Nano-iron　has　received　extensive　attention　in　the　repair　of　contaminated　soil　and　groundwater.　In　order　to　further　explore　its　migration　behavior　in　porous　media,　nano-zero-valent　iron　(nZVI)　was　coated　with　sodium　carboxymethyl　starch　(CMS),　and　the　sedimentation　test　of　modified　nano-zero-valent　iron　was　carried　out.　The　zeta　potential　and　particle　size　distribution　were　measured　to　explore　its　dispersion.　The　column　experiments　of　modified　nano-zero-valent　iron　in　pickled　sand　and　washed　sand　under　different　pH　conditions　were　carried　out.　The　effects　of　chemical　heterogeneity　and　pH　on　the　migration　of　nano-iron　in　porous　media　were　analyzed.　The　results　showed　that　CMS　coated　nano-iron　not　only　stabilizes　the　nanoparticles　themselves,　but　also　reduces　their　deposition　on　the　surface　of　porous　media,　which　greatly　improves　the　mobility.　When　pH=6　to　8,　the　zeta　potential　of　nZVI　was　reduced　from　18.3mV　to　2.9mV,　the　effective　particle　size　increased　from　685nm　to　880nm,　and　the　stability　was　deteriorated.　When　the　zeta　potential　of　CMS-nZVI　increased　from　-19.7mV　to　-53.5mV,　the　electrostatic　repulsion　between　particles　was　enhanced　and　the　stability　was　improved.　According　to　energy　dispersive　spectroscopy　(EDS)　analysis,　there　were　oxide　impurities　such　as　carbon,　aluminum　and　iron　on　the　surface　of　the　washed　sand.　These　impurities　have　a　positive　charge,　which　will　enhance　the　adsorption　of　negatively　charged　CMS-nZVI,　which　is　not　conducive　to　its　migration.　After　pickling　quartz　sand,　the　surface　impurities　were　greatly　reduced.　At　pH=8,　the　maximum　mobility　of　CMS-nZVI　in　pickled　sand　was　77.0%,　which　is　63.0%　better　than　that　of　washed　sand.　In　addition,　the　higher　pH　environment　helps　to　increase　the　surface　negative　charge　of　the　quartz　sand　medium,　reduce　the　adsorption　of　particles　and　the　medium,　and　promote　the　migration　of　the　nanoparticles.　©　2020,　Chemical　Industry　Press.　All　right　reserved.