The utilization of mine waste, such as Coal Gangue (CG), as a binding material to stabilize Black Cotton Soil (BCS), holds greater significance in waste management and sustainable engineering. However, CG does possess a mixture of heavy metals that could affect surrounding ecosystem of improvised soils. In order to suggest these binders, understanding the mobility of these heavy metals is of prime concern. Literature suggests geo-polymerization of different waste binders is an effective remedy to encapsulate the heavy metals. To confirm the effectiveness of geo-polymerization, evaluating the leaching behavior of BCS stabilized with coal gangue and coal gangue-based geopolymers is of primary importance. A combination of Sodium Silicate (Na2SiO3) and Sodium Hydroxide (NaOH) in equal proportions was used as an alkali activator, with the activator-to-binder ratio of 0.5 and NaOH of 10 M for geo-polymerization. However, from preliminary testing addition of CG-based geopolymer alone is found to have limited improvement in contaminant encapsulation and hence thermal treatment (calcination) is adopted for effective geo-polymerization. Accordingly, BCS samples treated with calcinated coal gangue (CCG)-based geopolymer were also included as part of this study. To understand the leaching potential of modified soils various testing procedures like column test, batch tests, and toxicity characteristics leaching process (TCLP) are available. To conduct TCLP tests, two different extraction fluids are to be used for treating improvised soils according to their pH levels. For this purpose, in this study, pH of different combination of BCS improved using varying proportions of CG, CG-based geopolymer, and CCG-based geopolymer are evaluated. Further, alongside pH, the electrical conductivity of modified soils is also evaluated to understand the chemical characteristics of the modified soils. Such a study helps us in preliminary understanding of the environmental effects of BCS treated with CG.