釹鐵硼永磁體工業廢料之鹽酸選擇性溶解與化學沉澱回收稀土

近年來環保節能風氣盛行，新推出的電動機及電器產品為達到環保綠能之目的，皆以低耗能、高效率為開發目標。為減少產品之耗能，許多電動機及電器產品逐漸將稀土永磁體投入產品中使用。目前國內經廢棄回收的電動機馬達中，磁鐵材質多以含量99%以上之氧化鐵的軟鐵氧體為主。稀土永磁體於發明後逐步改良，開發出具優異磁能積表現的釹鐵硼磁鐵；但其產品在廢棄後多以占70%的低價金屬鐵為回收主體，投入電弧爐煉鋼，降級回收處理鐵，而無法有效回收產品中所含30%的稀土元素。因此，有必要研發技術，回收廢稀土永磁體所含稀土元素。本研究使用鹽酸選擇性溶解法，回收釹鐵硼永磁體工業廢料，去除鐵、硼及其他雜質，浸出稀土液，並使用無水草酸與碳酸氫銨兩種沉澱劑，回收稀土元素。本技術主要以800℃高溫氧化焙燒1小時，促使永磁體工業廢料中的鐵金屬，完全的氧化轉變為Fe2O3，使其不易於鹽酸液中溶解。再使用4N鹽酸以1:20之酸溶固液比，於60℃攪拌溶解1.5小時，可將99%之稀土元素浸出，將pH值調整至pH 3.01~4.30，並於40℃攪拌15分鐘沉澱除雜，進而達到選擇性溶解的效果，取得純度91.4%之稀土浸出液。再使用此稀土浸出液，分別測試無水草酸與碳酸氫銨作為沉澱劑，於稀土沉澱之效果。在沉澱劑的選擇上，以無水草酸為最佳選擇。沉澱劑添加量固液比=1:20，並於沉澱溫度60℃的條件下，混合攪拌1.5小時。最終取得稀土純度96%，稀土回收率96%，並於高溫爐升溫至850℃鍛燒1小時，生成氧化稀土。

關鍵字

永磁體；稀土；選擇性溶解；化學沉澱；草酸沉澱

並列摘要

Following the rise of environmental protection and energy conservation trends in recent years, novel electric motors and devices have been developed based on low energy consumption and high efficiency, so as to achieve environmental protection and realize green energy. In order to reduce the energy consumption of products, many electric motors and devices have gradually shifted to using permanent rare-earth magnets in their production. At present, soft ferrites, which are iron oxide-based, account for over 99% of the magnetic materials in electric motors recovered in local waste recycling centers. Improvements in the development of permanent rare-earth magnets had resulted in neodymium-iron-boron magnets with excellent magnetic energy products; however, low-cost metal-based iron, which account for 70% of the magnets’ composition, are primarily recovered from the waste magnets in the electric arc furnaces of steel mills. As a result, it is difficult to efficiently recover the rare-earth elements which account for 30% of the waste magnets. With this issue in mind, it is necessary to develop selective chemical precipitation techniques for the recovery of rare-earth elements in recovered waste permanent rare-earth magnets. This study employed the selective dissolution by hydrochloric acid method to recover industrial waste from neodymium-iron-boron magnets. In an attempt to recover the rare-earth elements, a solution containing the elements leached after removing iron, boron, and other impurities was subjected to chemical precipitation by anhydrous oxalic acid and ammonium bicarbonate. In this method, the waste permanent rare-earth magnets were subjected to calcination at 800℃ for one hour, thereby fully oxidizing the metal-based iron to Fe2O3, which does not dissolve well in acidic solutions. Afterwards, 99% of rare-earth elements were leached from the waste magnets through stirring at 60℃ for 1.5 hours, with 4N hydrochloric acid as the leachant and a solid-liquid ratio of 1:20. The pH of solution was then adjusted to 3.00 to 4.30, and was stirred for another 15 minutes at 40℃ to remove impurities, thereby achieving selective dissolution and obtaining a rare-earths leachate with a purity of 91.4%. The leachate was then subjected to chemical precipitation by anhydrous oxalic acid and ammonium bicarbonate, respectively, so as to achieve rare-earths precipitation. With regard to the selection of precipitants, anhydrous oxalic acid was shown to be the optimal choice. At an added solid-liquid ratio of 1:20 and a temperature of 60℃, the solution was mixed and stirred for 1.5 hours. The resultant rare-earths recovered had a purity of 96%, and the recovery rate was 96%. Furthermore, rare-earth oxides were yielded through calcination at 850℃ for one hour.