Beta 1


Title Rensning af imprægneret træ for kobber, krom og arsen
Author Hansen, Bjørn B. (Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Supervisor Thomsen, Kaj (CERE, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Bachelor thesis
Year 2010
Abstract Today newly impregnated wood contains no arsenic and only few heavy metals. It hasn't always been like this. Since January first of 1997 Denmark prohibited import, export, sale and use of arsenic impregnated wood [MST.dk]. Before 1997 arsenic impregnated wood was heavily used in outdoor wood constructions. In Denmark it is estimated that about 4 million tons of CCA impregnated wood is still in use today. CCA is an acronym for copper, chromium and arsenic which is the impregnation chemicals used to conserve the wood. The CCA treated wood will need to be disposed of in the future. Arsenic is the most problematic of these chemicals and only 0,1 wt% is enough to classify the wood as hazardous [MST.dk]. In this report it has been attempted to remove the CCA chemicals from impregnated wood, using oxalic acid and NaOH. It has also been attempted to add NaCl to the oxalic acid. Previously the reports [Rasmussen, 2008] and [Vegger, 2009] have described how CCA chemicals can be removed from impregnated wood. Their work has been used to guide this project in the right direction with respect to cleaning chemicals. The experiments have shown that it is possible to clean more than 80% arsenic and approximately 75% chromium from CCA impregnated wood using oxalic acid. Copper showed to be more difficult than expected and only about 25% could be removed. The experiments clearly showed that the highest oxalic acid concentrations gave the best results. The oxalic acid experiments were performed over 1, 3 and 6 hours and it was shown that longer extraction times may improve the results even further. It was also attempted to add NaCl to the oxalic acid, but this affected the result in a negative way. NaOH was also attempted as a chemical for the removal of CCA chemicals from wood. This was done in the hope that NaOH could selectively remove arsenic while leaving copper and chromium in the wood. This was found to be the case, but as only 20% of the arsenic was removed NaOH was shown to be infective. After the CCA chemicals had been removed from the wood it was attempted to recover the cleaning liquid. To do this could make the extraction more profitable. The cleaning liquid was attempted cleaned by am electrochemical method developed by RecoMeta. Unfortunately it was not possible to show results that indicated that the method would be viable. An experiment using a synthetic arsenic solution did, however, show that >99% of the arsenic was removed. This result indicate that further experiments may have more success than the ones performed here.
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Pages 74
Admin Creation date: 2010-07-06    Update date: 2010-07-06    Source: dtu    ID: 264776    Original MXD