Thermochemical Remediation of Preservative-Treated Wood
R Sabo, C A Clausen, J E Winandy
Remediation methods continue to be developed and refined for CCA-treated wood in order to divert this material from landfills and create secondary products from the wood fiber. A two-step thermochemical remediation method was developed to assess the efficiency of metal removal from CCA-treated spruce flakes. Nearly all the metals (As, Cr, and Cu) were thermochemically extracted from chromated copper arsenate (CCA) treated Spruce using solutions of oxalic acid and sodium hydroxide. Oxalic acid was found to be highly effective for removing As and Cr, whereas mixtures of oxalic acid and sodium hydroxide were more effective for removing copper. Up to 100 % As and 97 % Cr were removed from treated flakes after one hour using a 1 % oxalic acid solution (pH 1.4) at 80 °C, but less half of the Cu was removed at pH 1.4 even after six hours. Nearly all the As, Cr, and Cu were extracted from the treated flakes after six hours using a 1 % oxalic acid solution adjusted to pH 3 with sodium hydroxide. However, the removal of As and Cr was slower with oxalic acid solutions that contained sodium hydroxide. A two-stage process in which the flakes were first extracted for one hour with oxalic acid (pH 1.4) then extracted for another hour after adjusting the solution to pH 3 with sodium hydroxide removed 99 % As, 96 % Cr, and 92 % Cu. The effects of temperature, pH, time, mixing, rinsing, and liquid to solid ratio on the removal of metals from CCA-treated Spruce flakes and particles is discussed.