BACKGROUND　Iron　(Fe)-containing　groundwater　treatment　residual　is　a　kind　of　waste　from　groundwater　treatment　plants,　showing　good　potential　to　be　reused.　Attention　has　been　paid　to　Fe-based　magnetic　water　treatment　materials　for　their　easy　magnetic　separation,　and　in　the　meantime,　kinds　of　adsorbents　were　developed　to　address　the　severe　global　dyes　pollution.　RESULTS　Black　magnetic　material　was　obtained　with　using　the　iron-containing　wastes　as　iron　source　without　adding　other　iron　chemical　reagents　by　hydrothermal　reaction.　The　X-ray　diffraction　(XRD),　X-ray　photoelectron　spectroscopy　(XPS)　and　Fourier-transform　infrared　(FTIR)　results　show　that　the　product　is　comprised　of　crystalline　iron(II,III)　oxide　(Fe3O4)　core　and　amorphous　carbon　shell　(Fe3O4@C),　and　the　core-shell　structure　can　also　been　seen　clearly　in　transmission　electron　microscopy　(TEM)　images.　Vibrating　sample　magnetometer　(VSM)　result　shows　its　saturation　magnetization　is　33.56　emu/g.　This　sample＇s　sorption　experiments　for　methylene　blue　(MB)　removal　were　conducted,　and　the　experiment　results　indicated　that　this　sample　could　be　used　in　a　wide　range　of　pH　(5-12)　and　the　adsorption　might　be　a　complex　chemical　diffusion　process　consisting　of　boundary　layer　effect　due　to　kinetic　modeling　fitting　analysis.　The　maximum　sorption　amount　of　MB　was　16.33　and　19.13　mg/g,　respectively　at　298　K　and　308　K.　This　sample　after　five　regeneration　cycles　still　had　72.1%　MB　removal　rate.　CONCLUSION　The　Fe3O4@C　particles　with　good　magnetism　were　synthesized　successfully　with　Fe-containing　water　treatment　residuals,　water　treatment　waste　sludge,　via　a　one-step　hydrothermal　reaction,　which　could　be　of　reasonable　analogy　for　treating　other　Fe-containing　industrial　waste.　Furthermore,　this　sample　could　be　used　as　adsorbent　for　MB　molecules　removal　from　dyed　water　with　good　reusability　and　easy　magnetic　separation.　(c)　2019　Society　of　Chemical　Industry