Leaching of chromium and other cca components from wood-cement composites made with spent CCA treated wood
D Qi, P A Cooper
Wood cement composites are an attractive option for recycling spent treated wood, since the CCA treatment enhances the physical, mechanical and biological resistance properties of the composite. However, we have noted a higher than normal leaching of chromium from these products and this appears to result from conversion of some of the trivalent chromium to the more leachable and toxic hexavalent chromium from the trivalent chromium in the wood. The effects of hexavalent chromium reducer --FeSO4, the pH value of mixing water and different kinds of accelerators on the leaching properties of this composite were tested. Arsenic and copper components of CCA in treated wood were well fixed after mixed with cement. Although total chromium leaching amount was reduced greatly in the CCA treated wood-cement composite compared to CCA treated wood, more hexavalent chromium was detected from the leachate of the composite. Cr+6 leaching accounted for about 80% of the total chromium leaching. FeSO4 had a positive effect on decreasing chromium leaching amounts, especially when used in the board having more potentially leachable chromium. Reducing the pH value of mixing water decreased the total chromium leaching amount, but its effect on Cr+6 leaching was not significant. The leaching of Cr+6 and total chromium also depended on the accelerators used; boards with added CaCl2 showed less Cr+6 and total chromium leaching amounts, while Na2CO3 increased chromium leaching.