Dropping gold out of poor mans aqua regia

[ruencab312]

This is my second drop in poor mans aqua regia sum gold dropped but it’s still showing positive for gold in solution I put a lot of smb in hot water probably doubled aqua regia

 

[jarlowski1]

Did you denox the solution? When adding smb if you don't denox the solution the gold will be re-dissolved back into solution by the free nitric that remains so you need to get rid of that nitric acid by adding sulfamic acid until you get no fizzing when adding more sulfamic acid. Secondly how much gold are you expecting from this? You should only add about 1.2-1.5 times the amount of gold expected. If you add too much smb when you test the solution with stannous it will show positive for gold even when there is no gold left in solution. You can heat the solution up and for 20-30 min (don't boil it) let it cool back to room temperature and check with stannous again.

 

[anachronism]

Did you denox the solution? When adding smb if you don't denox the solution the gold will be re-dissolved back into solution by the free nitric that remains so you need to get rid of that nitric acid by adding sulfamic acid until you get no fizzing when adding more sulfamic acid. Secondly how much gold are you expecting from this? You should only add about 1.2-1.5 times the amount of gold expected. If you add too much smb when you test the solution with stannous it will show positive for gold even when there is no gold left in solution. You can heat the solution up and for 20-30 min (don't boil it) let it cool back to room temperature and check with stannous again.

Apologies but this simply isn't correct. You add as much SMB as it takes to get a negative Stannous result. Also the "false positive" people talk about is a completely different colour to the colour you get with gold. It's a brown colour.

 

[jarlowski1]

Did you denox the solution? When adding smb if you don't denox the solution the gold will be re-dissolved back into solution by the free nitric that remains so you need to get rid of that nitric acid by adding sulfamic acid until you get no fizzing when adding more sulfamic acid. Secondly how much gold are you expecting from this? You should only add about 1.2-1.5 times the amount of gold expected. If you add too much smb when you test the solution with stannous it will show positive for gold even when there is no gold left in solution. You can heat the solution up and for 20-30 min (don't boil it) let it cool back to room temperature and check with stannous again.

Apologies but this simply isn't correct. You add as much SMB as it takes to get a negative Stannous result. Also the "false positive" people talk about is a completely different colour to the colour you get with gold. It's a brown colour.

Yes you are correct but many times I have seen people just put scoop after scoop of smb into the solution when they only expect a gram or so. The reason most do this is because they are dealing with a "dirty" solution and they think since it didn't react immediately they need more so they just keep scooping it in. The 1.2-1.5 is written on the forum somewhere and it is a starting point to avoid the false positive. You should always check you solutions after you drop to avoid losing gold. If you blindly add too much smb to start like you are suggesting then how will the newguy know when he has a false positive or if there is still gold or if he simply was being wasteful with the smb. Following this method that again is pointed out by senior members here on the forum somewhere(I will search for it and post it here for you) I have only had a few instances where I added too much smb and rarely do I ever need to add more.

 

[kurtak]

Did you denox the solution? When adding smb if you don't denox the solution the gold will be re-dissolved back into solution by the free nitric that remains so you need to get rid of that nitric acid by adding sulfamic acid until you get no fizzing when adding more sulfamic acid. Secondly how much gold are you expecting from this? You should only add about 1.2-1.5 times the amount of gold expected. If you add too much smb when you test the solution with stannous it will show positive for gold even when there is no gold left in solution. You can heat the solution up and for 20-30 min (don't boil it) let it cool back to room temperature and check with stannous again.

Apologies but this simply isn't correct. You add as much SMB as it takes to get a negative Stannous result. Also the "false positive" people talk about is a completely different colour to the colour you get with gold. It's a brown colour.

Jon is right - positive test for gold is purple to purple/black --- a FALSE positive (from adding to much SMB) is brown

However - that said - you can add (way) to much SMB & you can (will) Still get a TRUE positive

That happens when you have "free" nitric & don't de-nox the free nitric & that is because though some gold "may" drop - some gold stays in solution as a result of the free nitric (oxidizer)

in that event your stannous test will likely show "both" purple & brown

Example; - cotton swab = purple at one end - brown at other end --- drop on paper towel = purple in center - brown ring around it --- spot plate = same as drop on paper --- if you are not sure about a spot plate test - try the drop test on paper towel or with cotton swab

if you get the "double" test result (purple & brown) you have free oxidizer - need to de-nox - or cement with copper

Kurt

 

[jarlowski1]

Here is a post where Palladium responds and gives an explanation about how much smb.

https://goldrefiningforum.com/viewtopic.php?f=37&t=15733&p=286791&hilit=how+much+smb#p286791


I'm not that good at posting a link so I hope this is right but Palladium's post is 2nd.

 

[anachronism]

Here is a post where Palladium responds and gives an explanation about how much smb.

https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=15733&p=286791&hilit=how+much+smb#p286791



I'm not that good at posting a link so I hope this is right but Palladium's post is 2nd.

Palladium's post is correct but it's theoretical chemistry. In the real world it doesn't work that way because there are far too many variables to take into consideration.

For one- excess oxidant and the precipitate/redissolve cycle.
For another the temperature of the liquid - the warmer it is the more SO2 is wasted therefore more SMB required.
For another the redissolving from the action of high valency base metals. A cyclic reaction that needs to be run to conclusion before the last of your gold will drop.

There are also others too, the point being there is no hard and fast rule as to how much SMB you can (or should) use.

On a practical level SMB costs far less than gold per gramme. 8) 8)

On a final note I really try and avoid using the stuff as much as possible.

 

[jarlowski1]

Here is a post where Palladium responds and gives an explanation about how much smb.

https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=15733&p=286791&hilit=how+much+smb#p286791



I'm not that good at posting a link so I hope this is right but Palladium's post is 2nd.

Palladium's post is correct but it's theoretical chemistry. In the real world it doesn't work that way because there are far too many variables to take into consideration.

For one- excess oxidant and the precipitate/redissolve cycle.
For another the temperature of the liquid - the warmer it is the more SO2 is wasted therefore more SMB required.
For another the redissolving from the action of high valency base metals. A cyclic reaction that needs to be run to conclusion before the last of your gold will drop.

There are also others too, the point being there is no hard and fast rule as to how much SMB you can (or should) use.

On a practical level SMB costs far less than gold per gramme. 8) 8)

On a final note I really try and avoid using the stuff as much as possible.

While I'm not trying to argue with you at all, but the oxidant/precipitant dissolve cycle is not relevant since you should be getting rid of the oxidant before precipitation. That is why we denox a solution furthermore that is also why when using Hcl and bleach to dissolve gold we wait for the excess chlorine to be driven off before precipitating. Now as far the temperature of the liquid goes Im not sure if I agree with your statement that the SO2 is "wasted". The rate of reaction in most reaction is increased with the increase in temperature therefore the hotter the solution the faster the S02 will react to precipitate the gold (within reason obviously). However I personally always precipitate from a solution that is cold or room temperature. Again I don't want to argue but if you can explain what you mean I would certainly like to learn (I am considering on becoming a chemical engineer at the moment 8) ) Finally I agree there is no hard fast rule with how much precipitant to use.. this is chemistry afterall. The point is that the 1.2-1.5 times your estimated yield is a starting point so that you don't over shoot the "right" amount.

Cheers

 

[g_axelsson]

I'm with Jon on this.

Even small amounts of nitric left takes a lot of SMB to drive off. I usually try not to use too much nitric as I'm paying a lot for it if I even can get it, but it happens. When I can see the gold precipitate and then the solution goes clear again I've learned that I need to denox properly. Experience will tell you if there is just a bit of nitric left or if there are massive amounts left. I usually doesn't worry a lot about denoxing nowadays, I just observe how the solution is reacting to my SMB and adjust accordingly.

The acidity of the solution is another factor that Jon failed to mention. High acidity releases a lot of SO₂ in a short time and bubbles are formed. If you can smell it (don't do it, it gives me an asthma attack immediately if I do) it means there are SO₂ leaving the beaker.
Copper chloride can also steal some of the SO₂, CuCl₂ is reduced to CuCl so it consumes SMB too.

For SMB to work the solution has to be acidic, that is what releases SO₂ to begin with. If there is something else that affects the pH it can also precipitate other metals as oxides or hydroxides.

To get back to the original poster. Personally I think the tests looks brown and are a sign of too much SMB has already been added. What's wrong here is hard to tell as he hasn't told us what we are looking at, how much gold he is expecting and what he has done to the jars to get to this point. Are there any pictures from the liquid before adding SMB and a positive test for gold?

We can guess for all we are worth, but I'm going to wait until the original poster answers our questions.

Göran

 

[Shark]

If the solution is not denoxed properly the gold will go back into solution, even using HCl and Bleach this will happen. A few years ago I videoed a solution of HCl/bleach doing just that. It took several teaspoons of smb to get all the gold to drop and stay dropped. The gold recovered was just under one gram.

 

[anachronism]

Thanks Shark - yeah that's why I used the term oxidant as opposed to Nitric because it applies to both scenarios.

 

[Shark]

This is my second drop in poor mans aqua regia sum gold dropped but it’s still showing positive for gold in solution I put a lot of smb in hot water probably doubled aqua regia

How long have you let this settle?
When I enlarge the picture, it looks like you may have just added the smb and you may have gold powders floating around in it as well.

What material did you process?