Solidification behavior of the FeOt-SiO2-CaO-Al2O3-(ZnO) slag system

Abstract

Slag solidification behavior significantly influences the tapping of the Zn fuming process and slag valorization. In this work, the effect of ZnO and CaO concentration on slag solidification was investigated under a pO2 of approximately 10−10 atm using confocal laser scanning microscopy (CLSM) at various cooling rates. It was concluded that in the low CaO slag, the ZnO increased the onset formation temperature of the fayalite phase. An increase in CaO concentration facilitated wustite precipitation and prevented spinel formation in the slag at cooling rates exceeding 1 °C/s, while it enhanced melilite generation and inhibited fayalite precipitation in the slag at cooling rates below 1 °C/s. Furthermore, the slag mineralogy was studied as a function of equilibration temperature and CaO concentration of the slag through water quenching experiments under the Ar atmosphere. When slags with a CaO concentration of 3–20 wt% were quenched from 1050 to 1200 °C, the amorphous and spinel phases were observed in all quenched slags, whereas the wustite phase was only identified in slags with a CaO concentration above 10 wt%. Additionally, the fayalite phase was detected in slags containing 3–5 wt% CaO, quenched at temperatures of 1150–1050 °C. Notably, as the quenching temperature decreases and the CaO concentration increases, the observed phases in the quenched slag become more complex, and the solid particles grow coarser. The FeOt-SiO2-(4.7–5.7 wt%)ZnO-(8.3–10.1 wt%)Al2O3–CaO-1.3 wt%MgO-1.1 wt%Cr2O3 (FeO/SiO2 = 1.44) slags with a CaO concentration of below 20 wt% is suggested to be quenched from 1150 °C or 1200 °C to prevent the precipitation of a SiO2-containing phase and coarse wustite.