Copper and Chromium Electrodialytic Migration in CCA-Treated Timber Waste

Abstract

Chromated copper arsenate (CCA)-treated timber waste is hazardous for the environment due to the leakage of copper, chromium as well as arsenic to the soil and the groundwater. The study concentrates on electrodialytic removal of copper and chromium and their migration behavior in the wood chips and sawdust matrix in an applied electric field. The method is based on the movement of the charged particles in the electric field, enhanced by incubation with oxalic acid (2.5% w/w) and various placement of the contaminated waste in the electrodialytic cell area to analyze the distribution of chemicals in the proposed matrix. The method was tested in laboratory scale experiments where the CCA contaminated wood chips and clean sawdust were placed in various places of the cell, i.e., adjacent to the cathode and anode compartments and in the mid-section of the cell. The duration of each experiment was 14 days and the current was kept constant at 40 mA. During the electrodialytic treatment negative copper and chromium compounds were mostly found in the anolyte or accumulated in the anion-exchange membrane. The amount of positive compounds found in the catholyte is negligible. The placement of contaminated chips close to the anode and cathode showed that copper and chromium moved towards the positively charged anode. If placed in the mid section of the cell, significant amount of contaminants remained bound to the wood matrix or slightly migrated towards the anode. To predict the formation of copper and chromium species at certain pH and Eh, the computer-modeling program MTDATA to generate Pourbaix diagrams was used.

Sequential electrokinetic treatment and oxalic acid extraction for the removal of Cu, Cr and As from wood

“…Thus, low pH conditions (<5) would be the most favourable for efficient electromigration of the small divalent Cu cations towards the cathode, and at least the maximum pH should be maintained at <10 to avoid precipitation of Cu hydroxides, co-precipitation of As and reversal in ionic charge. When the wood chips contained extraction residuals of oxalic acid, electrokinetic treatment turned the catholyte solution brown in colour and some dark, hard precipitate was deposited on the cathode surface, like reported previously [32]. Cu 2+ was obviously reduced to elemental Cu.…”

“…A quantitative mass balance was not determined, however, these amounts were significant as compared to the total amount of Cr removed from wood chips, 700-800 mg. In some previous papers movement of Cr towards the anode has been attributed to the formation of anions from Cr(VI) [26,30,32]. Radivojevic and Cooper [44] have found that in the presence of wood, Cr(III) is easily oxidized to Cr(VI) at pH ≥ 8.5.…”

“…Development of a sequential process consisting of one or two extraction steps and electrokinetic, or electrodialytic (with ion exchange membranes) treatment for CCA-treated wood has advanced to pilot-scale tests and mathematical modelling [23,[25][26][27][28][29][30][31][32]. Application of low-voltage direct current (DC) could improve desorption and transportation of the metals from the heart of the wood chip, then concentrate the metals in a smaller volume of wastewater or deposit them on the electrode surfaces.…”

The hindering effect of experimental strategies on advancement of alkaline front and electroosmotic flow during electrokinetic lake sediment treatment

“…One of these emerging technologies are electrokinetic remediation techniques, which offer a great potential for the removal of charged contaminants from sludge [4,5], soil [6], sediments [2] and copper chromated arsenate (CCA)-treated timber waste [7,8]. The electrokinetic phenomenon employs a low-level direct current across the contaminated medium, which induces the mobility of charged contaminants due to electromigration and electroosmotic flow [9].…”

Remediation of ACQ-treated wood waste by Mea extraction

“…Treating methods for these materials that have been evaluated include incineration (combustion) (Hirata et al 1993;Nurmi 1996), thermal disposal (pyrolysis) (Hata et al 2003;Helsen et al 2003), liquefaction (Lin and Hse 2005), steam treatment (Smith and Shiau 1996;Shiau et al 2000;, formation into wood composites (Wu et al 2010) and electrodialytic remediation (Virkutyte et al 2005). Chemical extraction can be a viable alternative process to remove and reuse metals from wood and produce decontaminated wood.…”