Abstract
Cerium oxide based abrasive material is widely used for polishing optical glass, glass circuit board etc. Rare earth elements contained in spent abrasive material are now disposed of without recycling. In order to develop a selective recovery process of rare earth elements from spent abrasive material, the chlorination behaviors of rare earth elements Ce, La and Pr and coexisting elements Al, Fe and Si were investigated.
The chemical forms of rare earth elements contained in the sample of spent abrasive material were estimated to be CeO2, LaOF and PrOF. When the sample was heated to 1100°C in a chlorine gas stream, Ce, La and Pr did not volatilize but remained in the solid phase. Fe, Al and Si were released to the gas phase at the temperatures above 700, 800 and 900°C, respectively. When the sample with added carbon was heated in a chlorine gas stream, the coexisting elements began to volatilize from 400°C in the order of Fe, Si and Al. All of Fe and Si, and 85% of Al were released to the gas phase in the course of heating to 800°C. Ce, La and Pr were released gradually with the increase of temperature above 800°C, and the release reached from 10 to 20% at 1100°C. The experimental results of the carbon-added sample heated at the temperatures from 600 to 800°C in a chlorine gas stream for 1 h indicated that the treatment temperature of 700°C was appropriate to obtain the rare earth elements without any volatile loss and to lower the contents of impurities in the solid residue.
