Phase Transformation and Zinc Extraction from Zinc Ferrite by Calcium Roasting and Ammonia Leaching Process

Abstract

Zinc ferrite (ZnFe2O4), one of the major forms of zinc in electric arc furnace dust and zinc leaching residue, is very difficult to chemically dissolve in either acidic or alkaline solutions. It is therefore necessary to study the extraction of zinc from zinc ferrite to achieve the full recovery of the zinc resources. In this paper, CaO was used to degrade the structure of zinc ferrite and then the ammonia leaching method was applied to recover zinc. The thermodynamic analysis indicated that the zinc ferrite could react with CaO to form zinc oxide and dicalcium ferrite. The CaO–Fe2O3–ZnO phase diagram shows that Ca2Fe2O5 can be in equilibrium with ZnO rather than ZnFe2O4 at a higher CaO area. The experimental results indicated that the phase transformation of zinc ferrite, reacted with CaO, to zinc oxide and dicalcium ferrite could be completely achieved with a CaO addition of 2.4:1 (mole ratio). The peaks of zinc ferrite in the X-ray diffraction (XRD) patterns cannot be clearly observed after calcium roasting at 1220 °C for 2 h. The ammonia leaching tests showed that the zinc leaching rate was about 90% under optimal roasting conditions.

Mineral Phase Reconstruction and Separation Behavior of Zinc and Iron from Zinc-Containing Dust

“…The phase transformation of zinc ferrite by calcium roasting was reported in our previous paper [38]. The effect of the calcium oxide to dust ratio on the calcination product phase composition of the EAF dust was studied under a roasting temperature of 1150 °C and a roasting time of 2 h. Figures 2-4 are the XRD patterns of the roasted samples with 40%, 50%, and 60% calcium oxide ratios, respectively.…”

“…The mixture was pressed into cylindrical pellets, and then loaded into a corundum boat and roasted in a horizontal tube furnace at roasting temperatures. The selection of the roasting temperature and CaO additions was referred to in our previous paper [38]. We studied temperatures of 1150 • C, 1200 • C, 1250 • C, and 1300 • C. The CaO addition ratios were 40%, 50%, and 60% with respect to the dust.…”

“…The main phases of the roasting product at a 40% ratio were dicalcium ferrite (Ca 2 Fe 2 O 5 ), residual unreacted zinc ferrite (ZnFe 2 O 4 ), and a small amount of newly generated zinc oxide. According to thermodynamic analyses [38], under standard conditions, the ∆G of the formation reaction of calcium oxide and ferric oxide to calcium ferrite is much lower than the ∆G of the reaction of calcium oxide and zinc ferrite to calcium ferrite and zinc oxide, indicating that the added calcium oxide first reacts with iron oxide to form dicalcium ferrite. The obvious zinc ferrite peaks in the XRD indicated that 40% calcium oxide was insufficient to achieve a complete reaction of the zinc ferrite.…”

“…Many investigations have reported that zinc ferrite could be decomposed by hightemperature roasting with the addition of lime [29,[35][36][37]. The recovery of zinc from synthetic zinc ferrite by calcium roasting and ammonia leaching was reported in our previous paper [38]. The raw material in our previous paper [38] was synthesized zinc ferrite (ZnFe 2 O 4 ) without other elements and oxides.…”

“…The recovery of zinc from synthetic zinc ferrite by calcium roasting and ammonia leaching was reported in our previous paper [38]. The raw material in our previous paper [38] was synthesized zinc ferrite (ZnFe 2 O 4 ) without other elements and oxides. Zinc-containing dust from steel companies generally contains CaO, SiO 2 , MgO, Al 2 O 3 , and other oxides.…”