Rocketdoc Notes – Week of December 27, 2020
Can the right space program save Earth? - Part 3
This is part 3 of a writeup for my dry run for a talk I’m giving on David Goldsmith’s Age of Infinity Google Meet at 11:30 AM PST on January 14th. The title of the talk is the same as the title for this report. In the last two weeks I have covered the current overpopulation crisis and how it is made even worse by Global Warming. In the last report I covered Platinum Group Metals (PGMs) and the part these products mined on the moon can play in reducing some of the hardest to remove carbon dioxide emissions.
The week I’m going to discuss Rare Earth Elements (REEs), which it turns out, aren’t all that rare on Earth, just widely dispersed. First, there is no question that we need thousands of tons of REEs to affect the Green Revolution. For instance, every traction electric motor in a Prius electric car needs approximately 15 kg of lanthanum and 1 kg of neodymium each, plus two other rare earth elements, terbium and dysprosium are added to the alloy to preserve neodymium’s magnetic properties at high temperatures. Also, the electric generator in a one MWe windmill contains about a 1000 kg of neodymium. But exactly what are the Rare Earth Elements, and why are we even thinking of mining them on the moon? Figure 1 shows the periodic table with all the elements listed. The elements classified as REEs are Scandium (21), Yttrium (39) and the Lanthanum series near the bottom.
Figure 1 – Rare Earth Elements in the Periodic Table
Rare earth elements are a group of seventeen chemical elements that occur together in the periodic table (see Figure 1). The group consists of yttrium and the 15 lanthanide elements
(lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). Scandium is found in most rare earth element deposits and is sometimes classified as a rare earth element. The International Union of Pure and Applied Chemistry includes scandium in their rare earth element definition.
The usage of REEs has skyrocketed in the last 30 years has new uses have been found and this is especially true in the areas of catalysts, electrical motors and generators, and high temperature superconductors. Figure 2 below shows the production of REEs over time for the USA, China, and everybody else. The Democrats essentially shut down REE production in the USA in 2000 because of pollution from the processing facilities. We still mined REEs, but the ore was shipped to China for processing. The processing of REEs in the USA has been cleaned up and production of oxides has resumed. But, to replace all the fossil fuels worldwide we will need to increase the amount of REEs produced by roughly an order of magnitude and do it in few years. This is another reason we might want to consider mining them on the moon.
Figure 2 – Comparison of the Production of REE Oxides over time
The rare earth elements are all metals, and the group is often referred to as the "rare earth metals." These metals have many similar properties, and that often causes them to be found together in geologic deposits. They are also referred to as "rare earth oxides" because many of them are typically sold as oxide compounds. Several geologic aspects of the natural occurrence of REEs strongly influence the supply of rare-earth-elements raw materials. These geologic factors are presented as statements of facts followed by a detailed discussion.
Although rare earth elements are relatively abundant in the Earth's crust, they are rarely concentrated into mineable ore deposits. The estimated average concentration of the rare earth elements in the Earth's crust, which ranges from around 150 to 220 parts per million (table 1 below), exceeds that of many other metals that are mined on an industrial scale, such as copper (55 parts per million) and zinc (70 parts per million). Specific REEs are found in much smaller concentrations as shown in the figure.
Table 1 – Abundance of REEs in Earth’s Crust
Rare earth elements-bearing minerals, once separated, contain as many as 14 individual rare earth elements (lanthanides and yttrium) that must be further separated and refined. Unlike metal sulfides, which are chemically simple compounds, REE-bearing minerals are quite complex. Base metal sulfide ores, such as sphalerite (ZnS), are typically smelted to burn off sulfur and separate impurities from the molten metal. The resulting metal is further refined to near purity by electrolysis. Rare earth elements, on the other hand, are typically extracted and refined through dozens of chemical processes to separate the different rare earth elements and remove impurities.
The principal deleterious impurity in REE-bearing minerals is thorium, which imparts an unwanted radioactivity to the ores. Because radioactive materials are difficult to mine and handle safely, they are heavily regulated. When a radioactive waste product is produced, special disposal methods must be used. The cost of handling and disposing of radioactive material is a serious impediment to the economic extraction of the more radioactive REE-rich minerals, in particular monazite, which typically contains considerable amounts of thorium. In fact, imposition of tighter regulations on the use of radioactive minerals drove many sources of monazite out of the rare earth elements market during the 1980s.
The complex metallurgy of rare earth elements is compounded by the fact that no two REE ores are truly alike. As a result, there is no standard process for extracting the REE-bearing minerals and refining them into marketable rare earth compounds. To develop a new rare earth elements mine, the ores must be extensively tested by using a variety of known extraction methods and a unique sequence of optimized processing steps. Compared with a new zinc mine, process development for rare earth elements costs substantially more time and money.
By now you can see the problem. Unlike most commercially mined base and precious metals, rare earth elements are rarely concentrated into mineable ore deposits, they are difficult to separate into salable products, and often involve radioactive waste products. Therefore, it is the cost, not the availability, that might drive us to mine REEs on the moon, to insure we can afford the technologies we need to solve global warming. Mining REEs on the moon brings us to KREEP.
KREEP is an acronym built from the letters K, the atomic symbol for potassium, REE which stands for rare-earth elements, and P which stands for phosphorus. It is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat enhanced concentration of a majority of so-called "incompatible" elements (those that are concentrated in the liquid phase during magma crystallization) and the heat-producing elements, namely radioactive uranium, thorium, and potassium (due to presence of the radioactive potassium 40).
The bottom line is KREEP has been found in samples brought back from every Apollo moon landing, so it is fairly widespread, and is thought to be especially concentrated around Thorium deposits as shown in Figure 3 below.
Figure 3 – Thorium Concentration in the Lunar Regolith
The typical composition of KREEP includes about one percent, by mass, of potassium and phosphorus oxides, 20 to 25 parts per million of rubidium, and a concentration of the element lanthanum that is 300 to 350 times the concentrations found in carbonaceous chondrites. Most of potassium, phosphorus and rare-earth elements in KREEP basalts are incorporated in the grains of the phosphate minerals apatite and merrillite.
At this point in time, we have indications that KREEP ore bodies might be abundant in an accessible part of the moon, but we won’t know for sure until prospector landers are deployed and sample that region. If minable KREEP ore bodies exist on the moon and machinery to mine and refine them can be built (preferably tele-operated from Earth), then there is a good chance they will be cost competitive with the pollution-intensive methods used on Earth. This statement is based on the results of the Lunar mining of PGMs studied at the University of Washington back in 2012 (described in my book) as outlined in last week’s blog. Lunar pollution is not an issue for the foreseeable future.
The recent prices for PGMs and REEs mined on Earth are all over the map and are shown below. These can change by an order of magnitude over a few months based on supply and demand.
Platinum $1020/oz 30-60 grams/vehicle 130 mT/yr worldwide
Lanthanum Cerium Metal (Battery Grade) $4,440/mT
Pr-Nd Alloy $77,000/mT
The bottom line is that we are going to need to increase production of PGMs and REEs by an order of magnitude to enable replacing fossil fuels worldwide by 2050 and I really doubt that can happen without use of lunar resources.
Thanks for reading.