At what point to throw in the towel...

[dsroten]

First of all, let me say hello to the Forum. I joined a while back, haven't posted, and have been lurking, reading both here and Hoke every chance I get. Meanwhile I've been trying some small experiments to go along with my reading so I could get a feel for how things will go in the future. I started with fairly foolproof things like the AP method on gold fingers, leaching a few pins with nitric, etc. and gathered up my gold foils and flakes from these processes for AR later on. I tried the aqua regia on those the other day and it went flawlessly. I now have a beaker with a layer of beautiful brown powder in the bottom of it after dropping with SMB.

This brings me to the reason for the title of this thread. Since my first foray into refining went so well I decided to try something different. I decided to try to recover from the ceramic CPU's I had gathered up. I broke them up, covered them with HCL, and began adding nitric acid in small doses. Now I was doing this outside with no heat so I knew the process would be slow. After a couple days of this (full time job means I walk by it a couple times a day and observe - adding a drop or two of nitric when I saw gold still on the chips), finally there was no more gold visible. I filtered the solution to remove the small chip pieces, washed my chips 2 or 3 times and added this to my impregnated solution, which was very dark colored I may add. I proceeded onward, my solution at ambient temp, with SMB precipitation. My first observation was that much fizzing was involved when adding SMB. From Hoke, this tells me I used to much nitric. Apparently thats a common rookie mistake, Hoke even says so. I understand that I can just keep adding SMB and eventually the excess nitric is consumed and the precipitation will proceed on. I decided to try this instead of the evaporation technique, since I cant really babysit the process all day. Well the fizzing kept on and kept on. I'm thinking, surely to goodness I didnt get that carried away with the nitric, but thinking back on it I probably did. Finally today I added SMB and got no fizzing. However, I didnt really see the muddy look that I saw with my first successful precipitation either. I forgot to add earlier, my solution does test positive for gold with stannous. However, I didnt test the solution before adding SMB, because I thought, well surely thats where the gold is since I cant see it. I mention this because I've read a time or two about getting false positives upon overuse of SMB.

So after that whole wall of text (I wanted to explain what I had done) here is my question. At what point should I just chunk a piece of copper in there and try to recover the resulting powders? I'm going to let my solution rest a day or two and check for settled out powder. But if there is none, what would you do? I know by the color of my solution there is evidently quite a bit of base metal in solution (confused me since I thought the ceramic chips were Kovar based and the AR wouldn't really dissolve it). Was using SMB to drive off the nitric a bad move? The forum's thoughts are much appreciated.

 

[upcyclist]

First off, I'm glad to see that "throwing in the towel" refers to resorting to cementing on copper, not on giving up entirely

On denoxing your AR solution, just search the forums for something like "denox" and "sulfamic"--one of the members has a thread (and accompanying youtube vid) on using sulfamic acid (found dry in Home Depot as a grout cleaner) to denox AR solutions. Since adding a ton of SMB may make your solution pretty messy, sulfamic acid is a lot cleaner. It also has the benefit of dropping out any lead as insoluble lead sulfate, so denox, then filter your solution, then precipitate.

I'll leave it to the more experienced folk here as to how to best get the gold out of your solution. If you kept your reaction vessel covered (like with a watch glass), you shouldn't have fizzed away any of the gold in solution. If it was uncovered, especially if your solution level was close to the top of the container (like 550mL of solution in a 600mL beaker), you may have lost some of your gold in that effervescence, but not all.

On doing some small amount of work in absentia: obviously there are safety considerations to observe. But one thing that will help is doing what you can to keep solutions in motion. In some cases (especially recovery/AP and waste treatment), bubblers are appropriate. In other cases, a stirrer bar or good old fashioned stirring is called for. You may have been doing this, but you didn't say it, so to be clear: when you stopped by to add more nitric to your AR solution, did you stir the solution first, then observe it to see if there was any reaction? It could be a slow reaction at room temps, so you'd need to look closely for the formation of bubbles; shining a laser through it will also help to identify small bubbles and particles.

Another thought: Stannous chloride testing does not work reliably with excess nitric present. So to amend my above statement, denox, then test, filter, precipitate, etc.

Last one: When you said you broke up the processors, how small are your bits? Did you break them in half, or did you end up with a 100 mesh powder?

 

[dsroten]

On doing some small amount of work in absentia: obviously there are safety considerations to observe. But one thing that will help is doing what you can to keep solutions in motion. In some cases (especially recovery/AP and waste treatment), bubblers are appropriate. In other cases, a stirrer bar or good old fashioned stirring is called for. You may have been doing this, but you didn't say it, so to be clear: when you stopped by to add more nitric to your AR solution, did you stir the solution first, then observe it to see if there was any reaction? It could be a slow reaction at room temps, so you'd need to look closely for the formation of bubbles; shining a laser through it will also help to identify small bubbles and particles.

This is a good point, and when I think back to "did I really add that much nitric" I think the answer was yes. I tried to swirl it about some when I added nitric, though I was pretty ginger with it, not knowing if the sharp edges of the ceramic chips would bust my beaker.

Another thought: Stannous chloride testing does not work reliably with excess nitric present. So to amend my above statement, denox, then test, filter, precipitate, etc.

The experience I gained with this go round seems to match this statement perfectly. Once all this fizzing began with no precipitate I decided to test with stannous. It was negative. So off to the forum I went to read and repeatedly I found examples of excess nitric monkeying with stannous tests. Now that the fizzing has stopped I get a purple stain with stannous.


Last one: When you said you broke up the processors, how small are your bits? Did you break them in half, or did you end up with a 100 mesh powder?

I used a hammer to break each chip into 5 or 6 pieces

 

[Smack]

That member with the video is Kadriver aka sreetips on youtube.

 

[Shark]

Testing your solution is always important, especially when your in doubt of your skills.(I still have doubts on my skills at times) As for cementing on copper, your at a good point in your learning to try it. Think of it as one of those small experiments Hoke mentions. Later on, when you need it, you will have a better understanding of how and when to proceed with it. If your at the point you don't know how to proceed, then you are at the point of trying cementing on copper. With that said, Sulfamic works great, but it is really not a cure for over use of nitric. The best cure is learning to use nitric in amounts that get the job done without an excess. At times this in itself seems like more of an art than a skill to me. Personally, I feel your doing a good job, you just need more hands on work to get a grasp on that next step. I never have learned much from things that went perfect, but I have learned learned a great deal from those things that went wrong. If your willing to wait a few days to proceed, then try heating the solution (below the boiling point of course) for an hour or so when you get back to working with it. Then try dropping it again with your SMB. The wait can help to deplete the nitric although slowly compared to heating or sulfamic. You can also add more material to the solution to help use up nitric. Harold's method of using a small gold button is one method that comes to mind (works well). Keep studying and don't give up is the key to success.

 

[nickvc]

Well done on reading and studying and trying small experiments.
When dissolving using nitric I would suggest heating your solution this will ensure the nitric is fully consumed, your solution may be barren of gold if you didn't dissolve all the base metals as the base metals will cement your gold back out.
I'd suggest getting your processors and putting them into a fresh beaker adding enough HCl to cover put on heat and then add small increments of nitric but only when all reaction ceases,the reaction will be quite violent if you still have base metals so use a beaker large enough to allow for that, good luck and keep us informed.

 

[maynman1751]

Was there any chance that you ran out of HCL during the process? If you run short of HCL and are just adding Nitric the process will also come to a halt. I believe that this would also allow the gold to cement back out on any remaining base metals. Just a thought!!!!

 

[dsroten]

Was there any chance that you ran out of HCL during the process? If you run short of HCL and are just adding Nitric the process will also come to a halt. I believe that this would also allow the gold to cement back out on any remaining base metals. Just a thought!!!!

Well I'm not really experienced enough to know for sure, but anything is possible. My beaker is setting on the bench covered this morning and I'm going to check on it at lunch. I didnt look at it on purpose this morning so I wouldn't have to be frustrated before my coffee I switched gears for the meanwhile and am gently boiling some fiber CPU pins in HCL. I figure that should be done by lunch.

Then I'm going back to the solution that created this thread. I figure I'll pour my solution off and see if anything is in the bottom. I also kept all the CPU's, they are in a jar and I did go ahead and cover those with HCL this morning. Depending on what I see in my original solution I may run AR on them again. I do have a hotplate I picked up on the cheap a while back, so I'm going to start using some heat for my reactions, as was mentioned above.

Many thanks folks, I'll keep you posted as I learn my way through this mess I've created.

 

[4metals]

It is hard to imagine that you have added more nitric than hydrochloric but I guess it is possible when you are doing so many different things at once. Been there, done that!

What I always did to keep track of my acid additions was to measure the acids required out. Generally a liter of Aqua regia will dissolve 7.5 ounces of metal. That's metal, not gold. If the metal is higher in copper, it's a bit more and it depends on the ratio of other metals but 7.5 ounces per liter is a good rule of thumb. So if I had 1 pound of metal with my gold and base metals on it, the math would go like this;

1 pound = 14.583 troy ounces (always a good number to remember in the refining business)

14.583 ounces starting metal / 7.5 ounces digested per liter = 1.94 liters, close enough to call it two. So to consume all of the metal we will consume 2 liters of aqua regia.

I prefer Aqua regia in a covered vessel to be 4:1 so for every liter (1000 ml) there is 4/5 or 800 ml of Hydrochloric and 1/5 or 200 ml of Nitric.

Using a 4:1 formula for aqua regia for the 1 pound example, you would need 1600 ml of Hydrochloric acid and 400 ml of nitric acid.

I would add the hydrochloric to a beaker with the scrap, and measure out the nitric into a separate covered beaker. Then I would slowly add nitric to the reaction. Starting with about 1/4 to 1/3 of the total volume you have measured out. Then whenever you walk by and the reaction appears to have slowed or stopped (after mixing to assure everything see's the same concentration of solution) you can slowly add more in small increments. This technique will assure you that you never exceed the 4:1 ratio of hydrochloric to nitric and once you set up to do it you don't have to think about it much or do any remembering. Do not add more nitric than you need, and it is entirely possible you may not need all you measured out, so it is perfectly fine to pour the unused nitric back into the bottle where you store it.

It is also advisable to periodically test your solution with stannous chloride along the way. It is possible, actually quite probable when the base metals are high in concentration, to test positive for gold after a few minutes of digestion and at some point before you are finished reacting test negative for gold. If this happens you have cemented your gold with base metals and it is on the bottom. No worries, just allow everything to settle and either decant (or preferentially) filter the solution to collect the undissolved and guesstimate the weight and start the process over.

I do question why aqua regia was your first choice. I would always prefer to use a nitric / distilled water digestion to rid myself of as many base metals as possible but there are plenty of refiners who just jump into Aqua regia first. You will also with circuit boards kind of guesstimate the percentage of the boards or ceramic that is not metal and not use those figures in your starting weights. This gets easier with experience as I always weighed the insolubles after metal digestion for different scraptypes to get an idea of what percentage was plastic or ceramic or teflon or whatever insoluble.

 

[dsroten]

Time for an update. I let my solution settle for a day or two, and did some evaporating to help denox my solution, which I have discovered, is a painfully agonizing process...while that was going on I was working on some fiber CPU pins, my goal with them was to have enough gold to make myself a "standard solution" of aurachloric acid to use to make sure my stannous was good. Now I have no idea what the concentration of it is, but I do have a beautiful yellow liquid in a small beaker, and really that was my goal. Just to have something to use a baseline, since I had several beakers of various solutions around and I didnt trust my stannous at that point. At any rate, my stannous is good to go, made a nice purple stain with my test solution.

So off I went to check the AR solution from my ceramic process. After denoxing, my solutions are negative. YAY! All hope is not lost. I sorta had a feeling after it was mentioned above that my gold may have cemented back out due to maybe still having base metal present. I kept all the processors in a jar, and covered them up with HCL, and it now has a deep blue/green color. So there must have still been a lot of copper in there. I filtered the AR solutions in case of any solids and put them in my stock pot, and will get back to the processors soon.

Thanks to every body that has commented. The little pointers and direction to proceed helped immensely, mentally as much as anything.