Aqua Regia refining of karat gold scrap

[Noxx]

Here is two pictures of one gold nugget I made using Butyl Diglyme. It weights 2 grams. It seems to be very pure.

But there is a «hole» in the middle. It formed when I cooled it in water. Is there a way to avoid that ?

Thanks

 

[lazersteve]

Excellent Button Noxx!!!

I see the BDG served you well!

The hole is what's known as a 'pipe' and is a sign of high purity as is the bright shine on the button. You can avoid the pipe by slow and even cooling of the button.

Great job with the BDG.

Steve

 

[catfish]

Hey guys:

I have just finished up a batch of gold that started out looking bad. It was black, very fine and spongy. I used the method that Harold has outlined in this post on purifying gold. I am waiting on some new cupels to melt it.

I followed all the steps as far refining in AR, boiling in Hydrochloric for 5 minutes, rinsing, then boiling in water for 5 minutes, then rinsing, boiling in Ammonium Hydroxide for 5 minutes, rinsing, boiling in water for 5 minutes, boiling in Hydrochloric again for 5 minutes, rinsing, and boiling for 5 minutes in water. After all this I put it back in AR again and redid the entire process.

Attached is the finished product. Notice the gold is very light brown, clings together, and falls very fast in water. When I get it melted, I am going to send it to my gold buyer and have it assayed. I think it will turn out good.

Please note, the gold is still in water when I took the picture.

My many thanks to Harold and his fantastic knowledge and him sharing it with us.

My hat is off to you, Harold.

Thanks,

Catfish

 

[goldsilverpro]

Great looking stuff. Is that a Corning Ware dish I see? I think you would be wasting money by having an assay done. I think the results would be meaningless. Fire assaying is the most accurate of all methods. Its accuracy is .02%, but only at the hands of an excellent assayer, running duplicate (or, more) samples. By the looks of the material, its purity is likely out of the realm of fire assaying's accuracy.

At this purity, the only inexpensive way to determine purity is to look at the ingot. You want no discoloration (usually reddish), great brilliant color, well defined crystal, and a pipe (a hole).

 

[catfish]

GPS:

Yes that is a corning ware bowl. I buy them for practically nothing at garage sales. My wife will not let me use hers. They are great for washing gold powder, and other things, etc. They will handle a lot of heat; the only problem is that you have to watch the level of fluid in the bowl when you are boiling something, for you can loose valuable gold due heavy bubbling effect with a shallow liquid level. (Been there, done that, and got the T-shirt to prove it)

Cris, I guess I am somewhat confused on your recommendation of not having the gold tested by fire assay method. What method would you recommend? I want to achieve a very high quality of pureness of my gold.

I get test results back on all my gold buttons that I sell, but they are tested by fire assay method. They test fairly well but I would like to improve the end results, but need an accurate method to let me know when I get there.

Any suggestions, you can give me would be greatly appreciated.

Thanks

Catfish

 

[jimdoc]

Catfish,
I think he is trying to say this you are posting in the wrong section.
You don't need any help, you got your diploma dude!!!!!!!!
I can't wait to see those results myself.
Also let's see the ingot when you are done, and that should show
what GSP is talking about with the crystals and the pipe, what he is
saying is that is a sure sign of very high purity, and a fire assay
will be a waste of money, because you will be able to tell from the
appearance of the final ingot or button. He is saying that an experienced buyer will be able to tell from seeing your results how pure it is.
Unless of course you are curious about the results for your own records,
and proof of your diploma.

 

[PhillipJ]

Thanks Harold.

Here is what I got using your cleaning method. I ended up redoing my 1st nugget.

 

[Ignatz61]

Harold,
I can't claim six 9's purity but thanks to advice/admonishment from Harold I slowed down and followed tried and true procedures for dissolving and washing my gold. The two buttons in the photo are before and after following Harold's advice. I haven't had it assayed yet but the last one I sent in was .9214 I know this one is better than that. And the next will be better still. Thanks Harold.

 

[Harold_V]

And the next will be better still. Thanks Harold.

You're very welcome, but if you'd like another tip, washing will improve your gold immeasurably, but if you really want to clean it up, consider refining a second time.

While I have no scientific evidence of what I'm going to say, everything I experienced indicates it's probably true.

When you precipitate gold from a dirty solution, impurities are dragged down along with the gold. Persistent washing appears to remove the majority, but not all of the contamination. A second processing liberates the trapped contaminants. Only when I started refining my gold a second time did I see an improvement.

If you choose to give that idea a go----do what you've been doing right along, stopping short of melting. After you've washed the gold well and rinsed it so it's free of acid or ammonium hydroxide, re-dissolve the gold for a second filtration and precipitation. I used to force dry mine to insure it was free of chemicals. I'd heat it in the beaker until it had quit emitting fumes.

When you re-dissolve, use the formula of a (fluid) ounce of nitric for a troy ounce of gold, and no less than 4 fluid ounces of HCl per ounce. A few drops of H₂SO₄ will insure you don't carry lead through the process.

This may sound like a lot of extra work with little benefit, but you'll easily be able to see what you leave behind after you've precipitated the gold, especially if you use SO₂ gas. I routinely double refined my gold, and almost always ended up with traces of blue in the residual solution after precipitation.

The second precipitation yields gold of excellent quality, due in part to very little in the way of contamination being dragged down. Regardless, use the same extensive washing procedure as you did previously. I think you'll be pleasantly surprised at the improvement. If that be the case, please post your results, so others will benefit by your experience.

Nice improvement, by the way. Thanks for trusting my advice.

Regards,

Harold

 

[wop1969]

Add 3 times its volume of tap water. This dilution will precipitate about 99% of the silver as silver chloride

Will this trick work on AP or AuCl "AKA" HCl/Clorox

To about 4 gallons of dilute aqua regia, add about 60 mL of battery acid and stir. This precipitates the lead.

and will this work on AP or AuCl "AKA" HCl/Clorox as well

 

[butcher]

Silver is pretty much insoluble as a chloride in water (if high acid and oxidizer slightly more soluble). So this is where letting solution sit or heating to lower chlorides and not using too much acid or oxidizer and adding water several volumes of water help to precipitate the silver.

Lead is insoluble as a chloride in COLD water (more soluble if acidic high or oxidizer) lead is slightly soluble in boiling hot water,
lead sulfate is insoluble, hot or cold, this is where a few drops of H₂SO₄ (sulfuric acid) can help to get the lead out.

Lead is not very soluble in acid peroxide it is usually not too acidic and if you haven't used too much peroxide it settles to bottom. Silver similar.

Lead can be in the HCl / bleach, letting sit and adding water will precipitate it if contents are not too high, if you dissolved a lot of lead adding couple drops of sulfuric will also help. Silver will also precipitate when diluted and less acidic.

Since silver and lead are insoluble as chlorides they won't hardly dissolve in solution of HCl, although with high oxidizer some will this is a contaminate we eliminate by lowering the oxidizer in solution and diluting with water etcetera, then after precipitating gold with washing procedures, we still are after these contaminates, and sometime by re-refinining a second time.

 

[wop1969]

Butcher, would it be a good practice for me to take my AuCl filter it clear then add few drops of Sulfuric and filter solids then dilute with water, let it sit and filter out whatever is on the bottom?
then precip, rinse and repeat.

My AuCl sometimes has white stuff that does not sink well, and sometimes it looks kinda grey, and the longer the AuCl sits seems the more whitish stuff, like something is preciping as the acidity goes down from gassing off. Now, since I know their is only Au, Cu, and solders going into my AP baths then it has to be either lead or silver from the solder, Correct?

 

[butcher]

It can help to boil a little chlorides off or just let it sit for a day or so, if you have lead few drops of sulfuric can help remove it in later step,
filter, add water to dilute ( this also lowers acid concentration so the silver chlorides and lead will precipitate, if after a day you still see some white powder in a dilute solution add a little HCl or table salt to help precipitate the silver as chlorides, in this dilute solution it should not be salts of your acids you are seeing. It is pretty much similar for Aqua regia solutions.

 

[wop1969]

Sounds good.

One thing struck me when you said salts from the acid, I did not know about that and I noticed if there is white stuff floating on the bottom and I dilute it goes away instantly. Am I correct to say that would indicate it is acid salt?

 

[butcher]

Table salt can be made from HCl + NaOH muriatic acid and sodium hydroxide to make sodium chloride NaCl and H₂O,
when you add sodium hypochlorite (bleach ) to HCl hydrochloric acid (Muriatic acid), NaClO + HCl, you will also be making some table salt in solution.

Any acid and a metal like sodium or copper when added together make salts of those metals the sodium metal salt is just one of the salts we put on our french fries or food, some salts are water soluble some are not, some are soluble in acids, and some are not,

hope this helps

 

[wop1969]

IT does TYVM

Now I feel confident that the white stuff is salt not silver but, for the sake of getting clean gold I will use dilution and drops of sulfuric to get out any silver or lead..

 

[MargueriteMingorance]

I'm sure I used enough nitric (70% Lab Grade). I even poured off the first batch and added more to be sure. I didn't get much more action. I think heating is the issue. Since I don't have a fume hood yet I do everything cold and just wait it out. As I've stated many times, I'm in no hurry.

There were a few batches I ran that were difficult to process. In my case it was a matter of not having added enough silver, so the end result is much as you describe. Even with a hard boil for a prolonged period of time, there were occasions when all action ceased, yet the core of the material being processed didn't have the base metals removed.

What I discovered in that instance is that you're more or less between a rock and a hard place. The only thing that works with certainty is to melt any un-dissolved pieces along with an ample amount of silver, to lower the gold content. Seems like if you run the first results in AR to exclude the gold, by the time it has been removed, the silver exposed will have formed a hard crust and makes running the balance of the material in nitric next to impossible. Re-melting eliminates all the headaches.

Have you tried hammering it out into a thin sheet? More surface area will stop the gold from blocking access to the silver and other base metals.

 

[Harold_V]

Have you tried hammering it out into a thin sheet? More surface area will stop the gold from blocking access to the silver and other base metals.

I didn't consider that as a viable option. I ran my operation for gain, and couldn't spend that kind of time messing with the material when I could remelt, adding more silver, and have it back in acid in just a couple of minutes, with no fear of loss.

I'm not suggesting it wouldn't work---it would---but chasing the splintered values and spending the time just made no sense to me.

By the way, more surface area isn't why it works. It works because the inquarted material, now being thinner, is dissolved to the core before a hard, impervious crust can form, isolating the remaining material from nitric. The increased surface area just happens to be the result of thinning.

Harold

 

[FrugalRefiner]

The moderators would like to thank all of the members who contributed to the original thread that this post was based on, as well as those who asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above, consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Getting pure gold (shining).

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