Science and Technology
Rare earths and climate change
In a hole?
Demand for some rare-earth elements could rapidly outstrip supply
MANY plans for reducing the world's emissions of carbon dioxide-at least, those plans formulated by environmentalists who are not of the hair-shirt, back-to-the-caves persuasion-involve peppering the landscape with wind turbines and replacing petrol-guzzling vehicles with electric ones charged up using energy gathered from renewable resources. The hope is that the level of CO2 in the atmosphere can thus be kept below what is widely agreed to be the upper limit for a tolerable level of global warming, 450 parts per million.
许多全球性减排二氧化碳的计划是要建造星罗棋布的风力涡轮发电机，并以再生能源发电为电动汽车充电，摈弃狂吞汽油的汽车。哦，至少那些并不坚决主张严酷节俭、回返穴居社会 [注] 的环保主义者是这样计划的。人们希望，这样一来，大气中CO2的含量可以保持在百万分之450以下。人们普遍认为，这就可以让全球气候变暖的程度处在可容忍的上限以下。
Wind turbines and electric vehicles, however, both rely on dysprosium and neodymium to make the magnets that are essential to their generators and motors. These two elements, part of a group called the rare-earth metals, have unusual configurations of electrons orbiting their nuclei, and thus unusually powerful magnetic properties. Finding substitutes would be hard. Motors or generators whose magnets were made of other materials would be heavier, less efficient or both.
At the moment, that is not too much of a problem. Though a lot of the supply of rare earths comes from China, whose government has recently been restricting exports (a restriction that was the subject of a challenge lodged with the World Trade Organisation by America, Europe and Japan on March 13th), other known sources, such as the now-abandoned Mountain Pass mine in California, pictured above, could be brought into play reasonably quickly. At current levels of demand any problem caused by the geographical concentration of supply would thus be an irritating blip rather than an existential crisis.
这一问题当前还不甚突出。尽管大量稀土来自中国，而该国政府最近一直在限制出口（美国、欧洲与日本已就此于3月13日向世贸组织（World Trade Organisation）提起诉讼），但其它已知矿源，比如现在已放弃开采的加州帕斯山（Mountain Pass mine in California）（上图），可以在较短时间内重新开采供货。按照当前的需求水平，供应来源集中于某地的会引起的任何问题都只不过会让人烦恼一时，不会造成生存危机。
But what if the environmentalists' dream came true? Could demand for dysprosium and neodymium then be met? That was the question Randolph Kirchain, Elisa Alonso and Frank Field, three materials scientists at the Massachusetts Institute of Technology, asked themselves recently. Their answer, just published in Environmental Science and Technology, is that if wind turbines and electric vehicles are going to fulfil the role environmental planners have assigned them in reducing emissions of carbon dioxide, using current technologies would require an increase in the supply of neodymium and dysprosium of more than 700% and 2,600% respectively during the next 25 years. At the moment, the supply of these metals is increasing by 6% a year. To match the three researchers' projections it would actually have to increase by 8% a year for neodymium and 14% for dysprosium.
但如果环保主义者的美梦成真了呢？到那时，镝与钕的需求也会得到满足吗？这就是麻省理工学院的三位材料科学家伦道夫?科尔臣、伊利莎?阿隆索和弗兰克?菲尔德（Randolph Kirchain, Elisa Alonso and Frank Field）最近向自己提出的问题。他们在最近发表在《环境科学与技术》（Environmental Science and Technology）的文章中给出的回答是：如果要让风动涡轮发电机和电动汽车以现有科技完成环境规划者赋予它们的二氧化碳减排使命，在未来25年间，钕与镝的供给量将需要分别增加600%和2500% 以上。这两种金属现在的年供给量增长为6%；要达到三位研究人员预计的水平，镝与钕的年供给量实际增长必须分别为14%与8%。
That will be hard, particularly for dysprosium. Incremental improvements to motors and generators might be expected to bring demand down a bit. But barring a breakthrough in magnet technology (the discovery of a room-temperature superconductor, for example) the three researchers' figures suggest that the world's geologists would do well to start scouring the planet for rare-earth ores now. If they do not, the mood of the Chinese government may be the least of the headaches faced by magnet manufacturers.