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

Abstract 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.