Help with Stannous test results

[nh6886]

let me start by saying I asked for help from one of the members in a PM because I saw him online while trying to decide where to post this. I was reminded that the forum works best the way it's set up so maybe he will add his answer here as well. I have an idea of what I am going to try next but welcome any and all input.

This should be Pd in solution but here are two Stannous tests;
2nd picture is 300ml of solution
1st picture is same solution evaporated down to 125ml
I thought maybe free nitric was causing problems so I evaporated down to 1/3 original cooled added HCL to 200ml evaporated back to 125 ml. Did all evaporation just below boil, takes a long time.
So my question is does this test result look familiar?
The solution is dark red with a gold cast at the edge.
Raw material was 2toz MCC's
All the Best,
John

 

[Geo]

your picture is hard to tell what color is showing. it looks brown to me.

other than that, you are evaporating to rid the solution of nitric but you are not doing it correctly. im afraid you didnt remove any nitric with what you described.

 

[nh6886]

Geo,

Thanks for the reply. I evaporated it down trying to expel excess nitric I was looking for any colored gas coming from the solution and thought I was following the directions from Hoke so I am very interested to hear where I went wrong.
The solution spot on the filter paper is close to colorless then when the Stannous is added it turns dark red then quickly changes too more brown with a yellow ring like in the photos.

Thanks Again,
John

 

[butcher]

John,
It is better to ask good questions like this on the open forum this way several members can be helped by answers, and if someone has a better answer they can also help you with it, and if I make a mistake in what I say others will chime in and say something.

When you have two metals dissolved in solution it can be hard to tell with the stannous test, when both metals can react with the same testing solution (in this case Pd & Au) with the two metals precipitating with the tin solution the two precipitants give a mixture of their colors the color can vary depending on how much each of these metals react.

So we need to remove one metal from solution to test the other, lucky for us this can be done many times with using reagents that are selective for one metal, and that which will give us a colored indication of that metal being precipitated, then we can test the remaining solution for the other metal, this can be done in a ceramic spot plate test with several drops of solutions and test reagents.

If you believe you have gold and palladium here is some tests I would try,

Basically we will try to separate these metals in the test.

Test in a ceramic white spot plate dish, (or using a few white plastic spoons will work as a substitute spot plate).

Put a few drops of solution to be tested in a well spot in the plate (or white spoon), add a crystal of ferrous sulfate, if gold is in solution it will be reduced to a brown ring around the crystal (the gold in the test will precipitate out of solution (leaving palladium in solution) use a pipette to move the solution (barren of gold) from this test to the next spot now test this solution with DMG solution to see if you get a yellow precipitate, (an alternative is test the solution by a drop of solution from the first test on Q-tip and a drop of stannous chloride) the DMG test is usually a better choice for Pd.

This test can be done the other way around using DMG in the first test to indicate and precipitate out the palladium leaving gold in solution, and then using stannous chloride or ferrous sulfate to test for gold.

Say we had three metals in solution Pd, Au, Pt in solution we could test these (in this order) with DMG (Pd yellow), FeSO4 crystal (Au Brown), then SnCl2 (Pt orange).

When you get to the refining of palladium there are other members with much more experience than me in that area.

Our fellow member Patnor 101 sells some testing solution's including DMG at a reasonable price to help out members, I think he has a link in his signature line, I believe he also has a small tutorial with colored pictures on the advertisement in his ebay link also you may wish to look at.

 

[Geo]

Geo,

Thanks for the reply. I evaporated it down trying to expel excess nitric I was looking for any colored gas coming from the solution and thought I was following the directions from Hoke so I am very interested to hear where I went wrong.
The solution spot on the filter paper is close to colorless then when the Stannous is added it turns dark red then quickly changes too more brown with a yellow ring like in the photos.

Thanks Again,
John

when you follow Hoke's process to evaporate to expel nitric from solution, you have to evaporate almost to the point of crystallizing the solution. it has to be very thick like syrup or honey. when you render a solution down that low, you are only leaving a few percents of the original volume.its a process you have to be standing beside of because its a visual process. too much and the solution dries out,too little and no nitric is released. when you add the hcl to the hot mix, if you dont see red NOx fumes evolved from the mix, its still there.

 

[butcher]

If the drop of solution on the filter paper changed colors when you added the stannous chloride, it is a good indication that you have removed the free nitric from solution successfully, if there was free nitric in solution the stannous chloride would not have reduced the metals in solution to give you a color change.

Sulfamic acid is good to remove free nitric from solution (byproduct is sulfuric acid), sulfamic acid can be used with a small amount of solution to be tested if the solution had free nitric in solution.

 

[nh6886]

Next step added a little sulfamic acid and got a white precipitate I filtered in a bucner funnel with a med filter so I can check it with XRF later to see what it is later. Solution turned dark red see photo. Added zinc to cement Pd until reaction slowed near stop. Let stand overnight for black powder to settle. Checked this morning no powder? Tested with Stannous positive for Au? No idea where Au would come from. Added swag amount of SMB dissolved in 200f water a little at a time with a fairly strong reaction to each addtion. After four hours there is a spiderweb of gold crystals on the surface and the solution is now bright green? The picture didn't turn out but I will add one later. I appreciate all the help this has been one of the most interesting things I have worked on so far!