Why Colour of AR Different For Filing scraps & Buff Scraps?

[rohaneha]

I refine scrap filing gold seperately and buffing scrap seperately. at both the cycles i get 2 different colours of AR. For filing scrap refining i get clear emerald green colour AR, while i get murky brownish yellow colour for buffing scrap.
why so much difference? Scientifically, one must get emerald green colour to be safe with the process. Is there any calculations or measurements required to get the colour?

 

[Harold_V]

I refine scrap filing gold seperately and buffing scrap seperately. at both the cycles i get 2 different colours of AR. For filing scrap refining i get clear emerald green colour AR, while i get murky brownish yellow colour for buffing scrap.
why so much difference? Scientifically, one must get emerald green colour to be safe with the process. Is there any calculations or measurements required to get the colour?

A great deal depends on your method of operation.
If you process filings by a wash in hot dilute nitric, a rinse in water, followed by dissolution in AR, you should expect a green solution, for there's no way you can remove all of the copper and other base metals from alloyed gold that is higher than about ten karat, even when it's finely divided, such as filings. (That would not be true of inquarted material. I'm talking about karat alloy.)

Polishing wastes are a whole different matter. The particles are so small that they can be freed of base metals easily by a prolonged boil in HCl alone. That was my customary method of processing polishing wastes, and they routinely yielded yellow solutions. I recommend the HCl wash instead of a nitric wash in this instance because the HCl wash yields a solution that is easy to filter, unlike one with nitric.

You are mistaken in saying that a green solution is desirable. It is not. That is a sign of an impure solution, one that has unwanted contamination. When you have done your preliminary work well, gold that is then dissolved will yield a nice yellow solution, a sign of absence of base metals and a preponderance of gold. That should be your objective.

To be clear, I processed filings by simply giving them a digest in heated dilute nitric, then they were dissolved in AR. My solution was always green in color, and the gold that resulted was always of questionable quality. It was this gold that got melted to a button and used in my evaporation process, where it was dissolved a second time, eliminating some of the traces of impurities. The gold quality isn't horrible, just not as good as that which comes from a second refining.

Harold

 

[Texas]

Hi Harold, I'm already getting the aqua regia of a dark yellow, and precipite it with copperas.
But in my last refined, aqua regia is green, then, I add copperas, wash, dry, melt and return to inquartation ?
Or is there any way to remove the remains of other metals of precipitate gold?
I take a oz of liquid to trying with oxalic, (Hokes repurifyng) but still does not precipitate
thanks
Texas

 

[Harold_V]

Hi Harold, I'm already getting the aqua regia of a dark yellow, and precipite it with copperas.
But in my last refined, aqua regia is green, then, I add copperas, wash, dry, melt and return to inquartation ?

Do--do not melt, and especially do not inquart. With your gold finely divided as it is, wash it very well in HCl, then simply re-dissolve in AR, and re-precipitate. The second refining will yield gold of excellent quality, but it, too, must be well washed with HCl (and ammonium hydroxide) before melting.

I take a oz of liquid to trying with oxalic, (Hokes repurifyng) but still does not precipitate
thanks
Texas

In all my years of refining, I tried oxalic only once, and did not apply it properly. I was so satisfied with the use of SO2 that I used it exclusively once I purchased the first bottle. As a result, I'm not much help where oxalic is concerned.

One thing I can tell you---if you refine your gold a second time, and follow a good washing procedure, you should achieve excellent results---all without issues. If you make it a habit to do this, it becomes routine and takes very little time as you get more comfortable with the process.

Harold

 

[Texas]

thanks for answer me Harold, then, the precipitate I wash it again like Hokes says, with water, with HCl, water again, and finally with ammonia, but ammonia, do I mix it with hcl? (could make a reaction?, I'm not chemical).
sorry if my questions are very obvious Harold, but Hoke says nothing of ammonia, except to mix with oxalic, or have not I noticed?

Thanks again.
Texas.

 

[Harold_V]

sorry if my questions are very obvious Harold, but Hoke says nothing of ammonia, except to mix with oxalic, or have not I noticed?

Thanks again.
Texas.

No, you are correct. Hoke does not discuss washing the gold powder with ammonia. It was a procedure I incorporated to insure that I eliminated traces of silver (chloride), but it serves a useful purpose in exposing gold that is not pure. When you use ammonia, if there's traces of copper present, they are displayed as a brilliant blue color.. and removed by the wash process. It's a good process to add to the wash cycle if your have a goal of producing high quality gold.

The use of ammonia (ammonium hydroxide) comes after the rinse with water. I applied it in this sequence: My final procedure (after precipitation) was to wash with HCl, rinse, wash with ammonium hydroxide, rinse, wash with HCl, rinse, then dry the gold. Without failure, the final HCl wash was clean, yielding no color at all. It was used to insure that the wash cycles had done their jobs.

Note that I used the ammonia wash cycle only on gold that I refined a second time.

Harold

 

[Texas]

When you use ammonia, if there's traces of copper present, they are displayed as a brilliant blue color.. and removed by the wash process. It's a good process to add to the wash cycle if your have a goal of producing high quality gold.


Excellent! the use of ammonia helps to clean gold powder, and is truth, sometimes I had traces of silver chloride. Them, when I use ammonia if I have a traces of cooper, ( blue) can I clean with wash? thats great!! well, every day, learn something new....in the right place.
thanks for the explanation and how to use, Harold.
Greetings
Texas