Characteristics of Sludges Produced by Destabilization of CCA Preservative Solutions

Summary

Chromated copper arsenate (CCA) working solution is partially destabilized over time as a result of hexavalent chromium (Cr^VI) reduction by wood extractives and reactive additives such as water repellents and polyethylene glycol (PEG) wood softening agents. Hot water extracts of several softwood and hardwood species were used to prepare 2% CCA type C solutions. The softwoods included sapwood and heartwood of red pine (Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana Mill.), balsam fir (Abies balsamea (L.) Mill.) and sapwood of southern yellow pine (Pinus spp.). Hard wood samples were mixed sapwood and heartwood of red maple (Acer rubrum L.), basswood (Tilia americana L.), yellow poplar (Liriodendron tulipifera L.) and red oak (Quercus rubra L.). In a similar way, 2% CCA solutions were prepared containing 4% PEG and 1% paraffin wax formulated water repellent. The pH and hexavalent chromium content of the CCA solutions were monitored over time until sludge formation was observed. The obtained sludges were separated and analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) in the mid-infrared range and by atomic absorption spectroscopy (AAS) for chromium, copper and arsenic contents. The results of FT-IR and AAS analyses of the sludges indicate that the products of sludging are of comparable chemical nature regardless of the agent responsible for the destabilization of CCA solutions. Arsenic and chromium are the major and copper the minor constituent of the sludges produced by destabilization of CCA solutions examined here.