CCA-Treated Wood Waste Remediation Process Optimization with Successive Recirculation Loops Study

This study aims to improve a decontamination process developed for chromated copper arsenate (CCA)-treated wood waste. This process included metal extraction from the wood by a sulphuric acid-leaching step, and the treatment of metal-loaded leachate by precipitation with ferric chloride and sodium hydroxide. This study showed that sodium hydroxide can be advantageously replaced by calcium hydroxide to enhance performance (> 99% metal precipitation above pH 6.5 with Ca(OH)(2) and above pH 7 with NaOH) and lower chemical costs [US$30.8/ton of treated wood (TTW) with Ca(OH)(2) instead of US$50.83TTW with NaOH]; however sludge production and sludge disposal cost were higher when using Ca(OH)(2) for precipitation. Moreover, this study investigated the possibility of recycling the final process effluent obtained after metallic sludge separation. This effluent was successively reused in the process for the leaching step. Five recycling loops comprised of one leaching step, one precipitation step of the leachate with Ca(OH)(2), and three rinsing steps were conducted. Arsenic removal from the wood varied from 96 to 98%, chromium removal from 91 to 93% and copper removal from 95 to 96%. Metal removal stayed relatively stable along the five loops, meaning that process water recycling did not influence metal extraction. Leachate treatment with calcium hydroxide and ferric chloride was efficient and allowed, beside metals precipitation, DOC and sulfate partial removal. This avoided fast accumulation of these compounds in the system. DOI: 10.1061/(ASCE)EE.1943-7870.0000474. (C) 2012 American Society of Civil Engineers.