Upgrading of fine residual electronic waste by microwave pyrolysis - Material Influence

Licentiatavhandling, 2012

The large and increasing volumes of waste electrical and electronics equipment (WEEE) in society today make it important to collect and recycle these materials to as high extent as reasonable. Conventional recycling methods are based on mechanical treatments such as shredding, sorting and separation. These methods give a residual fraction that still contains valuable metals in a heterogeneous mixture of small particles obstructing further recycling. The content of total organic carbon (TOC) is however often too large to allow landfill. Novel methods are thus needed in order to improve the recycling possibility of these waste fractions and to improve the total recycling process of WEEE. The aim of this project is to increase the recyclability of residual WEEE fractions by microwave pyrolysis and thus reduce the amount of organic matter and liberate metal pieces in the material, making it more suitable for treatment methods such as leaching and extraction. Choosing microwaves as heating source gives the advantage of volumetric heating which, if controlled correctly, can be more efficient than conventional heating. Microwave pyrolysis was shown to be a feasible method for upgrading 6 different WEEE residual fractions, from light dust to larger particles (up to 20 mm). A treatment time of 60-80 min was concluded to be sufficient to pyrolyse 1 litre of waste. The major mass reduction took place during the heating phase for all the materials tested. The particle size was here found to be important; dust exhibited a higher heating rate. To better control the microwave process the dielectric properties of the waste fractions must be determined. Considered the complexity of the WEEE material, determination of the dielectric losses was not straightforward and a method for measurement was developed. Samples of large particles showed high microwave reflection when measured as-received due to the presence of longer metal wires, which impaired the measurements. The dielectric losses could however be determined for all of the fractions after removing these wires.