Abstract Arsenic (As)-contaminated drinking water is a major problem around the world. The removal efficiency depends strongly on the size of Fe3O4 sorbents.Fe3O4 prepared in laboratory is more efficient in the removal of As and is also more easily recovered from column of magnetic separator than the commercial materials. This would be beneficial in a water treatment system because the As-contaminated Fe3O4 could be flushed from the column permitting reuse of the separator system. The dispersed Fe3O4 nanocrystals can be removed from the solution through interactions with a magnetic column. The 20 nm commercially made nanocrystals were permanently retained in the column and could not be recovered, while the laboratory prepared nanocrystals were able to be recovered when the magnetic field was turned off.