AR error and proposed solution

[IdahoMole]

I am working with karat gold. I inquarted with sterling silver and poured into shot/corn flake and digested in water/HNO3. Then into AR. The AR started to work normally but began to shift to a dark green color and the reaction slowed and eventually stopped. I believe that I didn't allow for a complete digestion in the nitric and prematurely went to AR. I am now planning to decant the AR from the remaining solids, remelt them and re-digest in nitric, and return that to the AR for a complete dissolution. Have I correctly identified my error and a proper solution to my problem?
Eagerly awaiting your input.

 

[4metals]

No mention of testing the AR with stannous. A properly inquarted and leached AR solution should be red as all of the base metals leached with the silver in nitric. What color was the nitric?

 

[IdahoMole]

No test was done yesterday but this morning I removed all doubt. The green, filtered AR can be seen in the flask along with the test. The beaker I used for the AR has a dark brown, almost black, sandy looking material in the bottom.

The nitric solution was green. I cemented on copper and today it is blue. A stannous test is negative as well as a salt test for silver.

A properly inquarted and leached AR solution should be red as all of the base metals leached with the silver in nitric. 

I am confused. My AR is usually a beautiful yellow.

 

[anachronism]

Your AR colour depends upon what is in it. If there are other metals apart from gold then it will change colour accordingly.

 

[Topher_osAUrus]

Gold chloride will shift from yellow to a lovely red depending on concentration.
Its yellow because you are using too much acid for the amount of gold.

 

[anachronism]

Gold chloride will shift from yellow to a lovely red depending on concentration.
Its yellow because you are using too much acid for the amount of gold.

Topher that's not what he was referring to - it was the green colour. Also does yellow necessarily mean too much acid? Not actually come across that before but I'm willing to learn.

 

[nickvc]

What sort of karat scrap exactly were you working with?
Do you inquart before using AR ?
If not as stated it could be contaminates from the alloys, it could possibly be Pd but if you cemented the solution the chances are it will be in with your gold powder, when refining white gold scrap test the solution after precipitating the gold for any PGMs that may be there and then cement them.

 

[4metals]

I am confused. My AR is usually a beautiful yellow.

This is adding to the confusion. Your acid is normally yellow but this time it isn't yellow because we can see the picture and it is green. Lets stick to this lot please.

Base metals contributed the green color as you did not either inquart properly or add enough nitric to part it completely. If all you had was a nice ruby red aqua regia before dropping the gold that is because it only contained gold or at least the vast majority was gold. Once the gold is dropped it is yellow.

I never heard that too much acid makes the solution yellow, but my experience is from clients doing as I tell them to do the process so there is no over addition of acids. Of course once I'm gone that may change so what Topher said may be true but it is not my first hand experience. Very low concentrations of gold will be yellow but a solution with a few ounces per liter will be nice ruby red if gold is the metal in solution with minimal other impurity.

 

[Topher_osAUrus]

Topher that's not what he was referring to - it was the green colour. Also does yellow necessarily mean too much acid? Not actually come across that before but I'm willing to learn.

I was referring to the last line of his last post, (which 4metals quoted)

It could just be dilute, whether its water or acid, is irrelevant. I was guessing it was acid, as newbies always use too much.

But, as 4metals said, we should stick to this lot, and i agree. Keep it simple, and keep the thread straight. Green is from copper.

But, that is a good point of interest. Yellow could mean a GREAT many things...from dilute gold chloride to no gold at all and just iron in solution.

 

[upcyclist]

Green is from copper.

To clarify (for the OP), blue is from copper. The most likely scenario: Blue (copper) + Yellow (gold) = Green.

Other metals, depending on the alloys in your karat mix, may also be at play. Nickel, often used in white gold alloys, has a green color in solution. Iron often lends a greenish-yellow color as well. As was mentioned earlier, a proper nitric soak to remove ALL base metals is key. Dirty solutions lead to dirty drops. And as Nick mentioned, check your solution after the gold has been dropped for other precious metals (using stannous and/or DMG)--palladium is also used to whiten gold.

For the varying yellow-to-red color of gold, depending on it's concentration, think of yellow food coloring. It's actually reddish-orange coming out of the bottle, but it turns yellow when diluted.

 

[Barren Realms 007]

Quit going by color and do your proper testing. HCL can also turn yellow just by setting open and oxygen mixing with the liquid.

Assumption is the mother of all evil.

 

[upcyclist]

Quit going by color and do your proper testing. HCL can also turn yellow just by setting open and oxygen mixing with the liquid.

Assumption is the mother of all evil.

Indeed. That's why I brought up nickel and iron. It's like identifying gemstones - going by color alone only leads to ruin. Test it. Once you gain a lot more experience AND if have a solid idea of the exact composition of your source material, you can go by color a bit more.

Sent from my SAMSUNG-SM-G891A using Tapatalk

 

[IdahoMole]

A big thank you to everyone that took the time to read and/reply to my post. This is a great place because of the members. Everyone shares knowledge freely when they can and others, like myself, can learn a great deal just by reading the threads.

This discussion is a good one but has gone astray of the big question I had in my head. That fault may well be my own. I find this form of communication difficult for myself personally, so I lurk alot. :lol: . Plus I use a tablet so that makes long posts a real pain in rear.

And the "big question" I had is this. What is a reasonable thing to do with the undissolved solids in the AR? The reaction stopped. Now i have a beaker with some gold in solution and solids on the bottom. I believe that was due to an incomplete digestion (as a few mentioned) in the nitric. I could be wrong but I base that on observations made during the process (omitted for brevity).

Let me tell you what I have done over the last 24 hours. I separated the gold chloride from the solids. I rinsed and dried them and remelted in a dish. As a side note, the only interesting thing I noticed was that something in the material melted sooner than the metal. I poured it off into water, it was black and shattered into small pieces. I don't know what it is. It may be irrelevant.
I proceeded to melt and poor the metal into flake and there it sits. I will test a bit in nitric and a bit in AR. It may need re-inquartation.

I also dropped the gold yesterday with SMB. I got a heavy precipitate and it began to dissolve as expected. I knew there was free acid because I tried to kick start the reaction when it stalled. I haven't checked it yet today. I am hoping that there is still some precipitate in the beaker because that should indicate the free acid has been consumed. If not I may be learning the evaporation technique sooner rather than later.

The color of the solution is interesting as well. I know mine is contaminated but I am unsure with what. I have limited testing equipment and experience. I have stannous and a standard gold solution.
4metals, I have never seen red AR. That will be a fun time for me when that moment arrives! Mine is (usually) yellow but I am doing lots of 2-8 grams so it is probably dilute. This lot is my largest to date at just over an ounce troy.

There was a question about the starting material. It was all 14K yellow gold.

Thanks again, I hope my thinking is along the correct path. If I am veering off course give me shove back in line.

 

[nickvc]

Based on your reply to wjphat the material was and the colour of the solution I think you are correct in saying that you didn't dissolve all the base metals and silver when you inquarted it, the green colour comes from the copper in the alloy and the dissolved gold, it should be fine to precipitate it just give it some good HCl rinses to clean it up, if your not happy with the colour of the powder simply redissolves it in the minimum amount of acids especially nitric, you should see a nice red solution.

 

[4metals]

This is a picture posted on a thread that is now in the library, his feedstock was doré gold so there was silver and copper in the alloy. (very little copper)





Fine gold, like from a second refining, in high enough concentrations is a beautiful red.

 

[anachronism]

Excuse the dirtiness of the cabinet it was in the middle of a batch refine. The jar in question is re-refining a good amount of shotted gold. Minimal impurities.

 

[IdahoMole]

I finished the batch so I wanted to let everyone know how I got through the problem I had.
After remelting the undissolved solids from the AR I put a single piece of shot into fresh AR and another piece into water/nitric. The nitric solution had no effect so I figured it was high in gold. The piece in AR began to dissolve and then the reaction stalled so I figured the silver content was too high. I removed both pieces from the solutions and put them in a melting dish along with the remaining pieces of shot and some sterling for re-inquartation.
The next trip through nitric acid worked perfectly. It then went into AR, precipitated the gold and combined it with the gold from the first batch of AR, washed it and melted it.

My conclusion is that the original digestion in nitric was not complete. I won't make that mistake again.

Thank you for the assistance from this great forum.