Karat scrap quality

[ppoowweerr]

I am a chemist and am extremely anal in my methods. I am working with scrap jewelry, all 14k, and when I do the math, I find that I am getting 90% of theoretical yield. I even have moved my calculations to considering the source and calling the gold 13.5k, to be realistic. Does anyone else have data consistent with mine or any Ideas concerning the <10% loss. I eventually get it out after a few weeks in solution, but I am really irritated that I am not getting a better yield? Any thoughts? Criticism is welcome as well (Constructive).

 

[goldsilverpro]

You haven't told us specifically how you are doing this, so I can only make general statements.

You're not going to be able to pinpoint the exact value of jewelry by the markings. About the only way to find out how much gold to expect is to melt, sample, and assay the gold before refining.

Are you inquarting or, are you dissolving the karat gold directly? If the latter, you are likely to have more gold in the residues. Also, if you are running small amounts, the percentage of gold hung up in the filters, etc., is more likely to be higher than it would be with larger amounts.

After precipitating and separating the gold from the solution, there can be a small quantity of very finely divided gold still suspended in the solution. If you let the solution settle for a few days, you will often find a thin layer of gold powder settled on the bottom of the container.

You could lose gold from the solution if you allow the dissolving action to be too vigorous or if you boil the solution. Are there any purple stains around your work area?

If you keep (and burn) all the papers, test all solutions, and if your lab techniques are solid, you should be getting essentially 100%.

I eventually get it out after a few weeks in solution

Can you explain what you mean by this statement? Does that mean that you dissolve the gold and then wait a few weeks to precipitate all of it or does it mean that you precipitate and separate the gold and then, a few weeks later, you get the rest of it from the solution?

 

[ppoowweerr]

My apologies for being fairly(very) vague, I guess I was wanting you to read my mind. Sorry.
1st off is quantity, I am using about 1 oz of 14k jewelry at a time but that is going up soon (unless that is a bad idea).

2nd is method. I am doing a series of acid peroxide washes being careful not to use a too great concentration of H2O2. I do about 3 soaks in small volumes (just enough to cover the gold) then I dry out the jewelry between soaks and process the material some for surface area sake. Then after I feel like the base metals have ceased to react, then I go to an aqua regia using the same idea as AP method. Always vacuum filter with clean glassware and keep the filtrate or supernatant depending on which step. Filter papers go into a holding container for a second process later. Then urea followed by SMB and then I take the precipitated gold and do one more AP then wash and one more AR/urea/smb. The gold is beautiful quality IMHO.

3rd point. I keep all my solutions after precipitation so if I return to the containers after a week or so, I have some silver (or whatever) precipitated out. I collect this and the filter paper material for another run of the system.

I think that (hopefully) cleared up my last post. Now, any thoughts and/or criticism is welcome. I have thick skin so any help is good for me. Thanks

 

[goldsilverpro]

Were I you, I would inquart (melt with enough silver to reduce the gold content to 25%) the karat gold with silver (sterling scrap can be used), shot the alloy, and then dissolve the silver with nitric. The silver is recovered from the nitric solution with copper buss bar and reused.

You end up with about 99% gold powder which can then easily be dissolved with AR. I would cover the gold powder with a slight excess of HCl (I would use about 130 ml per ounce of gold), heat, and add HNO3 in very small increments, allowing each addition to fully react. You know you are finished when a very small addition of nitric produces no reaction. It will take about 25-30 ml of nitric per ounce of gold. If you do it right, there will be just a trace of free nitric in the solution and you won't have to boil the solution down or use urea.

 

[Palladium]

One thing that might be affecting your results could be that you are going by the karat markings. I know that some jewelry that is made in other countries can very greatly when it comes to standards of hallmarking. I have even heard of jewelry that is stamped say 18 K gold when in fact it is only 14 K gold. Especially when you go by the numbers that are stamped on the hasp of chain and necklaces I think India has a problem with this.

Chris, Wasn't it you who did a thread or topic on this subject ?

 

[goldsilverpro]

Both Harold and I have discussed it on a number of threads. Finding those threads is a different story.

 

[Oz]

I find that if processing average quality or better (not junk) karat gold from jewelry using inquartation that the yield is typically one karat lower than stamped (made in USA jewelry) on the items. Actual yield is a fuzz more as I save my “spent” solutions and let them settle for a month then siphon off the top. It isn’t much more left in the bottom after settling, but I figure if I worked for it I want to keep it. The same with saving filters for later processing, it all adds up.

 

[Harold_V]

The nature of my refining was such that I didn't monitor individual batches to determine yields, due in part to the wide and varied types of materials that were submitted. However, I did process a large lot of nothing but class rings for one of my customers, which presented a perfect opportunity to determine the yield.

When one reflects the old marking standards, I found the lot of class rings to be legal, and nothing more. They were just inside 9 K, which would be acceptable for the regulations of the time. A ½ K was permitted for alloy error, and another ½ K was permitted for soldered assemblies, which is how the majority of class rings are made.

As Chris has alluded previously, new marking standards dictate that gold must be plumb----but that hasn't prevented a number of bench men from under karating. One of my customers reported (proudly) that he did so routinely. <sigh!>

It is entirely possible to process an ounce of gold and effect a full recovery, assuming the gold is pure at the outset, and the filter is properly rinsed after filtration. Having an excess of solids in the filter (silver chloride, for example) can be the source of lost values, for they can be difficult to remove from the solids. It is for that reason anything that is removed from gold chloride solutions should be processed for values. Furnace reduction is one of the most effective methods, assuming one fluxes properly.

Harold

 

[ppoowweerr]

Being a man of common sense, I knew that it was likely that 14k marked probably meant 13 ish or whatever they could get away with. I am however unfamiliar with the range that was mentioned in this thread (1/2k alloy, 1/2k solder). Thanks guys, you all have helped out in this situation a lot. I will work on the inquartation method and see how that works.
Thanks
Jasin

 

[Harold_V]

I will work on the inquartation method and see how that works.

Take note that I never recommend karat gold be processed without inquartation. Not because it can't be done, but because inquartation yields very acceptable results, with minimal effort. Done correctly, I have no doubt, you will achieve a much better yield.

Don't shoot for an alloy that is too low----try to keep the gold in it's form after pouring corn flakes. By doing so, you won't lose any fine particles when you decant the nitrate solutions after the preliminary digest. An ideal ratio is 25% gold. The end result, assuming you give your material a boil with dilute nitric, will be pieces that are a dark bronze color, but are honeycombed to the core. They dissolve readily in AR, and yield very little silver chloride, which has a tendency to trap values.

I expect that if you have been processing karat gold (yellow, or anything that contains silver), you've had some difficulty getting all of it in solution. I know, from experience, along with reading, that you can boil 14K gold in AR endlessly and never get it to dissolve, assuming it has a great enough cross section. A hard, impervious film of silver chloride forms on the gold, preventing any further dissolution.

Read Hoke, and follow her advice. I even inquarted white gold, to simplify the process, and to eliminate base metals before dissolving the values. My motto was garbage in, garbage out. It's true.

Harold

 

[goldsilverpro]

I might mention that, if you were to take an accurately weighed ounce of very pure gold and go through the steps of refining, it is unlikely that you, or anyone, would end with a full ounce of gold. You always will have a little hung up here or there. It's not lost. You'll get it sooner or later.

 

[Lou]

Welcome to the board from another chemist.

As you have been advised by others in this thread, your methodology is poor. Inquartation is indeed an easy and simple process which will afford excellent results. While massive form karat golds may be dissolved in aqua regia, it will not happen quickly unless the gold has been melted and cornflaked, or preferably melted and rolled into thin coronets. In this case, it is useful to use more hydrochloric acid than is required for a typical aqua regia mixture. The excess HCl will help to complex and solvate AgCl which forms on the surface of the gold.


Goldsilverpro and I talked in another thread about sonication of karat gold. Since you are a chemist, you are no doubt familiar with ultrasonic baths and the wondrous effects that cavitation may have on reaction rates and physical systems in general. This allows one to directly process gold alloyed with silver--the sonication decrepitates the normally adherent layer of silver chloride.


Under the techniques subsforum and stickied at the top you will find a method for producing gold of exceptionally high fineness. It has a few points you might appreciate.


As was said earlier, there is no reason for any loss. You must keep your solution transfer to a minimum, use proper heating and filtration practices, and make sure to use fresh reagents.

 

[ppoowweerr]

Nice to meet you as well Lou, Thanks for all the help, that goes for everyone. You guys amaze me with how much information you all have on tap. One quick question slightly off topic;
I have acquired a decent amount of ammonium nitrate. If I attempt poor mans AR with it, it seems like I may have a silver azide byproduct. Has anyone had any experience with this situation. It is simply a situation of availability and I don't have a source for nitric yet.

 

[Lou]

No, azide formation is highly unlikely to impossible from a thermodynamics perspective.

If you have concerns over the ammonium cation, remember that it will oxidize to nitrate, going from NH4+ to NO3- with the formation of some waters. This will eat up nitric acid, as much will go to oxidizing ammonium.

Do you remember what the azide bond looks like? Think now why that would ever form in an acidic, oxidizing solution


Are you a biochemist?

 

[ppoowweerr]

BIO chemist? nope. I actually thought about the thermodynamics about 5 minutes after I posted. I am guilty of making the post before common sense kicked in. I will openly accept the bio- shot since I had it coming.
BTW what is your screen ID on sciencemadness?

 

[Lou]

It's ok, we all say silly things.

It just seemed commonsense to me that azide is an extraordinarily unstable polyatomic anion which would not be favored under the relatively extreme conditions of aqua regia.


My username on sciencemadness is Fleaker.