Reducing Cement Clinker Sintering Temperature Using Fluorine-Containing Semiconductor Waste

This study investigated the potential use of fluorine-containing semiconductor industrial sludge as a mineralizer in Portland cement clinker production. Raw mixes were prepared by partially replacing raw materials with 6%, 9%, and 12% sludge and sintered between 1300 and 1500 °C. The clinker burnability, phase composition, and chemical integrity were evaluated through FreeCaO measurements, X-ray diffraction (XRD) with Rietveld refinement, and X-ray fluorescence (XRF) analyses. The results showed that sludge addition reduced the sintering temperature by up to 150 °C, enabling near-complete clinker formation at 1300 °C for blends containing 9% and 12% sludge (FreeCaO ≤ 0.6 wt.% compared to 62 wt.% in the reference sample). Fluorine incorporation stabilized the re-active β-C₂S polymorph and shifted the alite (C₃S) phase distribution from stable M1 to metastable M3 and T3 phases. Additionally, the C₃A phase content decreased, and a unique fluorine-containing phase, Al₇Ca₆O₁₆F, formed, promoting clinker formation. Lowering the sintering temperature led to energy savings of 15-22.5% and reduced CO₂ emissions by 0.10-0.20 tons per ton of clinker, positively impacting the environment. This study demonstrates that recycling industrial sludge can enhance cement production efficiency and support environmental sustainability.