I know youtube is not the bast place for learn video's but I thought this was pretty nice video.
Sreetips : So2 precipitation.
Sreetips : So2 precipitation.
Looking for learning,
- Thread starter leHAI
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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?
Nothing wrong with destilled water.
For Silver thst is neccessary.
kurtak
Well-known member
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
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.
I'd be very appriciated if you could give the link detail about (2) (c), I try but see cementing for another previous metaol.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 would like to update the status of my product after about 36 hours of precipitation with SMB, tested with tin chloride, it is still light black, I will leave it for another 24 hours to see if the gold in the water is gone, I would like to receive your comments
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Is it light black or purple?
The Stannous reacts only with the Gold salts not the metallic Gold, so if there is enough SMB there should not be a reaction with the Gold.
SMB on the other hand if there is too much will react with stannous and create a false positive dark brown.
kurtak
Well-known member
Yes - that is where I first "learned" the benefits of cementing with copper "powder" - THANKS to you 4metals
That was right at 10 years ago that you taught me about that value of using copper powder to cement PMs (gold & PGMs) from solutions with copper powder & I have been using it ever since
In fact - in the last 10 years I rarely ever use SMB (&/or other chemical reducing agents) to drop my gold any more
I would say that 85 to 90 % of the time I use copper - & I use both heavy copper (like copper bus bars &/or HEAVY copper wire) &/or copper powder - depending on the volume of solution I am working with &/or the volume of gold expected to drop
AND - once you really learn how to use copper you can in fact turn out very pure gold --- like 999 + or at worst 995
There are a few tricks to turning out high purity gold using copper (& they are not hard) but once you learn/understand it you can most certainly turn out high purity gold
Kurt
kurtak
Well-known member
Per the bold print (above quote) & following up on my last post
I have to disagree - & I can say that with confidence because I have sold (4) 1 ozt bars of gold this year all cemented from solutions with copper & all 4 of them came back as "pure" gold after testing
I sold them to a "gold buyer" (that pays me a VERY good price for my gold)
He shot them with his XRF which came back saying 100% pure gold
Now we of course know that there is no such thing as 100% pure gold - it is always 99 something (99 +)
However - he has also sent my gold on to the refinery that he deals with - so they of course also tested that gold & they reported back him & paid him out on 999 + gold - resulting in him calling me to inform me of the refineries test results & informing me that he will buy any gold I have to sell at our agreed on "very" good price
And as a side note; - I have several more bars that he has tested with his XRF & they all read back 100% & they have all been gold cemented from solution with copper
In fact right now the only gold I have that was precipitated with SMB is about 7 grams (still as powder) which I can clearly see is contaminated - so I am likely going to re-dissolve it & then drop it with copper powder
So - how do I turn out this high purity gold cementing with copper ?
The first trick is to stop the cementing process "just a bit" short of complete cementing of the gold
Once you really get to know/understand this (cementing) process you can stop the process with 95 - 97 % of your gold dropped - the solution (decanted) then goes to the "standard" stock pot to recover that last 3-5 % gold
Side note; - as we know - when cementing with copper - the problem is copper contamination & "most" of that copper contamination is the result of not stopping the cementation process "a bit" short of complete cementation (for a number of reasons I don't have time to explain right now)
So by stopping the cementation "a bit" short of completion it minimizes the copper contamination "by a lot"
And this (small amount) of copper contamination is in the form of copper oxide not actual copper metal
And as we know copper oxide is soluble in HCl - so ALL of that copper oxide can be washed out with HCl
However - you DO NOT want to wash this cemented gold with the "standard" washing method of boil in hot water - boil in HCl - boil in hot water --- for whatever reason this washing method will not get all the copper out (this was brought to my attention when Lou posted his washing method)
Rather - after decanting - you want to go direct to a "cold" HCl wash/soak (which I will "try" to explain in more detail "if/when" I have more time) & then go to cold water washing (again all brought to my attention when Lou posted his washing method)
Then (& this is more of an assurance then an actual need - if you did a good job on the wash in the first place) but when I melt the gold i will throw a "pinch" of potassium nitrate on the molten gold before making the pour to your mold
I can assure you if you follow this procedure you can/will turn out high purity (999 +) gold by cementing with copper
For what it is worth
Kurt
it's hard to tell if it's light black or dark brown(attach pictures), but the truth is I only put 2 spoons of SMB in the AR, I think I'll wait until tomorrow, if the stannous chloride doesn't change I'll heat the solution and wait and see
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honestly this is the first time i heard of this method so i don't even understand how to do it (put a copper wire in the AR, or put a piece of copper in, or put spoons of copper powder in...), i will read all the posts, thank you for taking the time to explain it to me in detail
This sentence tells the whole story. When I first started using fine copper powder for cementation it was to concentrate precious metal values from very dirty solutions, and the copper powder, because of its high surface area worked faster. When you are looking for speed, vs looking for purity, over adding of copper is common. The only time I personally have done it slowly is when processing aqua regia that dissolved platinum jewelry. The acid is very clean and adding it slowly and stopping before it's done makes a high purity Platinum to sell without all of the toxic exposure to PGM salts.
A great way to do this and get results very quickly is to drop silver out of a spent nitric solution. If you inquart jewelry with Silver you have to do this anyway. Get some heavy copper wire and coil it around a fat dowel to make it like a spring. Put about 3 liters of Silver bearing parting solution on a 4 liter beaker and hang the spring so the top is above the liquid level and easy to grab. If the solution is without free nitric acid the reaction will be quick and the Silver will quickly grow on the copper coil. To the point that it looks like a snow globe. When it covers the coil and slows down, pick up the end and shake the copper spring which will dislodge the cemented Silver and allow more to deposit. This method will drop Silver as pure as 99% from the solution and is useful as a demonstration of cementation in action.
If your solution is still active with free nitric acid, add additional Silver metal to consume the free nitric. (leave it in until the solution no longer produces red fumes) This will give you a solution that will react quickly and give you a pretty good lesson in cementation. It is also a 100% quick and easy way to recycle your Silver used for inquartation over and over.
This looks like SMB surplus. It is brown.
