Selective Leaching and Recovery of Er, Gd, Sn, and In from Liquid Crystal Display Screen Waste by Sono-Leaching...

We report a facile, economic, and ecofriendly method for selective recovery of Er, Gd, Sn, and In from liquid crystal display (LCD) screen wastes by ultrasound-assisted leaching, followed by magnetic separation. Thermodynamic analysis showed that the pyrophosphate ion is an excellent leaching agent for Er, Gd, and In at pH values below 8. Dissolved screen waste powder was subjected to leaching at room temperature using aqueous solutions of 0.05 M of sodium pyrophosphate (Na₄P₂O₇) as the leaching agent; hydrogen peroxide (H₂O₂) (3 v/v %) was added as an auxiliary reducing agent, and an ultrasonic source was used in the process. Once completed, magnetic separation was applied to the leached residue. The average contents of Er, In, Sn, and Gd in the LCD screen were found to be 477, 2422, 835, and 93 mg·kg^-1, respectively, of which 93, 97, 72, and 99% were selectively recovered from the waste material by this method at pH 3 after 2 h of leaching. The proposed method emerges as an easy and selective process for leaching Er from LCD screen wastes and concentrating In, Sn, and Gd in a separable magnetic solid.