Recovery of valuable metals from argon oxygen decarburization (AOD) dusts by leaching, filtration and solvent extraction

• Zn and Mo were identified as the most valuable metals for recovery from two AOD dusts.
• Leaching selectivity of target metals was greatly improved by pH control.
• D2EHPA was found to be a selective extractant for recovery of Zn.
• Pure Mo/Cr mixture product was achieved with three extractants.
• Best Mo/Cr selectivity was achieved with quaternary ammonium salt Aliquat 336.

For each ton of steel produced from a typical steelmaking plant, up to several tens of kilograms of dust, containing significant amounts of valuable and/or environmentally harmful metals, are also produced. A hydrometallurgical route for the recovery of these metals from argon oxygen decarburization (AOD) dusts, with selective leaching, filtration and solvent extraction was studied experimentally. Batch leaching of dusts with concentrated H2SO4 was found to be difficult to optimize for yields for the target metals (Zn and Mo), while keeping Fe in the solid phase. Zn and Mo could be recovered with comparable yields, while keeping Fe totally undissolved, by controlled leaching at pH above 3. Water was successfully used to leach Mo with 45% yield, while Ca, K, Cr, Mg, Pb, and Mn were leached as impurities. It was found that solid/liquid separation of the undissolved solids by pressure filtration was challenging and it was further observed that the properties of the initial dusts have a strong influence on this process step. D2EHPA was found to provide good extraction selectivity for Zn from acidic leaching solutions, except over Fe. A pure Mo/Cr mixture was extracted with hydroxyoxime LIX 84-I, trioctylamine TOA and quaternary ammonium salt Aliquat 336. The best Mo/Cr selectivity was achieved with Aliquat 336.