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.

Graphical abstractFE-SEM micrograph and TEM image of magnesium chromite sample heated at 500 °C.Figure optionsDownload full-size imageDownload as PowerPoint slide