Oxidation and Evaporation Behaviors of Cr, Cu and As During Incineration of Wood Treated by Chromated Copper Arsenate Preservative

摘要

Woody materials treated by chromated copper arsenate (CCA) preservative containing copper, chromium and arsenic had been widely used, and thus it is anticipated that a lot of wood waste treated by CCA will be generated as the industrial waste in the future. The environmental pollution by the released heavy metals becomes a serious problem when the wood treated by CCA was incinerated inadequately. There needs the investigation for the behaviors of heavy metals during incineration of wood treated by CCA. The wood sample treated by CCA was incinerated at temperature range between 873 and 1673 K with the oxygen partial pressure between 0.21 and 0.40 atm completely. The proportion of evaporated arsenic increased with increasing temperature and most of arsenic evaporated at about 1600 K. It was suggested that arsenic evaporated as As_2O_3 or As_4O_6 during the incineration. On the other hand, most of copper and chromium remained in the bottom ash. The evaporation behaviors of arsenic largely depended on the incineration temperature, while the effects of the oxygen partial pressure of inlet gas and gas flow rate on those were small. Powder XRD analysis of bottom ash revealed that copper and chromium existed as CuCr_2O_4 and CuCrO_2. CuCr_2O_4 was mainly contained in the bottom ash incinerated at temperature below 1273 K, whereas the ratio of CuCrO_2 increased with increasing incineration temperature above 1273 K. Therefore, most of copper and chromium were bivalent and trivalent, respectively, in the bottom ash, and some copper was converted to a monovalent over 1273 K. Almost all arsenic was contained as pentavalent Cu_3(AsO_4)_2, and arsenic was not identified in bottom ash incinerated at temperature above 1273 K.