Selective formation of neodymium phosphate from iron-neodymium magnet waste

Abstract

Neodymium-iron-boron alloy, Nd 2 Fe 14 B, is used as a material for magnets. Neodymium is one of the valuable and expensive rare earth elements and is often recovered to reduce costs and environmental impact. Recently, a method for recovering neodymium as neodymium phosphate from mixed solutions was reported. This method was very useful because the main component of rare earth ores is rare earth phosphates, and there are well-established methods for refining rare earths from rare earth phosphates. This study attempts to obtain neodymium phosphate using acid to dissolve waste magnets, reducing agent, phosphoric acid, and pH adjuster. The diluted acid (hydrochloric acid and nitric acid), amount of ascorbic acid and phosphoric acid, and the pH values were studied to clear the suitable conditions. The color of the heat-treated product, the precipitate yield, and the Fe/Nd molar ratio indicated that a low concentration of acid is suitable and ascorbic acid is required. Excessive use of phosphoric acid improved the precipitate composition. The high pH value decreased the selectivity of neodymium phosphate due to the easy formation of iron phosphate and hydroxide. The process addressed in this study is very promising because it does not require heating at high temperatures or special reagents.