Extraction and Recovery of Chromium, Copper, and Arsenic from End-of-life CCA-treated Timber: A Review and Comparative Evaluation

Abstract End-of-life chromated copper arsenate (CCA)-treated timber contains chromium, copper, and arsenic, which restrict disposal and recycling. This review critically compares chemical extraction, electrokinetic remediation, electrodialytic remediation, and supercritical CO 2 extraction, with an emphasis on element-specific removal, process conditions, demonstrated scale, secondary streams, downstream recovery, and application-specific readiness. A structured search of peer-reviewed and grey literature published between 1990 and 2026 was conducted using Scopus, Web of Science, ScienceDirect, and Google Scholar. Direct studies of CCA-treated timber were distinguished from evidence transferred from analogous matrices. Because the studies differed substantially in feedstock and operating conditions, the evidence was synthesised through a structured comparison rather than a weighted ranking. Chemical extraction provides the strongest evidence for rapid and high removal and has been demonstrated at pilot scale, but reagent consumption, timber degradation and metal-bearing effluent remain major constraints. Electrodialytic remediation has also reached pilot scale and can achieve high removal after chemical conditioning, although long treatment times, energy demand and batch handling restrict throughput. Electrokinetic remediation remains predominantly laboratory-scale. Supercritical CO 2 offers solvent-recycling potential but is supported by only a small number of bench-scale CCA studies and has generally achieved limited chromium and arsenic removal. Current evidence does not identify a universally superior technology. Near-term deployment is best supported for chemical and electrodialytic routes, whereas supercritical CO 2 remains a research option. Standardised comparative testing, integrated metal recovery and arsenic stabilisation, pilot demonstrations, and CCA-specific life-cycle and techno-economic assessments are required.