Gold won't drop! HELP! Please!

[butcher]

Nitric and nitrate are basically two different animals of the same family here, nitrate is a salt of nitric, adding hydrogen from acid like HCl to the nitrate ion oxidizes it back into nitric acid.
(here the HCl is reduced to chloride ions).

There are many ways you can do it. you can always use a clean plastic 5-gallon bucket and a clean thick bar of copper...

Gold cement or reduced gold can be a fine powder making losses more noticeable when working with many small batches, and with a small loss in each batch, as opposed to working with one larger batch where one small loss would not be as noticeable.

You will want to eliminate nitric and nitrate salts from your gold, consider this:
You have the elemental gold powder in a pile, along with some insoluble nitrate salts,
OK, good now, but what happens when you go to wash your gold powder to remove some base metals, and you add an acid such as HCl to the gold powders? Well, by adding the acid or hydrogen ions, you have made some aqua regia to redissolve the gold, basically defeating your purpose of washing the gold...

 

[Alabama938]

Small loss with each batch is a great point. I was going to try to avoid the copper bar technique, but it’s a nice to have a bailout. Are there any conditions that would improve the rate of cementation like heating, stir bar in the beaker, pH manipulation, or using silver.

I majored in chemistry and biochemistry, but have been in medical field for last 20 years, so forgive my excess of questions but this is all so fascinating.

I was planning on denitrifying The solution with sulfamic acid. I’m thinking this is going to take longer then would normally be seen with nitric acid based AR.

 

[butcher]

I would consider using a combination of Hoke's evaporation technique. along with Harold's trick of adding a gold button, and then sulfamic acid to insure nitrate and nitric removal.

The Hoke evaporation method will help to remove nitric as well as the nitrate salts (as you reacidify the solution before further evaporation) this also can be seen as the solution evolves the red NOx gas fume during the process. the gold button consumes free acids, and the sulfamic acid can help as well as help with removing lead as lead-sulfate from solution, the sulfamic which helps to form sulfuric in the solution can also help to convert nitrate salts to nitric acid and thus to NOx in the evaporation heating process as well.

The batch that last dissolved the gold in the first corning dish, that gold can go to the second burner of the hot plate into the corning dish evaporating the solution, helping to minimize your volume issues...

I really do not know what material you are working with, as I could not find details in this thread, it can be better to keep the discussions in one thread, with pictures and as much detail as possible, I have a hard time following things spread out in different threads, topics, or different discussions, pictures, and ging clear details are also helpful, the more we understand of the problem the easier it may be to find an answer to that problem.

 

[Alabama938]

Another fair point

I have 20 chips, I 960, Tried heating in dilute nitric acid twice, and it doesn’t appear that the Kovar was dissolving at all. I rinsed and dry those chips off and let them sit for a few days while I researched straight AR which seems to be a favorite among members for CPUs. I decided to try poormans AR first.

I added the hammer crushed chips to a Tall beaker, covered in 600 mL hydrochloric acid, slowly added 1/2 mole potassium nitrate in a three molar solution to try to dissolve everything. That didn’t seem to be enough nitrate to dissolve all the metals before I had to go to bed adding it in 4 to 6 mL increments. So the solution was allowed to cool overnight and this morning had a negative stannous test on filter paper and in a white spoon.

That’s why the question about decanting a not pregnant solution, to use fresh reagents. The question about sulfamic acid comes from this forum as a possible denoxer(sp?) for HNO3 and I read some stuff about using it to remove free nitrates from lake water,
Which made me think it could help neutralize extra (K)nitrate ions in solution…

If the free nitrate ion is occasionally changed into nitric acid by the hydrochloric acid, a decent solution of sulfamic should gobble that up and drive the reaction forward, but it seemed like something that might be slower than with the actual acid.

I was trying to find a safe and cost efficient way to process e-waste, I also have a decent sized batch of acid peroxide cooking with a bubbler. I have the ability to acquire a large amount of fingers and CPUs for free and I wanted to see if this was something that I could pull off, and it sucked me in.

I really appreciate all the time you guys spend considering in typing responses, your experience is an invaluable resource!

Roll Tide

 

[butcher]

If you only have very a slight excess of nitric acid in solution, which is keeping you from precipitating your gold (which actually would mainly be just the unreacted Nox gases left in solution), then you can overcome the NOx gas keeping the gold dissolved, by adding more SMB and drive the reaction to the right of the equation.

Here the SMB is not very good at de-NOx-ing a solution but it can help to drive the reaction towards the right, by helping in removing active gases of NOx.
If you have overused nitric and have much left in the solution then adding an excess of SMB will do little, to almost no good, to get your gold to precipitate effectively, as it is not good at removing free nitric acid from the solution.

Ferrous sulfate can more effectively remove free nitric and actually de-NOx the solution, and precipitate gold.

FeSO4 will actually react with the free nitric acid in solution to decompose the free nitric acid and to de-NOx the solution and reduce the gold back into a metal powder form.

SMB in excess can help to drive off a little NOx gas from solution but is really not effective to destroy much free nitric in solution to any extent.

Both will precipitate gold if the solution has the free nitric eliminated.

ferrous sulfate or copperas will work to precipitate with some free nitric involved where SMB would not work to remove all of the excess nitric involved.