AR and Urea + Copperas

[overdriv]

I am using an AR process to refine. Hoke says to evaporate nitric acid and then to drop the gold with copperas. The process seems long... can I use Urea to kill the residual nitric acid and then use copperas to drop the gold? Or do I have to use SMB? Can I use sodium nitrite with Urea? I used a little sulphuric acid to drop the silver and lead.

There seems to be a lot of ways to process gold and a LOT MORE WAYS to screw it up.

 

[nickvc]

Yes you can use urea to kill the excess nitric and yes again to dropping the Au with copperas. Many members frown on the use of urea because your adding more chemicals to the mix but it can have it's uses. GSP advises adding nitric to the Hcl slowly so you don't add to much and Harolds approach was to add a button of fine Au to use up the nitric both seem excellent methods and will eliminate the need for urea.
The main thing in my opinion is to find a method that suits your needs and produces an acceptable product.

 

[Harold_V]

As Nick noted, my procedure was to use an added button of pure gold, but there was good reason to do so. A great deal of the material I processed yielded solids that were often indistinguishable from gold (I processed wastes from the jeweler's bench). An example would be bench filings, which generally contain bits of abrasive much the same in appearance of gold filings.

By using a slight excess of nitric, I was assured that I had recovered all of the values. There was proof positive when, in evaporation, the solution consumed a small amount of the added gold.

My method was not one of laziness, but one of treating the customer with total honesty. It is an excellent method to refine, but may not be necessary in all circumstances. In a case where one has little or no residue, GSP's method of adding the nitric sparingly is very good. The only real negative to that process is that when one has a large volume of solution and a tiny amount of remaining gold, it can be difficult to know when all of the nitric has been consumed, due to the slowed reaction.

I refined for years. Never once did I use urea. I saw no need.

Harold

 

[overdriv]

A great deal of the material I processed yielded solids that were often indistinguishable from gold (I processed wastes from the jeweler's bench). Harold

Thanks Harold. Let me get this straight.... do you start out as Hoke says:
Step1. to by adding the nitric acid first to clean out the base metals? Then pour off the solution after letting it sit for a half hour to an hour.
Step 2. add HLC instead of N, heat, then add nitric until the NO2 (brown fumes) stop. (?)
Step 3. add button.
Step 4. and precipitate of choice

My method was not one of laziness, but one of treating the customer with total honesty. Harold

I am impressed with you. I hope I can learn more from you. I once was in charge of managing the casting gold for jewelry manufacturer and the stone dept. as well. It was a fun job.

 

[Lino1406]

Urea "kills" NO2. With concentrated HNO3 it gives an
adduct, which you have to filter. The way to "kill"
HNO3 is: vaporizing, adding HCl, vaporizing, adding HCl...vaporizing
... to syrup consistency
Copperas and SMB also "kill" HNO3 but if you do that directly, you
lose some gold, you get a mess

 

[Harold_V]

Let me get this straight.... do you start out as Hoke says:
Step1. to by adding the nitric acid first to clean out the base metals? Then pour off the solution after letting it sit for a half hour to an hour.

Because I worked against the clock, I did exactly that, aside from letting it sit for a half hour. I always drove my solutions to the point of boiling. Otherwise, you risked having them cake to the bottom of the beaker. Once that happens, you risk breakage, so I added what I expected to be an adequate amount of nitric and water, and drove the contents to a hard boil. By the time boil was achieved, the nitric had pretty well done it's work. I'd take up the solution with (tap) water, stir, allow the contents to settle, pour off, then repeat with a small amount of nitric and water, again, driving to boiling. Note that I used tap water for processing, except for when working with my silver cell. I didn't care if I created traces of silver chloride. They were ultimately recovered, and I didn't mind the small amount I had to deal with. I do not make across the board recommendations for others to follow suit, depending on their particular circumstances.

Step 2. add HLC instead of N, heat, then add nitric until the NO2 (brown fumes) stop. (?)

This may sound like my ego talking, but bear with me.

Because I ran jewelry wastes on a daily basis, I was very comfortable with the reactions and knew what to expect. Right down to knowing how much acid to apply. Unlike Chris, I did not add my nitric separately---for good reason. Remember, I talked about running against the clock. I was so busy refining that I was putting in twelve hour days just to keep up. That includes working seven days per week.

I'd determine how much acid I figured I'd need, mix the AR at the ratio of 1:4, and pour it on. If I felt I had used too much, I'd withhold a small amount, allow the solution to work until action ceased, pour off the solution than add the small amount remaining. If there was undissolved gold, it was obvious. If not, I knew I had dissolved all of the values, and knew it was safe to move to evaporation.

Step 3. add button.

The small excess that might be present was consumed by the added button of gold. The routine I followed was fast and easy---the button was weighed before and after, so I knew how much gold was added to any given lot.

Step 4. and precipitate of choice

Right.
I started out using ferrous sulfate, but I wanted to keep my solutions as concentrated as possible---I had limited space, so doing so allowed the use of smaller beakers. To that end, not long after I started refining, I started using SO2 gas, from a cylinder. I did so until I sold the refining business and retired. It stands heads and shoulders above all other methods, but is not a necessity.

I hope I can learn more from you.

If reading my ravings doesn't do anything else for you, I have hopes that you take away the importance of being honest with your customers. I treated mine with the utmost of honesty, yet still lost a half dozen through the years because they had unreasonable expectations. In refining, you destroy the evidence, so if the customer thinks you've screwed him/her, there's not much you can do to redeem yourself. Acquiring a reputation for being dishonest certainly doesn't help.

I once was in charge of managing the casting gold for jewelry manufacturer and the stone dept. as well. It was a fun job.

Sounds like it would have been. You likely already have an understanding about one's credibility, having held such a responsible position.

Harold