Removal of chromate ion from aqueous solutions by sponge iron

Abstract

Hexavalent chromium ion is the most toxic form of chromium ions and it is considered as a hazardous pollutant. So removing this ion from effluents is very important. One possible approach is reducing Cr(VI) to Cr(III) by metallic iron. Sponge iron was used in this study, and the influence of parameters such as the amount of sponge iron in the solution, effect of acid washing of sponge iron, initial pH and temperature of the reaction on the efficiency of the reduction process were investigated. The possibility of reusing and regenerating of used sponge iron was also studied. Furthermore, the effect of sodium tartrate was investigated. This compound eliminates the precipitates of Cr(III), Fe(III) hydroxides, and Cr_xFe_1 − x(OH)₃ and thus reduces surface passivation of sponge iron. X-ray diffraction analysis and scanning electron microscopy images were employed to investigate the chemical composition and surface morphology of the sponge iron before and after the treatment. The results revealed that acid cleaning of the sponge iron, decreasing the solution pH, increasing the temperature and adding sodium tartrate to the solution improve the Cr(VI) removal efficiency. Furthermore, it was found that the used sponge iron can be reused after acid washing.

Keywords:

• Hard chromium plating
• Chromate ion
• Hazardous pollutant
• Sponge iron
• Sodium tartrate

Acknowledgements

The authors would like to thank the department of chemistry of Shiraz University for supporting this research.