LOW-TEMPERATURE PYROLYSIS OF CCA-TREATED WOOD WASTE - CHEMICAL DETERMINATION AND STATISTICAL-ANALYSIS OF METAL INPUT AND OUTPUT - MASS BALANCES

Low-temperature pyrolysis is proposed as an alternative method to disp ose of CCA-treated wood waste. In the frame of a study aiming at optim ising the pyrolysis of CCA-treated wood, an experimental facility has been built to examine the influence of important process parameters (p yrolysis temperature, residence time, heating rate, particle size, ... ) on the release of metals and on the resultant mass reduction. In ord er to perform a mass balance calculation for the total system, a metho d for metal analysis was developed. Two leaching procedures and one: d issolution procedure were tested and compared with each other, resulti ng in an optimal procedure to bring the metals into solution: ''the BS I method'' to determine the total amount of Cr, Cu and As in the dried wood and ''the Reflux method'' to determine the total amount of Cr, C u and As in the pyrolysis residue. These results illustrate that Cr is more strongly bound in the pyrolysis residue compared to the CCA-trea ted wood. The analytical technique used was ICP-MS and the analytical problems like interferences and matrix effects were solved by using th e appropriate isotope, an internal standard and mathematical correctio ns. The resulting optimal technique for CCA-treated wood (''the BSI me thod'') was applied to wood samples with different particle sizes. A s tatistical analysis of the Cr, Cu and As content in the CCA-treated wo od shows the heterogeneous character of CCA-treated wood samples. Hete rogeneity becomes less important when using samples with a small range of particle sizes. The smaller wood particles have significantly high er metal concentrations than the larger particles. Realistic mass bala nces for the metals were obtained and showed that most of the Cr, Cu a nd As remained in the pyrolysis residue. (C) 1997 Elsevier Science Ltd .