Remediation of chromium(VI) ions as chromium oxide xerogel via gamma-radiolysis of aqueous waste discharge

摘要

Radiolysis of water during gamma-irradiation produces oxidizing and reducing species which can be used for the bulk oxidation or reduction of target toxic species. In the present work, gamma-radiolysis of water has been used for the reduction of Cr(VI) to Cr(III) ions in the simulated chrome tan liquor solution samples, and simultaneously precipitation as a chromium oxide hydrate gel. Sodium formate scavenger has been found to be the best suited, among various scavengers studied, not only for the removal of oxidizing species produced during gamma-radiolysis of water but also simultaneous precipitation of thus formed Cr(OH)(3) as chromium oxide hydrated to gel. The chromium oxide hydrate gel has been subjected to thermal treatment for an objective of converting it to the chromium oxide xerogel which has potential applications for catalysis. Various techniques, such as BET, XRD, XPS, HRTEM and Raman spectroscopy, have been employed for studying the changes in the physical, crystalline and oxidation states in each step observed in thermal treatment starting from the hydrate gel to chromium oxide xerogel. The results showed the formation of crystalline mixed valence chromium oxide xerogel having specific surface area 20.9 m(2) g(-1) and pore volume 0.036 cc g(-1) after thermal treatment.