Selective separation of zinc and iron/carbon from blast furnace dust via a hydrometallurgical cooperative leaching...

Blast furnace dust (BFD) contains ferrous and nonferrous metals and carbon, and is usually categorized as a typical secondary resource and hazardous waste produced by the iron-making process. The thermodynamic calculation and experimental investigation of the selective separation of zinc and iron/carbon from BFD via a NaCl-HCl-H₂O system were carried out. Quantitative zinc and iron/carbon separation and recovery was achieved via a zinc-chloride (ZnCl_i^2-i (i = 0, 1, 2, 3, 4)) cooperative leaching methodology using 3 mol/L NaCl at pH of 4, an L/S ratio of 4:1, a leaching temperature of 70 °C, a HCl concentration of 0.25 mol/L, and a leaching time of 2 h. Moreover, the total Cl^- concentration used in for leaching was 2.09 mol (as concluded by the dosages of HCl and NaCl, and material). Results demonstrate that zinc was effectively leached from BFD, while the leaching of iron was hindered, in the acidic region. 93.2% of the zinc was extracted into a leaching solution containing 19.8 g/L zinc under the optimal conditions, and the ratio of the leaching agent to BFD was 300 mL to 75 g. The XRD and SEM-EDS analysis results of the residue reveal that ZnO and ZnS were leached, and the zinc-iron spinel (ZnFe₂O₄) was not leached and was present together with the iron oxide in the leaching residue. Iron and carbon in the leaching residue was enriched from 49.4% to 60.38%, and the iron and carbon were recovered as secondary resources that can be reused in the iron-making system.