Please I need your advise/help!

[Etyoin]

Hello!

Thank you for being part of this Community.

Let me introduce myself. I'm Robert and new in gold refining, base in the UK. I'm interested in gold refining as a hobby. I'm also an EPP licence holder.
I did lots of study before I've started my first experiment.
- Read Hoke's book.
- Studding the from and other sources for a while.

I bought all the necessary safety equipment (nitrile gloves, chemical resistant gloves, full face mask etc..), tools(beakers, wash bottles, lab heater, pipets, etc..) and built a fume hood(ply wood and acrylic sheet), and I have a waste solution plastic jerry can too.

Why I need your help? Please see my process below.

Chemicals involved:
- HCl 36%
- Nitric acid 69%
- Sulfamic acid
- SMB
- Sodium nitrate (by accidentally, I'll explain later)

- I have prepared 200g of well trimmed fingers from different computer parts (memory, video cards, etc.) to a 3L beaker.
- I added 300ml Nitric acid increasingly.
- Once I poured all the Nitric acid onto the fingers I started to heat the solution just enough to speed the reaction up. (red/brown fume shown). I stirred the solution few times the solution.
- When the reaction stopped after couple/few hours, I have filtered the solution and washed off the gold plates with tap water using a home made filter with big enough holes where the small gold plates can go through. Then I drained the water off from the filtered gold plates.
- I have tested the solution with Stannous. It was negative. I disposed this solution into my waste solution jerry can.

- I prepared all the clean gold plates into another 3L beaker and added 250ml of HCl 36%.
- Then added 10ml Nitric acid 69%. The reaction started in my AR. I heated up the solution gently (not to boiling point).
- When no reaction was visible I added another 5-7ml Nitric acid to make sure all the gold dissolved in my AR. I was waiting approx. 1-1.5 hour. I stirred the solution few times the solution.
- I have checked my solution the colour of it was clear brown/yellow and was a bit of waste at the bottom from the PCB's (not relevant).
- I have tested the solution with Stannous. It was positive (nearly black)
- I filtered the solution through a paper lab filter (10-20 micron)
- I have tested the solution with Stannous. It was still positive (nearly black)
- I wanted to Denoxing the AR with sulfamic acid but by accidentally I added Sodium nitrate to my solution (stupid me, it was in similar package as the sulfamic acid and of course I didn't check it). Luckily I only put into my AR a small lab spoon of Sodium nitrate approx. 1g or less and it didn't dissolve completely so I filtered it through a paper filter quickly. Then I heated up the AR and added sulfamic acid increasingly spoon by spoon but not much reaction occurred even when I stirred it. Also, the colour of the AR became more green/yellow.
- I have tested the solution with Stannous. It was still positive (nearly black)
- I cooled down the AR. I put the beaker into cold water as I hadn't got ice.
- So finally I was there to precipitate the gold. I added SMB approx. 3-4 spoon 3-4g. But gold hasn't dropped at all only white powder appeared at the bottom of the beaker. Could it be the undissolved SMB? I have tested the solution with Stannous. It was still positive (nearly black)

I was wondering may I didn't denoxed the AR properly or the sodium nitrate caused this issue.

I would be grateful if someone can help or advise me how to solve this problem.

Many thanks,
Robert

 

[nickvc]

Try adding a little HCl.

 

[Martijn]

Test with a bit of gold or copper if your AR still has oxidizer in it. I suspect excess nitric. 10ml HNO3 can dissolve 10 grams of gold, i doubt there was 10 grams Au on 200 gr fingers.

 

[Etyoin]

Thanks for both of you answers. I'll test it and let you know the result.

 

[kurtak]

I have prepared 200g of well trimmed fingers from different computer parts (memory, video cards, etc.)

- I prepared all the clean gold plates into another 3L beaker and added 250ml of HCl 36%.
- Then added 10ml Nitric acid 69%.

You have WAY to much "free nitric" in your solution

One pound (454 grams) of fingers will give you about (plus/minus) 1.5 grams of gold - so 200 grams of fingers is only going to give you between 1/2 - 3/4 gram gold

As a "general rule" it takes "about" (plus/minus) 1 ml nitric to dissolve 1 gram gold - that is when you are dissolving a sold chunk of gold like a gold coin or bar

I prepared all the clean gold plates

We call these gold foils - not gold plates

When you are dissolving gold foils with AR (HCl plus nitric) it only takes about half as much nitric - so it on takes "about" 1/2 ml nitric to dissolve 1 gram gold foils (instead of the 1 ml nitric to dissolve 1 gram gold as a solid chunk)

That means you used "about" 20 times more nitric then was needed to dissolve your gold foils & that is A LOT of "free nitric"

Before you can drop your gold you need to get rid of all that free nitric - we call that de-Noxing the AR

I wanted to Denoxing the AR with sulfamic acid

And yes - normally sulfamic is what we use to de-Nox our AR

BUT - sulfamic only really works well when there is a "small amount" of free nitric in the solution --- when there is A LOT of free nitric in the solution it does not work so well

When there is A LOT of free nitric in the solution you are better off using up ALL THAT free nitric by dissolving more metal with all that free nitric

So there are two ways to do that -------------

1) if you have more gold you can add more gold to the solution --- in your case you would need to add a 12 - 15 gram sold chunk of gold (you always want to add a chunk of gold larger then the amount of free nitric to insure ALL the free nitric is used up)

2) add a sold piece of copper to the solution - the free nitric will get used up dissolving the copper & once the free nitric is used up it will also do what is called "cementing" the gold out of solution

In other words - the copper will not only use up the free nitric - but it will also "recover" your gold

That "recovered gold will likely be contaminated with a small amount of copper --- but you can then re-refine that recovered gold using MUCH LESS nitric in the second go of trying to refine the recovered gold

For what it is worth

Kurt

 

[Etyoin]

Hi Kurt,

I much appreciated your detailed answer and clarifying wrongly used words.

First, I'll test my solution as Martijn advised above. It should be free nitric in my solution so I'm going to follow your advise and use up the free nitric with cooper because I haven't got any gold.

I have built earlier a cementation tank based on FurgalRefiner post. It is a small 2L jar built exactly the same way as it was in the post.

Shall I use this and how long I have to run the cementation process?

Many thanks all of your help,
Robert

 

[haveagojoe]

So there are two ways to do that -------------

Another way would be to drive off the excess nitric by heating- evaporating it off and concentrating the solution down to a dark-coloured syrup, then add fresh HCl and repeat. Sreetips does it this way sometimes. If there is a lot of excess nitric it might require 2 or 3 repetitions, and if possible it would still be a good idea to add a small piece of gold on the last repetition just to be sure the last bit of nitric was used up. But I would think if it was only 10ml of nitric to start with, 2 repetitions should be sufficient, followed by a small addition of sulfamic.