
        –   product decay m...
pilot-scale test

    five months of conductivity measurements in downstream well
       groundwater conductivity
        ...
Conclusion pilot test

     •    fast & full reduction of treated zone (<8 weeks after
          product arrival)

     • ...
Full scale remediation
                                               plan
   • grid of 56 injection wells

   • 10 tons N...
Questions?




                                   16

© MAVA - 20/09/2010
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Consoil 2010 Th S A17 Van Herreweghe

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In-Situ Chemical Reduction (ISCR) of Cr(VI) “A Belgian Case Study”

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Consoil 2010 Th S A17 Van Herreweghe

  1. 1. In-Situ Chemical Reduction (ISCR) of Cr(VI) “A Belgian Case Study” Samuel Van Herreweghe, Joris Nackaerts, Wim Vansina, Mark Van Straaten Consoil 2010, Salzburg, ThS A17 MAVA www.mava.be Gorislaan 49 www.EnISSA.com 1820 Steenokkerzeel info@mava.be Belgium 1
  2. 2. Site characteristics • Chrome plating facility near Brussels • Several overfillings of chromium baths <1999 • Geology: – Quaternary loamy toplayer (2m) – Tertiary Lede-Brussel Sands (25 m), calcareous, sandstones – Groundwater at 8m bgl 2 © MAVA - 20/09/2010
  3. 3. Project phases • Characterization study – plume delineation (monitoring wells) – risk assessment – groundwater model • Geochemical modeling • Conceptual site/remediation model • Bench-scale labtest • Pilot test • Full scale remediation plan 3 © MAVA - 20/09/2010
  4. 4. Characterization Study • Source zone: <200 m2; 350 mg/l Cr(VI) • Plume: 4.000 m2; +/- 350 µg/l Cr(VI) • minor co-pollution with TRI • Dispersion risk: remediation obligatory 4 © MAVA - 20/09/2010
  5. 5. Geochemical context • Speciation of chromium – Cr(VI): toxic & mobile – Cr(III): low toxicity & insoluble (Cr(OH)3•3H2O or Cr2O3) • MinteqA2 modelling: – Input: • general site parameters (pH, alkalinity, major ions, Eh, …) • Cr(VI) concentration – Output vs. varying Eh : • Cr speciation • Precipitation 5 © MAVA - 20/09/2010
  6. 6. MinteqA2 modelling – Cr(III) dominant if thermodynamic equilibrium – Cr2O3 supersaturated (Saturation-index=12,5) 6 © MAVA - 20/09/2010
  7. 7. MinteqA2 modelling Cr2O3 will finally precipitate (~ spontaneous attenuation) 7 © MAVA - 20/09/2010
  8. 8. Bench-scale lab test • In-situ redox manipulation (ISRM) is necessary • Lab test: – biological • molasses • HRC™ – chemical • zerovalent iron Fe(0) • dithionite and Fe(II)sulphate (divalent iron) mixture 8 © MAVA - 20/09/2010
  9. 9. Dithionite • dithionite creates a progressing plume of soluble Fe(II) by reducing native iron oxides 6Fe(OH)3 + S2O42- + 10H+ 6Fe2+ + 2SO42- + 14H2O 3Fe+2 + CrO4-2 + 8H2O → 4Fe(0,75)Cr(0,25)(OH)3↓ + 4H+ • aquifer low native “available” iron: extra FeSO4 must be added • optimal pH for Cr(VI) reduction is between 6 and 8 (site pH: ± 7.5) • In the presence of dithionite, soluble O2 concentration is low: 4Fe2+ + O2 + 2H2O + 8OH- 4Fe(OH)3 (no clogging) • Dithionite gradually degrades to sulphite (SO32-), thiosulphate (S2O3-2), … and finally sulphate (SO42) (harmless) 9 © MAVA - 20/09/2010
  10. 10. Remediation concept > 1% MnO2 O2 low pH Cr(III)aq Mn2+ complexation Cr(III) ↓ Cr(VI)aq spill Fe(II)aq SO42- Cr(III)aq Fe(III) S2O42- 10 © MAVA - 20/09/2010
  11. 11. Pilot-scale test In situ chemical reduction (ISCR) Fe(II)-dithionite (FeSO4-Na2S2O4) pilot test set-up • getting approval of pilot test by local authorities (OVAM) • exact composition injection fluid (fine-tuning) – soil matrix demand 0,14 M Na2S2O4 + – available native Fe 0,08 M FeSO4 – spreading (groundwater model): 4m3 injection volume • direct push not possible (sandstone layers) → injection via well 11 © MAVA - 20/09/2010
  12. 12. pilot-scale test • setting up monitoring scheme – installing new monitoring wells – product decay monitored by SO4 / Stot - ratio – tracer: Br- was added – continuous conductivity measurement (downstream well) 12 © MAVA - 20/09/2010
  13. 13. pilot-scale test five months of conductivity measurements in downstream well groundwater conductivity vs. time instantaneous reduction Cr (VI) , 140000 120000 concentration (µg/l) 100000 PBM4 80000 60000 40000 20000 0 01-12-08 22-12-08 12-01-09 02-02-09 23-02-09 16-03-09 06-04-09 27-04-09 Tijd 13 © MAVA - 20/09/2010
  14. 14. Conclusion pilot test • fast & full reduction of treated zone (<8 weeks after product arrival) • Cr(III) precipitation only slightly slower than reduction (5 weeks slower) • long term activity of the product (more then 6 months): large influential radius (>4m) • no clogging effects • sandstone banks hindering product spreading 14 © MAVA - 20/09/2010
  15. 15. Full scale remediation plan • grid of 56 injection wells • 10 tons Na2S2O4 and 3 tons of FeSO4 • estimated remediation cost 233.275 € (± 20€/m3) • plan approved by OVAM • planning synchronised with relocating plans of the plating facility (2011) 15 © MAVA - 20/09/2010
  16. 16. Questions? 16 © MAVA - 20/09/2010

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