# I forgot to neutralize! , help me please



## Denisse (Feb 25, 2021)

Hi I have a question:
How can I recover the gold from AR if I have already poured the SMB and the gold did not precipitate. ¿Is there a solution to this?, please help me


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## butcher (Feb 26, 2021)

Sulfamic acid ( grout cleaner in the hardware section) and using the heat of evaporation as mentioned in Hoke's book, the sulfamic acid produces some sulfuric acid which can precipitate lead as a sulfate, the lead salt will need to be separated from the solution before precipitating the gold, the added benefit of sulfuric acid is it will help drive off free nitric acid from the solution.

If you do not have sulfamic acid a little addition of sulfuric acid and heating to evaporate as mentioned in Hoke's book will also do the trick.

Adding a button of gold (Harold's trick), and using heat and evaporation to drive the nitric from solution as advised by Miss Hoke as she describes in the evaporation process.


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## Lino1406 (Feb 26, 2021)

SMB with acid produces SO2 which is a reducer and has a distinctive odor. Was brown NO2 produced? Was the SO2 odor felt? Was there a white precipitate of SMB excess?


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## Palladium (Feb 26, 2021)

Answer = SnCl2


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## g_axelsson (Feb 26, 2021)

Denisse, please don't double post.

I have removed your other post.

Göran


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## sayf (Feb 27, 2021)

Not a big problem , double the size of you aqua regia solution by tap water because gold loves to precipitate from diluted not concentrated solutions ,
You can eleminate the nitric using many ways :

1- nitric elemination by urea : (not recommended) 
heat your aqua regia for couple minutes until it is warm
add urea to the aqua regia, small spoon firstly a strong fizzing will start, wait until its finished then stir slowly
Add another small spoon if nitric is still there, strong fizzing will happen again wait until its finished and stir slowly again, repeat those stips until you notice that the fizzing is very weak, there are many videos explaining the nitric elemination by urea

2- nitric elemination by sulphamic acid :
same as above but replace urea with sulphamic acid 

3-nitric elemination with evaporation. 
4-nitric elemination with iron sulphate (recommended becausr This way will both eleminate the nitric and precipitate the gold) 

after you eleminate the nitric filter the solution and drop your gold with SMB or iron sulphate


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## kurtak (Feb 27, 2021)

sayf said:


> Not a big problem , double the size of you aqua regia solution by tap water because gold loves to precipitate from diluted not concentrated solutions ,



That just is NOT TRUE :!: 

Gold will precipitate from solution whether it is concentrated - or dilute :!: 

The more concentrated the solution is the larger the gold "particles" will be when they precipitate which in turn means the better/faster they will settle 

The more dilute the solution is the smaller the particles will be which in turn means slower settling of the particles

There is absolutely no reason why you can't precipitate your gold from a "fully" concentrated solution of AR --- provided there is no "free" oxidizer in the solution (free oxidizer is what cause's the gold to not drop)

In fact - dropping gold from a "fully" concentrated solution (provided there is no free oxidizer) will cause the gold to drop so fast (due to large particle size) the gold will pile up in the bottom of the beaker & trap gold chloride (dissolved gold) in the gold powder settling in the bottom of the beaker --- therefore you need to stir the settling powder up to bring the gold chloride up out of the settling gold to insure all the gold chloride gets reduced to gold

That said - diluting to double the volume of your concentrated AR wont effect the particle size enough to cause settling problems - whereas "over" diluting may/can cause settling problems --- the more dilute - the smaller the particle size - the longer it takes to settle

Also - the gold that precipitate last from the solution will be smaller then the gold that precipitates first --- so - the more dilute the solution is - the smaller those last precipitated particles will be --- in other words - if the solution is VERY dilute the particles that precipitate last can be so small that they can take a day or more to settle

Now then with all that said - there are reasons for diluting AR to double the original concentrate

Concentrated acid (to a point) does a better job of keeping/holding dissolved metal in the solution then dilute acid

I say to a point because -------------

Example; - HCl (generally speaking) does not dissolve silver & in fact will precipitate silver as silver chloride from a silver nitrate solution --- however - when concentrated - the HCl in the AR will actually allow "some" silver to remain dissolved in the AR - so - by diluting (doubling with water) the AR it makes the HCl weaker & therefore the HCl can no longer hold that "small" amount of dissolved silver in solution & it will drop out as silver chloride which can then be filtered out before dropping the gold - so that (small) amount of dissolved silver doesn't co-precipitate (as chloride) when dropping the gold

In fact - IF - SMALL amounts of silver chloride co-deposits with your gold - a "concentrated" HCl wash will re-dissolve that SMALL amount of silver chloride (thereby cleaning up the gold) - the concentrated HCl can then be diluted to drop the silver chloride

Like wise - this is true with "some" (other) base metals - therefore - with very dirty base metal solutions diluting (by double) can/may allow "some" dissolved base metal to drop out & be filter before dropping the gold thereby again allowing for "less" base metal drag down from really dirty solutions --- & again is why we do concentrated HCl washes to clean up any small amounts of base metal drag down 

As a note; - tin tends to act somewhat like silver

Also - with SMB - "some" water in solution "helps" to keep the SO2 (gas) in solution - so if the AR is "concentrated" it is better (but not needed) to dissolve the SMB with "some" water first - if the AR has been diluted you can put the SMB in dry 

Bottom line - though diluting is not "needed" to precipitate gold - it is done for the reasons above - & if nothing else it ends up getting diluted (to some point) during the filtering process

Kurt


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## Simonides (Mar 25, 2021)

Hello Kurt, you said everything important learning this is happening to me. I made a process with large ceramic CPUs, for sure my AR water was very contaminated with base metals, I made the mistake of putting too much water, the solution before it was too thin, although I used sulfamic to neutralize the nitric, I was not able to precipitate the gold. I used 200ml of HCI to 35ml of nitric acid HNO3 was not very nitric, but the excess water is making it difficult to precipitate. Thanks for the information I will work on the recovery and learn more. Thank you my friend I am learning a lot on the forum.


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## Simonides (Mar 25, 2021)

the water solution was yellow concentrated, then turned green after adding ice cubes in large quantities and sulfamic. NOTE: this is the end of the filtration before excess ice + sulfamic.

Thank My brother.


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## zumka (Nov 7, 2021)

I have a question about a similar problem. 

I made my AR with 350 ml HCI + 40 ml HNO3. There was the filter paper in the beaker that i filtered from a dirty solution. Simmered like 5 minutes. Gold&base metal dust dissolved completely. It was a sweet dark yellow colour, UNTIL, silly me, add a table spoon of urea. So the solution became light green... I did stannous test, and there wasn't a black (not even a light brown) colour. Added SMB anyway. A few black clouds took shape and dissappeared immediately. Still light green and no trace of gold. 

How can i recover that?


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## FrugalRefiner (Nov 7, 2021)

Two comments:

First, urea doesn't really eliminate excess nitric acid. While some professionals use it, they have the experience to know when and how much to use. To eliminate excess nitric, go to the hardware store and look for grout cleaner that is sulfamic acid. It will serve you much better.

Second, you really never want to see a brown color when testing with stannous. Gold will be anywhere from a faint purple to dark purple to black depending on the concentration of gold in the solution. Brown (often referred to as a false positive) usually means you've added too much SMB to a solution that has copper in it. The brown is caused by copper, not gold.

The fact that you saw "a few black clouds" that disappeared means you still have excess oxidizer in your solution. The gold is being reduced to metallic gold (the black cloud), but then it's being redissolved by the excess nitric.

If you have SMB that has settled to the bottom of your beaker, you may need to add some HCL.

Get some sulfamic acid, use it to deNOx your solution, then see what happens.

Dave


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## zumka (Nov 7, 2021)

Thank you, Dave.

So, the gold is still there but i need to add some HCL? But i don't see any SMB settled down. 

I have enough HCL and HNO3 left to do the process from the beginning. What would you suggest?


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## FrugalRefiner (Nov 7, 2021)

If all else fails, see When In Doubt, Cement It Out.

Dave


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## pawnshop (Nov 8, 2021)

zumka said:


> Thank you, Dave.
> 
> So, the gold is still there but i need to add some HCL? But i don't see any SMB settled down.
> 
> I have enough HCL and HNO3 left to do the process from the beginning. What would you suggest?





zumka said:


> I have a question about a similar problem.
> 
> I made my AR with 350 ml HCI + 40 ml HNO3. There was the filter paper in the beaker that i filtered from a dirty solution. Simmered like 5 minutes. Gold&base metal dust dissolved completely. It was a sweet dark yellow colour, UNTIL, silly me, add a table spoon of urea. So the solution became light green... I did stannous test, and there wasn't a black (not even a light brown) colour. Added SMB anyway. A few black clouds took shape and dissappeared immediately. Still light green and no trace of gold.
> 
> How can i recover that?


I use urea all the time when I am refining. I literally put a few grains in the solution. If it fizzes there is excess nitric. So I add a pinch at a time until the reaction stops. A tablespoon to such a small volume is beyond me.


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## ZiegenSauger (Nov 8, 2021)

I prefer to never have excess Nitric. I go incrementing after a calculated first load.
There are exceptions though depending on the scenario, my goal, or some change in between.

I use both, either Urea or Sulfamic, also depending on the scenario.
My preferred is always drop placer gold bits to the final, filtered, clean gold impregnated solution. Depending on how fast or how slow it goes. More or less I always have some bits of gold for a final and clean SMB treatment.

A question: has anyone tried to drop gold re-using a previous saturated SMB solution from where Gold was already dropped????

It came to my mind now. I just dropped Gold from my stockpot. The first SMB saturated solution went to the temp container (I use transparent 1 L plastic bottles from grape juice as temp. for each SMB drop and keep for a month before transferring the contents to the bucket).

I have my last batch of the week in AR now. I will try to re-use that saturated SMB.

Please comment, I am curious now.


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## orvi (Nov 17, 2021)

ZiegenSauger said:


> I prefer to never have excess Nitric. I go incrementing after a calculated first load.
> There are exceptions though depending on the scenario, my goal, or some change in between.
> 
> I use both, either Urea or Sulfamic, also depending on the scenario.
> ...


in theory, it is possible. anyway it depends on how pure was the gold solution from which you were dropping the gold. because the base metal impurities and other things will be added to your fresh batch.
second, the best is not to use large excess of SMB either. from my point, SMB or sodium sulfite as reducing agents are cheap for me, so i dont bother with any sort of recycling


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## dpgold (May 16, 2022)

kurtak said:


> e enough to cause settling problems - whereas "over" diluting may





kurtak said:


> That just is NOT TRUE :!:
> 
> Gold will precipitate from solution whether it is concentrated - or dilute :!:
> 
> ...


nice things being said here, I wonder what kind of oxidizers could be in AR which will prevent precipitation and if you can explain the mechanism by which it prevents precipitation, I am trying to learn


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## GoldUser (May 16, 2022)

kurtak said:


> That just is NOT TRUE :!:
> 
> Gold will precipitate from solution whether it is concentrated - or dilute :!:
> 
> ...


This is maby helpful to someone.
I had a solution (about 1l to 1 1/2l) with just 0.3g of gold in it.
It was dilluted and took 3 to 4 days to settle out.


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## Martijn (May 16, 2022)

dpgold said:


> nice things being said here, I wonder what kind of oxidizers could be in AR which will prevent precipitation and if you can explain the mechanism by which it prevents precipitation, I am trying to learn


Nitric acid, it dissolves the gold before it can settle out. As I show in this video. 
If there's not too much, SMB will do the trick.


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## dpgold (May 16, 2022)

Martijn said:


> Nitric acid, it dissolves the gold before it can settle out. As I show in this video.
> If there's not too much, SMB will do the trick.



I have just found this in the Hoke's book: Premixing Aqua Regia - In Hoke’s day it was common to premix aqua regia in a fixed ratio, then to combine it with the metal. While others have developed similar techniques, GoldSilverPro has championed the cause of adding nitric acid in increments. It is far better to add only the amount of nitric needed to perform the task than to add too much and have to deNOx after the metals have been dissolved.


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## dpgold (Jun 7, 2022)

sayf said:


> Not a big problem , double the size of you aqua regia solution by tap water because gold loves to precipitate from diluted not concentrated solutions ,
> You can eleminate the nitric using many ways :
> 
> 1- nitric elemination by urea : (not recommended)
> ...


So there are three things to do precipitate any lead from AR, denox (get rid of excess nitric) and precipitate. If I use sulphamic acid that will precipitate lead and denox the solution. ? Sulphuric acid will do the same?


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## Geo (Jun 7, 2022)

dpgold said:


> So there are three things to do precipitate any lead from AR, denox (get rid of excess nitric) and precipitate. If I use sulphamic acid that will precipitate lead and denox the solution. ? Sulphuric acid will do the same?


No. Sulfuric acid will precipitate lead(II) sulfate but does nothing to remove excess nitric acid.


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## Geo (Jun 7, 2022)

I've seen people refer to Hoke's when talking about evaporating and additions of HCl to denoxx solution. I'm not sure everyone grasps the scope of what's been said. The solution may have to be evaporated to a syrup. This is a very delicate process and needs a fair amount of finesse. It is a tiny step from syrupy to a burned crispy crud. Harold_V recommends adding a small volume of sulfuric acid to the solution before starting. Sulfuric acid is difficult to evaporate to dryness. As sulfuric acid becomes more and more concentrated, the more resistant to boiling or evaporation it becomes. It's not impossible to evaporate to dryness after adding sulfuric acid but it is much more difficult.


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## Shark (Jun 7, 2022)

Geo said:


> No. Sulfuric acid will precipitate lead(II) sulfate but does nothing to remove excess nitric acid.


This is why I use it. It makes the lead easily filtered out. Usually only a small amount of lead so I can still use sulfamic if it is needed to denox. It goes something like this…… add sulfuric and drop lead, cool and drop silver, denox as needed, filter to perfectly clear. Drop the gold. You can now cement or process for pgm’s or add to stockpot.


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## dpgold (Jun 7, 2022)

thank you Geo. While I was asking these questions (a few hours ago) I put some vintage gold plated circuit boards in AP (which I will label with solder) and I noticed it was pretty fast acting, some of the foils already started to move in a few hours. The lead or solder was gone. My concern is with how do I recover the foils if there is lead, the foils can become tiny pieces. Theoretically tin and lead and other things go in the solution and everything else which has not dissolved should be filtered and washed in the filter?


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## dpgold (Jun 7, 2022)

Shark said:


> This is why I use it. It makes the lead easily filtered out. Usually only a small amount of lead so I can still use sulfamic if it is needed to denox. It goes something like this…… add sulfuric and drop lead, cool and drop silver, denox as needed, filter to perfectly clear. Drop the gold. You can now cement or process for pgm’s or add to stockpot.


Thank you,


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## dpgold (Jun 7, 2022)

dpgold said:


> I have just found this in the Hoke's book: Premixing Aqua Regia - In Hoke’s day it was common to premix aqua regia in a fixed ratio, then to combine it with the metal. While others have developed similar techniques, GoldSilverPro has championed the cause of adding nitric acid in increments. It is far better to add only the amount of nitric needed to perform the task than to add too much and have to deNOx after the metals have been dissolved.


how do you know when there is enough nitric, how long do I wait before I add more or not add further?


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## Geo (Jun 7, 2022)

dpgold said:


> thank you Geo. While I was asking these questions (a few hours ago) I put some vintage gold plated circuit boards in AP (which I will label with solder) and I noticed it was pretty fast acting, some of the foils already started to move in a few hours. The lead or solder was gone. My concern is with how do I recover the foils if there is lead, the foils can become tiny pieces. Theoretically tin and lead and other things go in the solution and everything else which has not dissolved should be filtered and washed in the filter?


Lead chloride is water soluble as long as the water is hot and can be removed by adding it to hot water. It is also soluble in concentrated HCl. After collecting all the solids left behind, boil in water or add fresh HCl to remove lead chloride. When cool, lead chloride will look like long needle shaped crystals. Adding sulfuric acid creates a fluffy white powder of lead sulfate that settles quickly and is easily filtered out of solution.


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## dpgold (Jun 8, 2022)

Geo said:


> Lead chloride is water soluble as long as the water is hot and can be removed by adding it to hot water. It is also soluble in concentrated HCl. After collecting all the solids left behind, boil in water or add fresh HCl to remove lead chloride. When cool, lead chloride will look like long needle shaped crystals. Adding sulfuric acid creates a fluffy white powder of lead sulfate that settles quickly and is easily filtered out of solution.


Thank you again, this is really useful, all these details. I took out the test pieces last night and washed them in a separate bucket. How long shoul I wash it to get rid of any lead chloride and deal/dispose with the wash from the solution safely?


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## Yggdrasil (Jun 8, 2022)

Put the “gunk” in the bottom in a beaker and boil it while stirring. Then filter it. All lead residue should be out by then. The filters can then be leached in your preferred way.


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## Martijn (Jun 8, 2022)

dpgold said:


> how do you know when there is enough nitric, how long do I wait before I add more or not add further?


By watching the reaction in your beaker. And the changes you observe when adding something. You have to have some basic knowledge of chemical reactions to start performing processes. What does it do when hot, cold, dilute, concentrated, mixed with other.. etc. etc. first look up the reaction in theory, and then test if the expected outcome will occur. 
The acquaintance tests in hokes book help a lot. It's basically a way to study the different properties of acids and substances and how they react to each other before you throw all kinds of stuff stuff in a beaker and hope it wont explode in your face. Small beaker, small explosions big beaker.. well you can guess the rest.
Take your time and do small tests first.


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## dpgold (Jun 8, 2022)

Martijn said:


> By watching the reaction in your beaker. And the changes you observe when adding something. You have to have some basic knowledge of chemical reactions to start performing processes. What does it do when hot, cold, dilute, concentrated, mixed with other.. etc. etc. first look up the reaction in theory, and then test if the expected outcome will occur.
> The acquaintance tests in hokes book help a lot. It's basically a way to study the different properties of acids and substances and how they react to each other before you throw all kinds of stuff stuff in a beaker and hope it wont explode in your face. Small beaker, small explosions big beaker.. well you can guess the rest.
> Take your time and do small tests first.


The test was about how to get rid of the lead (Pb) and now I see that I did get rid of it (learning experience) but now is mixed with some of the gold which comes off in this old AP.(now when I don't want the gold plating to come off-Murphy's law) I understand that this lead chloride will dissolve in hot water or in concentrated HCL (which I can filter) or....


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## Yggdrasil (Jun 8, 2022)

Simple. Don’t mind the lead. It is in the AP as dissolved PbCl. Let it be there until you have filtered the foils from it, then drop it from the liquid with Sulfuric. Don’t make a problem from something that is not. If you over treat it, it will/can become a problem.


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## Shark (Jun 8, 2022)

Lead(pb) is one of the easiest metals to remove from AP or AR. If you follow good steps when using AR or AP the lead(pb) will follow the waste stream and not your gold. If it does happen to make it into your AR, it is still one of the easiest metals to remove at this stage.


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## dpgold (Jun 8, 2022)

Yggdrasil said:


> Simple. Don’t mind the lead. It is in the AP as dissolved PbCl. Let it be there until you have filtered the foils from it, then drop it from the liquid with Sulfuric. Don’t make a problem from something that is not. If you over treat it, it will/can become a problem.


Ok, thank you all, so I should treat it as other base metals in the AP process but when I want to filter the foils I now have that gray powder which will remain in the filter when I filter the foils from AP. 
So I had one dedicated small bucket with previously used AP but which did not have contact with any Pb. After dissolving the circuits it dissolved some AP from the boards. Then I took the test boards out and washed them in a separate bucket with water and that is where I have observed the grey powder. I am assuming this is the step which precipitated the Pb and other stuff beside copper which confused me.


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## Martijn (Jun 8, 2022)

Grey powder after filtering foils from AP, are you sure it's lead and not CuCl1? Lead is not very common in solder anymore. Only old electronics have it.


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## Martijn (Jun 8, 2022)

If it is lead, rinse the filter with hot water, if its copper chloride, rinse the filter with HCl.


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## Geo (Jun 8, 2022)

Copper(II) chloride (CuCl2) will create Copper(I) chloride (CuCl) when you add water. CuCl is a white fluffy powder that is normally colored green from remaining CuCl2. When you rinse CuCl2, it rinses away any green color and leaves the white powder. Any dark colored solids will make it appear gray. The lead that comes at the end of a CuCl2 leach will be ground up crystals and look like a white powder. It does not dissolve well in cold water. It is easiest to remove after the dissolution of the gold foils and before filtering the pregnant solution. After the gold is dissolved and the solution has cooled, add 10ml of sulfuric acid. If lead is present, and it will be seeing as it's in all electronics that we would be interested in, a white cloud will form. After some brisk stirring, it will settle quickly. Keep adding sulfuric acid until no more white cloud forms. Lead sulfate actually filters relatively easily. Lead is a problem for jewelers in gold because it makes gold less malleable and more prone to cracking or breaking when being worked.


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## dpgold (Jun 8, 2022)

Martijn said:


> Grey powder after filtering foils from AP, are you sure it's lead and not CuCl1? Lead is not very common in solder anymore. Only old electronics have it.


Yes, I did the test on some old electronics boards, I usually try to select materials, and the test was a separate batch with Pb solder boards


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## billgold (Jun 13, 2022)

If I recall correctly, Hoke also discusses incremental addition of nitric acid when doing the digestion.


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## dpgold (Jun 16, 2022)

Can anyone tell me what happens if you put a little of AR with everything that was in it in a AP batch, after the nitric is used up?


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## Yggdrasil (Jun 16, 2022)

dpgold said:


> Can anyone tell me what happens if you put a little of AR with everything that was in it in a AP batch, after the nitric is used up?


I have never done it, so I’m blank.
But why would you do it in the first place?
It does not make sense to me at least.


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## dpgold (Jun 17, 2022)

At first I had a very tiny test solution of AR and fingers then I added some pins which contained a bit of steel, then I did a stannous test and was positive. I added pins until the solution did not dissolve the plating anymore. Perhaps it needed more nitric but I decided to put everything into the bigger AP batch. I want to learn how and why things do what they do. The tiny AR batch started as a need to test my stannous solution which I was not able to do previously. So the stannous test was highly positive.


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## Yggdrasil (Jun 17, 2022)

dpgold said:


> At first I had a very tiny test solution of AR and fingers then I added some pins which contained a bit of steel, then I did a stannous test and was positive. I added pins until the solution did not dissolve the plating anymore. Perhaps it needed more nitric but I decided to put everything into the bigger AP batch. I want to learn how and why things do what they do. The tiny AR batch started as a need to test my stannous solution which I was not able to do previously. So the stannous test was highly positive.


If your AR is dissolving complete pins, most of your gold is already cemented out, unless they were completely dissolved.

You DO NOT use AR to reclaim gold.

Nitric, HCl or AP can be used and each has its pros and cons.

When ALL the base metals are dissolved you go to AR, HCl/Peroxide, HCl/bleach or similar.

To take out gold plating the Sulfuric stripping cell, Iodine-Iodide or Cyanide is used, never AR.


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## dpgold (Jun 17, 2022)

Yggdrasil said:


> If your AR is dissolving complete pins, most of your gold is already cemented out, unless they were completely dissolved.
> 
> You DO NOT use AR to reclaim gold.
> 
> ...


Is that because pins have steel, zinc and metals which are higher on reactivity series and unless totally dissolved will cement out metals less reactive from the AR solution?


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## Yggdrasil (Jun 17, 2022)

dpgold said:


> Is that because pins have steel, zinc and metals which are higher on reactivity series and unless totally dissolved will cement out metals less reactive from the AR solution?


Yes


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