The generation of WEEE in Europe has been increasing steadily over the last decades and is expected to reach 14 million tonnes by 2021. Its composition, although highly dependent on the type of equipment treated, consists of a significant amount of plastics, ferrous and non-ferrous metals, and a small but relevant amount of precious metals and so-called rare earths. The recovery of valuable materials from WEEE is of particular interest due to the different legislation in place and the high concentration of WEEE, which is, in many cases, higher than that of primary ores. WEEE treatment and recovery lines start with manual sorting of easily identifiable equipment or components, followed by a shredding process to reduce the particle size and release the components. This is followed by physical concentration processes focused on the recovery of materials, the by-product is a plastic material with heterogeneous granulometry. The finest fraction of this plastic by-product contains relevant concentrations of different metals, whose concentration depends on the efficiency of the treatment plant. In the case of the treatment plan studied, these concentrations were approximately 33.0 g/kg of aluminium and 28.8 g/kg of copper.

The present study raised the possibility of generating a secondary treatment line, based on densimetric and gravimetric treatments to achieve the recovery of these valuable metals under the following perspectives: the generation of a dense product of metal concentrate and the obtaining of a light plastic waste that can be used as a by-product.

The first approach developed for this treatment was based on the direct use of a wet shaking table as a simple but precise gravimetric treatment. The results obtained after the setting of its operating parameters based on both technical manuals and the equipment operator's own experience showed a metallic concentrate product with aluminum and copper concentrations of 250 g/kg and 360 g/kg respectively and valuable yields of 15% for aluminum and 50% for copper. An intermediate-density product with potential for aluminum recovery (concentration of 100 g/kg and valuable yield of 50 %) was also observed. By the visual study of this treatment, it was observed that a large percentage of the wet shaking table classification surface was focused solely on the classification by density of the plastic fraction, which, in comparison with metals, has very low densities generally not exceeding 2.00 g/cm³. 

Based on this assumption, a preliminary material roughing treatment was proposed that would allow the precise recovery of plastics according to their density and, on the other hand, allow the vibrating table to work with a better quality material for separation. For this roughing process, the LARCODEMS dense media separator was used with two cutting densities, 1.00 g/cm3 (using water) for the precise recovery of light plastics suitable for energy recovery and 1.33 g/cm3 (using a calcium chloride brine) for the separation of the majority of plastics, minimizing the loss of valuable metals that could be encapsulated in the plastic material. After this pre-treatment, the pre-concentrated product would be placed on the vibrating table. The results obtained show that after the two roughing processes, the material to be treated was reduced to 26% of the raw material, obtaining a concentrated metallic product of 315 g/kg aluminum and 490 g/kg copper, with a valuable yield of 37% and 66% respectively. The intermediate density (aluminium-rich) product improved its properties with a concentration of approximately 230 g/kg and a recovery of 44%.

The results obtained show how the roughing process prior to concentration significantly improves the operation of the shaking table. The results obtained after this process show an improvement in the concentration of aluminum and copper of 25 and 35% respectively and their recovery of 145% and 32% respectively. Finally, the material recovered after first roughing, with a density of less than 1.00 g/cm3, can be used for further energy recovery.