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As and Cr Speciation of New & Weathered CCA-Treated Wood

Dive into the speciation of As and Cr in CCA-treated wood, exploring their toxicity and mobility variations. The study aims to quantify species in leachates, estimating their impact on groundwater. From analytical methods to solvent extraction studies, discover the pH-dependent leaching patterns in new and weathered wood. Learn how environmental factors influence As and Cr concentrations, and the conversion processes from As(III) to As(V) and Cr(III) to Cr(VI). Uncover insights on retention levels and leaching behavior in different environments.

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As and Cr Speciation of New & Weathered CCA-Treated Wood

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  1. As and Cr Speciation of New & Weathered CCA-Treated Wood

  2. Outline • Purpose • Basic As and Cr Chemistry • Solvent-Extraction Leaching Experiments (Cr & As) • As Analysis of GW at Florida C&D Landfills • As Leaching from Lysimeters

  3. Purpose & Motivation of Study • Quantify As & Cr species in leachates from CCA-treated wood • As & Cr toxicity varies with each specie • As & Cr mobility varies with each specie • Estimate the impact of As & Cr leaching from • in-service & disposed CCA-treated wood on • groundwater

  4. As Speciation Arsenic Valence -3 0 +1 +3 +5 Arsine (g) Inorganic Inorganic Organic As(V) MMAA DMAA As(III)

  5. Toxicity & Mobility As Speciation Arsenic Valence -3 0 +1 +3 +5 Arsine (g) Inorganic Inorganic Organic As(V) MMAA DMAA As(III)

  6. Toxicity & Mobility Toxicity & Mobility As Speciation Arsenic Valence -3 0 +1 +3 +5 Arsine (g) Inorganic Inorganic Organic As(V) MMAA DMAA As(III)

  7. Toxicity & Mobility Cr Speciation Cr Speciation Chromium Valence +6 +3 0 Inorganic Inorganic Cr(VI) Cr(III)

  8. Analytical Methods for Speciation • As: HPLC-ICP-MS or HPLC-HG-AFS • Cr: IC for Cr(VI) • Total Cr by ICP-AES • Cr(III) by difference

  9. Solvent Extraction Study

  10. Solvent-Extraction of CCA-Treated Wood CCA-treated wood subjected to leaching solvent, rotated for 18  2 hrs & filtered. Filtrate analyzed for As & Cr species pH 1,2,3. etc.. Untreated 0.25 pcf 0.6 pcf 2.5 pcf TCLP New CCA-treated wood SPLP DI Water Playground Utility pole Fence C&D waste Weathered CCA-treated wood Rainwater

  11. 40 35 30 25 20 Arsenic Concentration (mg/L) 15 10 5 0 6.00 1.00 2.00 3.00 4.00 5.00 6.28 6.93 7.52 7.96 9.13 10.90 12.65 pH pH Experiment - New Wood (0.32 pcf) Total As (As(V)) – HPLC-HG-AFS Total As – ICP-AES Environmental pH • As(V) was the only specie detected • Highest concentration at extreme pH • Environmental pH range ~ 5mg/L

  12. As(III) As(V) Total As - HPLC-HG-AFS Total As – ICP-AES 45 40 35 30 25 20 Arsenic Concentration (mg/L) 15 10 5 0 1.27 2.56 3.72 4.15 5.16 5.41 6.54 8.04 9.43 10.19 10.68 11.91 12.76 pH pH Experiment - Weathered Wood (0.41 pcf) Environmental pH • As(III) & As(V) detected, As(III) up to pH 9.5 • Environmental pH range – Total As increase • Total As > 5 mg/L

  13. 12 10 8 6 4 2 0 I (9.12) E (3.86) S (3.16) P (1.96) F (3.62) T (1.41) B (4.06) R (5.47) J (46.01) D (5.90) C (5.63) A (1.49) V (1.86) Q (5.79) O (5.28) N (6.26) L (27.54) G (13.03) H (24.57) K (20.37) M (24.05) SPLP New & Weathered Wood (Simulated Rain Water) Weathered New SPLP As(III) As(V) Total As Arsenic Concentration (mg/L) Retention (kg/m3)

  14. Leachate As Conc. vs CCA Retention 10 New 9 SPLP Rainwater TCLP DI Water Seawater 8 7 Total As Conc. (mg/L) 6 5 4 3 2 1 0 kg/m3 0 5 10 15 20 25 30 35 40 45 50 14 Weathered 12 10 Total As Conc. (mg/L) 8 6 4 2 0 kg/m3 0 2 4 6 8 10 12 14 16 18 20 22 24 26

  15. pH Experiment - New Wood (0.32 pcf) Environmental pH • Cr(III) predominates • Cr(VI) observed at high pH values

  16. SPLP New & Weathered Wood (Simulated Rain Water) • Unburned wood Cr as Cr(III) • No Cr(VI) observed

  17. Ash – SPLP and TCLP • Ashing results in converstion of Cr(III) to Cr(VI) • Cr in ash leachate exists as Cr(VI)

  18. Low Retention Level Wood Leaches More Cr Ash Results for Chromium

  19. Summary • As & Cr species leaching pH dependent • At environmental pH range (6-10) • - As ~ 5mg/L • - Cr ~ 1 mg/L • More As leaching from weathered wood than new wood  As(III) • As Leaching in rainwater, TCLP, SPLP comparable. Seawater less. • Incineration results in the conversion of some Cr(III) to Cr(VI). Greater conversion for lower retention levels.

  20. ? ? ? Questions

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