Characterization of sinter flue dust to enhance alternative recycling and environmental impact at disposal

Dust emission is one of the main environmental pollution impacts associated with steelmaking. In this sense, electrostatic precipitators (ESP) are regarded as the best available technique for treating this type of emission, thus generating two differentiated fractions: coarse and fine. Thorough chemical and structural characterization of both materials was carried out to recycle these byproducts in either the sintering process or other steps of pig iron production. Both types of dusts are crystalline heterogeneous materials mainly composed of sepiolite (Mg₈Si₁₂(OH)₂·12H₂O), hematite (Fe₂O₃) and calcite (CaCO₃), the coarse fraction containing low amounts of Na (0.38 ± 0.04%) and K (0.17 ± 0.02%), which adversely affect blast furnace operation. Hence, the coarse fraction is suitable for recycling, whereas the fine one presents higher concentrations of these alkali elements. Besides, textural characterization revealed that dust particulates are essentially macroporous materials, with specific surface area values of 21.6 m²/g for the coarse fraction and 33.7 m²/g for dust fines. In order to ensure inoffensive dumpsites, the environmental behavior associated with dust particles accumulated in disposal areas was also evaluated by performing leaching studies simulating different rainfall scenarios. It was found that the specific leaching rates of Ca, Mg, K and S varied between 0.072 ± 0.001 and 0.75 ± 0.01 µg_element/(g_dust·d), whereas slower leaching rates were obtained for heavy metals (Fe, Mn and Cu), the values ranging from (1.20 ± 0.1) × 10^-4 to (1.8 ± 0.1) × 10^-3 µg_element/(g_dust·d). These low rates indicate that the leaching of sinter dusts compounds has minimal environmental impact.