Remediation of Cr(VI) via combined self-reduction and adsorption by chemically modified carbon sorbents

Hexavalent chromium, Cr(VI), is a highly toxic species, while trivalent chromium, Cr(III), is an essential trace element for humans and other organisms. In the present work, a simple, rapid, and efficient procedure for water treatment of Cr(VI) is described. Active carbon (AC) was chemically treated with HCl and NaOH for the formation of surface modified Acidic-AC and Basic-AC sorbents, respectively. In addition, AC sorbent was treated with HNO3 as an oxidizing agent and sodium sulfite as a reducing agent for the formation of Ox-AC and Rd-AC sorbents, respectively. The modified AC sorbents were tested to identify their potential applications in removal of Cr(VI) under various controlling factors using the batch technique. The results indicated that these sorbents can be used in water treatment due to their excellent and efficient reduction of Cr(VI) into Cr(III) with percentage transformation values in the range of 90%-100%. Acidic-AC was found to be the superior sorbent in the reduction process of Cr(VI). The produced Cr(III) was removed from aqueous solutions via adsorption on the surface of these sorbents. The reduction and adsorption processes of Cr(VI)-Cr(III) were evaluated and optimized under different experimental parameters. The potential applications of these sorbents in real water treatment were also explored.