<p>In-situ injection is recognized as the most efficient method for remediating sites contaminated with heavy metals. The injection parameters and the layout of the injection well group significantly influence the effectiveness of in-situ injection. This study involved the in-situ injection of B-K-nZVI (Bentonite suspension with kaolin-supported nZVI) remediation agent at a cadmium (Cd)-contaminated smelting site. The colloidal filtration theory and the chemical reaction kinetic equation of the remediation agent were incorporated into the migration model. Numerical analysis software was employed to investigate the effects of injection pressure, permeability coefficients, spacing between injection wells, and well group layout on the remediation rate at the Cd-contaminated site. The results indicated that the permeability coefficients of the B-K-nZVI remediation agent in various zones were 0.247&#xa0;m/d, 0.297&#xa0;m/d, and 0.395&#xa0;m/d, with corresponding theoretical injection pressures of 899&#xa0;kPa, 613&#xa0;kPa, and 510&#xa0;kPa, respectively. The migration model of the remediation agent, which considered the chemical reaction process, more accurately represented the actual conditions of injection remediation. The changes in concentration of both the contaminant and the remediation agent within the monitoring wells can be classified into three distinct phases: diffusion, reaction consumption, and stabilization. The influence of injection pressure and permeability coefficients exhibited a similar pattern, primarily modifying the diffusion rate of the remediation agent. The highest remediation rate (96.90%) was observed with well group layout 2 (7 wells) at a well spacing of 10&#xa0;m, whereas the lowest remediation rate (74.98%) occurred with well group layout 1 (5 wells). These findings could provide effective ideas for the remediation of heavy metal contaminated smelting sites through in-situ injection.</p> Graphical Abstract <p></p>