Fixation and leaching characteristics of acid copper chromate (ACC) compared to other chromium-based wood preservatives

Chromium fixation rates and leaching characteristics of acid copper chromate (ACC) were compared with those of four preservatives that contain chromium/copper: chromated copper arsenate types A, B, and C (CCA-A, CCA-B, CCA-C) and chromated copper borate (CCB), in red pine (Pinus resinosa Ait) sapwood. Three solution concentration/fixation temperature combinations were evaluated. The fixation rates were initially very fast for all conditions and preservatives, but slowed down as the pH of the expressed solution increased. The different formulations had significantly different fixation rates. The ACC formulation had the longest fixation times of the formulations evaluated. CCA type B had the fastest fixation rate, probably because of the lower chromium and higher arsenic content. The CCA-A fixation rate was similar to that of CCB and faster than CCA-C and ACC even though its initial chromium concentration was higher. The time to fixation was significantly increased at higher preservative retentions and significantly decreased at higher fixation temperatures for all preservatives. Leaching results after fixation showed that CCA-C and ACC had uniformly low losses of all preservative components. CCA-B had excessive arsenic and moderate copper leaching. CCA-A had low chromium and arsenic leaching but high copper leaching and CCB had moderate copper losses.

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