Effect of Linz-Donawitz slag addition on the hot stage slag mineralogy and fuming conditions: Output slag modification during the industrial Zn fuming operation

Abstract

Up to 39.35 wt% of CaO-rich Linz-Donawitz (LD) slag was gradually added to copper slag during an industrial Zn fuming process to investigate the influence of CaO content on the Zn fuming efficiency and slag high-temperature mineralogy. Multiple slag samples were taken from a standard fuming process and an LD slag modified fuming process. Microstructure analysis revealed that the fuming bath was primarily composed of the liquid phase and a small number of spinel particles prior to LD slag addition. In contrast, an additional wustite phase was observed after the LD slag addition. According to the FactSage simulation, the bath temperature in the standard fuming process was between 1139 and 1180 °C and the oxygen level was around 1 × 10−13 - 5 × 10−14 atm. Upon the addition of LD slag, the temperature decreased to 1085–1140 °C, while the pO2 increased to 1 × 10−12 - 5 × 10−13 atm. An increase in LD slag content facilitated the decomposition of fayalite and spinel phases, the generation of metallic Fe under pO2 of 1 × 10−13 atm, the formation of wustite under pO2 of 1 × 10−12 atm, and the precipitation of melilite. The optimal fuming conditions for Zn recovery and slag modification without Fe formation were pO2 of 1 × 10−12 atm, the temperature of 1168–1210 °C and an LD slag content of 28.6 wt%. Under these conditions, the CaO content in the liquid phase can reach approximately 20 wt% and ensure that the fumed slag is a suitable raw material for cementitious materials production.