The　migration　and　immobilization　of　heavy　metals　in　soil　and　groundwater　pose　significant　environmental　challenges,　particularly　in　the　context　of　Cr(VI),　a　highly　toxic　and　mobile　contaminant.　Self-hardening　slurry　materials,　commonly　used　for　trench　cutoff　walls,　have　gained　great　attention　due　to　their　potential　for　pollutant　containment.　However,　the　relationship　between　their　adsorption　properties　and　pollutant　diffusion　behaviors　remains　poorly　understood.　This　study　investigates　the　adsorption　properties　and　free-diffusion　behaviors　of　Cr(VI)　in　two　self-hardening　slurry　materials,　SCB　(slag-cement-bentonite)　and　MASB　(MgO　activated　slag-bentonite),　to　better　understand　the　pollutant　migration　and　immobilization　mechanisms.　Adsorption　experiments　reveal　that　MASB　exhibits　a　higher　Cr(VI)　adsorption　capacity　than　SCB,　resulting　in　greater　retardation　factors　and　longer　breakthrough　times,　improved　by　57.6%　and　94.9%　at　Cr(VI)　concentrations　of　2600　mg/L　and　26000　mg/L,　respectively.　However,　free-diffusion　tests　show　that　MASB　has　a　larger　migration　depth　and　shorter　breakthrough　times,　reduced　by　68.2%　and　57.9%.　Microscopic　analysis　reveals　that　the　presence　of　stable　and　ion-exchangeable　hydration　products　(hydrotalcite-like　phases)　in　MASB　enhances　its　Cr(VI)　adsorption　capacity　but　provides　favorable　conditions　for　Cr(VI)　diffusion.　SCB　demonstrates　superior　retardation　to　Cr(VI)　in　free-diffusion　due　to　the　transformation　of　AFm　phases　absorbed　with　Cr(VI)　into　stable　AFt　phases.　©　2025