Facemasks and ferrous metallurgy: improving gasification reactivity of low-volatile coals using waste COVID-19 facemasks for ironmaking application

Abstract

The global pandemic response to COVID-19 has led to the generation of huge volumes of unrecyclable plastic waste from single use disposable face coverings. Rotary hearth furnaces can be used to recover Zn and Fe from non-recyclable steelmaking by-product dusts, and waste plastic material such as facemasks could be utilized as a supplementary reductant for the rotary hearth furnace (RHF), but their fibrous form makes milling and processing to appropriate sizing for RHF application extremely challenging. A scalable method of grinding facemasks to powder by melting and mixing with Welsh coal dust reported herein provides a solution to both environmental challenges. The melt-blended PPE/coal dust shows a dramatically improved CO₂ gasification reactivity (E_a = 133-159 kJmol^-1) when compared to the untreated coal (E_a = 183-246 kJmol^-1), because of improved pore development in the coal during the pyrolysis stage of heating and the catalytic activity of the CaO based ash present in the facemask plastic. The results are promising for the application of waste facemasks in recycling steelmaking by-product dusts in rotary hearth furnaces and may also be suitable for direct injection to the blast furnace subject to further study.

Figure 1

Components of the disposable mask. (a) A photograph of a fully disassembled mask with the component pieces labelled. (b) SEM image of the untreated mask outer layer. (c) SEM image of the untreated mask filtration layer. (d) SEM image of the untreated mask inner layer.

Figure 2

Materials at various stages of the milling process. (a) Coarsely cut untreated facemasks, (b) GCI coal, (c) cut facemasks and GCI coal before heat treatment and (d) facemasks and GCI coal after 1 h at 250 °C and before milling showing the morphology.

Figure 3

TGA-DTG curve for (a) untreated facemasks under a 100 cm³min⁻¹ flow air, (b) untreated facemasks under a 100 cm³min⁻¹ flow carbon dioxide. DTG signals are denoted as dashed lines. TGA measurements to 900 °C under Ar and to 1200 °C under CO₂ atmospheres for (c) GCI coal (solid line) compared to GCI coal/20 wt.% facemask blend (dashed line) and (d) Charcoal (solid line) compared to charcoal/20 wt.% facemask blend (dashed line).

Figure 4

SEM images of samples of carbon and carbon/facemask melt blends. (a) GCI coal, (b) GCI coal with 20 wt.% facemask plastic, (c) charcoal, and (d) charcoal with 20 wt% added facemask plastic. (e) GCI coal after pyrolysis to 500 °C, (f) GCI coal with 20 wt.% facemask plastic after pyrolysis to 500 °C, (g) charcoal after pyrolysis to 500 °C, and (h) charcoal with 20 wt% added facemask plastic after pyrolysis to 500 °C.

Figure 5

Plots of α and dα/dt against T (°C) for different heating rates. (a) GCI coal, α against T. (b) GCI coal melt-blended with 20 wt.% facemask material, α against T. (c) Charcoal, α against T. (d) Charcoal melt-blended with 20 wt.% facemask material, α against T. (e) GCI coal, dα/dt against T. (f) GCI coal melt-blended with 20 wt.% facemask material, dα/dt against T. (g) Charcoal, dα/dt against T. (h) Charcoal melt-blended with 20 wt.% facemask material, dα/dt against T.

Figure 6

Friedman plots and calculated activation energy (E_a) against α for the combustion of carbon and carbon/facemask melt blends in CO₂ atmosphere. (a) Friedman plot for GCI coal. (b) Friedman plot for GCI coal/facemask melt blend. (c) Activation energy against α for GCI coal and GCI coal/facemask melt blend. (d) Friedman plot for charcoal. (e) Friedman plot for charcoal/facemask melt blend. (f) Activation energy against α for charcoal and charcoal/facemask melt blend.

Figure 7

Proposed process schematic showing the effect of the polymer fabric of facemasks on a coal particle as it undergoes heat treatment.