Separation efficiency of valuable and critical metals in WEEE mechanical treatments

The high demand of rare earth elements (REEs) in electronics industry and their high supply risk owing to the dependence on limited source countries have increased the interest towards Waste Electrical and Electronic Equipment (WEEE) as a potential secondary source of these elements, identified as critical metals. Although REEs are present in a wide range of high-tech products in relative low concentrations, the recycling of critical metals from WEEE is regarded as an important opportunity for promoting the conservation of primary resources and preventing waste production. However, the existing systems for WEEE collection and treatment mainly focus on the recovery of base and precious metals while the fate of REEs has not been addressed yet. To this end, the present study aims at evaluating the substance flows of critical metals in WEEE mechanical pre-treatments as these processes, preceding the metallurgical treatments of refining, determine the amount of metals entering the further recovery chain. The separation efficiency of a full scale mechanical process, including a sequential shredding and selection treatment of small WEEE, was investigated assessing the mass balance of both base metals and special metals as well as the quality of the output products. The mass flow analysis revealed that after pre-treatments only a third of precious metals entering the treatment process was conveyed to the target output destined to further recovery and less than 2% of REEs was concentrated in the potentially recyclable metallic fractions, while approximately 80% of these elements was distributed in the dust stream actually destined to landfill. Furthermore, the study pointed out that the fine fraction of the metallic outputs from the sorting process is characterized by a major degree of purity, indicating that both the dust stream and the fine grain fraction could be regarded as secondary sources for the recovery of valuable and critical metals from WEEE.