Optimization of recovering cerium from the waste polishing powder using response surface methodology

Abstract

Recovery of rare earth from the waste rare earth polishing powder is of great importance to improve the process economics. The current recovery methods result in the generation of large quantities of polluted discharge necessitating waste treatment systems. The present work attempts to extract cerium from rare earth slurry waste by thiourea reducing and hydrochloric acid leaching, towards which central composite technique of the response surface methodology is adopted to design the experiments and to optimize the process conditions to maximize the recovery rate. The effects of four major parameters such as temperature, duration of leaching, dosage of thiourea, and the concentration of HCl were assessed, and the optimal process conditions were identified. Analysis of variance (ANOVA) was utilized to identify the suitable model and to eliminate the insignificant model parameters. The optimized process conditions for maximizing the recovery rate are identified to be a leaching temperature of 90°C, duration of 150 min, thiourea dosage of 0.2 g/g, and HCl concentration of 3.5 mol/l. A recovery of 91.23% could be achieved and validated through repeat experimental runs at the optimized process conditions. The optimized process samples are characterized utilizing XRD to validate the recovery.

Keywords

• cerium
• leaching
• recovery
• thiourea
• waste rare earth polishing powder