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Studies on Weathered Waterborne Treated Wood: Leaching of Metals during Service and Metals Based Detection upon Recycle
Journal Title, Volume, Page:
Abstract of a dissertation at the University of Miami, (August 2009)
Year of Publication:
2009
Preferred Abstract (Original):
Weathered
waterborne treated wood is believed to behave differently than new wood
during service regarding the loss of its metallic-based preservatives.
Also, weathered preserved wood should be separated from the unpreserved
wood upon recycle. The first objective of this dissertation was to
evaluate losses from weathered CCA-treated wood samples at different
retention levels under normal field conditions and to compare leaching
to new ACQ (as alternative to CCA). Results showed that arsenic leached
at a higher rate than chromium and copper in all CCA treated wood
samples, while copper leached the highest from the ACQ sample. Overall
results suggest that the leaching rate of metals on a percent basis from
in-service pressure treated wood may increase as the wood weathers;
however due to lower retention levels of the metals in the wood as it
ages the yearly mass of metals lost would be at similar or at lower
quantities in comparison to new treated wood. The second objective was
to evaluate the use of automated X-ray fluorescence (XRF) systems for
identifying and removing As-based and Cu-based treated wood within the
recovered wood waste stream. A full-scale online automated
XRF-detection, conveyance and diversion system was used for
experimentation. At the different applied feeding rates and belt speeds,
online sorting efficiencies of waste wood by XRF technology were high
(>70% for both treated wood and untreated wood). The incorrectly
diverted pieces of wood were attributed to deficiencies in the wood
conveyance systems and not to deficiencies in the XRF-based detection.
Online sorting was shown to sort wood which would meet the residential
soil cleanup target levels in Florida when an infeed is composed of 5%
of treated wood pieces. Comparisons with other sorting methods show that
XRF technology can potentially fulfill the need for cost-effective
processing at large wood recycling facilities (> 30 tons per day).
Management of weathered CCA-preserved wood, due to its continuity of
leaching metals and the need to remove it upon the recycle of wood, will
likely continue until complete banning and removal from the
environment, a process that may extend up to the next century.
| Attachment | Size |
|---|---|
| Studies_on_Weathered_Waterborne_Treated_Wood_Leaching_of_Metals_during_Service_and_Metals_Based_Detection_upon_Recycle.pdf | 6.32 MB |
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