Odd solution separation?

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Nauticamark

Member
Joined
Jan 25, 2015
Messages
20
Hey all, quick question. I was processing some sweeps, with AR last night. I filtered, and filtered numerous times to make sure the solution was 100% clean and clear. Added the SMB, and immediately got the very dark brown cloud we all love to see! I allowed it to rest overnight after vigorously stirring it. This morning, I realized all the material did not drop out, after testing the solution with stannous chloride. But I noticed something odd. About eight millimeters below the surface of the AR, was a visible line separation in the AR. Like a chemical separation of some sort. Not sure why, or what this is. Did I just not add enough SMB, or is something else going on here? Any feedback from the forum would be very appreciated!
 

Attachments

  • FullSizeRender.jpg
    FullSizeRender.jpg
    347.5 KB · Views: 158
Ok, this is going from bad to worse. So, I decided to take a sample out of the 4000ml beaker, and put it into a coffee pot, about half full, attempting to evaporate the solution. My intention was to evaporate to a syrup, add three times volume of distilled water, filter and precipitate. Problem is now I have this 'snow' like material floating everywhere after evaporating approximately 2/3 of the AR solution that didn't drop the gold. And the AR solution now has a white scum looking film on top of the AR liquid. I keep testing with stannous, and the tests keep showing positive for Au. Is the cloudy white flaky liquid SMB from my first drop attempt? I have no idea whats going on with this. I need to 'reboot' this process. Any suggestions on getting the SMB out, or why the AR just quit dropping gold, etc?
 

Attachments

  • IMG_9455.JPG
    IMG_9455.JPG
    529 KB · Views: 141
How much Nitric acid was added and how was it neutralized before adding the SMB? How many pounds of sweeps powder were put into acid? And finally was the material incinerated and sifted before the acid step?
 
4Metals, thank you for the reply. To answer your questions:

"How much Nitric acid was added and how was it neutralized before adding the SMB?"

I used Harold_V's formula for my AR recipe. I actually went a little easier on the nitric additions, doing it slowly at the end waiting for the reaction to stop after a reasonable amount of time on the electric heater eye.

I followed Harold_V's outline of this---
1} Incinerate in a shallow pan, heating from below. Ignite the material to eliminate the majority of smoke and stink. It will readily burn once hot enough. Incinerate until all carbonaceous material has been eliminated. There should be no glowing embers. Allow them to burn completely. Insure the pan is hot enough by heating with a torch from the bottom. Don't burn through the pan. An old stainless fry pan works very well for this operation. Find them at Goodwill or other second hand stores. DO NOT USE ALUMINUM.

2} Screen after cooling, to remove any sizeable pieces that would be difficult to dissolve without inquartation.

3} Run a magnet through the material to remove free iron particles. They should be placed in the stock pot, not discarded. They generally will transfer miniscule traces of values.

4} Place screened wastes in a beaker, or a container that will tolerate being heated.

5} With an approximate mixture of 50/50 tap water and HCl, cover the contents with solution, then place on hot plate. Heat slowly until contents are brought to a boil. Stir regularly to prevent the container from overheating and breaking from thermal shock.

6} After a reasonable boil period, (contents will change color), remove from heat and fill container with tap water. Stir well.

7} After solids have settled well, decant solution. Test for values, then discard if barren. It is rare to find values in the solution unless you have allowed nitrates to be included.

8} Repeat the above operation until the rinse water is clear, or nearly so.

9} Apply AR @ 5 ounces per troy ounce of values expected to be recovered. Use only what is necessary, to minimize the amount of nitric that must be evaporated later. Heat to boiling, and stir regularly. Do not allow the material to dry on the bottom of your container, which will lead to thermal shock and cracking, as above. Make your AR @ 4 HCl/1 nitric, not less. If in doubt, move up to 5 HCl/1 nitric. Too much HCl does no harm, unlike too much nitric.

10} When values are in solution (note color change of solids, and the yellow color of the solution), and you see no fumes coming from the container, remove from heat and add a few ounces of water. Stir, then allow contents to settle.

11} Decant, then add more water to solids and stir well. Repeat this operation until you have removed the bulk of values. Note the color of the solution, which will slowly shift towards clear as it is washed.

After the final decantation, place the solids in a filter (Sharkskin works very well for this operation) and extract all solution possible.

Combine all solutions from the AR process and evaporate to eliminate water and nitric. Add a few drops of sulfuric to the evaporation process early on, which will precipitate any traces of lead that may be included in the process. Be very careful about adding sulfuric to hot solutions. It is best added while they are cold. Stir as it is added to prevent local generation of steam.

After evaporation, take up with water, filter, precipitate, and wash appropriately.

"How many pounds of sweeps powder were put into acid?"

One pound of polishing dust.

"And finally was the material incinerated and sifted before the acid step?"

Yes. The only thing I did not do, is completely evaporate the AR down to a syrup. That was the only step I missed.
 
The only thing I did not do, is completely evaporate the AR down to a syrup. That was the only step I missed.

Reminds me of a Miracle Max quote "There's a big difference between mostly dead and all dead. Mostly dead is slightly alive."

Your solution has active nitric acid, it wasn't completely dead and it is re-dissolving the gold you drop. If you had a watch glass or some cover on the beaker I suspect you would have seen the tell tale signs of red fumes accumulating as the gold re-dissolved.

A few things, first you said 1 pound, I assume that was before you burned it. Generally sweeps burn down to 50% of their pre burn weight so you started with half a pound. With sweeps I prefer to cover the acid with enough hydrochloric acid to have 2" over the top of the powder. A half pound of sweeps in a 4 liter beaker probably was 1" to 2" deep in the beaker. The nitric needed to be added slowly with agitation and periods of no additions until no more reaction takes place with more nitric added.

Then the filtered solution needs to have the free nitric acid removed. Years ago the only way to do this was the 3x evaporation process. That was a time consuming process and I can't say I honestly ever met a refiner who liked doing it. For a long time refiners added urea to do the job but for many reasons, which you can search for on the forum, urea was never a great choice. The preferred method today is to use sulfamic acid. (That little secret, sulfamic acid, was released from it's hiding place right here on the GRF.)

You have quite a soup of chemistry there now, it may be easier to cement out the values on copper until the stannous chloride indicates all of the values are out and start with fresh aqua regia. For every ounce of gold you are expecting add 133 ml of aqua regia. Classically sweeps rarely run over 1 ounce per pound so it will not take a lot of acid.
 
4Metals,
Huge appreciation for that most valuable information and your time to help. Sincerely appreciated! The nitric....oh the problems that causes. And you verified my worst fear, that I suspected. The weight of my polishing dust is post incineration. I use a heavy stainless pot to do the initial burn off, and the skillet to roast. Please see my picture attached. FYI, I own a very small town family jewelry store(and I am the jeweler, bookkeeper, janitor, etc.), thus the polishing dust from my collector unit.

If you do not mind me asking, I would like to inquire about the sulfamic acid. How do you determine the amount to use? Do you dissolve in water, then add? Or the straight granules? Also, I found some at Home Depot, is that a good source? And do you wait for a reaction, then stop when it ceases?

Again, thank you so much for sharing all your intellectual studies, methods, and help. You are very kind, indeed.
 
I can't explain the "snow deposit" you describe but it must be something that was dissolved but close to saturation point. The initial boil in HCl and decanting should have removed most of easily dissolved substances. So it must be something not dissolving in pure HCl but dissolving in aqua regia.
When the pH is changing (evaporation of acid) or the concentration gets too high it precipitate out of the solution. First thing I usually suspect is lead, but you took care of that by adding sulfuric acid. If another drop of sulfuric acid in your solution gives a white cloud then you still have lead present and that is something you want to eliminate as a goldsmith.

The clear layer below the surface is probably because oxygen is dissolving from air and creates a zone of different chemistry. If you still have free nitric then the zone might represent where NOx recombine with oxygen to form nitric acid, dissolving the gold. The particles at the layer might be small grains of gold suspended by gas bubbles as they are slowly dissolving.
The suspended particles shows that there is a quite steep density gradient in your solution. The liquid below the line is denser, probably from dissolved gold chloride.

Thanks for posting, this is an interesting thread. :)
Let us know which solution you picked and how it turned out.

Göran
 
Back
Top