Abstract
The purpose of this work was to study the feasibility at laboratory-scale of a new hydrometallurgical process for treating electric arc furnace dusts (EAFD). The proposed process is intended to extract zinc and lead from EAFD without destroying the iron oxides matrix. So, this material can be recycled by the steel industry. Independently of the origin of the samples, major mineralogical forms present in these wastes are Fe 3O 4, ZnO, ZnFe 2O 4 and PbOHCl. The proposed process consists of a hydrometallurgical treatment of wastes based on selective leaching of zinc and lead. Initially, a leaching is carried out utilizing a chelating agent, nitrilotriacetate anion (NTA 3−), as the protonated form HNTA 2−. Treatment of five EAFD samples for an hour at room temperature with a molar solution of reagent results in total leaching of the ZnO. In all cases the solubilized iron does not exceed 3 wt.%. The recovery of zinc and lead is performed by precipitation of metallic sulfides with a solution of Na 2S 4 sodium tetrasulfide 2 M. These metallic sulfides can be used as metallurgical raw materials and the chelating reagent can be reused in the process after pH adjustment. The results of the normalized leaching test AFNOR X31-210 conducted on the leaching residues, shows that all the samples meet acceptance thresholds for hazardous wastes landfill. However, the residues contain a considerable amount of zinc as ZnFe 2O 4. The extraction of the zinc element requires the destruction of the ferrite structure. In this process, ZnFe 2O 4 is treated by FeCl 3·6H 2O. The reaction consists in a particle O 2−/Cl − exchange allowing the recovery of zinc as ZnCl 2 and iron as hematite Fe 2O 3. The separation of these products is accomplished by simple aqueous leaching. All of the zinc is extracted in a 8 h treatment at 150 °C with a molar ratio FeCl 3·6H 2O/ZnFe 2O 4 equal to 10. Ultimate solid residues, which have been concentrated in iron, can be oriented towards the steel industry.
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