Separation of rare earths - Art vs.. Science (You III)

26. More 26. 2014 of Steve Mackowski

The separation process for the preparation of rare earth usually starts with a mixture of rare earth carbonate or oxide which is obtained by an acid, In general, hydrochloric acid or nitric acid, is solved, so that the further processing can begin. The starting material, say in this case the carbonate, has impurities, caused by the upstream extraction circuit was produced as the carbonate.

There are many rules for these raw materials, which are generally based on the impurities. Specific separation systems have been developed, To cope with these impurities, so that these do not enter the product. One of the common impurity is For example,. Aluminium. This poses a potential problem, as it happens with a similar valence in solution process as Rare earth. The separation by solvent extraction can be problematic here.

The solution process, in which the rare earth carbonate reacts with the acid, the time at which one can take care of the aluminum. This step also provides the opportunity for some of the radioactive elements, another level the. Have Quit, worry about. Since the radiation problem is currently a hot topic, I will come to this in more detail below.

It is a geological fact, that rare earths with uranium and thorium-bearing minerals are associated. Uranium and thorium are radioactive and must be handled accordingly. Some deposits contain high uranium or. Thorium Vorkommen, others low incidence. All of them require a careful management. At this point I have to include the science. However, I will keep it as simple as possible. For those who, who wish to learn more: Look for "uranium decay chain".

Uran und Thorium sind radioaktiv, they decay and emit radiation. Each decay an uranium molecule is transformed into another molecule. This new molecule is called a decay product. This is also radioactive and decays. There is a decay chain instead of to the last molecule adopts the stable form of lead. The same process occurs in thorium, although different here daughter products are produced in the decay chain.

Another problem that is observed, is that over 99% of uranium as the isotope uranium-238 (the Internet search can here provide a detailed explanation) occurs. The remaining uranium is another isotope, Uranium-235 is called. It is also radioactive and has its own decay chain, ending in stable lead. Means, there are three decay chains. Each with their own sequence of decomposition products.

The individual decay products are chemically different from their predecessors, because they are a different element. Those elements to which it applies is most concerned are to make the decay products of radium, Radon, Protactinium, und Actinium. There are other, but have short half-lives, that is, that they do not actually exist long enough, to represent a quality problem. They decay quickly (sometimes in microseconds). Therefore, it must be both the long-lived decay products as well as the parent uranium and thorium during the process (also evident from EHS – Environmental Health and Safety Gründen) be taken care of.

From processing point of view, nature is a little on our site. Radon is a gas, and is released into the atmosphere, and thus does not represent a process problem. However, it is an EHS (Environmental Health and Safety) Topic, especially in underground mines.

The process uranium and thorium is known to remove and fits into the processes before separation. There are several isotopes of lead, which occur as decay products in the decay chains, but most circuits use sulfuric acid and the resulting lead sulfate, which is insoluble and For example,. replacing with the residues.

The remaining decay products must be identified and tracked through the circuit. Here are the one obvious quality problems but also EHS. All these are, however, manage, and fall under internationally recognized standards, nevertheless they must be located.

Back to separation. Rare-earth carbonate has defined limits for uranium and thorium. However, it was found, that some decomposition products in the rare-earth carbonate can occur. This happens if they are not effectively removed in the processing stages prior to the deposition of the rare earth carbonate.

The resolution process (and the pre-stage solvent extraction) provides the opportunity for small leaks to bring under control. Naturally, mines with small amounts of uranium or thorium are less affected, the eventuality but still should be aware of. The elements that are most likely to emerge during the process protactinium and actinium - both are decay products of uranium-235 decay series.

This is not so much a problem thorium. If accumulates uranium ore mining at you then good luck when it comes to high-quality uranium and thus a valuable by-product. But then you need to take precautions in handling these decay products.

The state of knowledge concerning whether. the chemical properties of the two o.g. Decay products is not clearly defined, But a recently released research report seems to indicate, protactinium that usually follows praseodymium and lanthanum, actinium generally follows. It must be stressed, that this level is very low and there are well-known process solutions. It simply provides another level of process complications is. With the possibility of further complication process costs and an increased likelihood of loss increases.

As I have already mentioned, the separation process are specifically designed for the starting material, been designed that is the equipment is. The first stage, the dissolution of the rare earth carbonate is an important step, to start the process of unwanted impurities, which may lead to a higher probability of loss or reduction in product quality, off. Next week I'll present you with a simplified circuit configuration, that will show you, as HREO, MREO and LREO can be separated.








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