# Removing stones



## Anonymous (Apr 14, 2009)

Greetings.

First I want to say that I did search the board and google before I posted and was unsuccessful. However, being a bit of a newbie on this forum despite reading for a long time, I do want to apologize in advance if this is a well covered question already. I've followed most of lasersteve's posts but my question seems to be a little outside of that box.

I want to remove baguette and round diamonds from my gold jewelry. I know that the large refiners use a chemical process for this. Does anyone know what that process is?

I'd really appreciate it if someone would share it with me - whether it's dissolving the gold from the stones or dissolving the adhesive (?) if that is what is used. I didn't jump into dissolving the gold because I didn't know if the processes that are typically used would damaged the diamonds.

Thanks,
GOY


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## 4metals (Apr 14, 2009)

Diamonds rubies opals sapphires do OK, pearls are toast.
Emeralds lose their shine if they were oil enhanced, now legally the emeralds are not supposed to be oil enhanced and emeralds that were not come out fine but if they were enhanced the finish has small micro cracks which were disguised with the oil enhancing. I've been told the emeralds can be re-oiled but I don't know the technique. If you need details on cleaning up the stones and separating the stones from the chlorides, let me know and I'll tell you a technique.


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## Emil (Apr 14, 2009)

Thanks for the information 4metals. I will keep you in mind when I need that information.

Thanks for the quick response.

Emil


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## Harold_V (Apr 15, 2009)

One of my customers was a pawn shop. They removed stones larger than 20 points, but the small ones came to me in the scrap jewelry. They are not glued in, they are held in by prongs, or are bead set. The holding devices are easily cut with a small abrasive parting disc on a flex shaft. That way you can avoid chemical processing and chasing the diamonds. 

In order to trap the fine metal particles that are generated in the process, and to insure the stones were not lost, I made a simple "glove box" from a short piece of 6" pvc pipe. I removed a portion of the side and installed a plastic window so I could see my work. The stones can be removed quite rapidly once you get a rhythm. 

Harold


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## Anonymous (Apr 15, 2009)

It's pretty funny that you mention a pawn shop as that's where a lot of my material has been coming from as well. I think the glove box is a great idea. Did you use an abrasive disk on the bead set items, or just the prongs? (as I google bead set, lol).

By abrasive disk, did you mean a cutting wheel or something more along the lines of a gasket removal pad in the 100-300 grit territory? I just want to make sure I'm on the same page given that I'm the slow one in the group :lol:


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## 4metals (Apr 15, 2009)

The labor involved to physically remove anything but prong set stones is huge. I have been involved with stone removal for 4 different refineries over the years processing lots as small as a few ounces to over 1000 ounces and they were all processed in aqua regia, the stones were cleaned by tumbling in sodium thiosulfate, and after a minor amount of picking out of the undissolved pieces the stones were clean and shiny. Occasionally a lot was slow to dissolve, it was usually associated with an Indian manufacturer, they love their silver in the alloy. But for the most part they are easy dissolves.


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## Harold_V (Apr 15, 2009)

GOY said:


> It's pretty funny that you mention a pawn shop as that's where a lot of my material has been coming from as well. I think the glove box is a great idea. Did you use an abrasive disk on the bead set items, or just the prongs? (as I google bead set, lol).


Yes, on the bead set items as well, but as 4 metals alludes, that is slower than removing from prongs. Not generally as much metal retaining the stones, but it's harder to access. 



> By abrasive disk, did you mean a cutting wheel or something more along the lines of a gasket removal pad in the 100-300 grit territory? I just want to make sure I'm on the same page given that I'm the slow one in the group :lol:



I don't think you're slow----you just haven't been around jewelers, so you'd understand how they work. 

The discs I spoke of come from jewelry supply houses. They are commonly used in that trade. They're a resinoid bonded disc, about 1/64" thick, so the kerf is quite small, minimizing losses. They are mounted on a tiny arbor that has a screw in the end. The supply house will have them, too. They are available in two sizes, as I recall. One of them is about 1" diameter, the other slightly larger. It has been years, and my memory has dimmed. I do recall that they last a long time if you don't break them. They're surprisingly tough, however. 

I agree that acid removal is fast and good, but if you inquart your gold to process, that complicates things a little. Still works, and, in theory, diamonds are not harmed by the melting process. You have to fish them out of the remains, which often include some silver chloride. For me, it was best to manually remove the stones. They were not returned, so they provided extra profit and more than paid for the time it took to remove them. 

An added thought. Even small, broken diamonds have value. Not a lot, but it if you find chipped diamonds, save them until you have enough to ship. I used to get paid $25 carat for them. Better than tossing them. 

Harold


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## 4metals (Apr 15, 2009)

I have never seen anyone melt jewelry with stones in it to inquart before refining. The jewelry is put up in acid as is. As I said it dissolves well enough to remove the stones on most lots. A glove box and abrasive disk is a great idea for the few pieces that don't dissolve completely.


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## Harold_V (Apr 16, 2009)

Yeah, I understand, but my operation revolved around inquartation. I preferred that to fighting with alloys that were troublesome. That's why I used the abrasive process for removing stones. 

I didn't like the results I achieved without inquartation, although the only thing I processed that way was filings. Even they got a prolonged boil in nitric, where a great deal of contamination was removed, but the end product always left a great deal to be desired. 

I was a quality freak, so I re-refined my gold, although my gold with a first refining, aside from filings, was always quite good. I chose to re-refine to insure that my customers received no less than industry standard. The improvement in quality was very noticeable. My gold, prior to a second refining, always had traces of oxides, but I could melt my twice refined gold without flux and still have oxide free gold. The only flux I used was to line the melting dish, so the gold would flow freely. 

By now you've probably seen the picture, below, more than enough times, but this is an example of gold I turned to shot. It was melted exactly as I suggested, and was not pickled for appearance. I firmly believe I bordered on 4n quality, although I never made the claim. 

Harold


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## goldsilverpro (Apr 16, 2009)

Fineness is defined in the trade as parts per thousand.

Therefore:

4 nines gold = 999.9 Fine = 99.99% pure.
3 nines eight gold = 999.8 Fine = 99.98% pure. 
3 nines five gold = 999.5 Fine = 99.95% pure. 
3 nines gold = 999 Fine = 99.9% pure. 
2 nines gold = 990 Fine = 99% pure. 

99.9999% pure gold is 6 nines or 999.999 Fine

Just count the total number of nines.

There are some people on the web that believe that you only count the 9s after the decimal point when purity is expressed in percent. Thus, they think 4 nines is 99.9999% pure. This is totally wrong. I found this error to be common on colloidal silver sites.


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## 4metals (Apr 16, 2009)

Harold, 
It is interesting to me that you prefer to inquart karat whenever you can. I have successfully refined thousands of ounces of karat gold without inquarting. Here in the East refining rates are competitive and the most a refiner can hope to charge is 2%. Possibly for that reason I have never inquarted for standard aqua regia refining of karat gold. The expense of the nitric dissolve on top of the aqua regia dissolve adds to the cost. 

There were some precautions however. All karat gold (except stone removal) is melted and assayed for gold and silver. When a refining lot is put together, the goal is 7 1/2 % silver or less, this substantially decreases the chances of a lot coating up with chlorides and stopping the reaction. In a typical refining lot of 1000 ounces, the remaining undissolved shot averages out at about 2 ounces. The customer is paid on assay so he has been paid for the entire content of his job. 

The 2 ounces is tumbled in sodium thiosulfate to dissolve the chlorides and melted into a button to be included in another refining lot, it always assays at a higher gold percentage than the lot it was in as a lot of the base metals have been leached out. 

Another trick to gain purity in the precipitation is chilling of the loaded aqua regia. If the acid is cooled to 50 degrees before filtering (ice works for this) the solubility of any silver chloride dissolved in the warm acid drops way down so it can be filtered out easily. 

The gold is dropped with sulfur dioxide gas, the nitric is driven off by gassing because we never use urea in a system of my making. 

The gold is transferred to a polypropylene lined cement mixer and tumbled slowly while rinsing, it is washed in distilled water, followed by hot distilled water rinsing. The sponge is transferred to a large Buchner funnel and sucked dry and melted. The tumbling improves rinsing dramatically as the gold packed in a filter tends to channel the rinse waters leaving some sponge poorly rinsed, with good vacuum all of the decanted rinse waters are filtered quickly so there is no fear of losing small particles of gold with the changing of the rinses. Gold produced by this method consistently assays .9997 plus (Ledoux ICP) after melting. We claim .9995 and nobody ever has challenged the purity. We only have to drop once, our accountability is 99.7%. 

The silver chloride is reduced with sugar and the resultant bar is 97 to 98% silver and the gold in the chlorides approaches 2% on average. Adding in the gold content of the undissolved button and the silver bar the overall accountability approaches 99.9%. The resultant waste treatment sludges always have payable gold as do sweeps from burning papers used to wipe up drips and filter papers so the roughly 3/4 of an ounce of fine "lost" on each 1000 ounce refining lot turns up eventually.

I have owned a facility producing fine as described above and engineered 3 more refineries and similar results have prevailed. That is why, for the most part, I don't inquart with karat gold refining. As I have posted in the past I have set up a process where inquarting silver, for the purpose of refining silver via sodium formate reduction, gives me an easy high purity gold residue for subsequent refining. That product dissolves in aqua regia with nary a trace left undissolved.


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## Harold_V (Apr 17, 2009)

4metals said:


> Harold,
> It is interesting to me that you prefer to inquart karat whenever you can.


Well, let's say I used to. I am retired, and have been since 1994. I am no longer involved in refining, nor do I have an interest in refining. I am here to help others where I can. However, I inquarted everything (karat gold), even when it was not necessary. It served more than one purpose, so I didn't consider it a problem. 

I think it would help you a great deal to have an understanding of how I started refining for others, and my background. If you're interested, I'll lay it out for you. Most everything I did was for a good reason, so I'll offer my reasoning where it applies. 

For starters, I am not a chemist, nor am I educated. I was a terrible student, never doing home work and sleeping in classes regularly. I struggled to get out of high school, not knowing if I'd graduate until I did. I had little interest in being there, although in classes that held my interest, I did quite well. Unfortunately, my interests did not revolve around anything that would improve me in ways that might be significant. On the positive side, I had a keen interest in machining, which become my vocation. 

I started refining when it was illegal. As a result, I had to keep a low profile. No one was willing to provide the slightest bit of information, but I had the good fortune to acquire a copy of Hoke's book. Perhaps that will help you understand my processing choices. They may not be what industry uses, but they are effective and easy, yielding very acceptable results, as you might see by the quality of gold I have posted in pictures. Best of all, inquartation avoids the problem of high silver content.



> I have successfully refined thousands of ounces of karat gold without inquarting.


Understood, and I appreciate the fact that it's possible in a large operation---but one that operated as mine did, that wasn't always an option. I'll try to comment on that as it becomes appropriate. 



> Here in the East refining rates are competitive and the most a refiner can hope to charge is 2%.


Yes, 2%, but no mention of the other charges. Major refiners do not refine for the average customer for 2%, nor for 10%. The extra charges insure that they make a healthy profit--and they steal beyond that. I have dealt with enough major refiners to know that they are not to be trusted. I hesitate to mention names, but you'd be familiar with all of them, for they are all in the east. 



> Possibly for that reason I have never inquarted for standard aqua regia refining of karat gold.


Yes, I understand, but in order for any of this to make sense, you must abandon your concept of doing business. I allowed a business model to develop as was required. That was easy. All I did is apply the same procedure to the incoming work that had worked successfully for me in refining the values I could accumulate. Inquarting, for me, was an excellent idea, for sterling was very much a part of the material I received, so it was used in inquartation in order to process for the customer. That way, the silver was used for a purpose, not processed for the sake of processing. In a sense, it was getting two cats with one stone. It made all kinds of sense at my level of operation----and I'd do it again today, given like circumstances. I liked the processes I used, and was very comfortable using them. Remember, I did not, nor do I, have the ability to work things out chemically. I am very good at following procedures that are laid out for me, however.

Back to your business model---when you have limited supply, you are not afforded the luxury of waiting for enough to accumulate in order to selectively combine and melt. A great deal of my success revolved around my fast return and the excellent service I make mention of. For years, I ran my refining as a hobby---making my living at my chosen trade, that of being a machinist/toolmaker. I had my own business, and specialized in the aero-space industry, along with defense work. I also did a small amount for the pharmaceutical industry through various accounts. My expertise was in small, precision work. Refining, to me, was a way to get away from my routine. It was never intended to be a business. 

I processed each batch individually, with no assaying involved. Considering it was not uncommon to have dental gold as a part of the submitted material, I used silver as the carrier of platinum group values, so they were collected and concentrated such that they could be recovered easily when the silver was parted. It also permitted running batches, regardless of content. So then, you might rightfully conclude that in my case, inquartation was the best possible choice. It required no special handling---all batches received identical treatment, which became routine. There were far more benefits than negatives, at least in my mind. I had experienced dissolving karat gold directly and was not overly impressed. That was my method of processing filings. 



> The expense of the nitric dissolve on top of the aqua regia dissolve adds to the cost.


Moot point. As I said, the silver had to be parted, anyway. I also enjoyed the fact that my solutions were not heavily laden with contamination, so there was less drag-down of unwanted substances. I was also paying $4/gallon for nitric, and just over $1 for HCl. 



> Another trick to gain purity in the precipitation is chilling of the loaded aqua regia. If the acid is cooled to 50 degrees before filtering (ice works for this) the solubility of any silver chloride dissolved in the warm acid drops way down so it can be filtered out easily.


I precipitated from concentrated solutions, heavily iced. My routine when re-refining was to end up with anywhere from 15 to 18 ounces in a liter, which had three liters of ice added prior to precipitation. It was evident when adding ice that a trace of silver chloride was precipitated, but I also washed my gold with ammonium hydroxide in the final wash stage, so that was, for the most part, removed. 



> The gold is dropped with sulfur dioxide gas


I, too, used sulfur dioxide. I had a large cylinder that was plumbed from the main floor of my operation to the lab, which was upstairs. Only in my early learning years did I use anything else, which was ferrous sulfate. I didn't like using it because of the volume increase. 



> the nitric is driven off by gassing because we never use urea in a system of my making.


Never in my more than 20 years of refining did I use urea. I evaporated routinely, using a button of added pure gold to consume traces of excess nitric. Because of my method, I had to evaporate, so adding the button was added insurance, and permitted evaporating for concentration instead of for expulsion of nitric. 



> The gold is transferred <clip very interesting process>


You may understand that an operation that deals in low volume would not be suited to that procedure. Again, I suggest you abandon your concepts in this case. What I did was very successful, in spite of it being out of the ordinary. While I refined for over 20 years, the last ten years, refining was my sole source of income, and I had no problem selling the operation. It was not even advertised. 

My washing procedure consisted of a heavy boil in HCl, a boil in tap water to rinse (our water was relatively clean), a boil in ammonium hydroxide, a boil in tap water, a boil in reagent grade HCl, then another rinse in tap water. The gold was then force dried in the beaker by slow evaporation. Only minute traces of water hardness was observed, and the gold melted without oxides (no fluxing aside from coating the dish). The picture I posted is gold from that very process, and was the last gold I refined before selling the operation.



> Gold produced by this method consistently assays .9997 plus (Ledoux ICP) after melting.


Only on one occasion was my gold assayed, and I have no idea where the assay was performed. One of my customers, when he (they, two guys) first used my services, were concerned about my quality. They claim it assayed 9997. I have no way of knowing if that is true, or not, but the fact that there is no oxidation is a strong indicator that it is. 



> We claim .9995 and nobody ever has challenged the purity.


My packaging labels also claimed 9995. The only challenge was described, above. I had an excellent reputation for quality, honesty and fast delivery. Believe it or not, my business model worked very well. 

So then, it can be safely concluded that a small operation is unlikely to emulate a large one, and if an attempt is made to do so, it may well not succeed. 

Key to my success was my service. I picked up and delivered, and offered three day service in the beginning. As the operation grew, I could no longer provide the short service, but with rare exception, I did provide seven day service. I always offered an advance of gold if the customer was in need, and sold gold to or for them at spot price, free of fees. Buyer and seller alike got a fair deal, although I restricted my sales to my customers. 

The majority of my customers were small operations, so they submitted small lots, so I had to tailor the operation accordingly. I processed a lot of gold only because of my years of refining, and because of the large customer base. Regardless of how you perceive the operation, it was a resounding success, particularly when it was never intended to be a business. In the end, it had grown so large that I was working long, hard days, 365/7. Christmas day was just another work day for us (my wife and me).

For the record, I processed solutions, polishing wastes, floor sweeps and carpets. I offered all the services my customers required for their humble operations. 

What I had was a strong work ethic, coupled with a streak of honesty. You can't miss with that combination.

Harold


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## goldsilverpro (Apr 17, 2009)

4metals,

The process I used was almost identical to yours. I rarely inquarted and was still able to come up with at least 999.5 or 999.7 gold, with only one refining. Usually, I bought karat gold outright. When I took in gold on a refining basis, I did the same as you. I melted, sampled, and paid the customer on assay. That way, the small amount of gold that got bogged down with AgCl and didn't dissolve in AR eventually came out in the wash and I didn't worry about it. The only time I inquarted was on green gold, which is fairly rare. Good Black Hills jewelry usually has green gold on it.

Usually, the jewelry I bought outright was run directly in AR without melting and shotting. Every refiner I worked for also did it this way. The best refiner I ever knew did it this way. He ran about 200 oz of gold in karat gold a day. He never got rid of the base metals beforehand and he was a master at cleaning the slightly off-purity gold in the crucible furnace - he had to be. We sent the gold out for analysis of the impurities a few times and, like yours, the gold always figured about 999.7 Fine. It always had the pipe and the crystal, with no staining. For those occasional lots that he couldn't clean, he rolled out the gold very thin in a huge set of power rolls and quickly went through a second aqua regia. The gold was almost always in-and-out in 1 day.

I agree that getting rid of the base metals by inquarting would eliminate the need for cleaning in the melt. However, gold can easily be cleaned in the melt, if you know what you're doing. It's really not that hard. You just add pinches of niter, borax, and soda ash, here and there, until the surface of the molten gold appears flawless, without any appearance of a film (usually white in color). Of course, you have to know what to add and when and how much but, with a little experience, that's easily figured out when you're doing it. Every batch is a little different. Never add so much flux that the gold is covered. You need to be able to always see the surface of the gold. Also, it takes very little niter. When I had my last refinery, I torch melted and cleaned the gold in the same way, with probably 98% success with only 1 aqua regia. With torch melting, I only added 1 or 2 prills of niter at a time.

For the beginner, inquartation is probably the best since it most always works the first time without having to make adjustments. Also, I understand why Harold did it - he wanted to be 100% honest and, without fire assay capabilities, he had to get 100% of the gold out, all together. However, it's not absolutely necessary. There are always several ways to skin a cat in this business. Like Steve says, the proof is in the pudding. I love cliches.

Unlike Harold and 4metals, karat gold was not the primary type of material I ran in my refinery, although I always seemed to have a batch or two of it going. I ran lots of film, jet engine scrap, gold filled, cyanide strippable e-scrap, etc. Whatever I could make a profit on. I hated to inquart, I hated to boil down AR or use urea, and I hated silver chloride so, in my processes, I always tried to work around doing these things. Except for the inevitable AgCl from working karat gold, I was very successful in doing this.

On this thread there are three professional refiners doing things in three different ways, with all getting the same results. All 3 met the particular situation that each of us found ourselves in. All 3 work, even though all are different.


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## 4metals (Apr 17, 2009)

Harold,
I read your posts and suggestions both here and on other threads with great interest, it does help to know that your customer base was made up of customers producing the smaller lots for which your methods are excellent. For the purposes of this forum I think that your methods better serve the vast majority of the members than my methods, as my methods represent larger production lots. I do think that it can be useful to some to see the whole spectrum of refining from the small lot toll refining that you did to the large production, I always try to include why I choose a specific method and I've noticed you do the same. The bottom line is both of our methods will lead to the same result. One of the interesting things about the chemistry of refining is the number of varied routes one can take depending on what you start with, to get to the same endpoint. 
Oh and by the way Harold you may not have been formally educated, but you are an educated man.


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## Harold_V (Apr 17, 2009)

4metals said:


> For the purposes of this forum I think that your methods better serve the vast majority of the members than my methods, as my methods represent larger production lots.


Yes, I was hoping you'd see it that way. They tend to lower the bar, making a sure thing from some operations that may be challenging for those without a chemical education. That was Hoke's intention. 

I also fully understand why the methods you have revealed are relevant to large volume producers. The flow of my humble business made it very easy to pursue the processes I used, and as both you and Chris have mentioned, the end results appear to be identical. That, for me, was what mattered. I wanted to insure that I treated my customer honestly, and the customer got metal that was the equivalent of the industry standard. You might say I was a happy camper, living in my ignorant bliss. I really had no idea how major refiners dealt with their metals, not having anyone to talk to. Remember----everything I learned came from my own efforts. I had no one to recommend any changes, nor did I have the ability to create methods. 



> Oh and by the way Harold you may not have been formally educated, but you are an educated man.


   

Hey, stop it! :wink: 

Thank you. I attribute what little I know to a dogged approach to the things I do. I may not always have all the answers, but I generally have enough of the answers in order to perform in an acceptable fashion. Too bad that hasn't been true of computers, which have me in a state of constant confusion! 

Thanks for your understanding, and the very nice comment on my method of education, where I dance to my own drummer. 

Harold


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## Lou (Apr 17, 2009)

I think Harold communicates his views on things far been than many an educated that I know.

This is an interesting thread as it covers not just small scale processing, but also moderate lots (i.e., 200 ounces/day). There are of course methods which are more amenable (i.e., cheaper/economy of scale).

I personally believe that the future of refining and much of reclamation will be done via gas phase methods, rather than any aqueous workup. Currently, it's so underrated and isn't used as it ought to be.

Of course, for bulk quantities and the right setup, Miller's chlorine process is superior for upping the quality to around 99%, and then the gold may be processed electrolytically (usually plated out onto CP4 Ti or SS316) to get 4N purities.

Using the gas phase methods, one can simply melt their karat gold, cast it into an ingot, roll out thin, coil it up, and pack it into a quartz tube. Depending on the thickness of the material, the temperature, flow rates, gas mix and other factors, one can process much material in a few hours. What's left behind is a mixture of CuCl2, CuCl, and AgCl which is easily cleaned out with dilute HCl and/or hydrogen peroxide.


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## goldsilverpro (Apr 17, 2009)

Lou said:


> I personally believe that the future of refining and much of reclamation will be done via gas phase methods, rather than any aqueous workup.


I agree. Coincidentally, I was reading an article a couple of days ago about just that. The title was, "Evaporative Purification of Gold." It is in the book, Precious Metals 1981, published by IPMI.


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## 4metals (Apr 17, 2009)

Lou, 
The drawback to the Miller Process is the gold cells, where your metal can sit for long periods before accountability can be verified. If one is willing to mess with chlorine, try atomizing your karat into dust sized particles and digesting it with hydrochloric and chlorine gas. No nitric at all, no outgassing, the gold drops quickly with SO2. And as a side benefit you can inquart platinum with karat gold and drop ammoniumchloroplatinate after filtering no boiling down or fancy extractions needed. Just drop the gold after the platinum is down. The downside is chlorine gas is a bear to work with.


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## goldsilverpro (Apr 17, 2009)

4metals said:


> The drawback to the Miller Process is the gold cells, where your metal can sit for long periods before accountability can be verified.


That is somewhat true but, once you fill the pipeline, it is filled. As far as accountability is concerned, I see no reason why it could not be achieved almost on a daily basis. For very large quantities of gold, there is no better method, in my estimation. No nitric. No aqua regia. No silver dissolving problems. That would be glorious.


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## 4metals (Apr 17, 2009)

It may be the way of the not too distant future, in todays paper the EPA cleared the way for cutting back or regulating all of the greenhouse gasses. That includes nitric oxide. The nitric fumes we have to scrub are far from scrubber friendly, the fumes generated by the Miller process are chloride fumes and despite how nasty chlorine is, they are a water soluble fume and easily scrubbed. It does however put the squeeze on the little guy.


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## semi-lucid (Apr 17, 2009)

4metals said:


> That includes nitric oxide. The nitric fumes we have to scrub are far from scrubber friendly, the fumes generated by the Miller process are chloride fumes and despite how nasty chlorine is, they are a water soluble fume and easily scrubbed.



Metals

I thought the nitric fumes, NO2 ?, could be absorbed into water?

john


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## 4metals (Apr 17, 2009)

There are multiple nitrogen compounds released in an acid digestion. Since they are formed by specific conditions which can vary in the course of a digestion they are referred to as NOx. If you bubble the red fume through water at a pH of 12, it will surface as red as it went in. The most effective fume scrubbers break the fumes down to 1 species of nitrogen in one scrubber then pass through 1 or 2 more scrubbers to effectively scrub the fume. Most scrubbers in use today are single pass caustic scrubbers which the EPA will approve but they don't completely scrub the fume. If they clamp down on NOx emissions, I for one will be searching for alternatives from multi unit scrubbing to peroxide additions to the working acids.


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## semi-lucid (Apr 17, 2009)

Ok, From what I've read, (which is not that much, correct me where I'm wrong) the two species of NOx formed are NO and NO2. And I've read that NO reacts with atmospheric oxygen to give NO2, and that nitric acid is produced by reacting nitrogen dioxide (NO2) with water.

3 NO2 + H2O → 2 HNO3 + NO 

The residual NO would then react with O2, and could be scrubbed a second time.

My source for all this is Wikipedia.  

http://en.wikipedia.org/wiki/Nitric_acid

John


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## 4metals (Apr 17, 2009)

In a perfect world where other reactions are not going on all around the reaction you are describing where nitrogen peroxide and water react to form nitric acid and nitric oxide, the reaction would be simpler and more predictable. The nitric is actually a bit more involved in reacting with the hydrochloric acid to bump off a chlorine molecule which allows the acid to digest the gold. There is a bit of nitrosyl chloride action going on which decomposes in water and the soup of the reaction contains hydrogen, chlorine, oxygen all reacting and decomposing with the nitrogen compounds to form nitric oxide (NO) nitrous oxide (N2O) nitric anhydride (N2O5) which decomposes back into nitric acid, nitric trioxide (NO3), nitrogen dioxide (NO2) and nitrous anhydride (N2O3). All of these gases are swapping oxygen and nitrogen as they decompose in water and reform different compounds depending on pH and different flow characteristics inside the scrubber. The potential different reactions taking place are so difficult to predict that it is easier to consider them transient forms all grouped together and called NOx. In fact the name has such a neat ring to it our forum administrator adopted the name!


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## Refiner232121 (Jul 17, 2009)

> Never in my more than 20 years of refining did I use urea. I evaporated routinely, using a button of added pure gold to consume traces of excess nitric. Because of my method, I had to evaporate, so adding the button was added insurance, and permitted evaporating for concentration instead of for expulsion of nitric.



Hi Harold 
Can you explain how you did this


> button of added pure gold to consume traces of excess nitric.


Thanks


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## Harold_V (Jul 18, 2009)

Real simple. But first a comment. As GSP has alluded, time and again, the wise way to process is to use only the amount of nitric that is required. That can be time consuming, due to the small amount of gold remaining in often large volumes of solutions, with but traces of nitric present. Yes, his method works, but the time loss wasn't in the books for me. I prided myself on a fast turnaround for my customers, many of whom were small operators with little free gold at their disposal. A fast return was important to them. Therefore, I started using the added gold button to save extensive evaporation time. 

So then, to use this process, dissolve the values, using the required amount of AR, and heating the solution. That way you are assured of the fastest possible dissolution. Do keep the vessel covered with a watch glass, so vapors condense and drip back into the solution. 

When all of the values have been dissolved, temperature is lowered and the watch glass removed. A weighed button of gold is then added to the solution, along with some free HCl, which can react along with any unused nitric to dissolve the added gold button. By the time the solution has been evaporated to a dark red/orange color, any free nitric that may have been present will have been consumed. You can generally see small bubbles coming off the added gold, assuring you that it is working. 

If, when you have the solution concentrated, you see no signs of activity at the added gold, it is a good idea to add a small amount of HCl once again. Should you have exhausted the previous addition before the nitric was consumed, this will serve two purposes. The addition of the HCl will help eliminate any nitric that may be present in the way of brown fumes. It will also react with the now concentrated solution to rapidly dissolve more of the gold button. 

If, when the second addition of HCl yields no changes, no fumes, or no bubbling at the added gold button, you can safely consider the solution to be free of nitric, so it can then be diluted and filtered in preparation for precipitation. 

Remember to dribble a few drops of sulfuric in your solutions when you start the evaporation process. That will serve to precipitate any traces of lead that may have traveled in tandem with your values. 

Hope this helps.

Harold


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## golddie (Jul 18, 2009)

Hi Harold
I had to read it a few times so that it would sink in.
I guess when you actually perform the experiment it will be clearer.
This may sound trivial but I am not sure about it
The gold button, what should be the size and also what karat.
Thanks


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## Harold_V (Jul 18, 2009)

The added gold should be pure. That way you know what amount was added to a given lot, for the added gold is weighed after it has been recovered from the solution, subtracting the ending weight from the starting weight. The difference is the amount of gold added to the solution. It's important to do that if you want to know the yield of the lot in question. 

As far as size is concerned, the larger the amount you add, the faster it will work. The best scenario is if you add a rolled piece, so it has a large surface area. That can be negative in that as it breaks down, it often does so by making a lot of small pieces, which can be difficult to recover. Instead, I simply added more buttons. I'd use the very small ones, remnants from previous use, first, so they would be totally consumed by the unused nitric, adding a large, new button when they were consumed. 

A word of caution. Don't drop buttons in a beaker. They will almost always crack the beaker (don't ask!) :roll: . I used to slide them to the bottom, pinning them to the side of the beaker with a stirring rod. 

Don't try to complicate this process. It's simple, and straight forward----you add a known amount of pure gold (that is sacrificial, but recovered when the solution is precipitated) to the solution ----used only to consume the free nitric. By weighing the gold before and after, you know how much you added to the solution. Simple as that. 

Harold

edit: corrected typo


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## golddie (Jul 19, 2009)

Hi Harold
I don't know if you have already mentioned this or not.
But I was wondering how you prepared aqua regia.
Also 
I was wondering what you did for nitric acid.
Did you buy it ready or make it yourself
Thanks


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## Harold_V (Jul 20, 2009)

When I was refining, buying chemicals wasn't much of an issue. I purchased all of my acids. Nitric, purchased in 55 gallon lots, cost just over $200 per drum. I owned my own stainless 55 gallon drum, so I exchanged for a full one. 

The ratio for aqua regia is not commonly agreed upon. Many say 3 parts HCl, 1 part nitric. I used 4 parts HCl, 1 part nitric. I also used water, but that is an option you may or may not use. It should extend the use of the acid, although it will slow its pace a little. 

My reasoning behind using a 4:1 mix?

Excess HCl does no harm. By providing a little excess, you insure consuming your nitric, instead of running short and assuming you have exhausted the nitric. 

Mix AR only as it is needed. It gasses, with terribly corrosive vapors. If you stopper a vessel tightly, you risk breaking from internal pressure. 

Harold


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## golddie (Jul 20, 2009)

Since I am getting so much from this forum.
I might as well give you a trade secret
To remove stones you use carbide disc 
It eats the beads and the claws and nothing happens to the diamond
If you have other stones that are softer than diamonds then they will get scathed.


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## qst42know (Jul 20, 2009)

I have never done more than a few stones at a time but I have had good luck with the rod of an ice pick pulled from the handle and sharpened to a tiny jewelers sized chisel point. Sometimes a push is all that is needed or a light tap with a small hammer will cut the end of the stubborn prongs off. A wooden woodworkers clamp will hold all sorts of odd shaped pieces while you work on them. It goes much faster than it sounds.


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## goldsilverpro (Jul 20, 2009)

A third generation jeweler friend once told me that, when removed, 90% of the diamonds under 1 carat, were damaged. I know zero about diamonds so, I'm just repeating his words.


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## qst42know (Jul 20, 2009)

I suspect it is the skilled jeweler who hides cheap flawed diamonds beneath the prong heads. I would think any gold alloy too ductile to damage a diamond. Opposing prongs are merely squeezed tight enough to grip the stone by pliers, peening, or by drawing a burr. 

Is a diamond really that brittle or was the stone already cracked or otherwise flawed?


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## Harold_V (Jul 21, 2009)

goldsilverpro said:


> A third generation jeweler friend once told me that, when removed, 90% of the diamonds under 1 carat, were damaged. I know zero about diamonds so, I'm just repeating his words.


I processed for a pawn shop that removed all substantial stones, but left anything smaller than roughly 20 points. I used to remove them regularly, and sold them for additional profit. Prong set diamonds are easy to remove, but bead set stones are much harder, due to the small exposed beads that hold the diamond. The use of an abrasive parting wheel and a flex shaft, working in a "glove box" to capture the diamonds and wasted values made removal easy. I made more money on the diamonds than I did on the refining. Diamonds so removed are not damaged. Stones of less value are, those that are not as hard as diamond. 

I'll share something with you you may find hard to believe. 

I screened polishing wastes after incineration, and recovered a fair number of diamonds in the process. What surprised me was when I ran the two 55 gallon drums of polishing wastes that I had accumulated. They were processed with AR for extraction, but I was aware that total extraction was not to be expected. I ran them in my agitation tank with cyanide, but in order to do so, they had to be run through the ball mill, where the pH was changed to basic. I introduced hydrated lime along with the wastes, shifting the pH to roughly 10. The material, upon being discharged from the ball mill, was classified by a fine screen. To my surprise, I recovered something like 100 small diamonds that had been through the ball mill---all without damage. Keep in mind, the ball mill had steel balls up to 2" diameter, and it ran at the proper speed, where the balls were dropped from the apex of the top curve, crashing down on the contents of the mill. 

Diamonds are very tough and can take some serious abuse. None of the man made, or naturally occurring abrasives harm diamond in the short term. They are used routinely for dressing grinding wheels made of silicon carbide, which is harder than aluminum oxide by a long shot. 

Harold

edit: corrected typo


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## golddie (Jul 21, 2009)

Hi Folks
Thanks for your interesting thoughts
I have been a setter for a long time and I have removed many stones.
When a diamond is of good quality and the cut is of good proportion you can just poke a sharp object and give it a wack from the back of the piece and it will come off.
But if the stone is set very well and the claws are holding the stone well then doing this can break the stone.
After a bit of experience you get the feel of the trade and things move along rapidly


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## 4metals (Apr 27, 2015)

The moderators would like to thank all of the members that contributed to the original thread that this post was based on, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Removing stones

The moderators have edited some posts in this thread that made reference to posts that were deleted. We strive to make these Library threads as concise as possible by deleting posts that do not add information to the original topic. All of the original posts are still preserved in the thread listed above.

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

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