Aqua Regia with TIN process

[rrantique]

Hello Everyone. I've been playing around with TIN! After a few weeks of doing all kinds of small test I wanted to try out a process. This test used pins off 4 ADM green CPUs and about two soda pop caps full of gold plated bronze connector pins. The main reason for this is to figure out a quick way to do the melted pin gold drops that are sold on ebay.
For this test they where dissolved in aqua regia. Lots of extra nitric was used and it was heated to under a boil. 100ml Solution was Dark Blue. Filtered and ice added with 2ml of H2SO4 then placed in freezer for about 1 hour. Once taken out solution was same as when it was put in nothing had settled to the bottom Since the solution still had lots of nitric acid I add about 300ml or distilled water. Solution was now a lighter blue. I added SMB in very small amounts looking for color change. Solution changed from the blue color to almost clear then went to a dark green. At this point I didn't add any more SMB and test for gold was still positive. After about 1 hour all the Tin had settled to the bottom and I poured the solution into another beaker (Should have filtered it). The 2nd addition of SMB took a lot to kill off the excess nitric gold dropped out and test was negative. Gold can be seen in the bottom of the beaker. Process worked very well.
Dissolved the content from 1st drop in HCI then filtered. Filter clean no gold.
Note: Meta-Stannic Acid in the picture wasn't made during this process. It's to show that the Stannic Chloride SnCI4 looks about the same.
Also the reason for using lots of extra nitric was to make sure that HCI alone didn't oxidize any tin into Stannous Chloride SnCI2 that would reduce the dissolved gold into colloids.

 

[nickvc]

As you created metastatic acid you will have gold tied up in the waste, you will now need to incinerate the powder and use HCl to remove the tin before you try to recover any more gold, chances are you also created colloidal gold which will be held in suspension in your waste solution.
What you have basically done is to reverse a tried and tested method of recovery and refining also increasing your loses along the way and now have a mess to sort out, I'm not trying to be harsh but stick to what is taught here on the forum as these methods work, when you have mastered all those methods then sure try to find better or quicker ways.

 

[Topher_osAUrus]

Ahhhh!

I had a nightmare similar to this... Where everything I tried to refine was just tin...everywhere..TIN!

Nick is spot-on, correct.

Keep the tin out of solution with precious metals.. It tends to reduce them, making it colloidal- afterall, thats how you test your solutions right? With stannous chloride? Same principles in action when they are being dissolved in tandum.

Even if you did get SOME gold to drop, most likely, with THAT much extra nitric, It probably redissolved a good bit of it.

You should try to just add it by the dropper after the first initial addition of HNO3 (i maybe do 10HCl to 1HNO3 and let it work and work until it calls it quits, then dropper by dropper til done).

If you must use excess nitric because of a time frame limitation, you should most certainly look into getting sulfamic acid to add after digestion is complete. It will remove the NOxx gasses, and in turn create sulfuric acid, which will then precipitate lead as lead sulfate. Which is insoluble and easily filtered before precipitation of your gold.

Hokes book is what i read my children for their bedtime stories...its a great book! You should most certainly download it and read it cover to cover until you can recite it, verbatim

 

[g_axelsson]

From what I understand... haven't done the test myself, so I'm speaking theoretically.

The use of excess nitric acid will oxidize any stannous tin into stannic tin, keeping it from creating a colloid. Some stannous tin will reduce gold chlorides into metallic gold and in so transform into stannic form. Any colloidal gold will be redissolved as long as there is any free nitric left.

So in the end, the only time you risk creating a colloid is when you haven't oxidized all tin to 4+ state and is out of nitric acid (or nitrate salts together with hydrochloric acid).

What I have tested is creating a colloid in aqua regia by dropping tin chloride into it. It created a beautiful red reaction that disappeared within seconds when the colloidal gold was redissolved.

One problem with metastannic acid is that the liquid locked up in the tin mud will contain dissolved gold. It can be extracted by filtering but the tin will clog the filter badly, slowing it down to a crawl. Or extracted by repeated decanting and dilution.

For example if you have 100 g of dissolved gold and can extract 90% of the liquid by decanting you still have 10g of gold mechanically locked in the remainder mud. Fill it up to the same volume, stir well and let it settle. This time you recover 90% of what's left and only 1g is still locked in the tin mud. Repeat as many times you need to recover additional gold until the value left is too little to worry about.

I might be wrong in this and missing some way that the metastannic acid would lock up the gold and I hope someone will point it out then.

Göran

 

[saadat68]

Hi
If I have metastanic acid in aqua regia solution I must evaporate solution and dry residue (because solution is colloidal and we can not decant it) with low temperature and then incinerate powders and ...

Right? Or it is better to decant and filter some of solution?

Thanks

 

[nickvc]

Filtering to recover the gold is a waste of time, dry the solution out and incinerate the powders left, then treat with Hcl to remove the tin and then hopefully any gold will be there to reclaim.

 

[saadat68]

Hi
I have two question about metastannic acid
1- Why tin produces metastannic acid in aqua regia but it doesn't produce metastannic acid in acid peroxide?

2- For rid of metastannic acid in aqua regia solution, we must precipitate gold > evaporate solution > incinerate residue > dissolve in HCl > wash with hot water > dissolve in AR (Right?)

When we dissolve residue in HCl, Is there any chance to dissolve gold? I ask this question because if we have gold chloride in residue, They dissolve in solution again

I think in incineration process, All of gold chlorides convert to gold oxides and then oxides decompose to gold metal. Right?

 

[Lino1406]

Adding zinc, e.g. in the form of threads, will reduce back SnO2 to soluble Sn++

 

[anachronism]

Hi
I have two question about metastannic acid
1- Why tin produces metastannic acid in aqua regia but it doesn't produce metastannic acid in acid peroxide?

2- For rid of metastannic acid in aqua regia solution, we must precipitate gold > evaporate solution > incinerate residue > dissolve in HCl > wash with hot water > dissolve in AR (Right?)

When we dissolve residue in HCl, Is there any chance to dissolve gold? I ask this question because if we have gold chloride in residue, They dissolve in solution again

I think in incineration process, All of gold chlorides convert to gold oxides and then oxides decompose to gold metal. Right?

1. Because AR contains Nitric acid- Metastannic acid is formed with Nitric. There's no Nitrate element in HCl/Peroxide. Check the chemistry.
2. Depends upon the solution. I've never once had to incinerate the drop from AR, and some of my dissolves are really really dirty!

Yes there is always a risk of dissolving gold when washing in HCl either from residual Nirates, residual Nitric, or from base metal interaction. In most cases you work on the assumption that it WILL happen ,and if it doesn't then it's a bonus.