Novel low temperature synthesis of spinel nano-magnesium chromites from secondary resources

• No study has been reported to prepare spinel magnesium chromite form waste resources.
• Novel low synthesis temperature of magnesium chromite.
• Selective removal of Ca ions from industrial waste tannery solution is rarely reported.
• The method applied is simple and safe.

A novel low temperature method for synthesis of nano-crystalline magnesium chromites from the tannery waste solution was investigated. Magnesium and chromium hydroxides gel was co-precipitated at pH 8.5 using ammonia solution. MgCr2O4 was obtained by heating the gel formed at different temperatures 300–500 °C for to 8 h. FT-IR, TG-DTG-DTA, FE-SEM and TEM were used to investigate the produced materials. XRD patterns of the primary oxides revealed the formation of amorphous oxide phase by heating at 300 °C. Heating at 400 °C produces nano-crystallite magnesium chromites partly having the structure MgCrO4 and mainly MgCr2O4 and traces of Cr2O3+ 500 °C MgCrO4 mostly decomposed into MgCr2O4 structure. After 8 h of heating at 500 °C, Cr2O3 completely disappeared. A high surface area about 42.6 m2/g and mesoporous structure was obtained for the produced sample at 500 °C for 8 h. A thermodynamic model has been suggested to explain the findings.

FE-SEM micrograph and TEM image of magnesium chromite sample heated at 500 °C.Figure optionsDownload as PowerPoint slide