<p>This study presents a novel synthesis of amino-modified X zeolite (NH₂–NaX) derived from low-grade coal gangue via an alkaline fusion-hydrothermal method coupled with a grafting technique. The material was systematically evaluated for its adsorption performance toward lead (Pb) and cadmium (Cd), its efficacy in immobilizing these metals in contaminated soil, and its long-term stability under simulated acid rain leaching. Batch adsorption experiments demonstrated high maximum capacities of 214.123 mg/g for Pb and 256.740 mg/g for Cd. Adsorption kinetics followed a pseudo-second-order model, indicative of a chemisorption-dominated process, while the Freundlich isotherm provided a superior fit over the Langmuir model, suggesting multilayer adsorption involving physiochemical interactions. A 30-day soil incubation revealed that NH₂–NaX application significantly increased soil pH from an initial 6.4 to a range of 7.42–8.13 and effectively reduced the bioavailable fractions of Pb and Cd. The amendment promoted the transformation of exchangeable Pb and Cd into more stable residual and reducible fractions, with an optimal dosage identified at 1.5% (w/w). Dynamic leaching experiments under simulated acid rain (pH 5.0) confirmed that NH₂–NaX substantially reduced the cumulative release of both metals. Speciation analysis post-leaching showed a marked increase in residual/reducible fractions and a controlled rise in exchangeable metals compared to the untreated control, demonstrating effective inhibition of metal remobilization. These findings collectively establish gangue-based NH₂–NaX as a highly efficient, stable, and sustainable amendment for the immobilization of Pb and Cd in multi-metal contaminated soils.</p>