Gold drop issue- where do I go from here ?

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grainsofgold

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May 28, 2007
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Not sure if this is the right area to post this or not- feel free to move it where it belongs if this is not correct


I started with a 20-22kt yellow gold bangle bracelet - I melted it and rolled it out thin -

in my hood , I put it in a beaker with HCL and added Nitric acid slowly bit by bit - according to the formula for AR to drop the assumed amount of pure Au I needed 128 ml of HCL and about 25ml and change of Nitric

I didnt use the full above amounts- the gold went into solution and was golden color. But at the bottom of the flask there was fine white granules, I had not seen this before - I then later added a few drops of Sulfuric .

Here is where I made mistakes -

I added ice and then filtered the solution in a buchner filter-

After the filtering- I added sulfamic and since the solution was cold the sulfamic did not react- no fizzing

I added SMB and there was fizzing - there was no end to the fizzing so I stopped - then I decided to add sulfamic again and there was more fizzing and after a while strong sulphur smell.

To make a long story short Im sure I over added SMB and Sulfamic and did not expell the notric like I had thought I had. -

I have the mix in a beaker with added water and tested the solution near the top with stannous and no indication of gold in it-

Here is what I am thinking about doing-

1. Siphon off the solution , check it again with stannous
2. Once siphoned off and no gold in solution then add HCL to it and small amounts of Nitric to put the gold back into solution
3. add a pure gold button known weight and then leave to ensure all the free nitric is used up
4. filter it with the buchner set up
5. if solution is crystal clear then add smb while stirring

Doe this make sense as I want to put the dropped gold back into solution and drop again but I want to leave the sulfamic and extra SMB behind

I want to avoid another mix up on my part- so please advise -

Normally I do inquarte but this time I decided to go AR and do a drop - I hurried and this is what happens when you do
;(

I have the white granules on the filter paper- what could they be if they were left in the beaker after the AR put the gold into solution but not these ?

Thanks in advance

GOG
 
grainsofgold said:
in my hood , I put it in a beaker with HCL and added Nitric acid slowly bit by bit - according to the formula for AR to drop the assumed amount of pure Au I needed 128 ml of HCL and about 25ml and change of Nitric



GOG

What was your expected gold yield? Also what formula were you using and where did you get it from?
 
Have you got your gold powder precipitate on the bottom of your beaker?
If yes then decant and wash well with hot water then decant and add Hcl and heat then several hot water rinses to remove the Hcl,that should clean your gold powder for you.
If you have no powder and the stannous test is right you have no gold in solution.
 
Thank you -

Last night - I thought the same after I posted- I will siphon the solution off and test with Stannous and if null then wash whats in the beaker-

From the looks of settling this am it appears the gold powder from the digestion and using SMB did work -

Still not sure what the white granules were that were left on the bottom of the beaker after the AR treatment-


GOG
 
anachronism

Sorry for the late post-

I have it that it takes this amount of AR / 118.29 ML of HCL and 29.57 ml of HN03 to dissolve 1 troy oz of Au

assuming that I had 22k that weighed 29.5 grams I assumed that I needed 102.92ml of HCL and 25.72 HNO3

29.5 g x .917k = 27.042 g Au

27.042/31.1 = .87

I took 87 percent of the amounts used to drop 1 troy oz of AU

102.92 HCL, 25.72 HNO3

I used 96 ML of HCL and 20 ML of HNO3

It appeared that the gold went into solution leaving behind on the bottom of the beaker a white granular substance-

Today the the gold did drop and the solution on top tested negative with Stannous. However , there is a white film in the solution along with the excess sulfamic and the SMB on the bottom mixed with the Au-

I decanted what I could without disturbing the Au at the bottom and have added tap water with heat. THe top liquid is now much clearer so I will decant and do this several times.

I'm just guessing that the white is some type of lead salt maybe ? I haven't seen this before -

Thanks

GOG
 
Final drop/melt

25.37 grams Au

started with 29.5 grams so the bracelet marked 22kt ended up 20.64kt actual

I have large batch so this will get refined twice

Final note- when I washed the residual au with smb and sulfamic with hot water, the white did cloud up and looked like shear paper whirling inside the beaker- It rinsed clean , however to be sure Ill re refine it to rid it of any traces-

Lesson learned- do not add SMB or sulfamic to cold solutions

GOG
 
It may be a moot point, but when you are dissolving karat scrap, you can't just calculate the needed acid to just dissolve the gold involved. You have to take into account the base metal that is present as well. The white solids left behind sounds like silver chloride. An easy test is to expose it to sunlight. If it is AgCl, it will start to darken instantly. You should add the nitric incrementally with pauses in between additions to let the acid work before adding more. If you cover the reaction with a watch glass, some of the nitric acid from the dissolution will be returned to the reaction so the calculations would be skewed in any case. it's always good to know how much will be needed for the dissolution but knowing how and when to add is just as important.
 
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