Effect of leaching temperature and water acidity on the loss of metal elements from CCA treated timber in aquatic applications. Part 1: Laboratory scale investigation

IRG/WP 95-50046

G M F Van Eetvelde, R J Orsler, G E Holland, M Stevens

In order to investigate the applicability of current prestandard leaching test methods, a series of experiments has been performed on CCA impregnated wood dealing with the influence of pH, temperature and agitation of the surrounding water. The leaching method used in this first part of the investigation is the European prestandard drafted by CEN/TC38/WG11, a short term dynamic leaching test under laboratory conditions of test. Parameters of study are water acidity, stirring of the leaching water, type of fixation and wood species. With increasing acidity of the leaching water, the release of copper is strongly enhanced whereas chromium is lost on a low and fairly constant rate irrespective of pH. In general, significantly greater quantities of metal elements were leached when stirring the leaching water compared with the static experiments performed. Both natural and steam fixation appear to be effective in fixing the CCA components to a large extent. However, the overall detectable copper quantities still indicate incomplete Cu fixation. Likewise, with steam fixed timber a higher loss of copper is observed in the early leaching cycles, likely due to the presence of copper salts on the wood surface. With regard to the wood species investigated, no major differences in loss patterns are observed with pine and spruce specimens. However, the difficulties met when impregnating spruce at toxic limit level attempting full penetration of the wood blocks seem to be reflected in the loss data obtained. The results obtained in this leaching study tend to support the prestandard test procedure examined. However, more detailed information is required on certain parts of the test method as described in this study as well as on data-interpretation procedures to evaluate the results obtained and translate them to conditions under service.


Keywords: LEACHING; CCA; pH; STIRRING; FIXATION; EMISSION

Conference: 95-05-11/16 Helsingør; Denmark


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