Atmospheric leaching of EAF dust with diluted sulphuric acid

T. Havlik et al. / Hydrometallurgy 77 (2005) 41–50 49aMetal extraction [%]80604020Zn extraction; a/d = 1.2Fe extraction; a/d = 1.2bMetal extraction [%]80604020Zn extraction; a/d = 0.4Fe extraction; a/d = 0.4020 40 60 80Temperature [ • C]020 40 60 80Temperature [ • C]Fig. 10. (a) Dependency of metal extraction vs. leaching temperature at a/d=1.2. (b) Dependency of metal extraction vs. leaching temperature ata/d=0.4.temperature/pressure leaching). This is the reason thatonly a small amount of calcium remains in the solution.Fig. 10a to b show the dependencies of metalextraction on the leaching temperature for the highestand lowest dust charge, each in relation to theamount of acid available for the leaching. For thelowest charge amount of a/d=1.2, the zinc extractionis higher having the tendency to increase at a highertemperature. Yet, when using the lowest chargeamount, also the quantity of the dissolved iron ishigher compared to a/d=0.4. The comparison withthe experiment at 100 8C, presented in work (Havliket al., 2004), reveals that this, under normal temperature/pressureconditions, is the optimum temperaturefor the maximal zinc extraction. However, theamount of extracted iron is several times higher at100 8C than at 80 8C. It seems that higher values ofselectivity are obtained by lower temperature and,perhaps, a/d ratios.4. ConclusionAccording to the results obtained in this work, thehydrometallurgical recovery of zinc from EAF dust isfeasible with a relatively high recovery yield, whileiron mostly stays in solid phase. A similar conclusioncan be drawn in the case of high temperature/pressureleaching under equivalent experimental conditions.Comparing the results of this work with thoseobtained by high temperature/pressure leaching manifestthat, concerning the zinc extraction, the last ismore effective. Yet, this does not relate to iron.Additionally, calcium permanently remains in thesolution. Although in high temperature/pressureleaching calcium is dissolved first, it later precipitatesas calcium sulphate. This does only relate to temperaturesup to 150 8C and pressures up to 4.1 bar. Evenin higher temperatures/pressures leaching calciumpermanently remains in the solution. This behaviourresults from using a low concentration of sulphuricacid. This also causes in fact a decrease in the zincyield, yet the amount of dissolved iron is low. In sucha way, it can be possible to set up the conditions for anoptimum zinc yield into the solution with a minimisediron dissolution. However, the problem persists thatthe chemical and mineralogical composition of eachsteelmaking dust is individual and that for each onethe conditions of processing have to be studied.AcknowledgementThe authors wish to express their gratitude toSlovak grant agency VEGA (Grant 1/9379/02) forfinancial support.ReferencesBarrett, E.C., Nenniger, E.H., Dziewinski, J., 1992. A hydrometallurgicalprocess to treat carbon steel electric arc furnacedust. Hydrometallurgy (30), 59–68.