Neodymium Recovery from Post-Consumer Computer Hard Drive Magnets using H_3PO_4 and HCl Solutions

摘要

The permanent NdFeB magnets are known as fundamental components in hard disks structure because they have replaced the traditional ferrite magnets that are too much heavier and their magnetic field intensity is lower. The post consume computer hard disks magnets were demagnetized by heating (350 °C, while 4 h), they were characterized by X ray diffraction (Fe_2O_3, Fe_3O_4 y NdFeO_3) and atomic absorption spectrophotometry (57,9 % Fe; 32,5 % Nd). The leaching agent concentration (H_2SO_4, HCl, HNO_3 and H_3PO_4) (100-350 g/L), the effect of leaching time (1-24 h), the solids percentage (1 -20 %), the purification of the leached solutions by solvents extraction (HDEHP, TBP, Hostarex PO-224 y Lix 984) and the precipitation with NaOH (pH 1-6) were studied to determinate the best conditions for the neodymium recovery. The excessive presence of iron in the magnets motivated to modify the traditional methods. A phosphoric acid pretreatment was included, it was followed by a hydrochloric acid leaching. The process showed a removal (76,7 % Fe) corresponding to phosphoric acid (250 g/L, 24 h y 10 % solids) and a secondary leaching recovery (100 % Nd) with hydrochloric acid (100 g/L, 24 h and 10 % solids). The purification of leached solutions with extracting agents reaches a 60,2 % Nd recovery with HDEHP (2 M in n-hexane). Regarding to sodium hydroxide (pH=2) precipitation, an x-ray diffraction analysis (DRX) (Fe_2O_3, Fe_3O_4 and NdFeO_3), revealed the neodymium phosphate obtainment with 99 % purity.