# 5g of Gold in Aqua Regia



## kwxj61b (Jul 14, 2016)

Hi!
I had a 5g 18k gold and I wanted to refine it to 24k. So I decided to put it in to AR w/ 1:4 250ml at start. I heated up. I add 2x 1:4. Then 2x 1:3 of AR...today's the second day, it's takes so damn long time to dissolve it. How long does it takes to dissolve 5g of 18k gold in aqua regia?
The beaker picture is today. I was wondering what's with that white precipitate? Is it lead?


----------



## FrugalRefiner (Jul 14, 2016)

The white precipitate is probably silver chloride. The silver content of the 18k alloy is part of the reason it's taking a long time. It forms a coating on the metal as the AR is working and slows down the dissolution process because the acid can't get to the gold. That's why we usually inquart karat gold, dissolve the silver away with nitric, then dissolve the relatively pure gold with AR.

You've used WAY too much acid.

Dave


----------



## Topher_osAUrus (Jul 14, 2016)

What are the constituent metals making up the alloy? 
If its all silver and gold, you may be creating too much silver chloride for it to readily attack the gold.

Silver chloride can and will create a crust that cannot be penetrated by the acid.

I have read a few people take 18k straight to AR, but it depends on the type of gold... Yellow, red, green, white, etc..

Most everyone doesnt add AR to their gold, but enough HCl to dissolve the amount of gold there, and then slowly add small nitric increments.

Are you heating the reaction? It helps alot.

Topher


----------



## kwxj61b (Jul 14, 2016)

Dave, thanks for the tip!
Toper, now I understand why Sree from Youtube add HCL and Nitric acid separately.

Thanks guys!


----------



## kwxj61b (Jul 14, 2016)

First I filter out that solution. Then w/ that gold sample and white precipitation/residue, I put it into a beaker with 100ml of nitric acid. I add heat for 15 minutes. But I notice that white stuff did not dissolve...so no silver? Then what is it? 
Dave, if I bring that sample into a nitric acid solution, how do I know that all the silver has been dissolve?

I appreciate your help guys! Thanks!


----------



## 4metals (Jul 14, 2016)

Silver chloride won't dissolve in nitric. You need ammonia to clean it up. 

This thread from the library may help.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=85&t=22228



Sent from my iPhone using Tapatalk


----------



## FrugalRefiner (Jul 14, 2016)

kwxj61b said:


> First I filter out that solution. Then w/ that gold sample and white precipitation/residue, I put it into a beaker with 100ml of nitric acid. I add heat for 15 minutes. But I notice that white stuff did not dissolve...so no silver?


That will not work. You already have a crust of silver chloride on the undissolved metal. Silver chloride will not dissolve in nitric acid. 

The reason we inquart is to prevent the situation you have run into. 

If you put a piece of karat gold in nitric acid, only a bit of the alloying metals like copper and silver will dissolve near the surface, but fairly quickly the reaction will come to a stop because the gold shields the alloying metals deeper inside the chunk of metal from being reached by the acid. The result will be a piece of metal that is fairly pure gold at the surface of the piece, but pretty much the original alloy deeper inside. 

If you put the same piece into AR, the AR will dissolve the gold at the surface, but as it does so, it forms the crust of silver chloride you now have, which shields the gold from being contacted by the AR.

When you inquart, you add enough silver to the original piece to bring the gold content down to about one quarter of the total metal weight. You can put this inquarted metal into nitric acid, and the nitric will dissolve the silver. Because the gold content is only about one quarter of the total, it does not shield the inner parts from the acid, so the nitric acid can dissolve virtually all of the silver. This will leave you with relatively pure gold that can then be dissolved in AR.

There is a solution to your problem. First, you can put the remaining piece of undissolved metal in some ammonia. The ammonia will dissolve the silver chloride. Once it has done so, remove the remaining, cleaned piece of metal from the ammonia. *Promptly* add some HCl to the ammonia solution to acidify it. If you don't, the ammonia and silver can form explosive compounds. 

Next, take the remaining piece of metal and hammer it as thin as you can. I don't mean a whack or two. I mean beat it till your arms are sore. You need to get it very, very thin. If you get it thin enough, you'll be able to put it back into AR to dissolve the gold. By beating it very thin, you expose a lot more surface area to the acid, and while the silver chloride will again form on the surface, if you've beat it thin enough, the acid will be able to penetrate to the center and dissolve all the gold. Before you put it in the acid, twist the thin metal so it doesn't lie flat on the bottom of your beaker so the acid can get to it from all sides. If the same problem happens again, you can repeat putting it into ammonia to dissolve the silver chloride crust (remember to again acidify the ammonia), then returning it to AR till it has all dissolved.

Stop using so much acid! It's a huge waste. You started with 5 grams of 18k alloy. If it was thin enough, it could have been dissolved in about 20 to 25 ml. of AR. If you had inquarted it by adding around 13 to 14 grams of silver, the silver could have been dissolved with about 15 to 20 ml. of nitric acid and an equal volume of distilled water.

Please understand that what I've given you here is a very brief description. You need to do more studying. All of these processed are described more thoroughly in Hoke's book and on the forum. My goal was to provide you enough information so that you can search out more complete descriptions of the processes.

Best of luck with your studies and your gold.

Dave


----------



## g_axelsson (Jul 14, 2016)

I have to step in here and say that Dave's answer above must be one of the best examples I've seen in a long time to how to answer a newbie when they arrive here with problem. He first explains what have gone wrong and what happened, then gave two solutions and in the end told him to study more without being demeaning.

Nice work, Dave! 8) 

Göran


----------



## kernels (Jul 14, 2016)

g_axelsson said:


> I have to step in here and say that Dave's answer above must be one of the best examples I've seen in a long time to how to answer a newbie when they arrive here with problem. He first explains what have gone wrong and what happened, then gave two solutions and in the end told him to study more without being demeaning.
> 
> Nice work, Dave! 8)
> 
> Göran



I was just thinking exactly the same thing, usually newbys aren't lucky enough to get answers like that when they have done something silly through not spending 30 minutes reading the relevant section in Hoke.


----------



## Topher_osAUrus (Jul 14, 2016)

Dave is a wise man.

Not only did he help the new member of our forum in a great way.

He gave the rest of us an example to live by.
Treat others with respect, be helpful, and not be a jerk about it, but be a guiding hand to show an answer and instill curiousity for the reader to want to learn more on their own. So the joy of discovery is still there for him.

You're a damn fine gentleman Dave, and you would make an excellent professor.

Not everyone ( like me..) can be as graceful with their help.
Hats off to you sir.


----------



## kwxj61b (Jul 15, 2016)

Dave,
Thanks for the info.
I'm treating the sample w/ ammonia. I add heat. Are you suppose to add heat? Anyway, I'm seeing white residue and not being dissolve. Should I add more ammonia or discontinue heating?

Rick


----------



## kwxj61b (Jul 15, 2016)

i add more ammonia and no heating. Residue gone but samplr still had that coating. should i give it more time or add heat?


----------



## FrugalRefiner (Jul 15, 2016)

Since the ammonia dissolved the loose precipitate, it will probably dissolve the coating too. Ammonia is usually pretty dilute, so it can't dissolve a lot of silver chloride. I'd probably pour off the ammonia and dissolved silver that is in there now (remember to acidify it with some HCl after you pour it off and you'll see the silver chloride form a precipitate again), then add some fresh ammonia. Heat usually speeds up most reactions, but keep in mind that ammonia is a gas dissolved in water, and when you heat it, it drives the gas out of the solution more quickly. You can also take the piece of metal and give it a whack or two with a hammer, which will break some of the crust loose and start the flattening process.

Dave


----------



## alexxx (Jul 15, 2016)

In this case, since the AgCl is in very small quantity and its value is probably lower than the time & regents used to remove it, would it be possible to just remelt all solids with an oxy - acetyle torch to get rid of the silver chloride and start over with proper inquartation?


----------



## 4metals (Jul 15, 2016)

Household ammonia is not very strong but when in a refinery and you talk about ammonia, it is ammonium hydroxide which is much stronger. 


> In this case, since the AgCl is in very small quantity and its value is probably lower than the time & regents used to remove it, would it be possible to just remelt all solids with an oxy - acetyle torch to get rid of the silver chloride and start over with proper inquartation?



YES, that is essentially what was done in the post I linked earlier in this thread. At some point kwxj61b will have to start reading on the forum rather than asking. These procedures are well documented on the forum and easy to find in the library.


----------



## myfalconry76 (Jul 15, 2016)

Could you not pound it super thin and use peroxide and nitric to dissolve the silver, filter out the gold and then use AR? This is a question, not a response! Not trying to hijack any threads but I just got some 18kt the day befor and have not started it yet.


----------



## nickvc (Jul 16, 2016)

Yes you could pound it really thin and add nitric alone this will dissolve all the base metals and silver, you could also in that situation just use AR as the silver cannot form an impenetrable barrier so all the gold and other metals will dissolve leaving just silver chloride behind.
Alloys from 14k and above should easily dissolve in hot AR as the silver content is usualaly below the problem threshold but if in doubt inquart it saves a lot of trouble later.


----------



## 4metals (Jul 16, 2016)

The exception to this is 18 karat green gold, it is not common these days, and it isn't all that green either but it does have up to 20% silver in it and inquartation is by far the easiest route.

I would guess the 5 grams in the OP was green gold.


----------

