# yellow color nitrate solution turns orange-red after heating



## master1008 (Feb 21, 2015)

Dear Senior members,

I have an unknown sample mostly containing platinum and platinum iridium alloy. On heating with nitric acid, I am getting a yellow color solution, please find the attached photo. On further heating and keeping the solution as it is for a day or two I am getting orange-red color solution. I have added table salt for any silver precipitate and DMG for any palladium but does get any satisfactory result. Kindly inform me what can the solution be.

Regards
Master1008.


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## nickvc (Feb 21, 2015)

Try testing...
Lazersteve did an excellent post on ways to test for all PGMs.
If you can't be bothered add some zinc powder and see what precipitates but it could be anything!


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## solar_plasma (Feb 21, 2015)

The changing color remembers me to a post about testing for rhodium. Don't know if this is relevant.

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=41&t=2007


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## Harold_V (Feb 21, 2015)

The degree of coloration, assuming it is the result of a precious metal, I would expect to show some indication with stannous chloride. If the degree of free nitric is excessive, the display may be fleeting, flashing and then disappearing. 

Assuming no reaction with stannous, and nothing with DMG, you might check Hoke's book for a test for iron. I don't recall the reagent(s) involved, as I have not refined in more than 20 years now, but the reaction to iron in solution is a blood red color, much like the test for silver. I also seem to recall that there's another test that would display a blue precipitation (Prussian Blue), similar to silver chloride in consistency. 

Harold


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## g_axelsson (Feb 21, 2015)

Check Hoke page 100 for iron test, http://goldrefiningwiki.com/mediawiki/index.php/Hoke:Refining-Page-100

Göran


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## master1008 (Feb 23, 2015)

Dear Senior Members,

Thank you for your reply and suggestion, as per Hoke's book ammonium thiocyanate is use to test for any iron, but she has mentioned that if the solution has excess of nitric acid, then also the solution gives red and therefore suggest to avoid it. My solution contains only nitric acid. Kindly suggest if there is any way to determine the presence of iron or other precious metals.

Regards
Master1008.


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## butcher (Feb 23, 2015)

From Hoke's Here is a second test for iron in solution: add a few drops of potassium
ferro-cyanide, and if iron is present an intense blue color
will appear, either immediately or after exposure to the air.

This was the Prussian blue test Harold spoke of in his post above.

You can change a small sample to a chloride if you wished, add a couple of drops to a test tube, add a few drops of HCL, evaporate as you would an aqua regia sample, adding a drop or two of HCl as the solution thickens or concentrates you may have to concentrate it a couple of time to drive off the nitric, the nitric is more volatile and can be evaporated out leaving you a metal chloride solution to test.


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## master1008 (Feb 23, 2015)

Ok Sir I will do it and inform you the result.


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## butcher (Feb 23, 2015)

Only a suggestion someone else may have a better idea.

I suspect some base metal as nitric would not attack platinum or iridium, palladium yes but you did not mention it, what base metals do you expect in solution?

Lou would be the best help with this material, I am not even sure what your starting material was except with what you stated above, what was it you dissolved in nitric?.


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