環境資訊中心外電；姜唯 翻譯；林大利 審校；稿源：ENS
美國普渡大學開發出更環境友善且具商業可行性的稀土開採技術。新技術已獲專利，有機會改寫產業生態，幫助美國創造更穩定的本土供給。
舉凡電腦、手機、DVD、充電電池、觸媒轉換器、磁鐵、風力渦輪機和日光燈、雷射測距儀、導航系統和精準武器都需要稀土金屬，但是在自然界中往往濃度不高，很難進行商業開採。
此外，目前以酸為基礎的稀土金屬分離和純化技術不利環境，世界各地的大多數公司無法進入市場。
碳酸鑭的結晶體，鑭是稀土之一。照片來源：ZEISS Microscopy（CC BY-NC-ND 2.0）
中國是全球稀土主要生產者。17種稀土金屬的全球儲藏量，有36％掌握在中國手上。目前中國已不再像1980至1990年代，以低於生產成本的價格出售稀土，其他國家也有機會成為稀土生產者。
但是當中國在2010年降低稀土金屬的出口配額時，一台風力渦輪機的稀土磁體成本從8萬美元飆升至50萬美元。18個月後中國放鬆了出口限制，價格又回到了低於2010年的水準。
中國目前仍是本土和出口市場中，用來生產電子產品的稀土金屬的主要消費國，緊接著是日本和美國。
幾乎60％的稀土金屬都用於生產磁鐵。具有永磁性的稀土磁鐵幾乎日常生活無所不在，不論是電子產品、飛機、油電混合車或風機。開發出新技術的普渡大學化學教授王念華（音譯）說：「目前稀土只有一個海外供給，如果因故供給受限，將嚴重影響人們的生活。美國也有這種資源，但需要一種更好、更乾淨的方式來處理這些稀土金屬。」
新的專利提取和純化技術使用配體輔助層析法，經證實可以安全有效地從煤灰、回收磁鐵和原礦石中分離出稀土金屬，對環境幾乎沒有不利影響。
鎦是一種銀白色金屬，稀土金屬之一。照片來源：
維基百科／Alchemist-hp（CC BY-NC-ND 3.0）
稀土金屬的生產每年全球有40億美元的市場。隨著新的電子產品、飛機、軍艦、電動汽車、磁鐵和其他需要稀土金屬的重要產品的開發，這個市場繼續成長中。每年靠稀土金屬作用的產品價值超過4兆美元。
王念華解釋：「傳統生產高純度稀土元素方法採用兩階段液相萃取法，這需要用到數千個串聯或併聯的混合沈降槽，產生大量有毒廢物。我們的兩區域配體輔助置換層析系統使用一種新的分區方法，可生產高純度（> 99％）金屬並達到高產率（> 99％）。」
王念華的配體輔助方法有機會從廢磁鐵和礦石回收高效、環保地純化稀土金屬，並有助使稀土加工成為循環永續的過程。
普渡大學化學工程教授喬．佩克尼（Joe Pekny）說，王念華的創新技術使美國能以環境友善、安全和永續的方式重新進入稀土金屬市場。佩克尼說：「美國的稀土金屬可以滿足美國和全球其他市場不斷成長的需求，減少對外國資源的依賴。」
這項研究部分由美國國防部（Department of Defense﹐DoD）資助。
現在美國國防部正在與美國稀土礦供應鏈簽訂新合約，加州沙漠中一度停產的鈾礦礦場，也是北美唯一的稀土礦開採和加工基地可望重新啟用。
Greener Process Grows U.S. Supply of Rare Earth Metals WEST LAFAYETTE, Indiana, May 11, 2020（ENS）
Mining for rare earth metals is about to become more environmentally and economically feasible though a process newly developed and patented at Purdue University.
These new environmentally-friendly technologies promise to be game-changers in this field and could enable the United States to create a more stable and reliable domestic source of these essential metals.
Used in computers, cell phones, DVDs, rechargeable batteries, catalytic converters, magnets, wind turbines, and fluorescent lights, and for defense in laser range-finders, guidance systems, and precision-guided weapons, these metals are difficult to mine because it is unusual to find them in concentrations high enough for economical extraction.
In addition, the detrimental environmental impact of current acid-based separation and purification of rare earth metals prohibits most companies everywhere in the world from entering the market.
China is currently the world leader in rare earth production, although it controls just 36 percent of the world’s reserves of these 17 metals. This provides an opportunity for other countries to become producers now that China is not selling rare earth materials below the cost of production as it did in the 1980s and ’90s.
But when China reduced the export quotas for rare earth metals in 2010, the costs of rare earth magnets for one wind turbine soared from $80,000 to $500,000. After China relaxed the export restrictions 18 months later, prices returned to lower levels than in 2010.
China is also the dominant consumer of rare earth metals for manufacturing electronics products for domestic and export markets. Today Japan and the United States are the second and third largest consumers of rare earth materials.
“About 60 percent of rare earth metals are used in magnets that are needed in almost everyone’s daily lives. These metals are used in electronics, airplanes, hybrid cars and even windmills,” said Nien-Hwa Linda Wang, the Purdue professor of chemistry who developed the new processes.
“We currently have one dominant foreign source for these metals and if the supply were to be limited for any reason, it would be devastating to people’s lives,” Wang said. “It’s not that the resource isn’t available in the U.S., but that we need a better, cleaner way to process these rare earth metals.”
The new patented extraction and purifying processes use ligand-assisted chromatography, a separation method that has been shown to remove and purify rare earth metals from coal ash, recycled magnets, and raw ore safely, efficiently and with virtually no detrimental environmental impact.
The production of rare earth metals is a global US$4 billion annual market that continues to grow as new electronics, computerized engines for aircraft, warships, electric automobiles, magnets, and other critical products are developed that require rare earth metals to perform. The value of the products using rare earth metals to function is valued at more than $4 trillion per year.
“Conventional methods for producing high-purity rare earth elements employ two-phase liquid–liquid extraction methods, which require thousands of mixer-settler units in series or in parallel and generate large amounts of toxic waste,” Wang said.
“We use a two-zone ligand-assisted displacement chromatography system with a new zone-splitting method that is producing high-purity (>99%) metals with high yields (>99%).”
Wang’s ligand assisted method has the potential for efficient and environmentally friendly purification of the rare earth metals from all sources of recyclates, such as waste magnets and ore-based sources and helps transform rare earth processing to a circular, sustainable process.
Joe Pekny, a Purdue professor of chemical engineering, said Wang’s innovation enables the United States to reenter the rare earth metals market in an earth-friendly, safe and sustainable way. “What’s exciting is that the U.S. has the rare earth metals to meet the growing demands of the U.S. market and other markets around the globe and reduces our dependence on foreign sources,” Pekny said.
This research was funded in part by the U.S. Department of Defense, DoD.
Now, the Defense Department is supporting the U.S. rare earth supply chain with a new contract to a once defunct uranium mine in the California desert that is now the only rare earth mining and processing site in North America.
※ 全文及圖片詳見：ENS
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