# About gold percipitation



## margsu (May 25, 2010)

I have a question about gold percipitation from AR. I read that ferrum sulfate, copper chloride will do that. Can anybody confirm that or comment. If I use Ferrum sulfate must it be salt or liquid.


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## machiavelli976 (May 25, 2010)

FeSO4 in solution. use green crystals not brown !


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## Harold_V (May 26, 2010)

margsu said:


> I have a question about gold percipitation from AR. I read that ferrum sulfate, copper chloride will do that. Can anybody confirm that or comment. If I use Ferrum sulfate must it be salt or liquid.


Ok, lets get terminology straight here, so you don't make mistakes in the future. 

You do not "percipitate" gold -----it is _*pre*_cipitated.

The process you are speaking of is the use of ferrous sulfate, not ferrum sulfate. It's important that you get that right, because it is the solution, or salt of choice, of iron, that will precipitate gold. It can be used as a crystal, but I don't advise that. When you make the choice to use ferrous sulfate, insure that it is a light green color, not rusty looking. If it has rusted, it is oxidized and no longer has the needed electron that allows the precipitation of gold to occur. It is also no longer ferrous sulfate when it has oxidized. 

Ferrous sulfate is capable of precipitating gold at the rate of a troy ounce of gold per ounce of ferrous sulfate. It does no harm to use a little extra, to insure you precipitate all of the values. You should also test with stannous chloride to insure that you have. 

So then, using an adequate amount of ferrous sulfate (it is also known as copperas, not to be confused in any way with copper), dissolve the material in a small amount of water, perhaps a couple ounces, then drip a few drops of HCl in to the dissolved material and stir well. You'll notice it changes color ever so slightly, and brightens up, coming very clear (still light green in color, just not cloudy). You can then dump this solution directly in your gold chloride. If you have eliminated free nitric, you should see an instant cloud form, which is gold precipitating. 

Allow the material to settle VERY well before decanting. It's not uncommon for the fine gold particles to stratify and slowly sink to the bottom. It can take as much as 24 hours, so allow plenty of time, so you don't lose any values. 

Hope this helps.

Harold


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## margsu (May 27, 2010)

Can I make copperas by my self? Iron + H2SO4? Is battery acid enough for this reaction.


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## philddreamer (May 27, 2010)

Hi margsu!
Further down, on this same thread, there is a post titled: "what to do with spent sulphuric acid". lazersteve makes a comment to the fact & also says to visit his website & watch a video. It's in the silver section.

It confirmes what Harold stated in his post above.

philddreamer


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## goldenchild (May 27, 2010)

Harold_V said:


> margsu said:
> 
> 
> > When you make the choice to use ferrous sulfate, insure that it is a light green color, not rusty looking. If it has rusted, it is oxidized and no longer has the needed electron that allows the precipitation of gold to occur. It is also no longer ferrous sulfate when it has oxidized.



Besides making the mistake of not getting the green ferrous sulfate, are there any other disadvantages or advantages in using it over SMB?


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## Harold_V (May 28, 2010)

goldenchild said:


> Besides making the mistake of not getting the green ferrous sulfate, are there any other disadvantages or advantages in using it over SMB?


I chose to not use it routinely because I precipitated my solutions highly concentrated, using SO2 from a cylinder. That required the addition of ice to control temperature, plus I didn't want to increase volumes any more than was necessary. That's not to say that my process was any more right than that of others---it was a matter of personal choice for my operating circumstances. 

The one real advantage of using ferrous sulfate is that you are not held captive. It can be made from scrap steel with little effort. It need not be crystallized---it can be used directly after being made by dissolving iron (steel) with sulfuric acid, then filtering. Assuming one uses acceptable washing procedures, the quality of the resulting gold can be very good, although you likely would be hard pressed to exceed a purity greater than 9995. 

Harold


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## chemist (May 29, 2010)

Harold --- Why do you use ice? I understand that precipitation is exothermic (the solution gets hot). But even if it reached boiling, all you would lose would be water vapor, right? Why is it necessary to keep the temperature low?


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## goldsilverpro (May 29, 2010)

> Harold --- Why do you use ice? I understand that precipitation is exothermic (the solution gets hot). But even if it reached boiling, all you would lose would be water vapor, right? Why is it necessary to keep the temperature low?



You also lose SO2 gas when it gets hot.


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## Barren Realms 007 (May 29, 2010)

goldsilverpro said:


> > Harold --- Why do you use ice? I understand that precipitation is exothermic (the solution gets hot). But even if it reached boiling, all you would lose would be water vapor, right? Why is it necessary to keep the temperature low?
> 
> 
> 
> You also lose SO2 gas when it gets hot.



The fluid will also absorbe more of the SO2 for the reaction if it is cool.


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## Harold_V (May 30, 2010)

chemist said:


> Harold --- Why do you use ice? I understand that precipitation is exothermic (the solution gets hot). But even if it reached boiling, all you would lose would be water vapor, right? Why is it necessary to keep the temperature low?


I have discussed this issue previously,although I am at a loss to make reference to the particular post. 

I used SO2 for years, always processing heavily concentrated solutions. As you alluded, precipitation is an exothermic reaction, which liberates pretty much all of the heat energy that was required to dissolve the gold originally. As a result, I had solutions so hot (although not boiling) that all of the gold wouldn't come down. The addition of just a small amount of ice, once it hit the wall, resulted in an instantaneous precipitation of the remaining gold. From that I concluded, perhaps erroneously, that if the heat could not be absorbed, no more gold would precipitate. That was true in spite of having a solution that was liberating SO2 gas. 

If my conclusion is wrong, I stand to be corrected. This I know. It is impossible to precipitate five troy ounces of gold from a liter of solution without dealing with the resulting heat. 

I generally had about 18 ounces in a liter. To that I'd add three liters of small cubed ice. By the time the gold was down, the solution was too hot to handle---although it was not boiling. 

Harold


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## philddreamer (May 30, 2010)

Harold, thank you for explaining the "why". It has help me understand better what is going on in the process.


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## chemist (May 30, 2010)

Thank you for the explanations. It explains a lot. The solubility of gases decrease as the temperature increases. So, if the SO2 can't be absorbed and circulated within the solution, it can't cause precipitation. Cool (bad chemistry joke).
I am still trying to comprehend Harold's statement about 18 ounces of gold in litre of solution. Now, THAT is really concentrated.


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## 4metals (May 30, 2010)

Cold solutions drop cleaner gold, if you look up the solubility curves of silver chloride you will see it is soluble in water, the hotter the water the more silver is dissolved. As the temperature of the solution drops the silver chloride solubility drops off exponentially. After you drop the gold and rinse the silver will dropout and mix with your gold. So you obviously want less in there when you drop it to begin with. 

Cooling the solution before you filter it will cause less silver to be in solution and it will be caught in the filter before you drop the gold. Some on this board have suggested dilution of the acid with 2 or 3 times the volume of cold water to do the same thing. I never liked that as it necessitates more waste treatment, I have always chilled the solution with plain old ice with excellent results. Again it's just another route to the same end, I don't think there is a right or wrong here.

I have never chilled the solution when dropping the gold only before filtering the gold.


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## lazersteve (May 30, 2010)

4Metals,

I for one have been using your ice cube technique to remove silver chloride from my solutions and I can vouch for it's effectiveness. 

It's very important to get the solution very cold before filtering or the luke warm solution will allow some of the silver chloride to make it through the filtration process and end up as a sediment in the bottom of the receiving beaker.

I add the ice and wait a few hours for the solution to completely cool before filtering since 4Metals made the first post.

Steve


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