# Stopping Aqua Regia Process



## EcoBlu (Aug 24, 2017)

We are dissolving Au, PGMs, and Ag from a 200-minus ore using an Aqua Regia solution of 4:1. We want to stop the process a few hours into the reaction while leaving the metals in solution. We have a novel filtration system for collecting the metals directly from the solution for firing or possibly plating. Any suggestions for bringing the pH up slightly and lowering the ORP while stopping the reaction?


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## nickvc (Aug 25, 2017)

Welcome to the forum.
Instead of using premixed AR try adding an excess of Hcl and adding increments of nitric, that way the process can be stopped anytime you want....


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## EcoBlu (Aug 25, 2017)

Thanks. We are going to try starting with 4:.25 AR (not 4:1), and then adding .125 HNO3 every half hour to reach the desired results.


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## nickvc (Aug 26, 2017)

Do not premix it!
If you do you will need to consume all the acids, just adding Hcl will cause some reaction and can cause a large reaction so add an excess of Hcl and when all reaction from that ceases add small increments of nitric that way you should have a fully controllable reaction occurring.


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## 4metals (Aug 26, 2017)

You do realize that you will not be recovering the silver from the ore if you are using aqua regia. Why did you choose aqua regia?


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## Topher_osAUrus (Aug 26, 2017)

Would they even be getting the majority of the pm's?
Especially since it sounds like they are just wanting to stop the reaction, so the metals in solution do not cement back out on the baser stuff in the ore.


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## butcher (Aug 26, 2017)

Using aqua regia on most types of gold bearing ore is normally not only dangerous but a waste of time, one exception may be free gold on quartz, or placer gold, or recovered gold from other mining operations. and even there in-quartering the gold may become necessary because of silver content...

Gold in ore can be from several different types of minerals or rock, and salts of metals, some of which can evolve extremely deadly gases like arsenic,mercury... The gold can be locked up, where aqua regia, cyanide or other leaches cannot get to it, or the acids can dissolve the metals and base metal salts saturating solution and using up the expensive acids leaving most all if not all of the gold behind undissolved or still locked up in a chemical bond...

Using Aqua regia basically would not be a first choice on most ore, in fact for most gold ores it would not even be a good last choice to try and recover gold from the ore (with very few exceptions).

Acids can convert salts to ions in solution, lets say we have iron (most gold ore is associated with some types of iron salts) and sulfide ore also common for gold ore, now if we try to dissolve the gold we can also have iron dissolve as sulfates (normally more iron salts in the ore than gold), which can precipitate the gold back out of the acids we are using, before we can collect it. Roasting may help somewhat, but is not necessarily the cure for all of the problems.

Normally aqua regia on gold ore is not only likely to cost you more, than the gold any you might recover, but also create all kinds of dangers and environmental hazards to deal with, and with most ore would not work well or at all using aqua regia.

Did you get complete assay's of the ore to understand the chemical makeup of the ore?

Are you dumping acids blindly on rocks thinking you can get something out of it, unknowingly of the risk to yourselves?
Has the method been proven to work on the ore you are dealing with?

What type of ore are you working with? free gold on quartz? 
What type of gold ore are you dealing with? Tellurium, selinides, arsenic compounds, pyrites chalcopyrites, sulfide compound, chloride compounds...

http://www.chemistrylearner.com/arsenic-trioxide.html
http://www.galleries.com/Minerals_By_Name
http://www.conservation-us.org/docs/default-source/resource-guides/chart-of-heavy-metals-their-salts-and-other-compounds-nbsp-.pdf

I just cringe when I hear of people dumping aqua regia on rocks, thinking they can dissolve the gold out, without a complete understanding of what they are trying to accomplish, or the complications involved, not only will they most likely be very unsuccessful, but could easily end up very sick or dead. 

Without knowing more about your plans of using aqua regia on your ore, I would say you are not only wasting your time but are also putting yourself in danger.


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## Aristo (Aug 26, 2017)

EcoBlu said:


> We are dissolving Au, PGMs, and Ag from a 200-minus ore using an Aqua Regia solution of 4:1. We want to stop the process a few hours into the reaction while leaving the metals in solution. We have a novel filtration system for collecting the metals directly from the solution for firing or possibly plating. Any suggestions for bringing the pH up slightly and lowering the ORP while stopping the reaction?



I believe what they are try to achieve is to lift some of the precious metals without touching things like Iridium or similar PGMs. This an educated guess, nothing more.
If that's the case, then the situation will be better served using a very weak dilute AR solution , filter and repeat until you feel you have achieved your objective.
If the ore concentrate is properly pre treated, then the use of AR in different concentrations and strengths could be useful but it will be delicate and may require years of experience. Accurate and tedious control of temperature, Ph and ORP is paramount. After all, dealing with ore is far removed from playing with karat scrap and electronic waste.


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## Palladium (Aug 26, 2017)

If you want to stop the reaction just separate the solution from the materials.


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## 4metals (Aug 26, 2017)

> If you want to stop the reaction just separate the solution from the materials.



Easier said than done with -200 mesh material!


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## Palladium (Aug 26, 2017)

4metals said:


> > If you want to stop the reaction just separate the solution from the materials.
> 
> 
> 
> Easier said than done with -200 mesh material!



True! I just noticed that.


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