Radiochemistry, microbiology and environmental engineering - multidisciplinary approaches in nuclear legacy clean up.

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1 Radiochemistry, microbiology and environmental engineering - multidisciplinary approaches in nuclear legacy clean up. Dr Kath Morris Radiochemistry in Nuclear Clean Up & RSc Radiochemistry Group AGM November 23 rd 2005

2 Structure Background U mine remediation - PEREBAR project Biogeochemistry & radionuclides Biostimulation Summary

3 Background Global legacy - contaminated sites & radioactive wastes Radionuclides and stable contaminants UK Sellafield, Dounreay Post nuclear reactor key radionuclides include fission products (Sr, Cs, Tc); uranium and transuranics (Pu, Np) mining & milling (U, Ra, Rn)

4 UK Challenging Environments Radioactively contaminated sites legacy Energy Bill ~ 50 billion costs Site remediation, radioactive waste & new nuclear build related

5 Global - Hanford glossy Cr NO 3 - Tc U

6 Novel Remediation Approaches Reactive Barriers 1) PEREBAR Project Doug Stewart, Kate Barton, Civil Engineering University of Leeds

7 PEREBAR EU Framework V Long-term performance of permeable reactive barriers used for the remediation of contaminated groundwater

8 PEREBAR Pécs Hungary Range of materials for PRBs Fe (0) PANSIL tailored ligand system for UO 2+ 2 ligand deposited onto sand - permeability Performance under laboratory and field conditions Schematic showing UO 2 2+ sequestration by amidoxime Environmental Science and Technology, 37, EM of PANSIL after equilibration with uranyl solution

9 Batch experiments ph < 4 protonation of lone pair electrons on ligand Effective ph 5 8 ph > 8 anionic carbonate species Reaction at ph 8; slow; strong complexation Literature and experimental results suggest uptake of neutral species UO 2 (OH) 2 at ph 7-8 UO2 2+ left in S oln. (m g/l) Final ph Test Duration 24 hrs Liquid:solid ratio 30:1 Synthetic Groundwater Journal of Hazardous Materials (2004) B116,

10 Column Tests Synthetic groundwater ~30 mg U l -1 Residence time 6 hours ph 7.5; 180 mg l -1 carbonate Breakthrough ~ 1.5 g U per kg -1 PANSIL Pécs groundwater Hungary ~1.4 mg U l-1 Residence time 2 days ph 8.1; 600 mg l-1 carbonate Breakthrough ~ 35 mg U per kg -1 PANSIL

11 Differences in performance speciation key Lab 30mg l -1 U; 180 mg l -1 HCO 3- ph g kg -1 PANSIL ~ 1.5 % U as UO 2 (OH) 2 lab Pécs 1.4 mg l -1 U; 600 mg l -1 HCO 3- ph g kg -1 PANSIL < 0.05% UO 2 (OH) 2 in Pécs Pécs column exhausted - residence time key as UO 2 (OH) 2 trace species

12 Summary Speciation modelling gives key insights Site characterisation essential (difficulties) PANSIL can compete with e.g. ZVI engineering requires long residence time at circumneutral ph

13 Remediation Approaches biogeochemisty & biostimulation Jon Lloyd, Francis Livens, Rob Mortimer, Ian Burke, Chris Boothman, Joyce McBeth, James Fox, James Begg.

14 Microbiology Microbial reactions control sub-surface chemical environment mud, landfill Electron donor (e.g. acetate) and terminal electron acceptor Cascade Gross changes in geochemistry Microbial reduction using acetate - theory: Gibbs Energy (kj mol -1 ) CH 3 COO - + 2O 2 H 2 O + 2CO 2 + OH CH 3 COO NO 3 0.2H 2 O + 2CO OH N CH 3 COO - + 4MnO 2 + 3H 2 O 4Mn HCO OH CH 3 COO - + 8Fe(OH) 3 8Fe HCO OH - + 5H 2 O -361 CH 3 COO - + SO 2-4 HS - + 2HCO FeS

15 Microbiology and Radiochemistry Anoxia can affect radionuclide speciation and thus mobility Direct reduction UO 2+ 2 as terminal electron acceptor CH 3 COO O + 4UO 2 2+ (aq) + 2H 2 O 2UO 2(s) + 2CO 2 + 7H + Mechanism via disproportionation of U(V) Indirect reduction Fe(III) as terminal electron acceptor 2Fe 2+ (s) + UO 2 2+ (aq) 2 Fe 3+ + UO 2(s) Can these processes be used to treat radionuclide contamination?

16 Technetium Uranium T1/2 = 7.0 x 10 8 years -emitter Fission 99 Technetium 2.1 x 10 5 years -emitter High yield in nuclear reactors (6% fission yield c.f. 137 Cs) Groundwater contaminant in UK, USA, FSU Redox chemistry expected behaviour Oxic TcO - 4 (aq) soluble & mobile Reduced Tc(IV) S 2 / O 2 poorly soluble

17 Technetium Humber sediments Sediment spike with Tc(VII) Cap - anoxia develops Monitor Tc and stable redox indicators Control autoclaved

18 Technetium Humber sediments Tc(VII) (aq) is reductively scavenged to microbially active sediments Occurs during active Fe(II) ingrowth to sediments Microbiology diverse unable to identify one bug NO 3- ; Fe(III)-; SO reducers all present Similar behaviour observed in aquifer % Tc in solutio n Time (days) Environmental Science and Technology, 39,

19 Mechanism XAS Tc(IV)O 2(s) Indirect process in sediments Å Biotic Fe(III)-R SO 2-4 -R TcO 4 - (aq) + 4H + + 3Fe 2+ (s?) TcO 2(s) + 2H 2 O + 3Fe 3+

20 Robust microbial reduction occurs in wide range of sediments Mechanistic insights key and... novel approaches to remediation Biostimulation barriers

21 TcO Anoxic Removal Relevance Novel technology stimulate Fe(III)-bugs - inject organic matter & allow to go reducing - Tc(VII), U(VI), (Np(V), Cr(VI)) - during site remediation Biostimulation barrier USDoE, 2003

22 Biostimulation Field scale tests U(VI), Tc(VII) Site specific Column tests Relevance to other contaminants (Cr ) Reoxidation, environmental management, exhaustion of e.g. Fe(III)? Reoxidation studies indicate Tc is recalcitrant to remobilisation

23 Summary Multidisciplinary approach Real, novel treatment techniques Applications envisaged in site remediation, medium term Mechanism, and site specific studies key Significant funding possibilities industrial collaboration key