Effects of steam explosion processing and organic acids on CCA removal from treated wood waste

Abstract

Chromated copper arsenate (CCA) is the primary wood preservative used in the United States. CCA products are used for decking, fencing, retaining walls, docks, poles, and highway sign posts. Since CCA became popular in the early 1970's, it is estimated that over 140 million cubic meters of these products are in service. Although the EPA allows disposal of spent CCA products in landfills, increasingly they are looking at the possibility of restricting its disposal. One method for potential re-use of CCA treated wood fiber would be to remove the treatment chemicals and process the fiber into energy or consumer products. The objectives of this research were to determine which method(s) can improve the removal of copper, chromium, and arsenate from spent CCA-treated lumber. The best material, in this research, for leaching chemicals from treated wood with organic acids, were particles (compared to chips and steam exploded wood). Without the functions of organic acids, the best method to remove chemicals proved to be steam explosion and further extraction by water. Citric acid was the most effective acid used in the removal of treatment chemicals of the three acids evaluated: acetic, citric, and sulfuric. The time effect on the extraction process indicated that most of the treatment chemicals were removed within the first seven days of treatment. This study also indicates that steam explosion does not increase the extractability of the chemical components. Other methods need to be examined which may lead to better removal of the chemicals or more effective methods to recycle spent CCA products.