Immobilization of Heavy Metals by Co-pyrolysis of Contaminated Soil with Woody Biomass F. Debela & R. W. Thring & J. M. Arocena Received: 3 February 2011 /Accepted: 11 August 2011 /Published online: 26 August 2011 # Springer Science+Business Media B.V. 2011 Abstract We investigated the potential application of pyrolysis treatment to a mixture of woody biomass and a metal-contaminated soil as an alternative eco- friendly option to stabilize metals in soils. Our specific objective was to test the optimum combina- tion of high heating temperature (HHT) and heating time to effectively encapsulate metals in a contami- nated soil into a biochar. For this purpose, we used a laboratory bench batch reactor to react a mixture of multi-element metal contaminated soil with 0% (control) 5%, 10%, and 15% (w/w) sawdust. Each mixture was reacted at 200°C and 400°C HHT for 1 and 2 h heating times. Physicochemical and morpho- logical characterization along with standard EPA Synthetic Precipitation Leaching Procedure (SPLP) test were conducted to assess the effectiveness of the heat treatment to immobilize the metals in the contaminated soil. Compared to controls, we recorded up to 93% reduction in Cd and Zn leachability after 1 h heat treatment at 400°C, with the addition of 5– 10% biomass. Pb leaching was reduced by 43% by the same treatment but without the addition of biomass. At lower pyrolysis temperature (200°C), however, there was a substantial increase in both As and Zn leaching compared to the untreated controls. Our study suggests that several factors such as the type of metal, heating temperature, heating period, and the addition of biomass influence the efficiency of pyrolysis to immobilize metals in the contaminated soil. Keywords Metal leaching . Biochar . SPLP . Sequential extraction 1 Introduction Biochar is the product of a partial-oxidation (pyroly- sis) process, which is the decomposition of organic carbon bearing compounds at elevated temperature in the absence of oxygen (Brown 2009). Biochar is a multi-use soil amendment material with demonstrated environmental, economic, and social benefits (Cao et al. 2009; Lehmann and Rondon 2006; Steinbeiss et al. 2009; Warnock et al. 2007; Yu et al. 2009). In addition to the production of biochar, pyrolytic processes have been used to reduce metal leaching from several organic wastes such as municipal sewage sludge (Kistler et al. 1987), fly ash (Jakob et al. 1996), and biomass (Stal et al. 2010). Similar reductions in metal leaching from dredged sediments upon pyrolysis have been reported by Rienks (1998), Wijesekara et al. (2007) and Zhang et al. (2009). Water Air Soil Pollut (2012) 223:1161–1170 DOI 10.1007/s11270-011-0934-2 F. Debela (*) Natural Resources and Environmental Studies, University of Northern British Columbia, Prince George, BC, Canada V2N 4Z9 e-mail: debela@unbc.ca R. W. Thring : J. M. Arocena Environmental Science and Engineering, University of Northern British Columbia, Prince George, BC, Canada V2N 4Z9