Insights into the Roasting Kinetics and Mechanism of Blast Furnace Slag with Ammonium Sulfate for CO2 Mineralization

Abstract

A route for the indirect carbonation of different minerals using (NH4)2SO4 (AS) as a recyclable reagent has been recently proposed. For saving energy, the extraction of alkaline components, such as calcium and magnesium, is typically expected to occur at the roasting stage. To enhance the extraction efficiency, the kinetics and mechanism of the reaction between AS and blast furnace slag (BFS), a Ca/Mg-containing mineral, were investigated in this study. The results showed that the reaction consists of two steps: the decomposition of AS into ammonium bisulfate (ABS) and the reaction between the ABS and the BFS. Isothermal kinetics and equal conversion methods were used to determine the apparent activation energy and reaction-controlling steps in different temperature ranges. The results showed that the decomposition of AS was a chemical-reaction-controlled step with an apparent activation energy of 102 kJ·mol-1. On the other hand, the reaction between ABS and BFS, which was very quick, was controlled by the ABS supply. During the reaction, a product accumulation layer was generated around the nonreactive BFS particles. However, it was found that ABS can easily pass through this layer and react with the BFS core. The formation of ABS was the limiting step in the roasting process.