Optimising the recovery of high-value-added ammonium alum during mineral carbonation of blast furnace slag

Abstract

A route for the indirect mineral carbonation of blast furnace slag (BFS) with (NH4)2SO4 as a recyclable reagent has been proposed recently. To improve the economy of the process, an improved recovery route was put forward herein, guided by thermodynamic studies and phase diagrams. A purer, and thus higher-value-added byproduct, ammonium alum, can be obtained during the mineral carbonation of BFS. The effects of parameters such as roasting temperature and time, mass ratio of liquid to solid during leaching, and crystallisation temperature were investigated systematically. The results showed that the extraction reaction of BFS with ammonium sulfate occurred not only in the roasting stage but also in the leaching stage. The purity and recovery of aluminium as NH4Al(SO4)2·12H2O can reach 99.6% and 73%, respectively, at the optimal conditions. A preliminary economic evaluation predicted that this route can achieve 2.5 times the profit of the original process.