Sodium metabisulfite

[yellowfoil]

Hello friends. Finally I started to refine, after years of recovering gold mostly from computer cards and memory connectors.
I managed to get few grams of nice looking gold precipitate, but with lots of difficulties. My biggest problem was precipitation.
For some reason I would prefer to use solution of sodium metabisulfite in distilled water, which failed in my case, rather than
adding it in powdery form, but I am not sure what is appropriate in given situation or if it is ok in any circumstance. Would
anybody put some light into this issue? Thanks a lot.

 

[sirex]

So I see that you have gold powder. So you were successful to some degree.

What was the problem? You want to Add SMB as a solution in distilled H20 and it did not work?

But adding it in powder form did?

 

[4metals]

It should have worked either way. As a powder the sulfur dioxide often releases as a gas on contact with the acid at the surface and more is lost to outgassing. As a liquid it is dispensed into the liquid more efficiently.

 

[yellowfoil]

Thanks for responding to my problem. I really appreciate it.
To describe all steps I had to make to get it out would fill up few pages and I don't want to get into that. I used solution of SMB and later powder and it failed in ether case. At the end I cemented it on copper to get all precious metals out and started all over again. Second time I used copperas and it worked ok.

That's what I thought about outgassing of SO2, but didn't know if SMB in solution or powder form should be used in different situations or if it doesn't matter at all. Thanks.

 

[4metals]

When you added the metabisulfite was red NOx gassing off the reaction? Or was red NOx gassing off when you added copper to cement it?

 

[yellowfoil]

I believe that the solution was completely denoxed by sulfamic acid.
I didn't see any NOx when adding SMB solution (there was no reaction to SMB solution at all), or cementing with copper.

 

[Yggdrasil]

I believe that the solution was completely denoxed by sulfamic acid.
I didn't see any NOx when adding SMB solution (there was no reaction to SMB solution at all), or cementing with copper.

Maybe that should raise some concern. What was the pH?

 

[Golddigger76]

Even when denoxed SMB should have a reaction with your gold bearing acids. I will use dry smb- (Bonide Stumpout) for smaller gold refines 100ml or less and almost always for the 2nd refining.
For the larger refines I will saturate water with the SMB. Not sure if it really works better but for me there is less reaction on the surface and more reaction at the bottom of my beaker.
If you were able to cement your gold out with copper my thought is your smb is the possible problem.
Where did you get your SMB ?

Also were you expecting more gold than you recovered ?
Without more details we can only guess what the problem could be.

 

[yellowfoil]

SMB used was Bonide Stumpout, so there should not be any problem. I think that I should have incinerate the material first before refining.
There was some contamination with foils like remains of fiberglass, pieces of plastic wire insulation and some smd like capacitors and resistors, all after AP and clean. After cementing and redissolving the black powder, there was some grayish yellowish flaky material floating on the surface of AR and not getting wet. No idea what it could be. Solution was not yellow but orange. Unfortunately I don't have a picture handy to post. Could do it later.

 

[yellowfoil]

Maybe that should raise some concern. What was the pH?

Sorry, I have no idea what was the pH, but I didn't add large volume of sulfamic acid, if that is a concern.

 

[Yggdrasil]

The Sulfamic acid is no concern like that, but was your solution Acidic?
The SMB needs to be in an acidic environment to create the SO2 that precipitates the Gold.
Best keep it lower than 2ish.

 

[orvi]

Sorry, I have no idea what was the pH, but I didn't add large volume of sulfamic acid, if that is a concern.

pH for gold drop is very important. As Yggdrasil pointed out, you want it to be lower than 2.
SMB is basic - so it will consume acid (HCl) when added - and it release SO2 - which is active reducer for gold. If you do not have enough free acid in solution, SMB would have troubles to reduce the gold. And also, with raising pH, you can drop quite a bit of impurities together with gold - namely AgCl, base metals hydroxy/chlorides etc - making your gold less pure.

After adding SMB, you should test pH of the solution - if it isn´t acidic enough, slowly add HCL till it will be. Be careful as SMB would release SO2 - which isn´t super-soluble in water and could erupt from the solution, causing expensive mess. Stirr it while adding either dissolved SMB or fresh acid

 

[yellowfoil]

I poured about 300ml of Hcl into the beaker and then carefully added HNO3 till all gold was dissolved. Then I used sulfamic acid to denox it. I didn't see too much of reaction so after cooling I used SMB. I think it is frequently used approach which should work. I don't have pH strips to check for pH, because I didn't expect any needs for that. What could change the pH way out of the range, that SMB wouldn't work?

 

[orvi]

I poured about 300ml of Hcl into the beaker and then carefully added HNO3 till all gold was dissolved. Then I used sulfamic acid to denox it. I didn't see too much of reaction so after cooling I used SMB. I think it is frequently used approach which should work. I don't have pH strips to check for pH, because I didn't expect any needs for that. What could change the pH way out of the range, that SMB wouldn't work?

If the gold you are showing was refined using 300 mL HCL, I assume you had plenty of free acid. pH strips are lab neccessity, obtain some - they are cheap and versatile. You will also need them when processing waste solutions.

Easy answer - metals reacting with AR they deplete acid (logically), and if you add too much metals in the feed, they eventually consume all acid present, forming metal chlorides.

 

[yellowfoil]

When solution of SMB failed, I used powder and it was fizzling, so I would say
that pH was in necessary range. After few tee spoons i realize that it is going
nowhere, so I stopped and decided to cement it out.

You are right, I will get some pH strips. I will need them anyway. My waste
of Cu2Cl is few gallons now and it is time to deal with it.

 

[Shark]

The smb may not react to the solution If the PH is to far off. I don’t have the education in chemistry to fully understand this so if I run into the described situation I typically add more hydrochloric just to be sure the PH is in range needed for the SMB to work properly. Chemistry is at best difficult to understand, but the results are worth the effort, and saves time in the long run.

 

[orvi]

When solution of SMB failed, I used powder and it was fizzling, so I would say
that pH was in necessary range. After few tee spoons i realize that it is going
nowhere, so I stopped and decided to cement it out.

You are right, I will get some pH strips. I will need them anyway. My waste
of Cu2Cl is few gallons now and it is time to deal with it.

This is strange as SMB should always work. Sometimes it happen that you have very little gold in solution so it takes hours and hours for particles to properly agglomerate and sink to the bottom.

When I began refining some many years ago, I was teached to SO2 smell presence. When you drop the gold with sulfite or SMB (we used sodium sulfite because it was cheap and available), stirr it well, then let it sit for about like 15-30 minutes and came back, you should be able to smell the SO2 gas from the liquid. If you do not smell any, you need to add more SMB or sulfite.
This is how I uncongested my nose regularly every week I think I do not need to mention that this approach is nowhere safe and plesant

But you can get the idea. If once SO2 persist in solution for few minutes, reaction is done, gold is reduced. Maybe not agglomerated properly, but it is out already you will find stannous negative.

And if the stannous is positive, then add SMB and it become negative, all you need to do is wait till it all agglomerate and settle. Few stirs during first half hour can help particles to agglomerate. But only gentle stirring, not vigorous.

 

[yellowfoil]

Orvi, thank you for your advice. In this hobby, every hint is helpful.

My firs attempt to process 75g of ceramic oscillators last year didn't go well and I lost about 0.8g of gold. This was my second attempt to refine and almost failed as well. I am slowly loosing interest. In this run, to my surprise, I got 21.2g of gold and it is upping my spirit somehow.

Thanks to everybody for helpful input.

 

[eaglekeeper]

I got 21.2g of gold and it is upping my spirit somehow.

Gold in your hand has a tendency to do that...

 

[yellowfoil]

Now I have more pictures to post, which may help to identify what was the initial problem.


This is after first digestion in AR. Then it was denoxed, cooled to about 28C with ice and filtered. After that I attempted to drop gold with saturated solution of SMB, which failed. Stannous test showed dark brownish spot after failed drop. I underestimated the amount of gold by at least 50%, but there was good margin of dissolved SMB.


This is after cementing with copper, and redissolving with AR. There is some material floating on the top of pregnant solution which I didn't expect. Then it was again denoxed, cooled with ice, filtered and dropped with copperas. This time it worked.