Abstract

Currently, less than 20% of electronic waste (E-waste) produced in the U.S. is recycled. To improve the recycling rate of E-waste, the study aimed to: (1) identify the major plastics found within electronic shredder residue (ESR), (2) design solvents and processing conditions capable of separating out 90% of the plastic in ESR, and (3) estimate the energy efficiency of the solvent-based process developed. Preliminary screening showed 25 wt.% of the ESR was composed of plastics, with two polymers dominating the sorted plastic fraction—polystyrene (PS, 40 wt.%) and acrylonitrile butadiene styrene (ABS, 25 wt.%). Subsequently, solvents and anti-solvents were screened using Hansen Solubility Parameter Theory for PS, ABS, and ESR dissolution. The pre-screening results showed dichloromethane (DCM) and tetrahydrofuran (THF) as the most effective solvents for PS and ABS, with methanol (MeOH) and ethylene glycol (EG) as the most effective anti-solvents. By optimizing the dissolution time and the solvents used, the highest polymer dissolution yield (99 wt.%) was achieved using DCM for 48 h. Both MeOH and EG precipitated 71 wt.% of the polymer fraction of ESR. EG removed more phosphorus containing flame retardants (94 wt.%) than MeOH (69 wt.%). Energy analysis indicated that the solvent-based processes could save 25–60% of the embodied energy for PS and ABS. Characterization showed that the solvent-based processing could preserve the high molecular weight fraction of the polymers while removing flame retardants at the same time. The results from this study prove the potential of solvent-based processing to produce secondary plastic materials from E-waste for cross-industry reuse.

Highlights

  • Electronic waste (E-waste), containing computer equipment and consumer electronic components, is one of the fastest-growing waste streams (7–10% per year) globally [1,2]. E-waste embodies only 2% of America’s total municipal waste, it contains significant amounts of toxicants including heavy metals and flame retardants (FRs) [3]

  • To produce secondary plastic materials from E-waste for cross-industry reuse, this study aimed to demonstrate the potential of a solvent-based dissolution-precipitation process to simultaneously recover and purify the plastic fraction from real E-waste

  • For the actual chemical recycling process in this study, only the hand-picked polymer were selected for the solvent screening testing

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Summary

Introduction

E-waste embodies only 2% of America’s total municipal waste, it contains significant amounts of toxicants including heavy metals and flame retardants (FRs) [3]. These pose a significant threat to both human health and the environment given the current methods of disposal of it. Large amounts of E-waste are either incinerated or put into landfills [4]. When leached out from landfills, heavy metals found within E-waste including lead, cadmium, and mercury, pollute water sources and eventually the food chain. FRs are released uncontrollably into the environment when leached from landfill, with the added possibility of dioxin formation when incinerated [4]

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