Review of Thermochemical Conversion Processes as Disposal Technologies for Chromated Copper Arsenate (cca) Treated Wood Waste

Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Extraction experiments have been carried out on CCA treated wood and evaluated as a method to recover the metal compounds into either fresh wood preservatives or other useful industrial materials. Recycling and recovery processes of the metals in the metallurgical industry have also been studied, but not yet all metal products are transformed to usable forms. A study about biorecycling of CCA treated wood through bioremediation and biodeterioration has been initiated. Numerous studies and experiments have been carried out on burning contaminated wood. Direct electrodialytic removal of the metals from CCA treated wood, as well as electrochemical cleaning processes for ash resulting from combustion of CCA treated wood, are under study. Pyrolysis processes (both slow and flash pyrolysis) have been investigated as a major process for the disposal of cellulosic wastes, also CCA treated wood waste. The authors performed a lot of experimental and theoretical work to get more insight in the metal behaviour during the low-temperature pyrolysis of CCA treated wood waste. Experiments were carried out with CCA treated wood samples, as well as with arsenic model compounds and mixtures of arsenic oxides and reducing agents (glucose or activated carbon). The most important conclusion is that zero arsenic release during pyrolysis of CCA treated wood seems to be impossible since the reduction reaction (As2O5 → As2O3 + O2) can not be avoided in the reducing environment, created by the presence of wood, char and pyrolysis vapours. Once the trivalent arsenic oxide is formed, it is released. This release is driven by a vapour pressure controlled volatilisation process: the higher the temperature, the faster the release. The insights gained through these studies are used to evaluate other thermochemical conversion processes (flash pyrolysis, gasification and combustion) with respect to their applicability to the disposal of CCA treated wood waste. This evaluation is compared with observations and calculations reported by other researchers in the literature. Finally, the most appropriate thermochemical disposal technology is identified.