Oxidation states of copper in preservative treated wood as studied by X-ray absorption near edge spectroscopy (XANES)

Abstract

Copper is a common component in wood preservatives and is used to protect the wood against fungal degradation. Previous research has shown that the Cu++ oxidation state provides the best wood protection, and Cu++ is widely believed to be the oxidation state of most copper within treated wood. A recent study using X-ray absorption near edge spectroscopy (XANES) reported high amounts of Cu+ in wood that had been in contact with corroded fasteners. This study uses XANES to examine the copper oxidation states in wood treated with several different wood preservatives as a function of time after treatment. In contrast with previous literature which focused on the fixation reaction in the first few hours after treatment, this paper examines the oxidation state of Cu in treated wood at longer times (up to 1-year) after treatment. The results showed in nearly all cases, Cu was in the Cu++ oxidation state to within the measurement uncertainty. Cu XANES patterns taken approximately 1-year after treatment showed no discernable differences between preservative systems, indicating that regardless of the starting treatment the final Cu speciation is the same within one year. The results confirm previously held beliefs about the Cu oxidation states in wood and give further insights into the corrosion mechanism of metals embedded in treated wood.

Distribution and Speciation of Heavy Metal(loid)s in Soils under Multiple Preservative-Treated Wooden Trestles

“…In the profiles under CCA- and ACQ-treated woods, Cu existed mainly in residual and oxidizable fractions. Cu in preservative-treated wood took the form of Cu(II) regardless of the in-service time [ 90 ], and Cu mobility and bio-effectiveness in soils are largely controlled by the sorption–desorption behavior of organic and inorganic colloids [ 91 ]. The low rate of Cu(II) desorption in soils with high organic matter content is due to the ability of organic matter to form complexes with Cu, which enhances the stability of Cu in soils [ 67 , 92 , 93 , 94 ].…”

“…Similar to other metals, the toxicity and bio-effectiveness of Cu mainly depend on the form of Cu rather than the total amount [ 128 ]. Cu in preservative-treated wood is Cu(II), regardless of the duration of use for both conventional and micronized Cu-based preservatives [ 90 ]. Similarly, Cu is also present in soils in the form of Cu(II).…”