Characterisation, treatment and recovery of materials contained within automotive shredder residue

• Main Author: McGrady, Lucas J.
• Published: University of Brighton 2008
• Subjects: 628
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492199

A research project was undertaken to evaluate the performance of a typical metal shredding process in terms of inputs versus outputs and to characterise the component materials of the automotive shredder residue (ASR) generated by the metal shredder. Research focused upon the identification of specific components of the ASR amenable to separation, recovery and recycling. A controlled experiment where 16 End-of-Life Vehicles (ELVs) were shredded in isolation revealed the total metal recovered amounted to about 75% (comprised of 72% ferrous metal and 3% nonferrous) of the combined weight of the ELVs. The remaining 25% represented the ASR and was composed of three individual fractions based on particle size; ASR large size fraction (>130mm) 2%, ASR medium size fraction (10 to 130mm) 14% and ASR fines fraction «lomm) 9%. The main type of materials identified in the ASR large size fraction were (in order of magnitude) tyre (33% by mass), plastics (19%), ferrous metal (16%), foam (10%), textiles (6%), wire (5%), rubber and elastomers (5%), nonferrous metal (3%). The materials identified in the ASR medium size fraction were plastics (32%), foam (15%), rubber and elastomers (12%), metal and wire (9%), textiles (7%) and wood, paper and cardboard (7%). The (A)SR fine fractions were too small in particle SIze to allow macroscopic identification of composite materials. Therefore, pyrolysis was used to characterise the material composition of the fine fractions in terms of organic and inert constituents. Pyrolysis experiments were conducted at a temperature of 650°C using both laboratory and bench scale reactors. The pyrolysis product yields averaged 52-58% solid residue, 25-27% liquids and 19-21% gas. The pyrolysis solid and liquid products were characterised further using different analytical techniques. Structural analysis of the pyrolysis oil products were conducted using GC/MS, FTIR and NMR spectroscopy. The pyrolysis oils contained significant amounts of potentially useful alkanes, alkenes and aromatic compounds. The pyrolysis solid residues examined in this research were found to contain between 10-14% ferrous metals and 2-5% nonferrous metals. Elemental compositions of the resulting pyrolysis solid residues after ferromagnetic separation were determined using ICP-OES and XRF analysis. Subsequent tertiary recycling of the inert materials of the solid residues via the cement production process is restricted by maximum permissible limits of O.l%wt for lead, copper, chromium and nickel with zinc permissible at 0.5%wt (Origny & Obourg, 1998). Although efforts were made to reduce the levels of lead in the solid residues, by reducing the lead content of the shredder feed, the resulting lead concentrations continually exceeded the 0.1% limit. Accordingly, the inert materials of the pyrolysis solid residues have limited potential in terms of material reuse in this form. Additionally, treatment processes and deposition into the environment of such heavy metal containing materials will require due consideration with respect to the related potential health impacts. The original contribution to knowledge of this research lies in the processes and techniques used to determine the characteristics of the ASR and SR fines. This novel approach included determination of the distribution of selected analytes (particularly the heavy metals of copper, lead and zinc) throughout the individual particle size fractions of the inert materials of the ASR and SR fines. Comparison of the lead concentrations in the corresponding particle size fractions of the ASR and SR fines serves to indicate the contribution depolluted ELVs make to lead levels of general SR fines. The results of the research have increased our knowledge of the recycling potential of the constituent materials of the ASR and SR fines in terms of either energy or materials recovery.