## 1 Introduction  
The production of electrical and electronic equipment (EEE) is one of the fastest-growing sections of human activities [1]. With the expansion of the social economy, the demand for electronic products has rapidly increased [2]. During the 1960s, an average family possessed only a few electric devices: typically a radio, television, refrigerator, vacuum cleaner, and washing machine. Today, however, the number of electronic household appliances has greatly increased. This fast growth has led to the fast obsolescence and substitution of electronic devices. Thus, as the growth of EEE increases, the generation of waste electric and electronic equipment (WEEE) increases as well [1]. WEEE mainly consists of ferrous and nonferrous metals (such as Cu), and a large fraction of WEEE consists of plastic materials (Figure 1). The global estimation of the amount of WEEE is in the range of 50 million tons annually [3]. While in 2016 about 45 million tons of WEEE were generated globally, this will reach about 52.2 million tons in 2021 [4]. The composition of WEEE is largely dependent on the type and age of the discarded equipment [5]. In Europe, the total quantity of plastics used for the production of electric and electronic products is 3 million tons per year. In total, 1.2 million tons of mixed WEEE plastics arise from the separated collection of WEEE in Europe per year [6]. Managing WEEE is important from both an environmental and an economic perspective. The processing of WEEE involves removing hazardous parts and shredding magnetic and eddy current separators to retrieve ferrous and non-ferrous metals. The remaining material contains a high fraction of plastics, in addition to some glass, ceramic, and metals (Figure 2). This heterogeneous fraction, which is called shredder residue material (SRM), is the most problematic fraction from WEEE. The main plastic contents of SRM are as follows: acrylonitrile butadiene styrene (ABS), used in the casings of phones, microwave and flat screens; polystyrene (PS), used in refrigerators and small household appliances; and polypropylene (PP), used in components inside washing machines and dishwashers, and in the casings of small household appliances. A smaller fraction of plastics is polycarbonate (PC), which is used in housings for information and communication technology equipment (ICT); epoxy polymers are mainly used in printed circuit boards (PCB) [7]. The current options to process SRM are deposition in a landfill and incineration [8]. The options for treating SRM are limited. Another option to treat SRM is pyrolysis, which includes heating the material in the absence of oxygen. Pyrolysis turns the material into a liquid fraction, which can be used as fuel, and a solid fraction, which is ash and can be recycled [9]. The mechanical recycling of plastic waste is hindered by three main problems: the presence of hazardous substances, the degradation level of the polymer, and the miscibility of the plastics within WEEE. Hazardous substances include lead (Pb), which is used as a plastic stabilizer; cadmium (Cd), which is used as a pigment; and brominated flame retardants (BFR) used to prevent the products from burning. The use of these substances in new products is now restricted, but they can still be found in large amounts in certain waste streams. [7] Incineration as a method to recover the energy content has been a common practice for Sweden as it provides inexpensive district heating, but it is no longer carried out. Toxic compounds such as dioxins can be released from incinerators, which could be due to the high concentration of antimony and copper present in WEEE fractions, which favors their production [10]. Figure 1: Characteristic material composition of waste electric and electronic equipment (WEEE); values are in percent, adapted from [5]. One other possible option is the utilization of SRM in metallurgical processes.