# Partial gold drop



## Dougplogan (Jan 1, 2022)

I'll start with this is only my thrid time trying this step. I used hydrochloric acid and a few ml of nitric to put about ten grams of gold plating from several circuit boards. Basically when it was time to precipitate the gold it acted as expected when I added smb. Two teaspoons full and nice color change followed by a fast settling. Solution was warm or beacker was warm to the touch but not hot. After settling I did a stannous test and test was instant color. Which I expected because it looks like maybe a gram settled on bottom of beaker. Again the gold foil material was just over 10 grams so I expected atleast half that to drop. Anyways I added another teaspoon of smb at this point with a nice strong fizz reaction but nothing more dropping out. I might add not sure if this matters but solution is pretty acidic still. Only water used to dilute was the water I used to flush color out of previous container and through filter. Just curious what thoughts people might have? I'm going to leave till tomorrow and think and read.


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## Yggdrasil (Jan 2, 2022)

How did you get the foils?
AP?
Did you wash them in HCl before dissolving in AR?


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## Dougplogan (Jan 2, 2022)

Yggdrasil said:


> How did you get the foils?
> AP?
> Did you wash them in HCl before dissolving in AR?


Yes AP solution. Then hydrochloric boil to make sure they were clean. Then hydrochloric acid and nitric


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## Dougplogan (Jan 2, 2022)

I know it's not excess nitric acid because I've got a healthy layer of gold on bottom of beaker that is not going back into solution. What did drop looks great and is as expected. Problem is just it's alot less than expected and stannous test is a hard positive or shows a large concentration in solution. I tried 1 more teaspoon of smb got alot of fizzing but no more dropped. I'm thinking separate gold that dropped then either try a different method of getting the rest to drop or maybe just cementing out. I'm really curious as to what may cause partial drops or what may keep a high percentage from dropping out. Seems to me that it's possible cementing and repeating would do the same thing and only get a partial drop atleast it will without knowing what's causing it to not drop. Oh and solution is nice bright golden colored liquid still after the initial drop.


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## nickvc (Jan 2, 2022)

Try adding a little sulphamic to neutralize any excess nitric you may have , if you get no reaction try adding a little more HCl to your solution , if neither of those help separate your solids and add copper to the solution to cement the gold out.


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## Martijn (Jan 2, 2022)

How much did you expect? Did you weigh the foils? 
To see a good stannous test result, put some drops of distilled water in a spot plate and add one drop of solution to that. Then add stannous. Dilute more if it's still too dark. 
Brown is copper, purple is gold. 
Black can be anything. 

You have no excess nitric since you have gold foils left. So no worries there. 
Last option: cement it out or let the stockpot get it out. 

The only thing that would keep a part of gold in solution, is insufficient precipitant or not enough free HCL in solution to let the SMB react with. 

Martijn.


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## Dougplogan (Jan 2, 2022)

Martijn said:


> How much did you expect? Did you weigh the foils?
> To see a good stannous test result, put some drops of distilled water in a spot plate and add one drop of solution to that. Then add stannous. Dilute more if it's still too dark.
> Brown is copper, purple is gold.
> Black can be anything.
> ...


Not sure what to expect but I did weigh the foils prior to aqua regia. 11.6 grams in a coffee filter. It was dry. Thanks for the idea of diluting few drops for stannous test. When I did that I used a white 20 oz coke bottle top. I actually had to fill it half full and only use two drops of my solution to keep it from going jet black. It is most definitely purple. Also I got a weight on the powder that dropped it's just under 2 grams so a bit more than I thought. I tried a small test batch to precipitate by adding more smb no drop. Solution is yellow still. I think I'll just cement out on copper. What doesn't drop over next day or two that way can go in stock pot.


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## kurtak (Jan 2, 2022)

You still have "some" free nitric - but it is so little that it is allowing "some" gold to drop but not all the gold to drop

Some gold will drop because the free nitric is to weak to hold all the gold when you add your reducer (SMB) but once some of the gold drops the free nitric is then strong enough to prevent all the gold dropping

Try putting it on your hot plate overnight (set on low)

I am willing to bet one of two things will happen

1) your gold will dissolve because the heat will "drive" the "weak" free nitric to dissolve the gold that did drop

2) or - because you already have more then enough SMB in the solution - the heat will drive off the Nox & once the Nox is driven off the SMB will finish dropping your gold

Keep a watch glass on the beaker so you don't evaporate the solution all the way down (the Nox will go out the spout)

OR - just cement it with copper - if you cement it right with copper you should get 99+ gold back (not quite 999 gold)

Hint on cementing with copper - do NOT leave the copper in longer then needed to cement the gold - doing so will lead to more copper contamination

you know the cementing is done when there is no more reaction (foaming) &/or no more brown fumes

In fact - because you are on the boarder line of reduction/oxidation you can likely pull the copper before it is completely done reacting - that's because you really only need enough copper to use up the "little bit" of free nitric causing the problem at which point the SMB will finish the gold drop - do it right & you can get 999 back

Kurt


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## cejohnsonsr1 (Jan 2, 2022)

You have to use more SMB than you might think. A couple of spoonfuls isn’t enough to drop 10 grams. Your stanis test showed gold in solution. Keep adding SMB until it goes black and foams white on top. Might not hurt to dilute your solution with a little distilled water too.


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## Dougplogan (Jan 2, 2022)

kurtak said:


> You still have "some" free nitric - but it is so little that it is allowing "some" gold to drop but not all the gold to drop
> 
> Some gold will drop because the free nitric is to weak to hold all the gold when you add your reducer (SMB) but once some of the gold drops the free nitric is then strong enough to prevent all the gold dropping
> 
> ...


I don't think it was nitric. When I started the thread it had been 8 hours or so after that initial drop. This morning or about 24 hours after I attempted to drop gold out the powder seemed exact same amount as far as I could tell so over night any excess nitric would've been used up digesting that gold. Which didn't go back into solution. I suspected that at first so I waited several hours waiting to see if precipitate shrank which it did not.


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## Dougplogan (Jan 2, 2022)

Martijn said:


> How much did you expect? Did you weigh the foils?
> To see a good stannous test result, put some drops of distilled water in a spot plate and add one drop of solution to that. Then add stannous. Dilute more if it's still too dark.
> Brown is copper, purple is gold.
> Black can be anything.
> ...


The stannous Ive been using to test solutions with I made. But basically I had a 2 gallon bucket full of cell phone boards. I used a heat gun to depopulate then used hydrochloric to get rid of the soldering. I left them overnight and then saved that and it's been working for stannous test I think. It is a neon blue colored solution though. Is it possible contaminates could be in that effecting a stannous test results? I'm sure it has alot more than solder and copper in it, maybe even some gold as I have had plating partially dessolve in fresh hydrochloric when first covering stuff.


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## snail (Jan 2, 2022)

Recently I had some issues precipitating. I was using 2 to 3 times the weight of SMB to get the same results. 

The last sodium metabisulfite I purchased is such a fine powder it just floats and fizzes on the surface and little SO2 goes into the solution. Previous batches were more granular and tended to sink under the surface.

I now dissolve it in water before adding. Much greater effect than adding it dry. Never had to do this before this batch. I use much less now.


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## Dougplogan (Jan 2, 2022)

snail said:


> Recently I had some issues precipitating. I was using 2 to 3 times the weight of SMB to get the same results.
> 
> The last sodium metabisulfite I purchased is such a fine powder it just floats and fizzes on the surface and little SO2 goes into the solution. Previous batches were more granular and tended to sink under the surface.
> 
> I now dissolve it in water before adding. Much greater effect than adding it dry. Never had to do this before this batch. I use much less now.


I will have to try that. What I have is a very fine powder and just fizzes on top as well. I was having to stir it while I added


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## kurtak (Jan 3, 2022)

Dougplogan said:


> I don't think it was nitric. When I started the thread it had been 8 hours or so after that initial drop. This morning or about 24 hours after I attempted to drop gold out the powder seemed exact same amount as far as I could tell so over night any excess nitric would've been used up digesting that gold. Which didn't go back into solution. I suspected that at first so I waited several hours waiting to see if precipitate shrank which it did not.



Then try what nickvc suggested - add some more HCl

Edit to add; - if you are adding "more" SMB then needed to drop your gold & it is still not dropping then you need to figure what the problem is so you can fix that problem & not have the same problem in the future

what we know - you have already used more SMB then needed so it doesn't make a lot of sense to throw more SMB at it

did you try sulphamic as nickvc suggested

did you try what I suggested - low heat over night on hot plate - or are you just letting it sit a room temp

when you are on the boarder line as I described - HEAT can make ALL the difference

Copper is not always a last resort - copper can be your friend *& if done right* can give you back 999 gold

throwing more SMB at it when SMB is not working is NOT fixing the problem - work out the problem start with the easiest --- they are

1) heat --- 2) add some HCl --- 3) add sume sulphamic (sometimes spelled sulfamic) --- 4) add some copper just don't over do it you only need enough to use up any SMALL amount of free nitric you "may" have

Kurt


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## Dougplogan (Jan 3, 2022)

kurtak said:


> Then try what nickvc suggested - add some more HCl
> 
> Edit to add; - if you are adding "more" SMB then needed to drop your gold & it is still not dropping then you need to figure what the problem is so you can fix that problem & not have the same problem in the future
> 
> ...


I did add a few droppers of HCl. Don't have any sulfamic acid on hand. I used couple drops sulfuric before filtering. Left overnight with no change. I did ad a small piece of copper and within a few hours had a pile building at bottom of copper. When I thought it had finished I washed copper off well and filtered out the gold powder. It looks identical to what precipitated originally but I'll add that filter and all to next time I have something ready for ar


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## cejohnsonsr1 (Jan 3, 2022)

Dougplogan said:


> The stannous Ive been using to test solutions with I made. But basically I had a 2 gallon bucket full of cell phone boards. I used a heat gun to depopulate then used hydrochloric to get rid of the soldering. I left them overnight and then saved that and it's been working for stannous test I think. It is a neon blue colored solution though. Is it possible contaminates could be in that effecting a stannous test results? I'm sure it has alot more than solder and copper in it, maybe even some gold as I have had plating partially dessolve in fresh hydrochloric when first covering stuff.


Ok. I see 1 problem. A 2 gallon bucket of cell phone boards isn’t going to yield 10 gr of gold. Your stanis test showed gold in solution, so keep adding SMB until you no longer get a reaction except for white foam on top. I don’t know precisely what your yield will be, but I’d guess 1 gr max if you decant VERY carefully after precipitation is complete.


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## Dougplogan (Jan 3, 2022)

cejohnsonsr1 said:


> Ok. I see 1 problem. A 2 gallon bucket of cell phone boards isn’t going to yield 10 gr of gold. Your stanis test showed gold in solution, so keep adding SMB until you no longer get a reaction except for white foam on top. I don’t know precisely what your yield will be, but I’d guess 1 gr max if you decant VERY carefully after precipitation is complete.


The cell phone boards full of soldiering is how I got the liquid I'm using for stannous test. I didn't expect a 10 gram yeild. I was processing 10 grams of gold foils. Part of which came from the phone boards part were foils from cpu part were from trimmed ram fingers. Basically I'd been saving foils for a while now. I had them all in a single coffee filter that weighed 11 and half grams dried out. That was my starting material I expected 5 grams maybe more from that much in gold foils


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## timsiggins (Jan 3, 2022)

Hey guys have you notice if your solution is very dark it hard to notice when it time to stop add SMB, when you have a black solution what do you do


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## Dougplogan (Jan 3, 2022)

timsiggins said:


> Hey guys have you notice if your solution is very dark it hard to notice when it time to stop add SMB, when you have a black solution what do you do


Test with stannous. It will tell you if it's all dropped. Once it begins to drop that's usually enough from my experience which is very little. Lol this thread is about my 3rd attempt.


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## Noggin (Jan 3, 2022)

timsiggins said:


> Hey guys have you notice if your solution is very dark it hard to notice when it time to stop add SMB, when you have a black solution what do you do


Tim if your gold-bearing solution is very dark it implies that you used AR before it was clean enough to do so.


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## Martijn (Jan 4, 2022)

As said: test with stannous for gold in solution if it is all precipitated. 
if there is too much copper, or you've used too much SMB, You will have a dark stain, called a false positive. Dilute and try to see a purple color. It may be too dirty to properly see. 

Test after dissolution with AR if you have gold in solution. 

To get the suspended blacks to fall down, heat with a couple drops of sulfuric. 

OR when dropping dirty AR solutions, dark green from copper: *When in doubt, cement it out* on copper and redissolve. 

Martijn.


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