Leaching of Flakeboard Produced From Recycled CCA-Treated Wood Into Deionized Water

Leaching of Flakeboard Produced From Recycled CCA-Treated Wood Into Deionized Water

The disposal of preservative-treated wood is becoming a larger issue for the forest products industry due to increasing public concern and scrutiny as well as costs associated with traditional disposal, i.e., landfilling. Recycling of preservative-treated wood has great potential. In this study, flakeboard was produced from decommissioned guardrail posts that had been treated with chromated copper arsenate (CCA). The leaching characteristics of chromium, copper, and arsenic from flakeboards manufactured from five different ratios of recycled CCA-treated wood and untreated virgin southern pine wood were investigated. Five ratios of recycled CCA-treated wood and virgin, untreated wood were used for flakeboard furnish. The ratios were 100:0,75:25, 50:50, 25:75, and 0: 100. The guardrails generally showed higher amounts ofCCA in the outer horizontal areas and the middle vertical regions of the guardrail posts. As expected, the furnishes with greater amounts of CCA-treated wood had higher leaching values.

More than 6 billion board feet (BBF) (14.2 million m3) of lumber is treated with chromated copper arsenate (CCA) every year in the United States (Micklewright 1998). The average service life of CCA-treated wood is 2S years. At the end of the life cycle of treated wood, it faces a disposal problem. Many scientists have investigated recycling methods to reuse this waste material for value-added products. The recycling of decommissioned CCA-treated wood into composite panels is regarded as one of the most viable options to mitigate disposal problems (Felton and De Groot 1996, Cooper 1999). At the same time, the residual CCA content in the recycled wood can stil1 offer effective protection against decay and insects (Cooper 1997, Cooper et al. 1996). However, the leaching characterization of these recycled composite products needs to be further investigated Theoretically, once CCA-treated wood is dried, the CCA is leach resistant under normal (most) conditions (Hartford 1986). CCA resists leaching in service because of complex chemical reactions that take place within the treated wood. However, extended weathering causes a reduction of CCA content in the material exposed to exterior service conditions. The objectives of this study were to examine the residual CCA distribution in decommissioned guardrail posts and the leaching properties of flakeboard made from decommissioned CCA-treated wood.

Guardrail posts, manufactured from southern pine (Pinus spp.), were 0btained from Arnold Forest Products Company in Shreveport, Louisiana. The posts, which had been treated with CCA at 0.5 pcf (8 kg/m~, went in service in May 1986 in Abilene, Texas, and were removed in September 1999. The posts were about 69 inches (175.3 cm) long with a top diameter range of 6-1/2 to 7-1/2 inches (16.5 to 19.0 cm), and a bottom diameter range of 7 to 8-3/4 inches (17.8 to 22.2 cm). The mean specific gravity of the poles was 0.51 and was determined in the ovendry condition. These posts had been installed approximately 38 inches (96 cm) into the ground After passing under an electronic metal detector, foreign metal objects were manually removed and the posts were transported to Lee Memorial Forest in Franklinton, Louisiana. for processing into lumber. Twenty-two posts were sawn into l-inch- (2.5- cm-) thick lumber using a WoodMizer® sawmill, and three posts were retained for chemical analyses. Three disks, each I inch (2.5 cm) thick, were cut from the top, middle, and bottom of the posts and used for later chemical analyses. The top and bottom disks were removed I foot (30 cm) from the top and bottom of the guardrails, respectively. The middle disks were removed from the vertical center. Fresh southern pine lumber was purchased at a local retail lumber store.

Meet the Author

Dr. Todd Shupe is the President of Wood Science Consulting, LLC. He is a well-recognized expert on wood forensics, wood preservation, wood decay and degradation, and wood species identification. He has a broad background in new product development, quality management, and marketing and sales in both the public and private sectors. For more information please visit DrToddShupe.com.

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