Release of arsenic during the carbonisation of CCA-treated wood on a laboratory and pilot scale

Abstract

The release of arsenic during pyrolysis of CCA(chromated copper arsenate)-treated wood starts at a temperature below 327 ?C, but up to 600 ?C only 30-40% of the arsenic initially present in the wood is volatilised. The changes of heating rate, wood moisture, degree of the comminution and methods of pyrolysis (fixed bed or mechanically pushed and loosened bulk of chips) do not substantially change the situation. The release of arsenic can be eliminated or strongly reduced by use of carbonisation catalysts. The ways and means of metals regeneration or practical use of this contaminated charcoal are still to be elucidated. A substantial decrease of the As, Cr, and Cu content in charcoal from 2800-5550 ppm, 3700-14300 ppm, and 3500-8800 ppm, to 61 ppm, 1014 ppm, and 282 ppm, respectively, was achieved by carbonisation of the previously leached wood specimens. The leachability of CCA-salts from the wood treated with diluted sulphuric acid is good, and the amount of the leached-out metals exceeds 90-95%. Ultrasound treatment improves the leachability, although the effect is not high enough to achieve the full elimination of metals, especially chromium, to meet the concentration levels in charcoal set by legislation.