Study of impurity in blue spinel from the Luc Yen mining area, Yen Bai province, Vietnam

Abstract

In this paper, we present the main impurities in natural blue spinel from the Luc Yen mining area in Yen Bai province, Vietnam. Together with identifying impurities and their valence, we have taken into account the site of some impurities in the MgAl2O4 spinel structure by using sensitive techniques, including electron microprobe analysis (EMPA), UV-Vis-NIR, electron spin resonance (ESR), and X-ray absorption (XAS). EMPA results indicated that blue spinel contains different impurities, including V, Mn, Ni, Zn, Ti, Cr, Fe, Co and Ca. UV-Vis-NIR, ESR and XAS studies revealed that the oxidation state of Mn, Co, Fe and Ni is 2+ while that of Cr is 3+. Particularly, Co2+, Fe2+, and Cr3+ ions are identified. They contribute to the color variation of the blue spinel samples. Our study also indicated Co2+ and Cr3+ located in the octahedral position of Al3+ of the MgAl2O4 structure.