This study aims to develop the limestone calcined clay (LC3) as a low-carbon treatment to immobilize waste ferronickel slag (FNS) containing heavy metals. The results indicate that the ordinary portland cement (OPC) and limestone calcined clay cement (LC3) adequately immobilized the Chromium (Cr), with the leaching results of 0.10-0.30 mg/L. The LC3 cement provided superior Mn immobilization (lower than 5 mg/L) compared to OPC. Calcium aluminum silicate hydrate (C-A-S-H) and ettringite (AFt) were the two main hydrated products of LC3 that ensure the capacity to encapsulate metals. The LC3 specimens had the lower porosity between 50 and 10,000 nm compared to that of OPC. The Embodied Energy (EE) and Embodied Carbon Emissions (ECO2e) of per m3 LC3 remarkably decreased by 38.21% and 44.77%.