Recycling of rare earth magnet scraps: Part II Oxygen removal by calcium : Special issue on recycling and high performance waste processing

Abstract

Powder scraps of neodymium-iron-boron permanent magnet were deoxidized by using calcium vapor, liquid or CaCl 2 melt at 1223-1273 K. Because the scraps react with the acidic solutions during leaching of the byproduct CaO, the methods for removal of the excess amount of Ca and CaO were studied. When pH was controlled at about 8 during several times leaching, the dissolution of rare earth elements could be minimized. Ca vapor deoxidation could not supply enough amount of Ca through CaO layer. When a large amount of CaCl 2 was added, the dissolution rate of CaO into the aqueous solution became faster, but some amounts of rare earth components were lost. The deoxidation by Ca liquid and 5 mass%CaCl 2 and the subsequent leaching in distilled water with pH > 8 gave the better result so that oxygen, even in heavily oxidized scraps, could be lowered to 0.7 mass%.