Process Residues in Cement Clinker Production: A Review

Portland cement (PC) production accounts for about 8 % of global CO2 emissions. As the demand for cement grows, sustainable alternative raw materials for cement production are essential for reducing the impacts of its production. Process residues from industrial processes like mine tailings, metallurgical slags, incinerated municipal solid wastes (MSWI), glass industry wastes, and Kraft pulp mill wastes are being studied as suitable raw materials for clinker production. These materials contain CaO, SiO2, Al2O3, and Fe2O3, which are required for the formation of tricalcium silicate (C3S, alite), dicalcium silicate (C2S, belite), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF) clinker phases. However, these raw materials may contain impurities such as alkali oxides and heavy metals, which can significantly influence the clinkering process. While alkali oxides tend to lower the eutectic temperature, heavy metals can modify phase stability and hinder the formation of essential clinker phases. This review examines whether these residues are chemically and mineralogically suitable for alternative raw materials. It examines their impact on phase transformations, reactions, environmental sustainability, hydration and performance of the resultant cement. Process residues in clinker production present challenges and opportunities, affecting hydration, workability, and setting times. However, research remains limited to the combined effects of multiple residues on clinker reaction kinetics, durability, heavy metal stabilization, and life cycle impacts.