j200 said:
Hello!
Yesterday I tried to reclaim some gold from various electronic parts. I've cut off the gold plated parts from circuit boards,
What kind of parts were they? Sometimes it makes a difference, certain types of material are better to process in different ways. It might help us understand what else you introduced into your solution.
threw them into a jar and covered them with HCL acid. Then I've started to add Nitric acid in small portions until I saw that all of the gold is dissolved. After that, I've separated the plastic parts,
It's usually best not to introduce plastics or polymers into Aqua Regia. It sometimes creates a soupy mess that you then have to filter, cake/dry, roast, grind in a mortar and pestle, then re-dissolve into Aqua Regia. This can lengthen your process by days, or depending upon how much time you really have to dedicate to this if it's a hobby, much longer.
rinsed them with water and filtered the solution which had a dark-green color (really dark). I've started to add SMB in small portions and instantly I could see a brown powder precipitating.
If you could say what type of material you were processing, how much of it you had, what you think your yield should be then we can discuss how much SMB you should have used. General rule of thumb when precipitating with SMB is to use as much SMB as you are expecting in Au. So if you are expecting 5 grams of gold, you should use around 5 grams of SMB.
It seemed that everything is going just as it should but the solution didn't get clear at all. It was really dark and didn't get any brighter.
If you dissolved other things into your solution, that do not precipitate when you add SMB, they will stay in solution, and thus color it. When your solution goes totally colorless is when it is comprised almost entirely of Au, such as your second refining, when you are producing high purity gold. This is because your solution on your second refining is comprised almost exclusively of Au. When it precipitates out, your solution goes clear because there is very little if anything in solution.
I kept adding SMB. There was fizzling during each addition and as I kept adding it the powder that was precipitating was no longer brown but white.
Did the fizzing give off a brown rusty colored gas, if so that means you had free nitric in solution and burned it up when you added the SMB. If this is the case, if you have too much free nitric in solution then when you add SMB it will fizz, give off a brown rusty colored gas (NOx) which you should not breath because it could kill you. I hope you are taking all the correct safety precautions. Anyway, you might precipitate some gold as you add the SMB, but you have free nitric so almost as soon as the gold precipitates, it gets re-dissolved back into solution again. Then you keep added SMB. There comes a point when you add too much SMB and your solution can no longer hold it in solution, specially if it's cold.
The solution didn't change it's color a bit. So I've filtered off the powder and tried to dissolve it in AR. Everything was going smoothly at the beginning but after the powder has dissolved all of the deep black-green solution changed into a green sludge.
It's hard to tell what exactly you have done. It sounds like you put way too much SMB in your solution in the presence of free nitric, it was burned up, fizzed, you saw brown powder that now sounds like it disappeared and in it's place you have white powder. Then when you heated up your solution you dissolved the SMB into solution because it actually expands when heated, and now you have a soup that looks probably milky green?
But it also could be that you put tin into your solution, I cannot tell because I have no idea what type of material you were putting into your AR solution. If you did put tin into AR, it will probably turn into Stannous oxide (tin oxide) which will not dissolve in Nitric Acid, Hydrochloric Acid, nor Aqua Regia. However it sounded like your solution was milky white when heated so I am assuming it's too much SMB. Tin Oxide would have just sat at the bottom, laughing at you.
What now? I kept the solution from which I've filtered the powder as well as the sludge. I'm not sure where the gold. I know that I can use stannous chloride but it's going to be delivered to me in about 3-4 days. This was a small scale experiment because I was impatient. Any tips would be appreciated.
You seem like a smart guy, if I were you I would put everything to the side and wait to get your delivery. Have you read C. M. Hoke Refining Precious Metal Waste yet? 3-4 days you can have that read, and by the time your Stannous Chloride arrives you might be ready to test it properly. It's useless at this point to tell you that you should have waited, you already know that, but you probably should have done some reading before attempting this.
Keep everything, don't throw anything away, even the sludge that you filtered off. Wait until you can test for gold in solution, if it's not there it's probably in the material you filtered off. Even if it does test positive you probably still have values in the sludge/powder you filtered off. There also may be some plastics in your solution as well, but I cannot tell anything until you post more information.
So long as you throw nothing away, you still have your precious metals somewhere. And so long as that is the case, you will be able to extract them once you understand how. Pictures would be helpful, more information on what type of material it was, if you stripped base metals before digesting in Aqua Regia, etc. Think about it like this, if you were trying to help someone who had a similar problem, what information would you want to know so that they could try and help you. That's the information we need.
And by the way, welcomes to the forum. It's always good to see new people. You might be interested in taking the forum tour also. If you are serious about learning this stuff, this forum is THE place to be, bar none.
PS. I didn't read the whole Hokes book yet. I'm still reading it...
Cheers
Scott
