Dear Mr. Mikysek:

You did not provide us with a full-blown picture of the mineral assemblage making up the ore so that my answer cannot fully address your problem either. The small grain size will fraught each wet process with some difficulties. Nevertheless, quartz can be separated from the rest by using Na polytungstate. If the settling velocity is rather low a centrifuge will be helpful. One important question is what type of U minerals is present in the ore. Is it "black ore U minerals" or "yellow ore U minerals" or mixture of the two? Another question to be raised is concerned with the aim of your studies. Sometimes differential leaching may also yield good results. It is still a matter of conjecture and further recommendations need a definite answer to the two fundamental questions, otherwise you will make not very much progress.

Merry Xmas

H.G.Dill

I suggest flotation and heavy liquid separation or even magnetic separation will help you to get red of the quartz and clays

Dear Prof. Dill,

sorry for incomplete/vague information, I will try to refine it! The studied samples come from the North Bohemian Cretaceous Basin; low-grade U-mineralization of sandstone type, which is formed mostly by uraniferous hydrozircon, lecoxenes and own U-minerals (uraninite, ningyoite, coffinite, etc.). Most of them are strongly hydrated and has a colloidal nature.  

The main goal of my study is to determine ore-mineralogy of the samples and Zr bonding within U-mineralization. Elemental maps obtained by XRF show an evident relation between U-Zr and clay-matrix (see attached file). I think that one of the possibilities is to remove quartz and allows getting a bigger amount of ore-material for identification (e.g. using the XRD). Secondly, wet process of separation can be problematic due to the highly hydrated mineral phases. 

Thanks a lot!

Marry Christmas.

Petr Mikysek 

Hello Petr,

following the latest addenda to your question (your reply to H. Dill) you do not need a total separation of U-minerals from the matrix sediment. When your detection method is XRD the retrieve of an only relative enrichment of the U-mineral containing fraction (due to the generally high specific weight difference) should do. So it depends on the background of your intentions. For a total separation the use of Na-polytungstate is state of the art. However, Na-polytungstate is incredible expensive (about 2 $ / gram) and so I would prefer to find an approach to avoid this separation method if total separation is not necessary. In addition, matrix sediment of poorly defined composition slurried with your heavy liquid could spoil the liquid by forming tungstate precipitates (e.g. Ca, Fe, Mn…) which might result in rather enigmatic XRD pattern artifacts. In addition, the reaction deteriorates the quality of the polytungstate and impedes the otherwise possible recycling of the polytungstate solution.  Due to the reactivity (and prize) of polytungstate I would as a first step avoid the use of polytungstate and simply try the relative enrichment by using (sharply defined) grain size fractions of your sediment which are repeatedly subjected a sink separation using separating funnels. A repeated treatment of the retrieved lower heavy portion of the funnel material should yield a sediment fraction, which is suitable for an XRD identification assessment. (Possible solution processes of U-minerals during this procedure could be monitored by ICP-MS analysis.)

However, as already pointed out, the methodical approach depends on the definition of the problem, the sediment quality, and the analytical facilities and so you have to try out.

I wish you good luck. Have another nice Christmas Day.

D. Zachmann

Dear Dr. Towe,

I have added more information about this issue in the aforementioned comment. I hope that will be helpful. I would like to focus only on an investigation of ore-mineralogy, without quartz. Thanks a lot!

Kind regards,

Petr Mikysek

Dear Mr. Mikysek,

I expected a mineralization of the Königstein-Hamr type which is really delicate and obviously not confined to the sandstone-hosted U deposits of Cretaceous age in and at the edge of the Bohemian Massif as you can infer from the photographs attached. Methods which make use of the surface characteristics of the grain such as flotation are fraught with difficulties as the outer part may be rich in zircon or the other way round in coffinite which form a s.s.s. I have dealt with these minerals, a playground for all those who want to find new minerals. There are combinations (I do not use in this case the technical term s.s.s.) of U titanates (e.g. brannerite, U "leucoxene") U-Ti silicates and the Zr-U mineral association documented in the attached file.  In your country U deposits most closely resembling this type to my present knowledge, which I studied at Poppenreuth, are located near Zadní Chodov (Hinterkotten) and to a lesser extent well represented in the Dyleň vein-type deposit.

In this case I would try to deprive the ore mineralization as  much as possible of its siliceous gangue. If you want to avoid the  non-toxic but expensive Na polytungstate make use of bromoform or tetrabromethane. It is cheap and used for commercial swim-sink procedures. Then try and elaborate a differential leaching procedure for the different grain size intervals. I know that the U silicates and titanates respond in a different way  to the solvents (HCl, HNO3..). It is not a simple job but it may work. I attempted it for getting material appropriate for U/Pb age dating. I think nobody can provide you with a nice flow sheet or family-tree of mineral processing. But these different ways, combining heavy-liquid separation and differential leaching will get you a step closer to the enrichement of one or the other mineral types. To achieve an almost pure fractions seems a hard nut to crack and not possible. But for age dating it should work as well as for a more detailed description of the minerals.

Glückauf !

H.G.Dill

Dear colleagues,

many thanks for your comments! Some of them are really interesting and can be useful for my study. I want to say, the aim is not total separation of quartz; the partial removal of quartz can facilitate the observation and mineralogical determination of matrix sediment (with U-bearing minerals).

Secondly, the matrix is formed either by clay minerals (especially kaolinite, illite/muscovite) of size X0-X00 microns or authigenic Zr-matrix (so called hydrozircon) + clay minerals. The results from XRF mapping show evident correlation between uranium, zirconium and other elements in areas where dominate matrix (consisting of clay minerals). I don't know the exact relations between the individual mineral-phases as well as the reason what causes the uranium-bearing capacity of hydrozircon; but I think that it can be small inclusions of U-minerals; like here states prof. Dill (in attached file).

I have experience with the separation of heavy minerals using heavy liquids. This situation is somewhat different... ore-phases (with gel-character) can be modified due to this chemicals. Moreover, they are highly hydrated minerals, and any aqueous environment I consider problematic. In attached file you can see an example of uraniferous "hydrozirocon". To illustrate the complexity of this issue. 

Happy New Year!

Petr Mikysek 

attrition and scrubbing followed by classification might work.

Dear Petr,

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Thanks. Vlad

[email protected]