The containment of contaminants in landfill environments is crucial for groundwater protection and environmental sustainability. Traditional landfill liners, typically composed of clay or bentonite, face limitations in contaminant adsorption and structural stability under varying environmental conditions. This study investigates enhanced landfill liners by incorporating Granular Activated Carbon (GAC) and diatomaceous earth (DE) into bentonite mixtures to improve contaminant immobilization and mechanical performance. Laboratory experiments evaluate the basic properties of the materials, followed by permeability tests to assess the composite liner mixtures. Adsorption capacities and mechanical properties are further analyzed for varying proportions of bentonite, GAC, and DE. These additives are expected to significantly enhance the immobilization of heavy metals, improving the liner’s efficiency in preventing leachate migration. The modified liners are anticipated to demonstrate improved contaminant retention, reduced permeability, and enhanced structural stability compared to conventional clay liners. Integrating GAC and DE into landfill liners offers a sustainable and efficient strategy for mitigating leachate leakage, ensuring better landfill performance and environmental safety.