Background: The removal of toxic metals from sewage and wastewaters is one of the most important concerns in the twenty first century. The removal of poisonous Cr(VI) from aqueous solution by different low-cost available nanoporous adsorbents was investigated in the present study. 

Methods: Fumed silica, bentonite (BN), hydrotalcite (HT), MCM-41, Na-Y, mordenite (MOR) and SAPO-34 were used at different adsorbent-to-metal ion ratios. Two predominant species of Cr were considered including chromate and hydrogen chromate ions.

Results: Both HT and Na-Y adsorbed the toxic bichromate ions more favorably than other sorbents. Overall, the efficiency of the Cr removal followed the sequence of HT > SAPO-34 > MOR > MCM-41 > Na-Y > silica > BN. Because of its surface chemistry, HT with an uptake of 65.2 mg/g showed the highest toxic abatement among the seven adsorbents investigated under the acidic conditions, followed by the microporous materials SAPO-34 and MOR with uptakes of 41.2 and 41.0 mg/g, respectively.

Conclusion: Both HT and Na-Y adsorbed the toxic bichromate ions more favorably than other sorbents. The high pore volume and the apparent surface area of a non-functionalized MCM-41 were not effective in the adsorption of Cr compounds. Overall, HT was the best choice owing to its appropriate surface chemistry with respect to the Cr oxygenates.