Here I attach a PDF and a link to something that may help http://is.gd/yEaIQb

I do not know what collector you are using, but apparently phosphoric acid esters comprises a large number of products, which consist essentially of a mixture of mono and diesters of phosphoric acid. They differ in their non-polar hydrophobic radical that can he either aliphatic or aromatic. The non-polar group of the hydrocarbon radical is attached to the polar group via an oxygen bridge. Another group of these reagents is half esters, which were originally developed by Mechanobre and used for notation of apatite. They are regarded as strong collectors and can be used in either alkaline medium (notation of apatite and scheelite) or in an acid medium for flotation of titanium minerals (ilmenite, rutile and perovskite). A similar group of collectors called “phosphoten” was also developed by Mechanobre and consists of 25% of pentavalent phosphorus and 15% naphthenic acid. The resulting reaction product is a powder with a specific gravity of 0.9 g/cc. This product is soluble in alcohol but not in water. This reagent was used for notation of zircon, cassiterite and pyrochlore at pH values of 4-10.5

I know you also saw http://www.mindat.org/forum.php?read,6,380956,380960

Would Luminescent separation apply to you?

Luminescent separation is the mineral selection process based on luminance of minerals under the effect of ultraviolet and roentgen rays. It is made use of in dressing of minerals luminescent in roentgen (diamond-containing, scheelite, fluorite, zircon, apatite, spodumene and other ores) or ultraviolet rays (fluorite, scheelite and other ores).

Also see FLOTATION-SEPARATION of SCHEELITE from Fluorite and Calcite.

Dear David and Bill,

Thank you for your kind answers. I will study the documents you refer to. I understand that it will be reasonable if I specify some more details of what we do and what we are trying to achieve.

We produce tungsten (scheelite) concentrate by way of reprocessing old flotation tailings of a closed mine site in Uzbekistan.

We adopted technology to beneficiate old tailings that only contain ~0,08% WO3 and produce 55-65% tungsten concentrate. The technology is combination of “gravity” methods (spirals and tables in essence) and flotation. First, we produce 20-25% WO3 middling product out of gravity circuit. It is however overloaded with sulphides, with S sometimes over 15-20% and As > 1%. In order to remove sulphides we employ sulphide flotation of the said middling product. During the latter the sulphides report to froth product and scheelite mainly report to in-cell product.

The problem we faced recently is that our tungsten concentrate happens to contain excessive quantities of radionuclides, namely 238U, 226Ra and 232Th. Effective specific activity of radionuclides contained in the concentrate (A_eff) is about 7500-8000 Bq/kg.

The content of radionuclides in the primary wolfram ore and the tailings we reprocess is near Clark values. But they seem to concentrate together with scheelite due to similar gravity properties.

We did initial assessment of mineral forms that hold the radioactive elements and found that the main radionuclide-bearing minerals are zircon, uraninite and thorite. We are now double-checking these results.

So we are doing flotation of sulphides, not scheelite flotation. We use butyl potassium xanthat and T-91 reagents. We maintain pH at 2-3 in order to depress scheelite. The best solution for us would be a reagent(s) that we could add after sulphide flotation is exhausted. So we could remove zircon etc. into froth product thus cleaning scheelite. Since WO3 grade of in-cell product by that stage is very high (>50%) it's important that the reagent in question would not lift up scheelite.

The post in mindat.org is my post too.

Luminescent separation is of no use for us at the moment because we are reprocessing tailings, which is already a fine milled product. But as soon as we get our hands on scheelite ore (which we are planning to) we will test some ore sorting methods, including radiometric and luminescent. So thank you for that anyway.

Dear David,

You've mentioned in your post two reagents developed by Mechanobr known to float titanium minerals. One called "phosphoten" and the other you describe as being "regarded as strong collectors and can be used in either alkaline medium (notation of apatite and scheelite) or in an acid medium for flotation of titanium minerals (ilmenite, rutile and perovskite)".

What is the name of the second group of reagents? May be you have any recent experience with them and know where I could buy some for testing?

Thank you again for sharing your experience, best regards

Anton

Hi Anton, best get a copy of http://www.academia.edu/22691019/Handbook_of_Flotation_Reagents_Chemistry_Theory_and_Practice_Flotation_of_Sulfide_Ores