Efficient Cr(VI) removal from wastewater by activated carbon superparamagnetic composites

Activated carbon decorated with superparamagnetic iron oxide nanoparticles, AC/SPION, with high efficiency for removal of Cr(VI) from aqueous media in pH 3 to 8 range was realized, by exploiting the adsorption and reducing capability of AC and magnetite nanoparticles, allied to magnetic separation. However, iron(II) species was demonstrated to be very interesting as co-adsorbent since broaden the optimal pH range (pH 4 to 10) and enhance the removal capacity more than four times, by reducing hexavalent chromium to Cr(III) at the same time that produce iron(III) hydroxide, a colloidal material that tend to precipitate on the nanocomposite increasing its adsorption properties. Finally, AC/SPION can be dispersed in water maximizing the efficiency, and the chromium species loaded material can be easily separated with a magnet providing an alternative for the treatment of large volumes of contaminated wastewater. In fact, final effluents with Cr concentrations in the low μg/L range, suitable for direct disposal according to EPA recommendations, can be produced by the iron(II) assisted process demonstrating its potentiality in real applications. •Superparamagnetic nanocomposites for efficient Cr (VI) removal.•Nanocomposite offer good removal of Cr(VI) from water with a wide pH range.•Low cost nanocomposites for scalable wastewater treatment.