Retardance of rainwater-leached metals from CCA-treated (chromated copper arsenate) wood ash in soil
The burning of wood treated with chromated copper arsenate (CCA) preservative produces an ash that contains high concentrations of copper, chromium, and arsenic. The subsequent leaching of these metals from burn sites can produce soil and water contamination. Soils have varying natural abilities to reduce leaching and impact metals speciation and toxicity, by sorption, conversion and sedimentation related mechanisms. Recent regulations have resulted in increased quantities of CCA-treated lumber entering the waste stream, making the study of metals leaching from ash, and the amendment of soils to more effectively immobilize metals, important areas of investigation. The performance of various soil amendments to immobilize or retard Cu, Cr, and As species in soil/CCA-ash mixtures was studied. The amendments evaluated were agricultural lime (CaCO3/MgCO3), soil softener (CaSO4 . 2H2O), and iron sulfate (FeSO4). The evaluation was performed using batch and column leaching studies and pH studies. The control soil used in this study is from the Ultisol soil order, the dominant soil order in the Southeastern U.S. Ultisols form under humid, tropical conditions and are dominated by kaolinitic clay and lesser so by oxides of Fe and Al with a low percentage of organic carbon content. Results of this investigation show that native soil alone retards the mobility of As and Cr and amendments applied alone or in combinations further retard metal mobility compared to the control soil/CCA-ash mixture. The CaSO4 soil amendment is most effective in reducing the rainwater leaching of high concentrations of Cr and As from CCA-ash in soil reducing the mobility by 72% and 77%, respectively, compared to the control soil-ash mixture. Cu mobility at low concentrations relative to Cr and As is increased in the presence of the native soil and by all amendments compared to the CCA-ash alone.