Recovery of Pb and Zn from a citrate leach liquor of a roasted EAF dust using precipitation and solvent extraction

Abstract

Electric arc furnace (EAF) dust is globally one of the biggest metal-containing waste fractions, with a composition that challenges the recycling of dust back to the steel process due to the high Zn and Pb content, which also prevents it from being landfilled. The current study presents a process flowsheet with zinc and lead removal from EAF dust via citric acid leaching, lead removal by precipitation, and further solvent extraction (SX) of zinc for recovery. The process produces fractions that can be directly routed back to a steel plant (leach residue), a zinc electrowinning process (pregnant leach solution, PLS), and a lead smelter (lead sulfate, PbSO4 precipitate). Moreover, zinc separation by solvent extraction from citric acid leach solution originating from EAF was performed successfully with minimal impurity content in the final electrolyte, using di(2-ethylhexyl)phosphoric acid (D2EHPA). The total lead removal from PLS was achieved with an addition of only 0.012 M sulfate ion (from sulfuric acid) at room temperature. The optimization of zinc separation via SX was performed at a temperature range of 25–55 °C varying the D2EHPA concentration (10–25 vol-%) with different O/A ratios. With an optimized EAF SX process (pH = 5, t = 15 min, T = 25 °C, CD2EHPA = 20 vol-%, O/A = 1:1) and stripping process (t = 15 min, T = 25 °C, CH2SO4 = 1 M, O/A = 3:1), the zinc content in the electrolyte could be enriched up to 50 g/L, and the amount of impurities in the solution decreased down to a level where they have no adverse effect on the zinc electrowinning process and final zinc recovery. Moreover, the iron-rich leach residue was also shown to be chemically suitable as a raw material for the EAF process. With the proposed roasting-leaching-precipitation-SX-EW unit operation, EAF dust can be converted into three different secondary raw material streams, suitable for integration into state-of-the-art processes.