Magnetite nanoparticles were produced by the chemical co-precipitation of iron sulfates at alkaline conditions and were tested as a Cr(VI) adsorbent from water. Batch adsorption experiments showed a high removal efficiency, which is maximized at pH values below 6. This behavior was also verified in a continuous flow reactor, where nanoparticles were in contact with the polluted water. In particular, using a particle concentration of 1 g/L in water containing 100 μg Cr(VI)/L, a contact time of at least 2 h was required to achieve complete removal of Cr(VI). The recovery of nanoparticles after their use was accomplished using their magnetic nature. Application of an external magnetic field at the sides of the tube in which the suspension was flowing was sufficient to completely collect the nanoparticles in the outflow of the contact reactor, thus, providing water free of Cr(VI) and a solid phase.