Detoxification of Salt-Impregnated Wood by Organic Acids in a Pulping Process

Abstract

Salt preservative-treated wood contains large amounts of heavy metals to prevent microbial decay. The detoxification of salt-impregnated wood waste by applying the acidic Formacell- pulping process (Nimz and Schone 1992) is based on findings by Stephan (1994) concerning the leachability of heavy metal compounds from preservative-treated wood by organic acids. First test results obtained with wood chips from treated poles after approx. 20 years of service life containing up to 3800 mg/kg copper and 5400 mg/kg chromium show that the obtained pulp contained less than 100 mg/kg of chromium or copper, respectively. The leached heavy metals remain with the lignin whereas the acids are recovered in a simple system and recycled. The pulp properties were neither influenced by the residues of chromium and copper in the pulp nor by the aged wood of the poles. Therefore the Formacell-process seems to be a way to detoxify and furthermore utilize salt-impregnated wood.