The influence of heavy metals on the polymorphs of dicalcium silicate in the belite-rich clinkers produced from electroplating sludge

The purpose of this study is to utilize an electroplating sludge for belite-rich clinker production and to observe the influence of heavy metals on the polymorphs of dicalcium silicate (C 2S). Belite-rich clinkers prepared with 0.5–2% of NiO, ZnO, CuO, and Cr 2O 3 were used to investigate the individual effects of the heavy metals in question. The Reference Intensity Ratio (RIR) method was employed to determine the weight fractions of γ-C 2S and β-C 2S in the clinkers, and their microstructures were examined by the transmission electron microscopy (TEM). The results showed that nickel, zinc, and chromium have positive effects on β-C 2S stabilization (Cr 3+ > Ni 2+ > Zn 2+), whereas copper has a negative effect. The addition of up to 10% electroplating sludge did not have any negative influence on the formation of C 2S. It was observed that γ-C 2S decreased while β-C 2S increased with a rise in the addition of the electroplating sludge. Moreover, nickel and chromium mainly contributed to stabilizing β-C 2S in the belite-rich clinkers produced from the electroplating sludge.