beginner experiment, please comment

[Amber]

Hello,

I have been doing a lot of reading. I like hands on experiment to fully understand the processes described in Hoke and this forum. So I have made my first experiments and would love some input and direction.

My objective this summer is to become acquainted with techniques and processes in order to select a method for my scrap that I can process one or two times a year. I am somewhat familiar with nitric acid method but am also very interested in the sulfuric acid cell. I am unsure if I will carry my process all the way to fine gold with aqua regia, or will simply remove the gold from the bulk of the base metal to then sell to a refiner.

My scrap is cheap gold plated jewelry. I am not seeking this scrap out, it is a by-product of one of my hobbies. I buy lots of vintage costume jewelry at auction and resell the individual pieces. I set aside broken and mismatched pieces.

Description of my first experiment
I took a very small group of chains and cut them in half to make two close to identical lots of about 9 grams each. I tested these with a magnet to ensure no steel was in my experiment. I melted group A with a map gas torch and poured into a stainless steel bowl to make cornflakes. Group B was not melted. I then placed them each in a beaker and added distilled water, then nitric acid (70%) to digest the base metals. Group A digested very nicely and left a black powder that I let settle. I poured off the spent nitric into a filter and rinsed with distilled water several times, letting it settle and filtering off the water. Then I rinsed the powder into an evaporating dish and dried it on a bed of sand in an electric wok. Group B never digested to black sand. I added more nitric, then I tried warming the beaker on my sand bed, but chunks of metal never fully digested. While group A left me .1 gram of black powder, Group B was .2 grams.

My conclusion was that it was worth the time to melt and pour cornflakes to get better digestion.

I then took more scrap (non magnetic) and tried to melt and pour more cornflakes. This attempt failed. It never really melted and is now a big lump. Maybe I tried to melt too much at once?

I would love comments and directions on this experiment and ideas for more comparative experiments like Hoke suggests. Right now I am interested in the nitric acid method. I do intend put together a sulfuric acid cell to try also. At first it seemed very mysterious, but I am becoming more comfortable with the process as you describe it here.

My questions for discussion:
1. Do you agree with my conclusion that because group B would take more acid to properly digest, melting it first is a better use of time and resources?
2. Any ideas why the second melt failed? Would you advise continuing with treatment with acid?
3. Would the sulfuric acid cell work on scrap that is magnetic?
4. Any thoughts on pros and cons of doing the first refining steps, then selling to a refiner? Or is there benefit of getting fine gold before selling?

Thank you for reading my post. I have tried to post photos below, but all I see is the code. Hope it works. I look forward to your comments.
Amber

 

[jimdoc]

You would be far better off using the sulfuric cell on plated items than melting them.

Jim

 

[Amber]

You would be far better off using the sulfuric cell on plated items than melting them.

Jim

Thanks Jim,

Yes I believe that is where I am heading. Do you see any problem with the stuff that is attracted to a magnet?

 

[jimdoc]

I don't see a problem with magnetic gold plated items.
You take the item out right after the gold comes off.

Jim

 

[seawolf]

Some of the vintage gold plated items were plated over silver; you might want to check before discarding.
Mark

 

[Geo]

the magnetic scrap is possibly Kovar which has a melting point of 2640 degrees F.i don't think it will melt with map gas outside of a furnace.Kovar is used where the connection will be heated and cooled repeatedly like the pins on a CPU and the CPU socket.Kovar is a nickel-cobalt ferrous alloy.

 

[goldsilverpro]

the magnetic scrap is possibly Kovar which has a melting point of 2640 degrees F.i don't think it will melt with map gas outside of a furnace.Kovar is used where the connection will be heated and cooled repeatedly like the pins on a CPU and the CPU socket.Kovar is a nickel-cobalt ferrous alloy.

To elaborate on this a little, Kovar is commonly used on IC packages that have glass-to-metal seals, like pins on CPUs or hybrid packages. The coefficient of expansion of the Kovar is very close to that of the glass and therefore, with changes in temperature, there will be no separation where the Kovar meets the glass. For the same reason, it is also used in other ceramic packages, where the green ceramic contains a glass frit (usually about 5%). When fired, the glass melts and acts like a glue to seal the ceramic to the Kovar lead frame and prevent leakage. Kovar is 54Fe, 29Ni, 17Co.

 

[Amber]

Thanks seawolf for the heads up on silver. I might have tossed it
Is it safe to assume the magnetic stuff has no silver so if I run it separate in the cell I can just scrap the remaining metal?

Update on my experiment -

1. I am not going to melt any more plated material and will build a cell to de-plate it

2. The half melted glob is digesting in nitric bath

3. I have set aside the two tiny envelopes of my test results and am researching the aqua Regia method to dissolve the gold. I will use these samples and whatever black powder I get from the currently digesting glob to practice the steps for dissolving then dropping the gold. I am wondering if I should put group B back into a fresh bit of nitric first to digest more base metal.

Thanks to everyone on this forum. The information is amazing. I am surprised how much more I understand than 6 months ago. I bought Hokes book in 1987. I couldn't put it together until I started reading and looking at videos and photos here.
Amber
Amber

 

[Amber]

Success! I have gone through all the steps and produced my first gold button, well it's more like a BB. (photo below) I was working with a really small sample so if I made a mistake it would be small. And I think I did make some mistakes or at least identified areas where I can improve. But nothing helps understand a process better than giving it a try.

1. I think I missed some of the gold. My BB weighs 0.1 gram and I was thinking it should be 0.25 to 0.5. I read gold plated material is 1 to 2 % gold. I have two places to look; my first rinse filter does have a grey to brown dust stuck in it. Maybe I poured off spent solution before it settled well. And I have not checked my auqua regia with stannous yet. I am unsure if I was successful in exhausting the nitric with urea before adding ferrous sulfate to precip gold or even if I used enough ferrous s. to drop it all. I will keep it until I test it.

2. Let me know if this is a mistep also - I saved my first filter jar (we'll call it the silver jar per Hoke). During the rinses of the dropped gold powder I poured off and filtered the alternate water and hydrocloric acid rinses into this same solution. Right away I thought about the possible nitric in the jar and did I just make a weak aqua regia. Is this a problem for silver recovery later? I should think there is no gold in this solution as I used a filter when pouring off the initial nitric baths that were used to dissolve base metal.

So now I am gathering and studying to build my de-plating cell.

 

[philddreamer]

Good job, Amber! You have some gold to show for your efforts.
If my memory serves me right, gold plated or gold filled is marked 1/10 10k GF; or 1/20 12k GP & so on.
So, 1/10th = 10% of the weight of the GF or GP item. 1/20th = 5% of the weight of the item; but keep in mind the wear of the gold surface reduces that percentage. Also, if an item has less that 1k gold content it can not be marked as gold.

Do a stannous test to know if your solution still contains any gold.

Continue the good work!

Phil

P.S. Thanks GSP for catching my mistake!

 

[Amber]

...1/10th = .1% of the weight of the GF or GP item. 1/20th = .05% of the weight of the item; ...

Phil

Thanks Phil,

Math, ug. So simple it's easy to mix it up. So the size of my BB makes much more sense given I did not use any marked items.

I will keep my solution for sure. After I run the cell, I can recover and combine it with the results of the stripping. I plan on running a larger sample to get something over the 1 gram mark. If my math is right, about 10 times what I just processed should get me close.

 

[philddreamer]

Do you have stannous solution for testing?

 

[Amber]

Do you have stannous solution for testing?

Not yet. I've been reading and I think I will get some tin solder and a small bottle to make it in. Hydrocloric acid and tin, right? I read some threads that I want to re-read about it. I think the solution has a short shelf life unless you keep adding tin. So I think I'll wait until I have a larger sample run then I can work on testing both AR solutions at the same time. Also, I could check the new batch before precipitating the gold, i.e. a known solution = another acquaintance test.

Do you ask because you have a favorite method?

 

[philddreamer]

I ask because I was taught, if you processes without stannous testing, its like flying blindfolded.
If you have gold, for example, & proceed to process, you can expect a pregnant solution, so, you follow to precipitate & expect to see sediment. After precipitating, you test to make sure that there's no gold left in solution. If that's the case, then you pour your spent solution in a container for later proper disposal.
For making your stannous testing solution, Radio Shack sells 96%tin/4%silver
solder that works fine for making the test solution. Make sure no lead!!!
Cut about a 1" piece of solder & dissolve in 15ml HCl. Every so often, add another piece of solder into the flask. Don't be afraid to keep some always handy. Remember, its a must to always stannous test.
(+ for gold is a purple; for Pt is red; for Pd is green.)

 

[Geo]

[Amber Wrote] I have set aside the two tiny envelopes of my test results and am researching the aqua Regia method to dissolve the gold.

i would like to suggest that you try hcl+cl to dissolve your gold as it is less expensive and the most important issue, it is less toxic. both are toxic and can hurt you but chlorine gas, imo is less damaging than nitrogen dioxide (they call it "the red death" for a reason).

 

[Amber]

i would like to suggest that you try hcl+cl to dissolve your gold as it is less expensive and the most important issue, it is less toxic. both are toxic and can hurt you but chlorine gas, imo is less damaging than nitrogen dioxide (they call it "the red death" for a reason).

OK. Thanks for the suggestion. I'll look into it. I see information in the handbook to read through. So is it an alternative to AR and used in the same part of the process? - after you have removed base metals by either nitric bath or in a sulfuric acid stripping cell and washed the powder?

For safety I am using a 3M acid/gas respirator. I have some scuba air tanks and I was considering getting a face mask that fireman use. That would be even better than a fume hood. But then I found I like walking completely away from the area with the mask on before removing it. I wouldn't drag the tank around. I think I would always use the mask, even when working in a fume hood.

 

[philddreamer]

After digesting base metals either thru AP, nitric or deplating with sulphuric cell, the powder can be dissolved with HCl/Cl. This method is not as aggresive as AR, but for fine powders & foils is good & less expensive, like Geo noted. Also, its easier to get rid of excess clorox by heating & evaporating. In AR, getting rid of nitric is more challenging. Adding a small bead of pure gold can help get rid of the nitric faster, provided you didn't add too much nitric. You'll learn more details as you study & get into the AR process. Try to "master" one process before "tackling" the next.
Chlorine gas is also very toxic, & your clothes will have a strong smell of clorox. Protect also your eyes! 8)

 

[Geo]

almost every chemical we will deal with is corrosive and the fumes tend to "stick" to objects.without airflow to move the fumes away from you they will adhere to clothing,hair,skin and any metal in the area. the respirator is a good idea but still use a fan to move fumes downwind (unless its into the neighbors yard).wash ppe's every day in warm water with mild detergent. wash hands frequently and always before eating. safety is no accident.

 

[Amber]

Try to "master" one process before "tackling" the next.8)

Good point. While reading it is easy to get some of the methods confused. Also, after being unsure if I used enough urea, It is clear why the gold button would do the job.

Protect also your eyes! 8)

I have a question about that. I have pesticide application training. Most of the concerns with pesticides and agriculture chemicals are skin contact, ingestion, or splashes to the eyes. Here I am wondering about fumes. Do you recommend eye protection that seals the air out to prevent fume contact? I am wearing safety glasses, but thought an upgrade might be needed. If so I might upgrade the respirator to a full face one. I don't think I'd get a good seal with goggles and the half face piece I use.

You also mentioned hand washing before eating. I'd like to add, we also wash before using the WC or smoking (if you smoke).

 

[samuel-a]

I have a question about that. I have pesticide application training. Most of the concerns with pesticides and agriculture chemicals are skin contact, ingestion, or splashes to the eyes. Here I am wondering about fumes. Do you recommend eye protection that seals the air out to prevent fume contact? I am wearing safety glasses, but thought an upgrade might be needed. If so I might upgrade the respirator to a full face one. I don't think I'd get a good seal with goggles and the half face piece I use.

Actually, there are very few applications that needs full face mask to protect the eyes from fumes/vapors, e.g. - melting Zinc or Mercury, dealing with Oxmium^--

In all cases, working in a fumehood of down the draft will protect you from most dangers involved.

Very nice work on the gold, btw.