Pb-Zn Smelter Residue (LZSR) Stabilized Using Low-Carbon, Low-Cost Limestone–Calcined Clay Cement: Leachability, Chemical Speciation, Strength, and Microstructure

Abstract

The low-carbon and low-cost cement known as limestone–calcined clay cement (LC3) is used in this study to investigate the immobilization potential of Pb-Zn smelter residue (LZSR). The performance of LC3 treatment on LZSR was determined through a series of experiments, including pH, unconfined compressive strength (UCS), toxicity characteristic leaching procedure (TCLP), Community Bureau of Reference sequential extraction procedure (BCR-SEP), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy along with energy dispersive spectroscopy (SEM-EDS). The findings show that, after 14 days curing, the transition in the pH from acid to alkaline increases the UCS up to 2.5–3.6 times compared with untreated specimens. The leached concentrations of Pb, Zn, and Cd decreased considerably with increasing binder and curing time. Chemical speciation analysis showed that >50% of bioavailable phases (acid-soluble and reducible phases) were transformed into less soluble (oxidizable and residual) phases. The XRD and SEM-EDS analysis demonstrated that the formation of favorably insoluble alite (Ca3SiO5), meionite (Ca4Al6Si6O24CO3), and portlandite (Ca(OH)2) was responsible for the immobilization of Pb, Zn, and Cd. As a result, LC3 supports the green and sustainable remediation approach for the immobilization of heavy metals for the potential valorization of LZSR.