boron and tebuconazole

Numerical simulation of the leaching behaviour of treated wood is the most pertinent and less expensive method for the prediction of biocides' release in water. Few studies based on mechanistic leaching models have been carried out so far. In this work, a coupled chemistry-mass transport model is developed for simulating the leaching behaviour of inorganic (Cu, B) and organic (Tebuconazole) biocides from CBA-amine treated wood. The model is based on experimental investigations (lab-scale leaching tests coupled with chemical and structural analysis). It considers biocides' interactions with wood solid components and with extractives (literature confirmed reactions), as well as transport mechanisms (diffusion, convection) in different compartments. Simulation results helped at identifying the main fixation mechanisms, like (i) direct complexation of Cu by wood-phenolic and -carboxylic sites (and not via monoethanolamine; complex) on lignin and hemicellulose and strong dependence on extractives' nature, (ii) pH dependent binding of tebuconazole on polarized OH moieties on wood. The role of monoethanolamine is to provide a pore-solution pH of about 7.5, when copper solubility is found to be weakest. The capability of the developed model to simulate the chemical and transport behaviour is the main result of this study. Moreover, it proved that characterization leaching tests (pH dependency and dynamic tests), combined with appropriate analytical methods are useful experimental tools. Due to its flexibility for representing and simulating various leaching conditions, chemical-transport model developed could be used to further simulate the leaching behaviour of CBA treated wood at larger scales.

Topics: Azoles; Boron; Computer Simulation; Copper; Disinfectants; Fixatives; Hydrogen-Ion Concentration; Models, Chemical; Triazoles; Wood

Treated wood is frequently used for construction. However, there is a need to ensure that biocides used for the treatment are not a threat for people or environment. The paper focused on Pinus sylvestris treated with copper-boron-azole (CBA), containing tebuconazole as organic biocide and monoethanolamine (Mea). This study investigates chemical mechanisms of fixation and mobilisation involved in the leaching process of the used inorganic and organic biocides in CBA. A pH dependent leaching test was performed, followed by a set of complementary analysis methods in order to identify and quantify the species released from wood. The main findings of this study are: - Organic compounds are released from untreated and treated wood; the quantity of released total organic carbon, carboxylic and phenolic functions increasing with the pH. - Nitrogen containing compounds, i.e. mainly Mea and its reaction products with extractives, are released in important quantities from CBA treated wood, especially at low pH. - The release of copper is the result of competitive reactions: fixation via complexation reactions and complexation with extractives in the liquid phase. The specific pH dependency of Cu leaching is explained by the competition of ligands for protonation and complexation. - Tebuconazole is released to a lesser extent relative to its initial content. Its fixation on solid wood structure seems to be influenced by pH, suggesting interactions with \\OH groups on wood. Boron release appears to be pH independent and very high. This confirms its weak fixation on wood and also no or weak interaction with the extractives.

Topics: Azoles; Boron; Copper; Disinfectants; Hydrogen-Ion Concentration; Pinus; Triazoles; Wood