Evaluation of the accessibility of CCA metals in liquefied CCA-treated wood sludge for recovery and reuse
CCA-treated wood was liquefied with polyethylene glycol/glycerin and sulfuric acid. The heavy metals were precipitated by Ca(OH)2 from liquefied CCA-treated wood. The original CCA-treated wood and precipitated wood sludge were fractionated by a modified BCR (Community Bureau of Reference) sequential extraction procedure. The purpose of the BCR sequential extraction used in this study was to exam the accessibility of the heavy metals in CCA-treated wood for reuse. The two different size CCA-treated wood particles used for liquefaction had similar heavy metal distributions. As and Cr showed similar distributions as original CCA-treated wood and principally existed in an oxidizable fraction (As, 67%; Cr, 88%). Cu was largely present in the reducible fraction (49%) and exchangeable/acid extractable fraction (34%) in original CCA-treated wood. The distribution of As and Cr changed markedly after liquefaction. The amount of As in the exchangeable/acid extractable fraction increased from16% to 85% while the amount of Cr increased from 3% to 54%. Based on these results from sequential extraction procedures, it can be concluded that the accessibilities of CCA metals was increased markedly by the liquefaction-precipitation process. Only a small amount of heavy metals were precipitated by direct centrifugation and most were precipitated with Ca(OH)2. The distributions of the heavy metals didn’t vary markedly between the liquefied CCA-treated wood sludge samples obtained by filtration and centrifugation methods.