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Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/29834

Title: Influence of Alkaline Copper Quat (ACQ) Solution Parameters on Copper Complex Distribution and Leaching
Authors: Pankras Mettlemary, Sedric
Advisor: Cooper, Paul
Department: Forestry
Keywords: Alkaline copper quat
wood preservative
quaternary ammonium
copper amine
copper ammonia
copper leaching
copper speciation
copper distribution
Issue Date: 31-Aug-2011
Abstract: The effects of ACQ solution parameters such as copper to quat ratio, pH and copper to ligand ratio on distribution of copper complexes in solution and insoluble precipitates, and on fixation and leaching of copper in treated wood were evaluated. The distribution of ionic complexes, predicted by equilibrium speciation model (MINTEQA2), was related to laboratory fixation and leaching results at controlled ACQ solution parameters. A decrease in the relative proportion of copper in the ACQ formulation from a copper oxide (CuO) to didecyldimethylammonium carbonate (DDACb) ratio of 2:1 to 1:1 and 1:2 resulted in lower copper retention in the treated samples and substantially decreased the amount of copper leached per unit area. For monoethanolamine (Mea) based ACQ, solution parameters which favour a higher proportion of monovalent cationic complex, which consume one reactive site in wood, and the presence of insoluble carbonate precipitate of copper in wood during preservative treatment resulted in higher leach resistance compared to the neutral copper complex present at higher pH. Ammonia (NH3) based ACQ can fix more copper at high pH as there is no chelated neutral complex as in Mea based ACQ; however divalent copper-NH3 complexes may consume two sites to fix in wood. Addition of NH3 in Mea based ACQ at Cu:Mea:NH3 ratio of 1:4:6 at pH 10.6 significantly reduced copper leaching compared to 1:4:0 (without ammonia) at pH 9 due to increased divalent copper-ammonia complexes and decreased neutral copper amine complex at elevated pH. Ammonia addition with a lower proportion of Mea (1:2.5:4 at pH 10.5-10.7), significantly reduced copper leaching compared to 1:4:0 at pH 9; no reduction was observed for ammonia addition in ACQ with a higher proportion of Mea (1:4:4 at pH 10.45). The lower copper leaching from 1:2.5:4 resulted from the higher amount of divalent copper-NH3 complexes at higher pH without compromising the amount of copper precipitated at lower pH. The higher percent copper leached from tetramethylethylenediamine (Tmed) based ACQ compared to Mea and NH3 based ACQ suggested that highly stable complexes tend to stay in solution and do not result in leach resistant copper in the wood.
URI: http://hdl.handle.net/1807/29834
Appears in Collections:Doctoral

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