Aqua Regia Questions

[Miner Jim]

I am new on this forum and have a bunch of questions about how to purify gold using the aqua regia. I have looked around online and it seems like just about everyone has different ideas of the best way to do it.

I have a gold mine that is starting to show some nice color and the vein yields 18 karat gold. I crush the ore to powder in a mill and am left with fine gold. I got to thinking this fine gold would easily dissolve with aqua regia, so I'm curious if this is really a good idea. These are my main questions to start with.

1. Does this method result in 100% recovery of the gold?

2. The gold is 25% silver and 75% gold. Is there any way to recover the silver that is not too complicated?

3. What is the best mix of chemicals to use for aqua regia? I have seen nitric acid and HCL or muriatic and sodium nitrate mentioned as both being good.

4. What is the general process of precipitating the gold out of solution?

5. What are all of the chemicals I would need?

 

[nickvc]

1. Does this method result in 100% recovery of the gold?

2. The gold is 25% silver and 75% gold. Is there any way to recover the silver that is not too complicated?

3. What is the best mix of chemicals to use for aqua regia? I have seen nitric acid and HCL or muriatic and sodium nitrate mentioned as both being good.


4. What is the general process of precipitating the gold out of solution?

5. What are all of the chemicals I would need?[/quote]
Welcome to the forum.
1. Yes if you follow strict procedures and understand what exactly your doing. Read C.M.Hoke
2. This mix of metals will probably need to be inquarted which will require more silver...
Read C.M. Hoke.
3. It depends on several factors HCl and muriatic are the same but many people have problems sourcing nitric at reasonable cost or at all so make their own. Read more on the forum and form your own opinion.
4. Again there are varying methods employed depending on needs costs ease and preference read C.M.Hoke and read about what others employ in similar circumstances.
5. This is like asking how longs apiece of string read C.M.Hoke and read more on here to give you an idea of which method or processes you want to use then you will know hat chemicals and equipment your going to require.
READ C M HOKE.... It's the best start you can have.
I wish you luck but get reading and it will all slowly make sense.

 

[Oz]

I agree that if he is getting free milling gold from this vein in those percentages that inquartation would be a good path to follow. It would also allow him to inexpensively recover his silver values and any traces of the platinum group that may be present.

 

[goldenchild]

2. This mix of metals will probably need to be inquarted which will require more silver...
Read C.M. Hoke.

I agree that if he is getting free milling gold from this vein in those percentages that inquartation would be a good path to follow. It would also allow him to inexpensively recover his silver values and any traces of the platinum group that may be present.

If the gold coming out of this mine is indeed 18k why would he want to inquart it? 18k is the minimum karat before one could go straight to AR for recovery and refining. This would make the material coming out of the mine a perfect candidate for AR digestion, especially if it is finely ground. The silver would come down as chloride with the ore which can then be processed after filtering the gold chloride. Inquarting would be alot more unneccessary work.

 

[HAuCl4]

That stuff will not dissolve in AR goldenchild. Too much % silver. Very different than 18K jewellery scrap. It's more like green gold, but possibly with some PGM.

When in doubt, inquart!. :lol:

 

[nickvc]

2. This mix of metals will probably need to be inquarted which will require more silver...
Read C.M. Hoke.

I agree that if he is getting free milling gold from this vein in those percentages that inquartation would be a good path to follow. It would also allow him to inexpensively recover his silver values and any traces of the platinum group that may be present.

If the gold coming out of this mine is indeed 18k why would he want to inquart it? 18k is the minimum karat before one could go straight to AR for recovery and refining. This would make the material coming out of the mine a perfect candidate for AR digestion, especially if it is finely ground. The silver would come down as chloride with the ore which can then be processed after filtering the gold chloride. Inquarting would be alot more unneccessary work.

I must admit I did consider going straight for AR but I reckoned that even if the gold was small particles some might not dissolve fully and silver chloride always traps some gold so the process would have gold trapped in silver chloride and maybe in reasonable amount plus the point that Oz correctly made that should any pgms be present they will recoverable from the silver by inquiring.

 

[goldenchild]

2. This mix of metals will probably need to be inquarted which will require more silver...
Read C.M. Hoke.

I agree that if he is getting free milling gold from this vein in those percentages that inquartation would be a good path to follow. It would also allow him to inexpensively recover his silver values and any traces of the platinum group that may be present.

If the gold coming out of this mine is indeed 18k why would he want to inquart it? 18k is the minimum karat before one could go straight to AR for recovery and refining. This would make the material coming out of the mine a perfect candidate for AR digestion, especially if it is finely ground. The silver would come down as chloride with the ore which can then be processed after filtering the gold chloride. Inquarting would be alot more unneccessary work.

I must admit I did consider going straight for AR but I reckoned that even if the gold was small particles some might not dissolve fully and silver chloride always traps some gold so the process would have gold trapped in silver chloride and maybe in reasonable amount plus the point that Oz correctly made that should any pgms be present they will recoverable from the silver by inquiring.

Wouldn't pgms also dissolve with the gold?

 

[Miner Jim]

Thanks for all of the answers guys! It is quite apparent there are many different opinions about the best way to do things.

 

[nickvc]

Thanks for all of the answers guys! It is quite apparent there are many different opinions about the best way to do things.

There may be different opinions but there will be only a few correct methods or even one if you have a high silver content in your gold and don't wish to lose gold In to your silver chloride which can be a real pain to deal with , by inquarting you end up with silver nitrate + any pgms if present which can be cemented out with copper leaving you with high purity silver 97-98% which can be melted after rinsing much easier than having silver chloride which will need converting back to silver metal and then re dissolving or putting through a cell to recover the gold.
If you have quantities of values from your mine I would suggest you have an assay done to check on any pgm content and to confirm your silver content as if it's a lot lower a straight dissolution in AR may be the way to go.

 

[butcher]

Guy's we are talking ore here not 18 karat gold. apples and oranges
Ore can have a lot of base metals, like Iron or others that can cause problems if using aqua regia, or any leach you choose, the base metals can use up the acid pretty quickly, also ore can have other chemicals like sulfide's that can give you much trouble if pretreatments are not done before trying to leach values, and may mess up your aqua regia, knowing the chemical makeup, and metals, of what you are dealing with will give you more of a chance of success, an assay should be first priority, this can also give you clues on how to pre-treat your ore (roasting and so on), before any leaching and also may determine any pre-leach method that may be needed (if high base metal content), and may also help you in choosing a cheaper and better leach method.

I would not think of aqua regia as a good treatment for ore normally, as ore will usually need more of a recovery process, and aqua regia is usually better for a refining process.

I would also consider cost of chemicals, and how you are going to deal with waste and byproducts from these processes, for a small lot of gold one chemical process may be economical, but when mining ore from a mine on any larger scale can be a totally different story.

get assay
get C.W. Ammmen's book (recovery and refining of precious metals) it will deal more with ore.
and if refining your gold after recovery from the ore definatly read Hoke's book

 

[Miner Jim]

I crush the ore to a fine enough state, so I'm able to sluice and pan the gold out of the crushed rock. My usual method is to use mercury to pull the gold together and then melt the gold sponges into metal. I was thinking of usuing the aqua regia to skip the mercury porcess and end up with 24k gold and some silver.

 

[goldenchild]

I crush the ore to a fine enough state, so I'm able to sluice and pan the gold out of the crushed rock. My usual method is to use mercury to pull the gold together and then melt the gold sponges into metal. I was thinking of usuing the aqua regia to skip the mercury porcess and end up with 24k gold and some silver.

So speaking from a person's point of view who deals with ore... would you say AR could be a viable way to process the ore described in this thread?

 

[g_axelsson]

Remember that we are not discussing raw ore, we are discussing an ore concentrate that's already gone through the recovery stage..
I've seen one mine here producing 80% pure gold from a shaker table. The major contaminants were silver, lead, antimony and rock fragments.

The rest of the sand went on to a flotation step, recovering sulphides which created a concentrate with a couple of percent silver and gold.

But sadly, I don't know how they processed the concentrated gold. The sulphides were sold to a copper smelter.

/Göran

 

[nickvc]

I crush the ore to a fine enough state, so I'm able to sluice and pan the gold out of the crushed rock. My usual method is to use mercury to pull the gold together and then melt the gold sponges into metal. I was thinking of usuing the aqua regia to skip the mercury porcess and end up with 24k gold and some silver.

So speaking from a person's point of view who deals with ore... would you say AR could be a viable way to process the ore described in this thread?

Were the material mine I think the first thing I'd do is get the powders assayed to discover what exactly I was dealing with.
If it's as Jim described 75% Au and 25% Ag then I'd still go down the inquartation route, I think I'd rather use cementation to recover most of my silver and keep the silver chloride down to a minimum as it's a pain to have in volume ,it traps Au and given the high Ag content going directly for AR may not dissolve all the material trapping even more Au in the chloride mix. If this were a more usual miners mix I think I'd leave it to someone else as the mix of metals and compounds creates unique situations that I wouldn't know where to start with