Effect of EDTA on removal of CCA from treated wood
S N Kartal
Since substantial amounts of chromated copper arsenate (CCA) remain in the wood for many years, the disposal of CCA-treated wood causes escalating environmental concerns. Additionally, wood waste is generated when treated wood is put into service, for which environmentally benign disposal technologies need to be developed. Novel approaches to remove copper, chromium, and arsenic from CCA-treated waste wood are needed to overcome such environmental concerns. Acid extraction, one of the most extensively used methods, has been studied by several researchers for removal of copper, chromium, and arsenic from CCA-treated wood. In this study, EDTA (ethylenediaminetetraacetic acid) extraction of copper, chromium, and arsenic from CCA-
treated wood was evaluated using batch-leaching experiments. EDTA is one of the most common chelator used to bind the metal ions in extremely stable complexes in heavy metal contaminated soils and thus to remediate such substrates. EDTA forms water soluble complexes with many metal ions and it is used to release for the various metals. In the study, chips and sawdust containing CCA were processed by EDTA extraction to remove the metal elements present in the form of oxides. CCA-treated wood samples were extracted with four different concentrations of EDTA (0.0, 0.01, 0.1, and 1.0%) for 4 and 24 hours at room temperature. Exposing CCA-treated chips and sawdust to EDTA extraction enhanced removal of CCA components compared to extraction by deionized water. Grinding CCA-treated wood chips into 40-mesh sawdust provided greater access to and release of CCA components. Extraction with 1% EDTA solution for 24 h released 60% copper, 13% chromium, and 25% arsenic from treated chips. EDTA extraction of treated sawdust samples resulted in 93% copper, 36% chromium, and 38% arsenic release. The pH of EDTA solutions ranged from 2.2 to 3.2, providing acid conditions, which facilitate release of copper element. The results suggest that EDTA extraction removes significant quantities of copper from CCA-treated wood. Thus, EDTA could be important in the remediation of wood waste treated with the newest formulations of organometallic copper compounds and other water-borne wood preservatives containing copper.
Keywords: Remediation, heavy metals, EDTA, CCA-treated wood