# Gold Filled Process - Clarification(s)



## kjt124 (Mar 26, 2013)

Hi guys,

I have an ongoing potential source for gold filled scrap, but it is certainly not free. I want to run a couple of controlled batches to try and estimate profitability and want to check in with you guys on what I propose to do to make sure I am not missing anything. The clarifications I am asking are mainly on processing as I have read plenty stating that it is difficult to know gold content without direct trail run type experience because of incorrect stamps, missing stamps, wear, etc.

First off, incineration is clearly the right way to start.

Next I am a bit foggy... I have seen reference to the 50:50 nitric/water and I have also seen reference to the HCl leach. Does one necessarily win out for the initial go or is that dependent on the scrap as well. Of course, if I see Lead I will remove it mechanically as best I can. I imagine anything that was known to have Lead would be an HCl candidate. I don't suppose there is an easy or tell-tale way of recognizing tin in the base metals is there?

Of course, before switching acids - incinerate. Quick question... as the integrity of what metal is left declines, how does the incineration process change? Especially when you get down to powder? Should this be done in a crucible or would a cast iron skillet or stainless steel pan be a sufficient vessel?

Next would be a rough calculation to get an idea of how much Nitric I could theoretically need for the initial base metal digestion. What is the best way to go about this? Take the overall calculated mass of base metals and figure it stoichiometrically with bivalent Copper? Is there another metal that is more prevalent or that would give a more realistic starting place?

Then the nitric digest where I get rid of the base metals slowly and incrementally with dilute nitric and a bit of heat being careful not to waste any expensive nitric. Is it a good idea at this point to introduce some H2O2 to extend my nitric a bit, or is this a situational thing that I don't understand correctly?

Once I feel the base metals are gone, should I incinerate and do another HCl digest for good measure, or is this not necessary? Or does it depend on the material once again?

After all of this I incinerate, dissolve with solvent of choice, precipitate, and re-refine if desired, right?

As far as the solvent, it would seem that AR is fastest with the lowest volumes of solution, but carries with it a relatively steep learning curve. HCl/Cl seems to be pretty easy, but has rather large solution volumes even when done correctly (possibly can be cut down some with concentrated bleach or solid bleach tablets). AP doesn't seem like a viable option because of the carry over of certain base metals like copper and probably large liquid volumes again - not to mention it is very slow if I am not mistaken.

Any guidance or clarifications offered would be greatly appreciated. I understand that no matter what method I use, repeatability will still be highly dependent on lab technique and predictions about yield will be highly dependent on small scale trials with detailed notes and repetition of types of scrap.

As always, thank you for allowing me to be a part of this community.

Kevin


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## nickvc (Mar 27, 2013)

Kevin gold filled material can be excellent yield wise compared to e scrap but it does have its problems.
The real first problem is what exactly is the non gold part, some is just copper but it can be brass or even worse bronze. Incineration is always a good start for this material especially if it's worn and then a simple wash to remove any junk and then I personally would add distilled water and increments of nitric while heat is applied, I'd use distilled water because the gold is karated and many karat alloys contain silver and for me it's easier to recover the silver by cementation than from chloride, when all the base metals have dissolved, no more reaction on small additions of nitric, decant and rinse and cement the silver and incinerate the remaining material. Once cooled put it back into your beaker and put it on a hot plate and add hydrochloric to cover it and heat to a near boil decant and repeat the process again and then personally I would use AR to dissolve the foils, the chlorox method is good for very thin foils or powders but struggles with larger pieces, add a little sulphuric and allow to go cold and settle add cold water or ice and filter twice, you may well have some silver chloride from the foils depending on how thick they were, and then precipitate with your method of choice. If you want really clean gold I would suggest digesting the gold straight off after rinsing and hydrochloric washes, this time using the chlorox method. 
I hope this helps and good luck, evaluating gold filled unless exactly the same items and new isn't easy as I know your aware of, it may pay for you to toll refine this and remove that area of doubt if your customer will let you.


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## kjt124 (Mar 27, 2013)

Thank you nickvc. It sounds like I am on the right track then and you filled in a few blanks for me. I have definitely entertained the idea of exploring some toll refining, but initially at least it seems like it would likely get cumbersome with shipping and such. However, depending on the volume that is available (which I will find out as I explore the relationship a bit), my facilities at hand may cap out my throughput. In that case I think the margins on toll refining may work out more advantageously.

So bronze is the culprit for the tin... probably not going to be able to eyeball the difference between brass and bronze without a lot more time under my belt. On old pieces I will likely have trouble distinguishing copper from either depending on oxidation and such.

As far as theoretical nitric consumption, it looks as though I should probably be safe figuring 2 moles of nitric per mole of base metal (estimating it all to be zinc for the atomic mass) and just cross my fingers I don't get too bound up on tin... I see myself frantically typing various tin phrases in the search box in the near future, haha.

For the AR part, is there typically a need for heat on this stage or more just patience? With careful nitric additions, am I correct in assuming the chance of boil over is low?

Last question I have for the moment before I start putting everything in order to start... The between step incinerations... Clearly at the beginning I could hold the stuff with a pair of pliers and hit it with a torch (flinging out lead if need be), but as this stuff soaks in acid it will continue to degrade in structural integrity. Is there any particular concern for what the vessel I use to incinerate in is made out of? Does it need to be stainless? I have a cast iron skillet that seems like it would be ideal for it - and no, this skillet will already never see food again.

Thanks again,
Kevin


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## nickvc (Mar 27, 2013)

Kevin most of the material will be copper or brass based but I mentioned the bronze as I had a nasty experience many years ago with scrap off cuts from blanking which was bronze based, nightmare !
There are calculators here on the forum for acid consumption the best usually by GSP, I'm old school and guess but I have been doing it a few years, 30+ , so look them up and always add acids slowly in increments and add more as all reaction ceases this should stop boil overs. Heating the AR is advisable as it makes the acids work harder, again there are calculators, but I'd advise adding the necessary hydrochloric plus say 10% first and then again slowly add your nitric, if all reaction stops after an addition of nitric add a little more hydrochloric to test if there is any material left to dissolve, this method should also stop you over using the nitric which is bad for precipitation and expensive.
For incineration the forum seems to vote for Corning ware, pyro ceram i believe, again look it up it's all been covered, Harold I believe used a cast iron skillet for incinerations if I remember correctly but again check that I'm right.
If you can access an xrf gun it should help identify the base metals your encountering, there is some gold filled that is over silver as well just to add to your fun.


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## kjt124 (Mar 27, 2013)

Thank you nickvc. This will be a fun adventure. I am imagining every new lot as a sort of pandora's box (without all the brimstone and dead souls and such...). Either way, it looks like a great opportunity to practice. I'll write back during the process with updates as I can (and as I remember to... I kind of tunnel vision on new projects).

Thank you for the advise - it has been well received and will be used carefully.

Kevin


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## kjt124 (Mar 27, 2013)

So I have my first 2 ozt lot and I've gone through the mechanical separation (a minute at the tools saves an hour at the chemicals  ).

Most of this stuff is clear to tell the difference on whether gold filled or base metals, there are 3 pieces that I am not 100% on. Would someone please weigh in on these three for me? I can't imagine the wire bit has any values on it, but close up all three pieces look to be suspect.



View attachment 1


I had to laugh when I read posts about cardboard and such inside these things, but sure enough, rolled up cellophane and folded up cardboard came falling out when I ripped out the end caps... wild stuff.

Thanks guys!

Kevin


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## kjt124 (Mar 27, 2013)

I am sorry - I do not know why it keeps posting doubles of some of my pictures


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## Geo (Mar 28, 2013)

one drop of nitric acid will solve the riddle quickly.


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## kjt124 (Mar 28, 2013)

Thank you Geo for the breath of obvious wisdom. Trust your own eyes.

I'll delay questions I come up with during this process by 12 hours at least in hopes of mitigating some of the easy ones like this


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## kjt124 (Mar 29, 2013)

So, I believe my nitric digestion is complete and here is what I have learned so far...

First of all when someone says wash your stuff after incineration, don't accidentally miss that step. Not unrecoverable obviously, but added difficulty. Lost about 5 grams in the incineration to junk hidden where you can't see it - now I have ash from where I couldn't see it  

Next, I definitely had a bit of tin as I recognize the hydrated tin oxide from a couple of acquaintance experiments I did a while ago. Not a lot, but when you don't let the solution settle before filtering, it is a very slow battle (I have no vacuum filtration yet).

Other than that the process is going well so far. I used a little too much nitric, but I certainly didn't go overboard. Also, the trick with adding a bit of peroxide to the mix (I did small splashes of 3%) really knocks down the red fog. It really amps up the activity of the digestion though - use a big enough vessel!

Filtering now before a good rinse, incineration, and first HCl boil. We'll see what happens to this tin monster :roll:


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## qst42know (Mar 31, 2013)

Most gold filled is assembled with soft solder as is the end of your wire, lots of tin. After incineration wash in HCL. It won't help if you encounter items of bronze but the solder is exposed and easy to deal with at this point. 

P.S. Harold incinerated in stainless skillets.


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## Palladium (Mar 31, 2013)

How big of batches are you trying to run?


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## kjt124 (Apr 1, 2013)

I am back for some tutelage (or at least some finger pointing and obvious correction )...

Here is what I have done since the hydrated tin oxide showed up.

Filtered, rinsed, incinerated to red hot, HCl boil for an hour. This resulted in a very grey liquid that was negative on the stannous test.

Then I filtered, rinsed, incinerated to red hot, second HCl boil for 30 min. Still grey liquid, but much more pale - obvious against white paper, but not terribly obvious just looking at it.

Then, I filtered, rinsed and covered the material with HCl and added Nitric with a bit of 27% peroxide in it nearly dropwise until the material was dissolved using heat the entire time. This went well I think as I kept the reaction calm, the peroxide kept the fumes down, and i waited (probably excessively) long between additions. I am pretty confident that I did not have much excess nitric, but I did the denoxxing the next day by boiling and adding bits of HCl. No brown fumes were noticable during the denoxxing, but I this was my first AR so I really have nothing to compare.

Next I added a small amount of conc. sulfuric (probably 3-5 mL) and then I chilled the liquid (which stannous was a strong positive on) with ice, but I didn't wait very long at all - probably only about 10-15 min (I feel this is where I may have gone wrong). I got some precipitate out of the AR solution upon filtration which I presumed to be lead sulfate. It was a dull grey and rather granular. It did not look very crystalline at all. So I proceeded with confidence.

Then I hit the solution with SMB assuming a 1:1 by weight with assumed gold and a 50% excess (6g SMB versus a theoretical 4g gold). I dissolved the SMB in water and added to the pregnant solution without heat. The addition looked correct as a short while of stirring later I got the characteristic gold drop color change and the "brown mud". I let it sit for a while (maybe an hour) and then gave it a bit of heat (not boiling) to start off-gassing the SO2. I left the solution on the back porch with a watch glass over it overnight (temp in the 30s, but not freezing) to allow it to off gas a bit.

Today, I have my gold in the bottom, but I also have a lot of needle-like perfect white crystals in my solution that appear to be insoluble in room temp water. A couple had grown on the sides of the beaker, but I would attribute that to not quite clean enough or pristine enough of a beaker as some gold 'shine' was on the sides as well. I believe if I do the HCl/Cl or another AR in the same vessel it will take that coating right off. Here is a picture after decanting and adding a bit of distilled water.
The gold is not nearly as light a color as I was expecting, but there was definitely still copper left in my starting material and I plan on redissolving and dropping another time. My concern is the white crystals. Have I accidentally not given enough time for the lead sulfate to precipitate out? If so, what is my best option at this point?

Any advice / criticism is welcome and appreciated.

Thanks guys,
Kevin


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## kjt124 (Apr 1, 2013)

Palladium said:


> How big of batches are you trying to run?



Not big at all yet - this is just a 2ozt batch to get my feet under me a bit, but there is quite a bit available. The guys I know are certainly not uneducated in gold and silver (they do not refine) so I imagine the margin could be pretty tight. Right now I know of various types in stock , fairly well sorted into watch bands, eye glasses, and other. Prices on the types vary.




qst42know said:


> Most gold filled is assembled with soft solder as is the end of your wire, lots of tin. After incineration wash in HCL. It won't help if you encounter items of bronze but the solder is exposed and easy to deal with at this point.
> 
> P.S. Harold incinerated in stainless skillets.



My stainless steel bowl (nice heavy gauge) seemed to work well. Also, one last peek at my stuff before dropping into the nitric revealed a big chunk of soft solder hiding. Really glad I checked again  

Thanks again guys,
Kevin


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## nickvc (Apr 1, 2013)

Kevin try boiling the water and rinse and boil several times, this should get rid of the white crystals. If your successful in getting rid of them then proceed to hot hydrochloric rinses, the gold from gold filled rarely comes out clean on the first refine so a secondary refining will almost definitely be needed and the cleaner the precipitate you start with the better the final result.


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## kjt124 (Apr 1, 2013)

Boiling water rinses seem to be perking this thing up. An incredible (to me) amount of fine gold powder is being freed up with every rinse. I'll post a pic once it seems hot water rinses are no longer benefiting things.

Thanks again, nickvc. I really appreciate the attention you are paying me  

Kevin


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## nickvc (Apr 2, 2013)

Your welcome Kevin we all need help at times.
Remember what I said about how clean your gold will be, it's rare to get really good gold from one refine with gold filled but good rinsing as advised by Harold will make the second precipitation really clean. As a reminder don't forget to use your stannous on all your solutions and allow all solutions that have been precipitated plenty of time to settle, I put all mine through the stockpot just to be sure I recover all the gold.


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## g_axelsson (Apr 2, 2013)

SMB could precipitate copper chloride from dirty solutions as white crystals, I've encountered it a couple of times. Try washing your dropped gold in HCl, that should dissolve any copper chloride.

Göran


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## kjt124 (Apr 4, 2013)

Regrets, successes, and a lot learned...

First my regrets are that my wife loaned the camera out to a friend for something and I currently have no real ability to take any pictures. I tried my cell phone and even I don't recognize my stuff from those pics... Anyway, I will get a pic up here of the finished button, at least when I get the camera back. I likely won't have the pic of the powder though. I likely gve it a nice wash in nitric by then.

Successes are in the fact that the white crystals cleaned up a lot with boiling water, but really cleaned up with HCl on boil. Took a lot to dissolve them though - very low solubility in either. I did get gold that appears to be pretty nice. Not quite as beautiful as some of you other guys, but I am pretty proud of it. I would say from what I have been able to read that g_axelsson hit the nail on the head with the copper chloride, but either way, I know how to handle that little hurdle now.

Original material was 62.4 grams of gold filled material - 48.5 grams after hardware and mechanical base metal removal. Final button is 1.6 grams. Yield (I think) is low, but I will go over some of what I believe happened next.

Things learned. I am a very hands on learner and this small project was perfect to take all the theory I've been taking notes on and solidify it into something I understand a bit better. SO many more steps make physical sense now.

First off, when nickvc (or anyone else) says boiling distilled water rinses, don't think you can get away with heating some water in a kettle and taking it to your beaker and pouring it in... You actually need to boil it for a while, haha. Same goes for HCl washes. First off for the solubility factor on a lot of the impurities, but I had no idea the effect it would have on the settling of the gold! I would bet I have somewhere on the order of 0.25 - 0.5 grams wrapped up in filter paper which I will get back later. Had I been boiling properly, I would have barely any wrapped up in filter paper. Doing it the cheater way I started out with, much of the gold would go through the coffee filter and it never agglomerated at all until I started boiling it. Also, I am starting to see the attraction of using SMB in solid form rather than pre-dissolving it. The solid seems to make much more handle-able powder, but it may be how varying my technique was throughout the process. Also, the second refining was every bit the improvement that you predicted nickvc. The first drop came out of a solution that was clearly loaded with copper still even after the drop. The second drop left the solution clear as spring water.

I am pretty sure I behaved myself pretty well on chemicals used for a first timer, although I can certainly see points for improvement next time. This was my second HCl/Cl precipitation and the relative volume of liquid was about 1/4 compared to the first time and it went much better. I found 8% Clorox (said concentrated on the bottle) as compared to the splash-less stuff the first time. Vast improvement. Next time I will know better what I am looking at and should be able to decrease excess even further. Was it a good idea to dilute the gold chloride solution before precipitation? I believe I remember reading to dilute for gold and to concentrate for PGMs. I was definitely using an excess of HCl at many points, but I suppose that is cheaper than nitric. I was cautious on SMB the first time and when my wife smelled my clothes a few hours later, I was even more cautious the second time :roll: .

Only one piece of my starting material was marked which accounted for less than 1/3 of the overall weight. It was stamped 1/6 10K, but who knows how accurate that is. That piece did hold up to both incineration and nitric digestion better than the others. I estimated theoretical yield assuming 1/10 10K for the lot which would have put it at 2 grams theoretical (assuming I am doing the math correctly). Since I hit 80% (without knowing anything about actual content), I'm going to call it a pretty good first shot  

I am going to see if I can get a similar lot a little bigger - perhaps on the order of 5 ozt to start and see if I can duplicate (or, better yet, surpass) results. At this kind of yield I would have to be doing some pretty large volumes of material to make anything off of it. I just don't think I have the time or the waste management capability to be doing that. At least not until I get much more repeatable in technique.

Once again, thank you to everyone that has contributed to this forum and especially to noxx for hosting this forum and Harold with his insistence in incineration and proper rinsing. It sounds trivial at face value, but makes all the difference in the world. Thank you very much to nickvc for being my own personal Yoda for a bit  This was a great journey and even my wife liked watching the SMB drop. She always hated the chem labs where everything was a clear liquid. She liked seeing colors for a change like they show on movies 

I'll definitely be giving this another go, but this time with much better eyes and hands. Even still I am sure I will be back with another "emergency" or unknown situation.

Thank you all,
Kevin


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## g_axelsson (Apr 4, 2013)

I would call that a success!

Congratulations Kevin, now you too got the bug! :mrgreen: 

When dealing with gold filled remember that if it's worn then it is some of the gold that has disappeared, 1/10 is only true if it's a new object. If you got 0.8/10 then there isn't a lot difference between that and the theoretical maximum.

Göran


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## nickvc (Apr 5, 2013)

Goran as I have stated before the stamped quality is true of the starting material whether sheet or wire but the manufacturing process will include polishing of the outer visible surfaces basically the gold while the base metal which is usually hidden is not polished so even new gold filled will not actually be plum, it's not a deliberate ploy to reduce the gold content but just a necessary part of manufacturing. Well worn pieces will be well below its stamped content again because it's the outer surfaces that get worn while the base metal will remain virtually untouched.
To verify what I'm saying I have had new 1/20 9 karat watch bands assayed which theoretically should have 1.875% Au but in reality had if I remember correctly had 1.4% Au or in other terms it was actually 1/27 9 karat and these came out of the original packets.


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## kjt124 (Apr 7, 2013)

Thanks Goran - yes, I think it is safe to say I have the bug, haha. I will definitely be doing this again. Like I said, at this cost and batch size I have my doubts of making any money, but garage sale season is coming up!

I'll have to study up a bit on watch bands and eye glasses as well as I know those are available. However, I believe they are more expensive than the couple bangles and locket from this batch. Anyone have a particular favorite type of gold filled to do? Is there anything that is traditionally less (or more) prone to bronze?

Thanks again to everyone - especially nickvc! I am definitely looking forward with a smile


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## kjt124 (Apr 7, 2013)

Well, got the camera back nearly in time for the powder, but here is the button anyway. I managed to get the reflection of the camera in this one!!


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## butcher (Apr 14, 2013)

That gold is pretty, what make it even more valuable is all of the hard work you did to get it, and the added value is the understanding you have gained along the way.
Nice job Kevin.


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## nh6886 (Apr 18, 2013)

Very nice looking button but I agree with Butcher the knowledge you gained is the real prize
Thanks for sharing
John


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