Reduction of environmental availability and ecological risk of heavy metals in automobile shredder residues Jiwan Singh, Byeong-Kyu Lee * Department of Civil and Environmental Engineering, University of Ulsan, Daehkro 93, Namgu, Ulsan 680-749, South Korea A R T I C L E I N F O Article history: Received 11 September 2014 Received in revised form 27 January 2015 Accepted 5 April 2015 Available online xxx Keywords: ASR Heavy metals TCLP Bioavailability Mobility factor Risk assessment code A B S T R A C T The present study investigated the recovery, reduction of environmental availability and ecological risk of heavy metals extracted from automobile shredder residue (ASR) using water with pH 2. The recovery rate of heavy metals from ASR increased with increasing temperature and L/S ratio at pH 2. The heavy metal recovery was found to be greater in the smallest size fraction than in the larger fractions. The residues remaining after extraction were analyzed for functional groups, morphology, toxicity characteristic leaching procedures (TCLP) and mobility factors (MFs) of the heavy metals. The TCLP test results revealed Cd concentrations below the threshold limits in all ASR fractions, whereas Pb concentrations exceeded the threshold limit in all ASR fractions, with the exception of the largest fraction. The MFs of all selected heavy metals were reduced after extraction. In the analysis of the risk assessment code (RAC), Zn, Cu and Cd were reduced from the high risk category into either low risk or medium risk categories after recovery of the heavy metals, whereas Pb remained under the high risk category. This confirmed that distilled water at pH 2 is not efficient for reducing Pb toxicity to the extent necessary for safe landfilling of ASR. Therefore, a stronger acid is required for the higher recovery of Pb and reduction of its toxicity before ASR is landfilled. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Leachate is generated through landfilling of heavy metals- contaminated wastes such as municipal solid waste and automobile shredder residue (ASR). It is considered a major source of metal contamination in nearby aquatic environments (Salem et al., 2014). Heavy metal release under acidic conditions is one of the major environmental concerns for the landfilling of automobile shredder residue (ASR) under acidic conditions. The heavy metals in ASR originate from residual metal pieces, solders, plasticizers and paints (Kurose et al., 2006). The heavy metals may leach out from ASR to pollute soil, ground water and surface water; these metals can transfer to the ecosystem and the food chain, posing a hazard to human health (Shaheen and Rinklebe, 2015). Thus, the leaching of heavy metals from ASR has raised public concern, with ASR classified as a hazardous waste that must be disposed of in controlled landfill sites after proper treatment (Gonzalez-Fernandez et al., 2008). Heavy metals in water-soluble fractions can leach out easily and become bioavailable in the environment (Liu et al., 2008; Singh and Kalamdhad, 2013a,b; Singh and Kalamdhad, 2014a). More attention should be given to the weakly bonded exchangeable (EXCH) and carbonate bound (CARB) fractions as they can equilibrate with the aqueous phase following changes in the ionic concentration and pH of the soil and consequently, become rapidly bioavailable (Sundaray et al., 2011; Singh and Kalamdhad, 2013a,b; Shi et al., 2013). Determination of the specific quantity of heavy metals in ASR can be performed using a risk assessment code (RAC) based on the proportion of these two fractions (EXCH and CARB) compared to the total concentration of each metal obtained after strong acid digestion of ASR (Huang et al., 2011). The toxicity or leachable fractions of heavy metals in ASR can be reduced by extraction with water, which is very important for reducing environmental risk. Therefore, the safe disposal of ASR into landfills necessitates the extraction/recovery of heavy metals from ASR using an economi- cally suitable extraction agent. Extraction of heavy metals from ASR using water is regarded as environmentally friendly and has been employed for the removal of heavy metals from fly ash generated during municipal solid waste incineration. The toxicity and leaching characteristics of heavy metals can be greatly reduced after extraction with water (Wang et al., 2001). Under acidic conditions such as pH 2, heavy metals in landfills are easily leached out from ASR during the rainy season. Therefore, the objectives of the present study were to recover heavy metals (Zn, Cu, Pb and Cd) from ASR by extraction using water at pH 2 and to reduce the * Corresponding author. Tel.: +82 52 259 2864; fax: +82 52 259 2629. E-mail address: bklee@ulsan.ac.kr (B.-K. Lee). http://dx.doi.org/10.1016/j.ecoleng.2015.04.036 0925-8574/ ã 2015 Elsevier B.V. All rights reserved. Ecological Engineering 81 (2015) 76–81 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng