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[Se]in and [Se]out : initial and final supernatant Se concentration PowerPoint PPT Presentation


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No association of Se 0 with purified Boom Clay Humic Acid (p-BCHA). pH-pe diagram [Se] tot = 10 -6 mol l -1 (NEA database project 2006). Se 0. Se(IV). Se 0 + p-BCHA + Fe(II); pellet. Se 0 + p-BCHA ; pellet. Se(IV) + p-BCHA + N 2 H 4 ; spn; pH 7.25.

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[Se]in and [Se]out : initial and final supernatant Se concentration

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Se in and se out initial and final supernatant se concentration

  • No association of Se0 with purified Boom Clay Humic Acid (p-BCHA)

pH-pe diagram

[Se]tot = 10-6 mol l-1 (NEA database project 2006)

Se0

Se(IV)

Se0 + p-BCHA + Fe(II); pellet

Se0 + p-BCHA ; pellet

Se(IV) + p-BCHA + N2H4;spn; pH 7.25

Se(IV) + p-BCHA + N2H4;spn; pH 5.25

Sample

Description

Solid/Liquid

[Se]in (M)

[Se]out (M)

[Se]S (mol/kg)

pH

3

FeS2 < 10 µm NPT

100 g·l-1

6.1010-3

4.8010-5

6.11×10-2

7.80

4

FeS2 < 10 µm PT

100 g·l-1

6.1010-3

8.63×10-4

5.25×10-2

7.42

  • Sorption-Reduction by Fe(II) containing minerals (FeS2, FeS, …) *

  • Batch tests of SeO32‑ with pure pyrite (FeS2) in synthetic Boom Clay water (no OM)

  • Selenium on FeS2 solid phase (mol g‑1) versus SeO32‑ concentration (mol dm‑3).

  • Short contact times (3 and 7 days) : linear Kd  sorption process

  • Longer contact times : progressive convergeance to 3 × 10‑9 mol dm‑3  reduction process.

Sorption-reduction of SeO32‑ on pyrite (FeS2)

Sample

Description

Solid/Liquid

[Se]in (M)

[Se]out (M)

[Se]S (mol/kg)

pH

TIME

9

FeS < 100 µm NPT

100 g·l-1

6.0810-3

< 10-6

> 6.10×10-2

7.89

10

FeS < 100 µm PT

100 g·l-1

6.0710-3

< 10-6

> 6.6810-2 mol/kg

7.86

  • Sorption on oxidic surfaces (edges) of clay minerals

SeO3-2 sorption on Illite du Puy (10 g/l; 0.01 N NaCl)

  • Association of Se with Boom Clay Organic Matter

TIME

State-of-the-art regarding selenium geochemistry under Boom Clay conditions

Bruggeman, C.; Breynaert E.; Maes, A Katholieke Universiteit Leuven, Laboratory for Colloid Chemistry, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium

Se Redox Chemistry

Se(0)

  • Oxidising Conditions

  • Selenate (SeO42-)

  • Weakly adsorbed on oxide surfaces

  • Reduction kinetically hindered / poorly known

  • No solubility limitation

  • Mildy Oxidising Conditions

  • Selenite (SeO32-)

  • Strongly adsorbed on oxide surfaces

  • Reduction faster than SeO4-2, important process for storage

  • No solubility limitation

Se(IV) + p-BCHA + N2H4;pellet; pH 5.25

  • Reduction of SeO3-2 to Se0 by pyrite (FeS2)

  • Reducing Conditions

  • Se0 , Selenide (Se2-)

  • Limited solubility

  • Not well known

  • [Se]in and [Se]out : initial and final supernatant Se concentration

  • PT and NPT: samples pretreated and not pretreated with 1M HCl after crushing

  • XAS analysis, Se K-edge (12.658 keV), fluorescence mode

Se(VI)

  • No significant reduction or sorption by Boom Clay components :

  • Illite

  • Pyrite

  • HS

Se(IV)

Se(-II)

  • Formation of FeSe by reduction of SeO3-2 by FeS, 18 days equilibrium

*Selenite reduction in Boom clay: Effect of FeS2, clay minerals and dissolved organic matter.

Bruggeman C, Maes A, Vancluysen J and P. Vandemussele. ENVIRONMENTAL POLLUTION 137 (2): 209-221

  • [Se]in and [Se]out : initial and final supernatant Se concentration

  • PT and NPT: samples pretreated and not pretreated with 1M HCl after crushing

  • XAS analysis, Se K-edge (12.658 keV), fluorescence mod

  • Short term (1 day) batch sorption edges of Se(IV) on illite du Puy

  • Typical anion adsorption edges

  • Conclusions

  • Under BK conditions

    • Se(VI) unaltered

    • Se(IV) initial sorption on oxidic surfaces

      reduction by FeS2

  • Knowledge Gaps ?

    •  Se(VI) sorption on Boom Clay

       Se(IV) sorption/reduction on CaCO3/FeCO3phases

       Se speciation on Boom Clay solid phase

  • Association increases with time  speciation/valence ?

Acknowledgements: ONDRAF/NIRAS – TRANCOM II – FUNMIG – FWO/NWO


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