Utilization of reduction slag and waste sludge for Portland cement clinker production

The feasibility of recycling the reduction slag, limestone sludge, iron-oxide sludge, and stone sludge produced in the manufacture of cement was investigated through compressive strength testing, differential thermal and thermogravimetric analysis, X-ray diffraction, and 29Si nuclear magnetic resonance analysis. The major crystalline phases of ecocement clinkers, namely C3S, β-C2S, C4AF, and C3A, were observed. C3S content decreased and β-C2S and α-C2S content increased in the reduction slag. The compressive strength of EcoA pastes (ecocement contain 78% of limestone sludge, 19.51% of stone sludge and 2.49% iron-oxide sludge) was similar to that of commercial ordinary Portland cement. The Q0 (−70 ppm) species shifted to the Q1 (−80 ppm), and Q2 (−87 ppm) species during curing. The addition of stone sludge, iron-oxide sludge, and limestone sludge had no negative effect on the hydration of the cement pastes. In contrast, the addition of reduction slag negatively affected the formation of clinker minerals. Cement samples with reduction slag content of 1–7 wt % had lower 28-, 60-, and 90-day compressive strength than did the control mix. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 669–677, 2018