Characterization of auto shredder residue — a Canadian perspective

Abstract

Abstract Auto Shredder Residue (ASR) the solid wastes produced by the Canadian Ferrous metal Shredding Industry has been found to be an extremely heterogeneous material. By employing a systematic cone and quartering procedure on a sufficiently large representative sample, reasonably consistent and repeatable results can be obtained regarding the chemical and physical composition of the material. Although some variability was observed between samples from one operation the data obtained for the most part was consistent. Surprisingly the variation from operation to operation was not large and when differences in specific properties were noted they could be attributed to specific operational conditions noted at the time of sampling. Essentially, a typical sample of ASR from a Canadian shredding operation has a bulk density of 405 kg/m3 and contains 6% moisture. 18% of the material will have a particle size greater than 25.5 mm, with 37% fines less than 2 mm. The split between the organic and inorganic fraction as determined by ashing is 42% to 58% with the material having a calorific value of 11.8 MJ/kg. After iron: zinc and copper were the principle heavy metals present in the material at concentrations of about 1%. Lead at a concentration of about 0.25% was the next major heavy metal present. Concentrations of cadmium and chromium meanwhile were less than 0.05%. In terms of the leachability of these heavy metals from the ASR when measured by the Quebec test protocol, zinc was found to be the most leachable at concentrations of about 250 mg of Zn per litre of leachant. Cadmium, chromium and copper meanwhile leach out at levels usually less than 1 mg/l. When evaluated by the Quebec test protocol the leachability of lead from ASR is a potential problem with an average concentration of 7.0 mg/l, which exceeds the allowable limit of 5 mg/l.