Issues with neutralizing nitric acid in my aqua regia solution

[Mostafa Ali]

I have quartz stone and I'm sure it contains gold but I'm unaware of the percentages of the minerals in it. I crushed the stone to small granules. I cleaned the crushed resultant using nitric acid with heating then I executed another cleaning process using normal tab water. Then again I cleaned the mixture with sulfuric acid then washed the mixture with water.
Finally after all this cleaning process, i prepared my aqua regia solution using the percentage of 1 nitric acid to 3 HCL in a glass container and then added my mixture of crushed granules to the glass container of aqua regia solution and then I heated the solution just before the solution boils, let the solution cool down a bit then heat again.
After the dissolving process, i filtered my mixture to remove the impurities and have a clean aqua regia.
Then I neutralized the nitric acid in the aqua regia using urea with heat.
My issue is that when I neutralize, the solution takes up so much urea until the reaction stops.
Then I try to precipitate using SMB but there is no gold precipitation and the color of the solution dims.
Then when i leave the solution and check it after a day, the solution's color sometimes lightens up a little bit.
Can you please advise us on what we could be doing wrong in any of the steps above?

 

[Yggdrasil]

I have quartz stone and I'm sure it contains gold but I'm unaware of the percentages of the minerals in it. I crushed the stone to small granules. I cleaned the crushed resultant using nitric acid with heating then I executed another cleaning process using normal tab water. Then again I cleaned the mixture with sulfuric acid then washed the mixture with water.
Finally after all this cleaning process, i prepared my aqua regia solution using the percentage of 1 nitric acid to 3 HCL in a glass container and then added my mixture of crushed granules to the glass container of aqua regia solution and then I heated the solution just before the solution boils, let the solution cool down a bit then heat again.
After the dissolving process, i filtered my mixture to remove the impurities and have a clean aqua regia.
Then I neutralized the nitric acid in the aqua regia using urea with heat.
My issue is that when I neutralize, the solution takes up so much urea until the reaction stops.
Then I try to precipitate using SMB but there is no gold precipitation and the color of the solution dims.
Then when i leave the solution and check it after a day, the solution's color sometimes lightens up a little bit.
Can you please advise us on what we could be doing wrong in any of the steps above?

Welcome
First of all, I have deleted your other post as we do not allow double posting.

Since you are sure you have Gold, what do the assay say?
I do assume you have an assay as that is the only way to know that you have Gold?

How did you concentrate it?

And the next wrong is that you really do not use AR or other acids on ore.

 

[Mostafa Ali]

Welcome
First of all, I have deleted your other post as we do not allow double posting.

Since you are sure you have Gold, what do the assay say?
I do assume you have an assay as that is the only way to know that you have Gold?

How did you concentrate it?

And the next wrong is that you really do not use AR or other acids on ore.

Thank you for your response. To clarify why I’m certain there’s gold:
1. After dissolving the material in aqua regia, I tested the solution with **stannous chloride (tin chloride)**, and it turned **black**, indicating the presence of gold.
2. I can **visibly see gold veins** within the quartz stone.

Could you advise what might be going wrong in the precipitation step based on this?

What do you mean by “how did you concentrate it?”?
I did no concentrate anything

 

[4metals]

Welcome to the forum.

What you do not mention is the quantity of crushed quartz you processed or the size you reduced the pieces to. Your method of using aqua regia is good to give you a stannous chloride indication of gold but if your sample processed was too small, the recovery process is difficult. Some information of the quantities you tested as well as the potential quantities you have to process will give us the information needed to help you proceed properly.

 

[galenrog]

Unless there is visible gold, without an assay you have a rock.

Also, black stannous test is NOT indicative of gold. Purple is. Of course, if the solution is concentrated, stannous test may be very dark, appearing to be black. If you believe this to be the case, dilute your solution. If it still shows black. Definitely no gold.

Time for more coffee.

 

[goldshark]

Some pictures of your material would be helpful, from raw ore, crushed, then solution color after AR.

 

[Marcel]

Consider crushing the material into a fine powder and then using a gold pan to concentrate the gold. After that, try aqua regia or another refining method. Not everything that appears to be gold actually is gold. Going directly to soak the gold in aqua regia is not best practice. Gold ore may contain other metals that negatively affect subsequent chemical procedures. Additionally, using aqua regia on ore is not economical—you will need large amounts and generate significant waste. It is better to concentrate the gold first (e.g., by panning).
If your gold is embedded in a calcite matrix, dissolve the calcite using vinegar and heat, for example.
Overall, it is best practice to remove any unwanted material, particularly base metals and calcite, before applying the chemical reagent aqua regia.

 

[Mostafa Ali]

Welcome to the forum.

What you do not mention is the quantity of crushed quartz you processed or the size you reduced the pieces to. Your method of using aqua regia is good to give you a stannous chloride indication of gold but if your sample processed was too small, the recovery process is difficult. Some information of the quantities you tested as well as the potential quantities you have to process will give us the information needed to help you proceed

Unless there is visible gold, without an assay you have a rock.

Also, black stannous test is NOT indicative of gold. Purple is. Of course, if the solution is concentrated, stannous test may be very dark, appearing to be black. If you believe this to be the case, dilute your solution. If it still shows black. Definitely no gold.

Time for more coffee.

Thank you for your guidance. To clarify:
- We processed **approximately 5 kg of quartz stone** (crushed to granules of ~1-2 mm size).
- We currently have **1 ton of quartz available**, and this quantity can be expanded if needed.

Could you advise on how to optimize the recovery process for these quantities?

 

[Mostafa Ali]

Some pictures of your material would be helpful, from raw ore, crushed, then solution color after AR.

 

[Yggdrasil]

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The pictures do not zoom well, but to me it looks like Pyrite or similar due to the sharp edges.
Are it cubic or orthogonal?

How much liquid did you use for this batch?
Did you heat it?
If there are Gold the most likely culprit is way too much Nitric.
Did you test the pH after dumping Urea into it?

Try to cement it on solid Copper in stead.

 

[Marcel]

Looks like Pyrite (FeS) yes. But often Pyrite is found together with Gold. Don't you have a sample with a small Gold vein?
Try to crack out a few of the golden cristals and then dissolve them.

 

[Yggdrasil]

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As Marcel said but much easier, squeeze or scratch it with something sharp.
Do it crush or smear?

 

[goldshark]

Like all above posters stated, crush to fine mesh (100 ) or so. Pan down to heavies. You will then be able to discern between pyrite and the metallic shiny of the Gold. Check screen for larger particles of Au which won't crush, in a separate clean pan. Since Au is usually alloyed with other metals, putting directly in AR may only put a passive coating on the outside, or create a complex soup of chemicals you will further need to deal with.. It is best to alloy with Silver, then inquart to find the relatively pure Au. Better to fire assay, if you can, to find the values in a ton or tonne of potential ore.

 

[4metals]

(crushed to granules of ~1-2 mm size).

It is entirely possible that as much gold as you can possibly leach from particles this size, an equal amount if not more remains encapsulated in rock and is not recoverable. Crush your powder down below 100 mesh (at the least) and pan off any overburden (the lighter non gold material). Then the heavier material can be processed as you described earlier. Still for a ton of material other leach methods would be preferable.