Slag or Reacted Binder, Which Dissolves First in Sulphuric Acid?

To boost the usage of non-ferrous metallurgy slag (NFS) into alkali activating material (AAM), durability analysis of NFS-based AAM is needed. For this purpose, the dissolution behaviour of NFS-based AAM in sulphuric acid was investigated. In order to answer the question whether unreacted slag in the NFS-AAM structure is the weak part during acid exposure, dissolution experiments were conducted both on raw NFS and NFS-based AAM paste sample. The results suggested that both NFS and reacted binder dissolve in sulfuric acid. The dissolution of the raw NFS was, however, significantly faster and to a greater extent than that of the AAM paste. For the raw slag, almost all Si and Ca were detected in the solution, while about 80% Fe and Al were dissolved after exposure to sulphuric acid. The lower values, compared to Ca and Si, could be due to the undissolved crystal phases or precipitation. For pastes, 88% Ca, 79% Fe and 75% Al ended up in sulphuric acid solution, while only 60% of Si was dissolved. This corresponds approximately to 100% minus the reaction extent of the slag, suggesting low Si dissolution from the AAM binder. This can be explained by the presence of a highly polymerized silicate network with high acid resistance. The results confirm the importance of the slag structure and reacted amount of slag on the sulphuric acid resistance of NFS-AAM. The findings here are instrumental in providing solutions to improve sulphuric acid resistance of NFS-AAM.