Researchers develop a new process to get lithium out of rocks

研究人员开发出从岩石中提取锂的新工艺

While we make batteries based on many different chemistries, nothing has approached the massive scale at which we can produce lithium batteries. That scale makes the economics of lithium-ion batteries hard to compete with. Even if we develop a superior battery technology, it’s unclear whether we can get manufacturing costs down quickly enough to compete with the efficiency of the lithium supply chain and manufacturing. 尽管我们制造电池所采用的化学体系多种多样，但没有任何一种能达到锂电池那样的生产规模。这种规模效应使得锂离子电池的经济性难以被超越。即便我们开发出更先进的电池技术，能否足够快地降低制造成本，以与锂电池供应链和制造效率相抗衡，目前尚不明确。

The one thing that could change the dynamics is a supply crunch. While lithium is extremely widespread, lithium that can be extracted economically is a different matter. It’s cheapest to extract it from brines, and lithium-rich brines are largely limited to South America. We do obtain some lithium from other sources, but it’s considerably more expensive. 唯一可能改变这种格局的因素是供应紧缺。虽然锂在地球上分布极其广泛，但能够经济地提取出来的锂则是另一回事。从盐湖卤水中提取锂成本最低，而富锂卤水主要集中在南美洲。我们确实也从其他来源获取锂，但成本要高得多。

In today’s issue of Science, however, a research team has identified an energy-efficient means of extracting lithium from rocks. The process they’ve designed uses far less energy than existing ones, regenerates all its starting chemicals, and produces byproducts that could also be sold. 然而，在今天出版的《科学》杂志上，一个研究团队发现了一种从岩石中提取锂的节能方法。他们设计的这一工艺比现有工艺消耗的能量少得多，能够再生所有起始化学品，并产生可供出售的副产品。

Reacting rocks

岩石反应

Like other metals, lithium shows up in various minerals. For example, the US Geological Survey recently took an inventory of all the lithium oxide deposits in the Northeast (they are extensive), which are found in a type of rock called pegmatite. Globally, however, the new paper indicates that the most abundant lithium ore is called spodumene, a lithium-aluminum silicate (LiAl(SiO3)2). 像其他金属一样，锂存在于各种矿物中。例如，美国地质调查局最近对东北部所有的氧化锂矿床进行了清查（储量巨大），这些矿床存在于一种称为伟晶岩的岩石中。然而，该论文指出，在全球范围内，最丰富的锂矿石被称为锂辉石，这是一种硅酸铝锂（LiAl(SiO3)2）。

And there is some processing of this material going on—it’s just energy-intensive and leaves behind a lot of waste. That’s because the process starts by heating the mineral to roughly 1,000° C to disrupt its compact structure, after which sulfuric acid is used to leach out the lithium. The resulting lithium sulfate solution is then converted into something useful for battery manufacturing (typically lithium carbonate), leaving behind sulfur-containing waste. 目前确实有一些针对这种材料的加工处理，但过程非常耗能，且会留下大量废料。这是因为该工艺首先需要将矿物加热到约 1,000°C 以破坏其紧密结构，随后使用硫酸浸出锂。所得的硫酸锂溶液随后被转化为电池制造所需的有用物质（通常是碳酸锂），并留下含硫废料。

The new work was done by a collaboration between MIT researchers and a couple of Boston-area companies. Their goal was a process that was far more energy-efficient and didn’t produce as much waste. What they came up with is a process where the key chemical used at the start of the process gets regenerated at a later step, and both the silicon and aluminum in the mineral end up in a form that we’re already using in commercial applications. 这项新研究由麻省理工学院的研究人员与波士顿地区的几家公司合作完成。他们的目标是开发一种更节能且废料更少的工艺。他们最终设计出的工艺流程，使得起始阶段使用的关键化学品能在后续步骤中再生，同时矿物中的硅和铝最终转化为我们已经在商业应用中使用的形式。

The key chemical in the process is ammonium fluoride (NH4F). It’s possible to use the salt directly in a molten form, but heating it invariably leads to some production of hydrogen fluoride, which is extremely dangerous stuff (although they end up using some later). So instead, they used it dissolved in water, which apparently keeps these reactions from occurring. 该工艺中的关键化学品是氟化铵 (NH4F)。虽然可以直接使用熔融态的氟化铵盐，但加热它总是会导致氟化氢的产生，这是一种极其危险的物质（尽管他们后来确实用到了一些）。因此，他们改用将其溶解在水中的方式，这显然避免了上述反应的发生。

In this process, heating the solution to about 70° C results in the formation of NH4F2 ions, releasing ammonia gas that’s used later in the process. This ion donates a fluorine to the lithium, leaving a water-based solution of lithium fluoride. The silicon also forms a soluble ion, (NH4)2SiF6), while the aluminum forms a similar ion that remains behind as a solid, (NH4)3AlF6). Each of these is processed separately. 在此过程中，将溶液加热至约 70°C 会形成 NH4F2 离子，并释放出后续工艺中会用到的氨气。该离子向锂提供一个氟原子，留下氟化锂的水溶液。硅也形成一种可溶性离子 (NH4)2SiF6，而铝则形成类似的离子，以固体形式 (NH4)3AlF6 残留下来。这些物质随后被分别处理。

Using everything

物尽其用

We’ll start with the aluminum chemistry, which is one of the simpler pathways. Initially, heating the (NH4)3AlF6 to about 300° C produces aluminum trifluoride and releases ammonia and hydrogen fluoride. Then, raising the temperature to 700° C causes the aluminum trifluoride to react with water, leaving behind aluminum oxide and releasing yet more hydrogen fluoride. 我们先从铝的化学反应开始，这是较简单的路径之一。首先，将 (NH4)3AlF6 加热至约 300°C 会产生三氟化铝，并释放出氨和氟化氢。然后，将温度升至 700°C 会使三氟化铝与水反应，留下氧化铝并释放出更多的氟化氢。

Again, hydrogen fluoride is dangerous stuff and needs to be handled carefully. But it’s also easy to react it with the ammonia (which is produced during two different reactions here) and reform the ammonium fluoride that was used to start the whole process. So, aside from minor losses due to inefficiencies, the process regenerates one of the key ingredients. 再次强调，氟化氢是危险物质，需要小心处理。但它也很容易与（在此过程中两次不同反应中产生的）氨反应，重新生成整个工艺起始时所用的氟化铵。因此，除了因效率损失导致的少量损耗外，该工艺实现了关键原料的再生。

Meanwhile, aluminum oxide is one of the key starting materials for the production of aluminum metal, and so can be fed into that, given that the purity of the end product here was over 98 percent. We’ll just note here that this is probably the worst aspect of the whole process, given the energy requirements for these temperatures and the highly dangerous chemicals involved. 同时，氧化铝是生产金属铝的关键起始原料之一，因此可以将其投入生产，因为此处最终产品的纯度超过了 98%。我们在此指出，考虑到这些温度所需的能量以及涉及的高度危险化学品，这可能是整个工艺中最糟糕的部分。

By contrast, the silicon purification is a walk in the park. Simply adding more ammonia to the solution caused the starting chemical (NH4)2SiF6) to react with water, releasing silicon dioxide and ammonium fluoride. Again, an ammonium fluoride solution is one of the starting materials; the silicon dioxide simply precipitates out of this solution. That has a variety of applications, but the team showed that it’s quite effective at strengthening concrete. 相比之下，硅的提纯则非常简单。只需向溶液中添加更多的氨，就能使起始化学品 (NH4)2SiF6 与水反应，释放出二氧化硅和氟化铵。同样，氟化铵溶液是起始原料之一；二氧化硅会直接从溶液中沉淀出来。它有多种用途，但研究团队证明它在增强混凝土方面非常有效。

All that leaves us with is the solution of lithium fluoride. That’s actually one of the raw ingredients for production of a common battery electrolyte, LiPF6. Alternatively, the researchers showed that you could react it with nitric acid and (once again) release hydrogen fluoride, leaving behind lithium nitrate. Heat that and it will decompose into lithium oxide, which is easy to convert into other battery raw materials. 剩下的就是氟化锂溶液了。这实际上是生产常见电池电解质 LiPF6 的原料之一。或者，研究人员展示了可以将其与硝酸反应，（再次）释放出氟化氢，留下硝酸锂。加热硝酸锂，它会分解成氧化锂，这很容易转化为其他电池原材料。

Checking the economics

经济性评估

While the process gets rid of the high temperatures for the initial processing of lithium-containing ore, there are several steps with elevated temperatures needed further down the line, both for the lithium and for the useful aluminum and silicon products. So, the researchers did a full economic evaluation of how their process stacked up to what’s already on the market. 虽然该工艺省去了含锂矿石初步加工所需的高温，但在后续流程中，无论是针对锂还是针对有用的铝和硅产品，仍有几个步骤需要高温。因此，研究人员对他们的工艺与现有市场工艺的竞争力进行了全面的经济评估。

The existing process, which involves roasting ore/sulfuric acid, came in at just under $9,000 for each usable tonne of lithium. By contrast, they estimate that the new process should only cost a bit over $5,000 per tonne. That’s roughly comparable to the cost of isolation from high-quality brines. 现有的涉及矿石焙烧/硫酸处理的工艺，每吨可用锂的成本略低于 9,000 美元。相比之下，他们估计新工艺的成本仅为每吨 5,000 多美元。这大致相当于从优质卤水中提取锂的成本。