# Comparative Studies on Leachability of Zinc and Iron from High-Energy Milled Waste of Scrap-Based EAF Steelmaking

## TL;DR

This study explores how high-energy milling affects the recovery of zinc from steelmaking waste, finding that mechanical activation improves zinc leaching efficiency.

## Contribution

The first study to examine how high-energy milling affects phase transformation, metal speciation, and leachability in EAF waste.

## Key findings

- Milling at 100 rpm increased zinc extraction to 67% in H2SO4 and 55% in NaOH.
- Higher milling rates (200–400 rpm) reduced zinc leachability due to refractory phase formation.
- Iron dissolved only in acid, while zinc leached efficiently in both acidic and alkaline solutions.

## Abstract

Electric arc furnace (EAF) waste, a mixture of dust and slag, was investigated as a potential secondary source of zinc. The waste primarily consisted of zinc and iron oxides, with the presence of refractory zinc ferrite, which hinders the complete recovery of zinc. This is the first study that examined the effect of mechanical treatment through high-energy planetary ball milling on the phase transformation, metal speciation, and leachability of the EAF waste. The raw material was characterized by particle size distribution, morphology, phase composition, and sequential extraction, and then subjected to milling at different rotation rates (100–400 rpm). The resulting powders were analyzed using XRD, SEM–EDS, and sequential leaching, and tested for acid (H2SO4) and alkaline (NaOH) leachability. Milling progressively reduced particle size, increased surface roughness, and induced structural changes, including the mechanical activation effect at low milling rates (100 rpm) and the synthesis of secondary franklinite at higher milling energies (200 rpm and 400 rpm). Sequential extraction revealed changes in zinc and iron speciation from acid-soluble to residual fractions for increased milling intensities. Leaching experiments showed rapid zinc dissolution in both acidic and alkaline solutions, while iron dissolved only in acid. The highest zinc extractions (67% in H2SO4, 55% in NaOH) were obtained from mechanically activated material at 100 rpm, while zinc leachability decreased for higher milling rates due to the induced mechanical synthesis of refractory phase. The kinetic model of leaching of the main components of the EAF was also established.