Looking for learning,

[adam mizer]

I know youtube is not the bast place for learn video's but I thought this was pretty nice video.
Sreetips : So2 precipitation.

 

[goldshark]

Hi,
I filtered the solution to 2 part:
Part 1 is the brown precipitate: I put to AR and Test Stannous give very black colour
Part 2 is the remain solution in liquid: I test Stannous also give black colour but less than Part 1
So I start solve 2 part as:
Part 1: I add HCL and water and boild to kill HNO3 , then add SMB but precipitate still not hard, i attach picture, please advise me
Part 2: U add HCL and boil to a thick syrupy consistence.
please give me your opinions

Have you tried Sulfamic acid to kill the excess Nitric? I am assuming you are using distilled water.

 

[leHAI]

Have you tried Sulfamic acid to kill the excess Nitric? I am assuming you are using distilled water.

Sulfamic acid is hard to find in my place so I use to used Urea, result is same, but maybe I still denox all Nitric, maybe I will try Sulfamic
please let me know what wrong with distilled water?

 

[Yggdrasil]

Sulfamic acid is hard to find in my place so I use to used Urea, result is same, but maybe I still denox all Nitric, maybe I will try Sulfamic
please let me know what wrong with distilled water?

Nothing wrong with destilled water.
For Silver thst is neccessary.

 

[kurtak]

The cyclic precipitate/dissolve reaction with precipitants

Other wise known as a redox reaction

So - to help the original poster that started this thread understand the reason he is having trouble precipitating his gold

Redox is a reaction when both reduction & oxidation take place at the same time

When we dissolve gold with AR we use nitric along with the HCl because the nitric is the "oxidizer" that makes the gold dissolve - so it is an oxidation reaction

Then - to recover the dissolved gold back out of the AR we use a reducing agent (such as SMB in this case) so we are looking for a reduction reaction when we add the SMB

However - if there is an excess of "free nitric" in the AR because you used more nitric then needed to dissolve the gold --- then when you add the SMB to reduce the gold what happens is the SMB "tries" to precipitate (reduce) the gold - BUT - at the same time - the excess "free" nitric goes to work re-dissolving (or oxidizing) the gold that is trying to precipitate (reduce)

In other words - you have a redox reaction taking place wherein the SMB is trying to reduce the gold - but - at the same time - the "free" nitric is oxidizing (re-dissolving) the gold that is trying to precipitate (reduce)

So - in order to stop that redox reaction from happening - you need to get rid of the "free" nitric in the AR that is causing the gold to re-dissolve when you try to precipitate the gold --- this is known as de-Noxing the AR

There are a number of different ways to de-Nox the AR & what works best for de-Noxing your AR depends on how much "free" nitric is in the AR

1) if there is not a lot of free nitric then you can simply leave it on the hot plate until you no longer see brown fumes coming off the AR - as Jon has pointed out

On the other hand - if there is A LOT of free nitric in the AR you will have to evaporate the AR down to a (thicker) syrup & then add HCl to the syrup to drive off the free nitric (this produces brown fumes when the HCl is added to the syrup) & this may (or not) need to be done more then one time - as Yaggdrasil pointed out --- this is the most difficult way to try to de-Nox your AR

2) is to simply let the free nitric get used up dissolving more metal & there are a number of ways to do that

a) - if there is not a lot of free nitric you can precipitate the gold with SMB & then let it sit on the hot plate so that the free nitric re-dissolves the gold (or at least "some" gold) & then re-precipitate with more SMB - this only really works if there is not a lot of free nitric in the first place - if there is A LOT of free nitric this does not work well

b) add more gold to the AR so that the added gold uses up the free nitric - as 4metals pointed out

c) put copper in the AR - the copper (like adding gold) will use up the free nitric & then when the copper has used up the free nitric it will also precipitate the gold --- this is called "cementing" the gold out of the AR --- I have posted "a lot" about this - so you can do a search about this using "cementing" by kurtak in the search

3) or you can do it chemically - some people use urea to de-Nox their AR but we do not recommend using urea - the other chemical method to de-Nox AR is to use sulfamic acid (not sulfuric acid) & this is the chemical we recommend

I have used all of the above methods & have personally stopped using all of them many years ago - with the exception of ether method (2) (b) or (2) (c)

In other words the ONLY methods I ever use to get rid of the free nitric in my AR is to ether add more gold until the AR will not dissolve any more gold & then precipitate the gold with SMB - or - cement the gold with copper

Kurt

 

[4metals]

c) put copper in the AR - the copper (like adding gold) will use up the free nitric & then when the copper has used up the free nitric it will also precipitate the gold --- this is called "cementing" the gold out of the AR --- I have posted "a lot" about this - so you can do a search about this using "cementing" by kurtak in the search

It is also good to understand that if you use copper, careful, timely additions of fine powdered copper metal with good mixing will yield a higher purity gold. Not pure enough to call "fine gold" but from a dirty solution, requiring a second refine anyway, it is an excellent method.

 

[leHAI]

Other wise known as a redox reaction

So - to help the original poster that started this thread understand the reason he is having trouble precipitating his gold

Redox is a reaction when both reduction & oxidation take place at the same time

When we dissolve gold with AR we use nitric along with the HCl because the nitric is the "oxidizer" that makes the gold dissolve - so it is an oxidation reaction

Then - to recover the dissolved gold back out of the AR we use a reducing agent (such as SMB in this case) so we are looking for a reduction reaction when we add the SMB

However - if there is an excess of "free nitric" in the AR because you used more nitric then needed to dissolve the gold --- then when you add the SMB to reduce the gold what happens is the SMB "tries" to precipitate (reduce) the gold - BUT - at the same time - the excess "free" nitric goes to work re-dissolving (or oxidizing) the gold that is trying to precipitate (reduce)

In other words - you have a redox reaction taking place wherein the SMB is trying to reduce the gold - but - at the same time - the "free" nitric is oxidizing (re-dissolving) the gold that is trying to precipitate (reduce)

So - in order to stop that redox reaction from happening - you need to get rid of the "free" nitric in the AR that is causing the gold to re-dissolve when you try to precipitate the gold --- this is known as de-Noxing the AR

There are a number of different ways to de-Nox the AR & what works best for de-Noxing your AR depends on how much "free" nitric is in the AR

1) if there is not a lot of free nitric then you can simply leave it on the hot plate until you no longer see brown fumes coming off the AR - as Jon has pointed out

On the other hand - if there is A LOT of free nitric in the AR you will have to evaporate the AR down to a (thicker) syrup & then add HCl to the syrup to drive off the free nitric (this produces brown fumes when the HCl is added to the syrup) & this may (or not) need to be done more then one time - as Yaggdrasil pointed out --- this is the most difficult way to try to de-Nox your AR

2) is to simply let the free nitric get used up dissolving more metal & there are a number of ways to do that

a) - if there is not a lot of free nitric you can precipitate the gold with SMB & then let it sit on the hot plate so that the free nitric re-dissolves the gold (or at least "some" gold) & then re-precipitate with more SMB - this only really works if there is not a lot of free nitric in the first place - if there is A LOT of free nitric this does not work well

b) add more gold to the AR so that the added gold uses up the free nitric - as 4metals pointed out

c) put copper in the AR - the copper (like adding gold) will use up the free nitric & then when the copper has used up the free nitric it will also precipitate the gold --- this is called "cementing" the gold out of the AR --- I have posted "a lot" about this - so you can do a search about this using "cementing" by kurtak in the search

3) or you can do it chemically - some people use urea to de-Nox their AR but we do not recommend using urea - the other chemical method to de-Nox AR is to use sulfamic acid (not sulfuric acid) & this is the chemical we recommend

I have used all of the above methods & have personally stopped using all of them many years ago - with the exception of ether method (2) (b) or (2) (c)

In other words the ONLY methods I ever use to get rid of the free nitric in my AR is to ether add more gold until the AR will not dissolve any more gold & then precipitate the gold with SMB - or - cement the gold with copper

Kurt

I'd be very appriciated if you could give the link detail about (2) (c), I try but see cementing for another previous metaol.

 

[4metals]

This thread is from the library. I copied it for you HERE I believe this is where Kurt was introduced to copper powder.