Grant: Collaborative Research and Development Grants

Large quantities of wood treated with waterborne wood preservatives are removed from service each year, and the amounts removed are expected to increase to about 1.5 million cubic meters per year over the next decade. At present, most of this material is treated with chromated copper arsenate (CCA) and it is disposed of in landfills. Over the next few decades, in-service residential CCA treated wood will be replaced by alternative preservative treatments: alkaline copper quat (ACQ), copper azole (CA) and potentially micronized copper systems (MiCu). Wood treated with these preservatives will enter the waste stream in increasing amounts. Considering the high cost of landfill disposal, the potential for leaching of preservative chemicals from the disposal sites and the loss of potentially useful materials to landfills, there is interest in developing technologies to recycle this material. The proposed research investigates the recycling of out-of-service treated wood by cost-effective extraction of the treatment chemicals for reuse by the wood treating industry as well as the potential of re-using the remediated wood for other applications. The extraction of CCA, ACQ, CA and MiCu preservative components from treated wood will be optimized using effective extractants such as strong mineral acids, or solvents that render the extracted materials re-useable as treating solutions. The chemical extraction process, which involves penetration of the extracting solution into the wood, dissolving or reaction of the preservative component, and diffusion of the dissolved component out of wood, will be modeled by diffusion with reaction equations to allow the prediction of optimized particle size and solution and process variables for efficient extraction of wood. The extractions will modify the wood fibre to some extent, and the effects of these chemical changes on the potential re-use of the wood for composting, production of construction materials or energy and other applications will be evaluated.