# Distribution and Enrichment of Heavy Metals in Fine-Grained Fractions of Crushed Electronic Waste

## TL;DR

Crushing e-waste produces fine particles that concentrate harmful heavy metals like lead and zinc, posing health risks but also offering recycling opportunities.

## Contribution

The study reveals how heavy metals are enriched in fine fractions of crushed e-waste, providing insights for safer handling and efficient metal recovery.

## Key findings

- Fine e-waste fractions (<0.25 mm) show significant enrichment of Pb, Zn, Cr, Ni, and Cd.
- Lead concentrations reach up to ~2 wt.% in the finest fraction (<0.15 mm), with a fiftyfold enrichment compared to coarse fractions.
- Fine fractions are identified as critical for both environmental risks and potential metal recovery.

## Abstract

Heavy metals show strong size-dependent enrichment during e-waste crushing.

Fine fractions (<0.25 mm) concentrate Pb, Sn, Zn, Cr, Ni, and Cd.

Lead reaches up to ~2 wt.% in the finest e-waste fraction (<0.15 mm).

Toxic metals are enriched in fine fractions and processing dust.

Size fractions enriched in polymers or metals were identified to support efficient recycling.

The concentration of heavy metals in the environment has been steadily increasing, raising concerns about their adverse effects on ecosystems and human health. Fine-grained particulate matter is of particular concern due to its enhanced mobility, bioavailability, and potential for inhalation exposure. Facilities involved in the mechanical processing of electronic waste (e-waste) represent a significant potential source of metal-containing fine particles. In this study, crushed e-waste components containing precious metals were separated into particle-size fractions ranging from 3.0 to 0.15 mm using a vibratory sieving system. The elemental composition of the individual fractions was determined by energy-dispersive X-ray fluorescence spectrometry (ED-XRF), while the spatial distribution of selected metals in fine fractions was further investigated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM–EDS). The results demonstrate that e-waste contains a wide range of heavy non-ferrous metals whose distribution is strongly dependent on particle size. A pronounced enrichment of metals was observed in the finest fractions, particularly below 0.25 mm. Compared to the coarse fraction (>3 mm), the zinc concentration increased by approximately one order of magnitude, while chromium, nickel, and cadmium exhibited increases of up to approximately 20-fold. Lead showed particularly high enrichment, reaching approximately 2 wt.% in the finest fraction (<0.15 mm), corresponding to nearly fiftyfold enrichment relative to the coarse fraction. Tin concentrations also increased markedly, in some cases by up to two orders of magnitude. Trace amounts of arsenic and selenium were detected in the finest fractions, whereas mercury was not detected. The combined ED-XRF and SEM–EDS results confirm that fine-grained e-waste fractions are the dominant carriers of hazardous metals and respirable particles generated during mechanical processing. These findings highlight the dual character of fine fractions as both a critical environmental and occupational risk and a potentially valuable secondary resource. The study emphasizes the importance of controlled handling, effective dust management, and targeted processing strategies to minimize human exposure while enabling efficient recovery of valuable metals from e-waste.