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Author: Subject: Rare earth metals, mischmetal, etc
DerAlte
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[*] posted on 1-7-2007 at 21:16
Rare earth metals, mischmetal, etc


As a new menber I feel a bit guiltly about opening threads. I did a search but found little. I have been accumulating odd ends of lighter flints due to incessant pipe smoking, and also have a few high gauss permanent magnets, cerium and possibly samarium, that I ordered years ago when designing & making circulators for millimeter wave applications.

The lighter flint end collection has reached critical mass of 5g. I am also prepared to sacrifice the magnets.

Has anyone, especially Woelen, king of the rare metals here, attempted separation of the rare earth metals, which I understand is a heroic task?

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DerAlte
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[*] posted on 1-7-2007 at 23:03


I have not tried any separation myself, but I can report what one of my books says... (Concise Inorganic Chemistry, 5th ed, J D Lee):

In general the separation is very difficult, but a few lanthanides have valence states other than +3 and this can be used.

If you have a solution of Ln+3 ions, Ce can be oxidized to +4, book says NaOCl in alkaline solution. The Ce+4 is separated by carefully controlled prcipitation of CeO2 or Ce(IO3)4, leaving the Ln+3 ions in solution. (Book has no details on the careful control...) Alternatively, Ce+4 can be readily extracted by solvent extraction in HNO3 solution using tributyl phosphate. 99% Ce can be obtained in one stage from a mixture containing 40% Ce. (This probably approximates your misch metal.)

Similarly, Eu+2 exists, and your Ln+3 solution can be reduced electrolytically with a Hg cathode or Zn amalgam. If sulfate ions are present, Eu(II)SO4 precipitates as it is insoluble. Sm and Yb can also be put into the +2 state ths way, but these ions are oxidized slowly by water.

Besides that, some sort of fractional separation is needed. Assuming you don't want to do hundreds of fractional crystallizations... Ion exchange chromatography is I think the best method. A solution of Ln+3 ions is run down a Dowex-50 or similar column, Ln is absorbed onto the column. The H+ ions resulting are washed through the column. The Ln ions are then eluted with a complexing agent, i.e. 'a buffered solution of citric acid/ammonium citrate, or a dilute solution of (NH4)3(H-EDTA) at pH 8'. Separation can be monitored spectroscopically with atomic fluorescence. (Maybe not at home!) The metals are precipitated as oxalates, then heated to give the oxides.
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[*] posted on 2-7-2007 at 00:45


As a slight extension to pantone159's post, see

http://www.chem.ox.ac.uk/icl/heyes/LanthAct/L3.html

which describes the current manufacturing technique as well, and gives a few references.

Andding hydrogen peroxide and then aqueous ammonia to a solution of the mixed salts will precipitate the 3+ hydroxides first, then Ce(OH)4. Usually the L(III) hydroxides would be redissolved and precipitation to fully remove Ce, and the cerium fraction would be treated similarly.

The 2+ ions reduce to form amalgams more quickly that the 3+, using a mercury electrode a solution of the 3+ ions can have the Eu, Sm, and Yb removed as an amalgam.

I believe that one of the Inorganic Synthesis volumes had a procedure for separating the REE.
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[*] posted on 2-7-2007 at 00:53


If you are going to use neodymium magnets as well, you should work them up separately as they only contain neodymium, sparing you its separation from the other rare earths.

In the german forum, there is the documented production of neodymium sulfate from magnets:
http://www.versuchschemie.de/topic,9178,0,-Neodym%28III%29-s...
Although there are some concerns about the purity of the product thus obtained.

[Edited on 2-7-2007 by garage chemist]




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[*] posted on 2-7-2007 at 06:19


I have never tried to separate rare earths from mischmetall. As already is pointed out by others, this is very difficult, certainly for a home chemist with limited equipment and resources. One rare earth (cerium) can be relatively easily be separated, because it can go in the +4 oxidation state and as such can be handled in a special way, but separating it from mischmetall hardly is of any use. I have seen all rare earths being sold on eBay for very decent prices, the cheapest ones being cerium, praseodymium, erbium, samarium and gadolinium.



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not_important
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[*] posted on 2-7-2007 at 07:30


Ceramilcs suppliers are another source of reasonably pure oxides for cerium and the coloured REE - erbium, europium (as II), neodymium, praseodymium. For example

https://protected.hypermart.net/uspigment/index2.html

But then there's not much challange, which here may think is an important part of doing home science :-)
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[*] posted on 2-7-2007 at 22:50


Thanks for the replies, all! I knew Ce was fairly easy to separate but it is also the least interesting. What makes the rare earths interesting is that unfilled shell, like the transition metals (one of my favorites in all inorganic chem..) It manifests itself as fluorescence, colors, sharp absorption bands – and hence the use in CRT phosphors and lasers (Nd, e.g). I’m a sucker for nice colors. Magnetic properties too.

The rare earths are not as rare today as in my distant youth. They now have considerable commercial uses. At present I am too busy with other projects to contemplate hairy separations so I will shelve the project and accumulate some more bits of flints, do some more research. Maybe even get a gram or two on ebay.

I wanted to see if anyone ever took on the challenge. I’m as ready as the next guy for a challenging fractional crystallization, I revel in it, but I currently draw the line at half a dozen attempts max., about what’s needed to really clean potassium chlorate from sodium contamination and get rid of that yellow flame - always use distilled water, never ‘de-ionized’… Perchlorate is a bit easier.

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DerAlte
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[*] posted on 3-7-2007 at 02:15


The characteristic colors of those rare earth cations which have unpaired 4f electrons, typically pastel shades of pink, green, yellow, blue, are due to transitions between energy levels of those electrons with energies which correspond to visible light wavelengths, and between the 4f and 5d orbitals. This, and paramagnetism and ferromagnetism, are most evident around the middle of the rare earth series, where the metals or their cations have up to 7 unpaired 4f electrons. See my recent post on the "High oxidation states of rare earth metals" in this section, for further information. Some of their oxides have recently found uses, in crystalline mixtures with Ba and Cu and some other oxides, as superconductors with transition temperatures higher than the boiling point of liquid nitrogen (77ºK).

As for separating them, I once had a final-year laboratory experiment on separating an unrefined mixture of rare earths (called "didymium", a crystalline mixture with a pale blue-green color), as the chlorides I think, by means of elution through a column packed with an ion-exchange resin, with aliquots of the eluted solution being collected separately and analysed by UV/visible spectroscopy and ESR spectroscopy.

As well as La and the following 14 metallic elements (the electronegativities of which steadily increase with atomic number due to increasing nuclear charge resulting in valence electrons being progressively more tightly held), "rare earth" elements also include scandium and yttrium, and also the actinide series, comprising actinium and the succeeding 14 elements of which only Th and U occur naturally significantly. They are found mostly as a mixture of the silicates in "pegmatites", huge crystals which occur at (originally) very deep levels in continental granite areas, having been the last part of granite masses to crystallize from the liquid state; rare-earth oxides are apparently very soluble in molten granite. Because of the depth at which these deposits occur, mining of them is possible only where a considerable thickness of granite has been removed by weathering and erosion, e.g. in Scandinavia. Some geochemical differential mineral formation occurs in places, resulting in some separation of Sc and Yt e.g. as the rare mineral thortveitite, Sc2Si2O7, found in Greenland, and of Th and U e.g. as pitchblende, U3O8.
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[*] posted on 3-7-2007 at 13:24


some of tit-o-matic's posts have been useful....or am i thinking of a different user?

Anyway, does misch metal react with HCl to form some rare earth chlorides.

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[*] posted on 3-7-2007 at 13:25


I imagine it does, though they may be prone to hydrolysis, especially if you try to crystallize. I would imagine CeCl3 is hard to produce, and CeCl4 impossible (Ce oxidizing Cl-).

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[*] posted on 3-7-2007 at 13:48


Yes, mischmetal makes chlorides with hydrochloric acid. The reaction is very vigorous and a lot of heat and hydrogen is produced.

The solutions are quite stable and hardly hydrolyze, but when an attempt is made to obtain the dry chemical, then things become different. I have made some solid PrCl3.xH2O from Pr-metal, but I needed several attempts before I obtained the nice light green material. Just slightly overheating the material results in loss of HCl and formation of oxide or oxychloride. And even then, I still think that my product contains a small percentage of oxychloride. It does not dissolve completely as a clear liquid in water. A single drop of dilute HCl, however, makes the solution clear.

Finally I succeeded, by VERY careful heating and slowly blowing away any water vapor, released from the solid:

http://woelen.scheikunde.net/science/chem/compounds/praseody...

The solid apparently looses water on storage. It still dissolves fairly easily.

[Edited on 3-7-07 by woelen]




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[*] posted on 3-7-2007 at 13:53


A vigorous reaction like aluminum or something more violent?

[Edited on 3-7-2007 by chemkid]




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[*] posted on 3-7-2007 at 19:03


I think if you choose to attempt to do a good separation of these compounds from michmetal, you may want to start with more michmetal as depending on the source of the michmetal the composition can have varrying ammounts of the various rare earths, and some make up a miniscule fraction of the michmetal.

You can buy lumps of it for cheap from camping stores, like these here http://www.campingsurvival.com/flintbar18x2.html.

"I feel a bit guiltly about opening threads"
no need to:)

One of the things I regret most is not making a video of the time I was instructed to cut a 1kg ingot of cerium into wafers, using a bandsaw:o:D. And followed it up with similar ingots of Nd, La, Pr.

The reaction of the rare earths with acids is along the lines of Al and HCl but milder, similar to calcium in cool water.

Crystalization of some are possible, I have not tried with many, only cerium and Nd, Ce did not work well at all, but NdCl3 I was able to obtain as light purple crystals from a slow room temp evaporation of the aqueous solution. I also did something with lanthanum chloride, but completly forget everything about it, I do not think the crystals were nice.




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[*] posted on 3-7-2007 at 20:05


One method for getting anhydrous chlorides of metals, when those chlorides are not volatile - not like AlCl3, is to mix the hydrated chloride with ammonium chloride, slowing heat the mixture to several hundred C, and then pull vacuum on it to removed excess NH4Cl. It's in one of the early Inorganic Synthesis collections, specifically for the lanthanides but it does work with other chlorides as well.
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[*] posted on 3-7-2007 at 20:47


The response has been far greater than I expected. Thanks!

@Pantone 159: chromatography is a bit beyond my capabilities, but emphasizes the difficulty of separation.

@ not_important: I read the Oxford article; again, shows it’s a tough proposition not to undertaken lightly. I believe Brauer has a bit on separation.

@ garage chemist: I read (as best I could) that fascinating German post. One thing I have plenty of is old hard drives – my son is always discarding them from old computers. My understanding of German is piss poor, unfortunately, just enough to get by with, but I shall be having a further look at that forum…

@Woelen: I am not an element collector, I guess it’s just the challenge that appeals to me. But as I said, not 100 fractional crystallizations!

@JohnWWW; Nice succinct summary of the lanthanides. I think I’ll frame it and hang it on the wall.

@tito-o-mac: You are a bit of a tit. Get a life.

@The_Davster: I feel I may not have searched the archives well enough, that’s why I am a bit bothered about opening new threads.

Have also been reading the contributions of Chemophiliac’s thread re Oxidation state of REE’s.

Regards,

DerAlte
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[*] posted on 4-7-2007 at 04:36


The_davaster: What sort of bandsaw are yolu cuting theese with?



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[*] posted on 4-7-2007 at 05:28


I am not a tool specialist, it was what was in the uni machine shop. it was over 6' tall, and had a blade about 1cm deep and 1mm wide. It was a medium toothed blade. I have no idea if this is what you mean?



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[*] posted on 4-7-2007 at 06:26


Sadly i am not much of a tool specialist either. However i would think, unless neodynium is a very soft metal, or you have access to a really nice bandsaw, that cutting neodynium would ruin most any blade. The bandsaw I use would have a tough time cutting aluminium (i'm not going to try either metal becuase it is a six hundred dollar bandsaw and it's not mine).

Chemkid




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[*] posted on 4-7-2007 at 08:17


Yeah some of those rare earths are really hard to cut, almost like to fracture rather than cut easily. I only have very small (<15g) samples of them though.

Still, with a high carbon blade, I've cut through 1" thick steel bolts on a horizontal band saw. Aluminum doesn't like to cut with a finer blade: "http://abymc.com/"




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[*] posted on 4-7-2007 at 16:45


The rare earths I cut were decently soft, I'd say similar to magnesium? You can shave off pieces of all of them with a pocketknife. We eventually gave up cutting the cerium, because of all the fires that started. Then I was given a hacksaw and did that for a few hours. I did not notice any blade issues.



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[*] posted on 5-7-2007 at 10:18


I have obtained fairly pure Nd salts from NIB magnets. The first thing I did was heat them until they stoped being magnets- I was annoyed every time I tried to do anything with them and they stuck together. Then I peeled off the coating (Ni I think) because that was going to be easier than removing it chemically.
The next step was to dissolve them in dilute HCl, I'm not sure what happens to the boron. I guess it oxidises to boric acid because I think I would have noticed BH3.
This gave a mixture of Fe and Nd as chlorides. Then I oxidised them with bleach to get the Fe (II) to Fe (III).
The separation relied on the fact that adding a base to a mixture of Fe(III) and Nd(III) causes the Fe to precipitate first. Once you can't see the colour of the Fe(III) chloride complex you can decant the solution and ppt the Nd as a hydroxide. Dissolving this in dilute H2SO4 and leaving it for the water to evaporate gave nice crystals.

Another possibillity would be to dissolve the mixed chlorides in fairly conc HCl and extract the "HFeCl4" complex with ether. Fine if you have lots of ether- I didn't.
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[*] posted on 5-7-2007 at 15:48


@ unionised

Now that I can do! In fact, I've already stripped a magnet. Any idea of the approx composition of the magnets and the Curie temp. for reference? I guess it's not really necessary to de-magnetize, though.

I'm curious - Is that "un-ionised" or "union-ised"? suspect the former, somehow...

Thanks,

DerAlte
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[*] posted on 5-7-2007 at 15:51


See my recent posts in the parallel thread "High oxidation states of rare-earth metals", and, for links for downloads of ebooks on the rare earths, in the Inorganic Chemistry thread in the References section.
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[*] posted on 5-7-2007 at 16:23


Der Alte,

I think JohnWW's suggestion to use an ion exchange resin would be the most feasible for the amateur. Given that you seem to be interested in only gram quantities, the relatively dilute solutions should not be too big a problem.

Maybe an approach closer to chromatography would work.
Years ago I worked in an oil refinery laboratory, and one of the tests was for aromatics content in power kerosene (and carrot spray for gods sake!). The medium was alumina and the identity of the eluent escapes my failing memory. Propanol I think. We cheated and simply used a UV light to show the relative lengths of the various components of the developed sample. Given a constant bore column, that was not a big problem.
Is there any varieties of activated alumina that has differential absorption properties for the rare earths? (charcoal?)
Perhaps a patent search would suggest a suitable resin, or something as simple as alumina may have the desired properties (not likely I guess).
Please continue starting new threads. I've loved every one!
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DerAlte
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[*] posted on 6-7-2007 at 00:03


Re the magnets, the initiator of the German thread cited by garage chemist states the composition as Nd2Fe12B. Further down the thread there is a suggestion (if my quick perusal and poor German are correct) that other RE metals may be involved, a sort of 'mischmetall/iron' magnet. In which case the Nd won't be as easy to separate. The process, as stated, depends upon the inverted solubility/temp curve of Nd sulphate - but, as one might expect, ALL the RE metals exhibit the same phenomenon (even La, Ce). At a given temp there is some difference in solubility, however. If it's a mixture, you will have the same separation poblem all over again...

Nitrates and chlorides are v. soluble, selenates like the sulphates, inverted curve. No surprises here - these elements are chemically too close, almost as close as recent presidential elections...

Regards,

DerAlte
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