Pilot scale evaluation of sorting technologies for CCA treated wood waste

Two sorting technologies including a chemical stain method and an x-ray fluorescence technique were investigated for separating chromated copper arsenate (CCA) treated wood from other wood types in the wood waste stream. Stains were investigated in both laboratory and field settings. Studies included specially mixed solutions with chrome azurol, 1-(2-pyridylazo)-2-naphthol (PAN) and rubeanic acid chemicals. X-ray fluorescence was tested in the laboratory using a commercially available x-ray fluorescence spectrometer. Laboratory scale experiments showed that both technologies were able to detect CCA treated wood in mixtures of treated wood and untreated wood, with detection limits on the order of 3 to 5% CCA. Results from field experiments at construction and demolition facilities indicate that although the chemical stains can be effectively used to identify CCA treated wood waste in field settings, their use will be limited to sorting relatively small wood waste piles due to increased labor and time needed for processing the wood waste. Operational parameters for sorting using x-ray fluorescence technology were established. These parameters concluded that arsenic was the most sensitive metal for analysis, analysis time was less than 2 seconds per wood sample, and the maximum separation distance between the sample and the x-ray probe was 2.5 cm. X-ray technology shows considerable promise for separating large quantities of CCA-treated wood from other wood types in the field using an on-line sorting system.