Reactivity of low grade kaolinitic clays. Impact of accompanying minerals on calcination

Abstract

Low grade kaolinitic clays have become the center of attention of the cement industry, because of their capacity of providing a reactive Supplementary Cementitious Material, SCM and their wide availability in various geographies. Most common are iron bearing phases such as Goethite or Hematite and sulphur bearing phases such as Alunite or Pyrite. During calcination these phases may have some interaction with the other components and influence calcined clay performance, mainly reactivity. This paper discusses the impact of iron phases on phase assemblage of the calcined product and how this could influence reactivity. Several clays with a varied composition were studied. They were calcined at lab and industrial conditions. The investigation included Q‐XRD and Moessbauer tests to identify the new phases formed, as well as the evaluation of the reactivity of the calcined product. Recommendations on how to mitigate its impact are made.