The application of static magnetic fields during adsorption as an unconventional method for the removal of heavy metals such as Cd2+ and Zn2+ was studied in this work. Two different materials were employed as adsorbents: activated carbon from bituminous coal and bone char. The magnetic characterization of these materials reveals that the activated carbon from bituminous coal is a ferromagnetic material, while the bone char is a paramagnetic material. Both adsorbents were used as received; i.e., no additional modification was employed to alter or improve their magnetic properties. Adsorption studies included adsorption isotherms at 30 °C, at pH 5, and equilibrium times of 72 h. The adsorption results obtained depended on the magnetic nature of both the adsorbent and the adsorbate. It was determined that because of its ferromagnetism (hence, its chemical composition), the activated carbon performed better when an external magnetic field was present during the adsorption process. An increase of 63% and 15% in its adsorption capacity was measured for Cd2+ and Zn2+, respectively.

Adsorption is a broadly used process for the removal of heavy metals and the world trend is directed to the application of new technologies to intensify existing processes. The properties of the magnetic field (intensity and arrangement) and the intrinsic magnetic properties of the adsorbent and the adsorbate are decisive for satisfactory results. The intensity of the magnetic field is important, because this implies that the greater number of spins present will align with the magnetic field according to the magnetic nature present, allowing the mobility of the adsorbate and generating heterogeneity on the surface of the adsorbent. Similarly, the arrangement of the magnetic field will determine the direction of the magnetic field lines. The application of a magnetic field as an alternative for the intensification of the adsorption process based on the consideration that the magnetic field is safe, environmentally friendly and economic.

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