Riverbank Sediment Characterization & Preliminary Treatment Results

Transcription

1 Riverbank Sediment Characterization & Preliminary Treatment Results 1 Carol Ptacek and David Blowes University of Waterloo Students: Krista Desrochers, M.Sc. Candidate Peng Liu, Ph.D. Candidate Blair Gibson, Ph.D. Candidate u Wang, B.Sc. Candidate 1

2 bjectives of Study Characterize solid-phase composition and forms of Hg in the bank sediments Assess variability in the release of Hg from bank leaching vs. bank erosion Identify potential geochemical approaches to decrease the release of Hg from the sediments 2

3 Site Location 3

4 Site Location South River RRM.1 Bank Stabilization Pilot Site 4

5 Sediment Studies Sediment Characterization Resuspension Experiments Bank Filtration Experiments Bulk chemistry Chemical extractions Mineralogy XRF & XANES XRD & clay speciation Sediment ratio variations Colloid characterization Flow rate fluctuations & stagnation Colloid characterization 5

6 Sediment Digestion Sediment Characterization Large variation in total Hg in sediment Hg correlated to Cu 6

7 7 Carbon & Sulfur Sediment Characterization Low C & S (SR) compared to other sites (LS) with elevated Hg % Total Sulfur % Total Carbon (J) (I) (H) (G) (F) SW-13(E) SW-12(D) (C) SW-2(B) (A) SR6 SR5 SR4 SR3 SR2 SR1 SR Total Sulfur Lake Seds Total Sulfur SR Total Carbon Lake Seds Total Carbon

8 Chemical Extractions Sediment Characterization Hg speciation highly variable in South River bank sediment F1 F2 F3 Extraction Solution Deionized Water.1M HCl +.1M CH 3 CH 1M KH Target Hg Species Water Soluble (HgCl 2, HgS 4 ) Human Stomach Acid Soluble (HgS 4, Hg, Hg ads ) rgano-chelated (Hg chel, Hg 2 Cl 2 ) A B C D E F(1) F(2) G HI J(1) J(2) SR1 SR2 SR3 SR4 SR5 SR6 SR F4 12M HN 3 Elemental Hg (Hg, thiol-hg, Hg amal ) % Hg Extracted F5 Aqua Regia Mercuric Sulfide (HgS, HgSe, HgAu) ~2-9% of Hg mass extracted by DI water Greatest mass in sulfide fraction 8

9 Sediment Characterization SR6 Synchrotron Characterization Micro X-ray Fluorescence (XRF) Mapping and X-ray Absorption Near Edge Structure (XANES) Analysis of South River Sediment 9

10 XRF Sediment Characterization 1

11 XANES Sediment Characterization All Hg XANES spectra from sediment are similar Implies same form of Hg at each location 11

12 XANES Sediment Characterization Spectra are very similar to spectrum for metacinnabar, implying HgS formation 12

13 Sediment Resuspension Tests Resuspension Tests Purpose: What is the variability in Hg release due to riverbank erosion? What portions are dissolved and colloidal? 5 MWC Filter Fraction 13

14 Ratio Variations Resuspension Tests Large variability in Hg release Possible Hg solubility control Total Hg ( g L -1 ) SR1 SR2 SR3 SR4 SR5 SR6 1 ph Eh (mv) Alkalinity (mg L -1 CaC 3 ) Mass of Sediment per 16 g SRW (g) 14

15 Filter Fractions Resuspension Tests Large variability in filter-size fractions Greatest variation for SR3, SR5 & SR6 samples Total Hg ( g L -1 ) SR1 SR2 SR3 SR5 SR6 1 ph Eh (mv) Alkalinity (mg L -1 CaC 3 ) Filter Pore Diameter ( m) 15

16 Dynamic Leaching Experiments Slow flow of river water through bank sediments to simulate advectivediffusive transport Fluctuate velocity to evaluate: mass transfer limitations colloid-facilitated transport 16

17 Total Hg (ng L -1 ) SR Pore Volumes PV/ week m Filtered.2 m Filtered.1 m Filtered 5 MWC Filtered 3X Flow Increase Control Columns SR5 SR3 SR6 Total Sed Hg ( g g -1 ) H 2 Soluble Hg ( g g -1 ) Large fluctuations in Hg concentrations Release of Hg not correlated to extraction and resuspension results Increases in effluent Hg observed after flow stagnations SR6 SR Total Hg (ng L -1 ) Total Hg (ng L -1 ) Pore Volumes Pore Volumes PV/ week PV/ week

18 Control Column H 2 Chemistry Control Columns Total Hg (ng L -1 ) SR5 Control Column SR6 Control Column SR3 Control Column Note very high concentrations of Hg in SR3 effluent ph Eh (mv) Eh (mv) ph 3X Flow Increase Alkalinity (mg L -1 CaC 3 ) (mg L -1 ) S Note decline in S 4 concentrations Pore Volumes Pore Volumes Pore Volumes 18

19 Filter Comparison Control Columns Resuspension experiments substantial differences in aqueous Hg for different filter sizes Transport experiments less pronounced variations in Hg for different filter sizes Resuspension Tests Saturated Control Columns Total Hg (ng L -1 ) m Filter.2 m Filter.1 m Filter 5 MWC Filter Total Hg (ng L -1 ) m Filter.1 m Filter 5 MWC Filter 2 5 SR1 SR2 SR3 SR5 SR6 SR3 SR5 SR6 19

20 Treatment Studies Static Screening Experiments Dynamic Treatment Experiments Hg-spiked South River water Stabilization additions Treatment of column effluent water Leaching from coblended reactive media/sediment mixtures 2

21 Treatment Treatment of Hg-spiked South River water Blended biochar and Hg-spiked water Mushroom Soil (B-MS) Pine Woodchips (B-PW) Poultry (B-P) Preliminary Treatment of Bank Sediment (SR4 Sample) Clays, chars and activated carbon, strong reductants, complexing agents 21

22 Biochar as a Reactive Media for Hg Desirable physical properties Large particle size distribution, macroporosity, nano-porosity Desirable chemical properties High charge density, hydrophilic, hydrophobic, acidic, basic Concerns High nutrient and trace element content Microbial habitat & substrate Potential applications Soil amendment, ex-situ reactors, in-stream reactors, in-situ reactive zones 22

23 Biochar Functionalities Treatment (2) (1) H H CH 3 R CH 3 (1) (1) (8) (9) H N H N N N H (13) N (12) H N (11) (1) NH 2 H 3 C (2) N N (3) H H 3 C (4) CH 3C H3 (5) (6) C H 3 CH 3 + (7) (4) N (3) H N N - N + (5) NH 2 (7) N CH 3 N (8) CH 3 (6) N (9) CH 2 xygen-containing Nitrogen-containing (1) S SH (2) SH SH (1) S SH2 (3) (1) P H H P (1) (3) S S S (1) CH 3 CH 3 (1) H P H H S (6) S S S (5) (4) Sulfur-containing P H (1) P H P H (2) P H Phosphorus-containing 23

24 Biochar Physical Properties A Treatment B Silica mineral C D 24

25 Biochar Physical Properties Treatment element wt % element wt % C P S.63 F.29 Cl.7 Na.2 K.54 Mg.36 Ca 2.21 Al.18 Fe 1.7 Si.7 A element wt % element wt % C P S.4 F.22 Cl Na.13 K.24 Mg.13 Ca.72 Al.78 Fe.2 Si B element wt % element wt % C Si P.32 Na K.67 Mg.22 Ca.67 Al.19 C element wt % element wt % C P S 1.52 Na.2 Cl.23 Mg.38 K 2.64 Al.25 Ca 2.45 Si.81 Fe.27 D 25

26 Biochar Batch Test Experiments Treatment Evaluate Hg removal Nutrient and trace element release Experiments Hg-spiked SRW 9 ng L -1 Hg NW SRW B MS B PW B P Hg Hg Hg Hg SRW B-MS B-PW B-P 26

27 Biochar Batch Test Experiments (Unwashed) Treatment 48 hours 2 weeks 8 8 Control Experiments T Hg ng L Hg Spiked Experiments SRW B-MS B-PW B-P THg ng L SRW B-MS B-PW B-P Greater than 95% removal of Hg from South River water at 2 weeks for all biochar samples 27

28 Biochar Batch Test Experiments (unwashed) Treatment 1 SRW B-MS B-PW B-P ph Eh [mv] 5 Alkalinity as CaC 3 mg L Time [Days] Control Experiments Spiked Hg Experiments Water Chemistry 28

29 Biochar Batch Test Experiment (unwashed) Treatment P 4 -P mg L SRW B-MS B-PW B-P Elevated phosphate, sulfate, chloride NH 3 -N mg L S 4 mg L Anions and Nutrients 16 Cl - mg L -1 8 N 3 mg L Time [Days] Control Experiments Spiked Hg Experiments 29

30 Biochar Batch Test Experiment (unwashed) Treatment As g L SRW B-MS B-PW B-P As ng L -1 Elevated As, Pb Pb g L Pb ng L -1 Pb ng L -1 Cu g L Time [Days] Control Experiment Spiked Hg Experiment Trace Elements 3

31 Comparison of Unwashed and Washed Biochar (Hg Removal) Treatment 2 weeks 1 Control Experiments THg ng L -1 5 Washed biochars Unwashed biochars Hg Spiked Experiments SRW B-MS B-PW B-P THg Removal% 1 5 SRW B-MS B-PW B-P T Hg ng L Greater than 92% Hg removed from South River for all washed biochar samples at 2 weeks 31

32 Initial Reactive Media Batch H 2 Chemistry Preliminary Treatment Treated SR4 Sediment Thiol I control ~ 1 g L 1 Thiol II control ph <1 Thiol I has elevated NH 3 B MS & Thiol II have elevated P 3 4 Treated SR4 Sediment NH 3 -N (mg L -1 ) SR4 Control Thiol I ATP B-MS B-WC Thiol II GAC MRM GI S ATP+Thiol I ATP+Thiol II GI+ATP GI+S S+ATP P 4 -P (mg L -1 ) SR4 Untreated. Alkalinity (mg L-1 CaC3) ph Total Hg (ng L-1) SR4 Control Thiol I ATP B-MS B-WC Thiol II GAC MRM GI S ATP+Thiol I ATP+Thiol II GI+ATP GI+S S+ATP Eh (mv) Controls - no sediment Total Hg (ng L-1) SRW SRW Thiol I ATP Thiol II GAC MRM GI S Alkalinity (mg L-1 CaC3) ph Eh (mv) 1

33 1 5-5 Thiol I ATP B-MS B-WC Thiol II GAC MRM GI S ATP+Thiol I ATP+Thiol II GI+ATP GI+S S+ATP S+MRM Total Hg Removed (%) Total Hg (ng L -1 ) Thiol I ATP B-MS B-WC Thiol II GAC MRM GI S ATP+Thiol I ATP+Thiol II GI+ATP GI+S S+ATP S+MRM Preliminary Treatment Initial Rewet SR4 Initial Untreated SR4 Rewet Untreated Rewetting of Treatment Batch Tests Reacted aerobically for 33 days Added second aliquot of SRW to each batch Batches reacted for 14 days before resampling

34 Implications Chemical extractions and synchrotron studies indicate large leachable fraction (2-3%) Remaining fraction is in the form: amorphous HgS Amorphous HgS present in unsaturated zone Both dissolved and colloidal fractions can be transported through bank sediments Effective Hg removal from SR water using all biochar types Co-blending of reactive media resulted in good treatment 34

35 Dynamic Treatment Columns Future Directions Treat bank porewater under flowing conditions GAC Biochar Dissolve reagents in influent solution (flocculants) Thiol Compound Blend reactive media into sediment and monitor leaching 35

36 Characterization of Treatment Longevity Future Directions Humidity Test Cells Assess Hg release from treatment media under enhanced weathering conditions and aging Sediment leaching Hg Reactive Media Reactive media after extensive Hg input 36

37 Additional Sediment Characterization Next Steps 2 nd Riverbank Transect Floodplain Soil Transect A 37

38 Acknowledgements Funding DuPont Natural Sciences and Engineering Research Council of Canada Advice R. Landis, N. Grosso, J. Dyer and E. Mack (DuPont) 38

39 Thank you 39