4 Mitutes on diamonds removal

[samuel-a]

I'm sure most of you guys already know all of that, but just in case there's anyone here who don't...

AR is quick to remove stones from gold jewellry. It's a bit more intense with yellow/green gold due to silver content and leave quite a mess in terms or refining the metal. But diamonds are well worth it. IMHO.

[youtube]http://www.youtube.com/watch?v=dYFVM9JKuO8[/youtube]

 

[4metals]

It is unfortunate that you chose to use white gold for your example because white gold has no silver in the alloy. Because of the lack of silver the alloy dissolves completely, with the possible exception of a few flakes of rhodium electroplate which will remain with the diamonds if the setting was in fact rhodium plated.

When most members try the identical procedure with karat gold which contains silver, as most every other alloy of gold contains, then the plague of silver chloride will raise its ugly head and make the process more difficult.

Consider re-making the video using karat gold with silver to show members how most of the jewelry they encounter will perform. The cleaning up of the silver requires additional steps which cannot be ignored.

 

[niteliteone]

Nice video,
I'm guilty of ruining afew diamonds myself.
They just didn't like the inquartation process I guess. :shock:

Tom C.

 

[samuel-a]

It is unfortunate that you chose to use white gold for your example because white gold has no silver in the alloy.

Hi 4metals

I agree.

As soon as i get the chance to, i will make another video with yellow gold.
This White gold pendent was the only thing available to me with real diamonds and i'd hate to do that procedure w/o precious stones... though, for demonstration sake it might be a good idea.

The cleaning up of the silver requires additional steps which cannot be ignored.

I'm planing to tuch this subject in one of my future articles regarding silver refining currently in the making. Though it will take some time to be ready....

Thank you for the constructive comment 4metals

 

[4metals]

I was referring to the silver chloride which will encrust the karat gold and stop or hinder the dissolution. Some use ammonia to dissolve the chloride and others prefer sodium thiosulfate. What is your preference?

 

[goldsilverpro]

Sam, I also watched the 2 videos on 22K gold refining. I have never used ice to ppt. the AgCl. However, I was under the impression that the AgCl was removed by filtration while the solution was cold. If allowed to warm to room temperature, I would think that some of the AgCl would re-dissolve in the strong AR. Then, when diluted by rinsing, some of the AgCl would re-precipitate into the gold powder. Of course, you could get rid of some of the AgCl with ammonia, but why not try to get most of it the first time? Instead of ice, I always diluted 3X with water before filtering.

 

[samuel-a]

I was referring to the silver chloride which will encrust the karat gold and stop or hinder the dissolution. Some use ammonia to dissolve the chloride and others prefer sodium thiosulfate. What is your preference?

Neither of them.

The key is to maintain boil which in turn maintain dissolution and somewhat vibretional forces on the gold piece.
Another key is the frequent nitric addition to maintain strong AR which also dissolve part of the silver chloride.

I did mentioned in the original video that a condensation setup is needed so no PM's losses will occur.

Tonight, I took another video with regular yellow gold passed through the same process (though w/o real diamonds), it will take me some time to edit & upload it.
I did so since i truly think your point is important and i did not provided the whole picture with the original video. For that i thank you again.

On the 1 hour marker, heat was removed and the stones broke loose with just a gentle shake of the tube.
I reckon that different Stonesetting, karatage and deviation of the actuall alloy then what it marked at, will effect the time needed to complete the process, some may take well over an hour and some may take less...

As you would expect, unlike the white gold, the yellow gold piece did not fully dissolved, but just enough to brake loose the stones.

p.s. - I know of some local refinery the usses an ultrasonic to do just that, but not sure if this is a common practice or not.

I would think that some of the AgCl would re-dissolve in the strong AR.

Chris

With no intention to offend you in any way, I believe you overlooked a very important part of the demonstrated methodology.
Which is, that the nitric additions are supposed to be masured and added just enough to dissolve the metals, therefore leaving only a slight chance for for a possible minimal excess nitric.

Therefore, eliminating almost completely the possibility for AgCl to re-dissolve.

This methodology, i learned from the best... i think you know who i'm talking about 8)
I went out of my way to emphasize this point both in the video and the article behind it.

In any case, the recommendation is to wash with Ammonia and re-refine again to ensure purity, so just in case someone will get "creative" and mess up with his nitric addition, he will still end up with good and fine product.

 

[4metals]

No matter how you slice it there will remain a significant quantity of undissolved silver chloride. If your doing stone removal in test tubes it is quite easy to pick out the diamonds and leave the chlorides behind. The same does not apply when you are doing stone removal on hundreds of ounces of scrap at a time, you end up with a mud which is not easy to separate the diamonds from the chlorides and undissolved metal.

To remedy this there are 2 options, first I like to rinse the chloride mud though a fine polypropylene screen to separate the bulk of the chlorides from the diamonds and undissolved, silver chloride encrusted metal. The 2 options come in when handling the diamond and silver chloride encrusted pieces. One option is to use ammonium hydroxide to convert the silver chloride to silver nitrate and the other option is to use sodium thiosulfate to do the same. Each route has pro's and con's which we can discuss further if you would like.

 

[goldenchild]

Can anyone think of a way to feasibly grind down jewelry into a fine dust? In a finely divided state 100% digestion is possible even with alloys high in silver content. I've dabbled with this idea before but came upon it again recently.

Making my own custom jewelry (video coming soon) I filed about 3 grams of high silver content 10k gold. 33% to be exact. I know this because I made the alloy. I placed the powder into a small beaker and the powder was completely digested with AR leaving behind a nice gray spongy powder (some silver going into solution). I believe atomizing is done to come up with basically the same results.

Maybe grinding or some other mechanical process could come into play when trying to recover diamonds in small quantity. In large quantity however chemical processing is a must as pointed out to me by one of our large scale processing members. I would also say that a boil in diluted nitric on karated jewelry could help no matter how small the digestion. Some diamonds are set very loosely and even the small amount of surface digestion could aid in diamond removal.

 

[4metals]

For 10 karat goods a boil in 50% nitric is often all that is required to loosen the stones. But then you have to separate the stones from the undissolved metal. In this case aqua regia cleans it up pretty well.

Another option for silver up to about 12% is tumbling action while digesting the acid in aqua regia. The benefit here is from mechanical agitation but it will tolerate higher silver content than just sitting in heated aqua regia.

 

[goldsilverpro]

Therefore, eliminating almost completely the possibility for AgCl to re-dissolve.

I don't think I can buy that, Sam. I think you'll find that silver chloride is about as soluble in concentrated HCl as it is in aqua regia. Also, it is impossible to end up with zero free nitric in the solution using that process of adding increments of nitric to an excess of hot concentrated HCl - there's always some AR there. Half of all of that nitric you added is still in there, in the form of nitrates, in a soup of mainly H+, Cl-, NO3-, and metal ions.

At any temperature, the AgCl will be saturated, at equilibrium, in the concentrated HCl/AR. The higher the temperature, the more AgCl dissolves, and visa versa. At room temperature, the concentration of saturated AgCl in the conc HCl can be considerable and any amount of dilution from such as rinsing can cause small amounts of AgCl to precipitate.

I know quite a lot about this separate acid business because I've been doing it that way for 30 years and I introduced it to this forum. When I got here, everyone pre-mixed their AR. Lazersteve was the first to try my separate acid method and he liked it. For about a year, he was about the only one. Now, everyone does it. It's the only way to fly.

 

[samuel-a]

I don't think I can buy that, Sam. I think you'll find that silver chloride is about as soluble in concentrated HCl as it is in aqua regia. Also, it is impossible to end up with zero free nitric in the solution using that process of adding increments of nitric to an excess of hot concentrated HCl - there's always some AR there. Half of all of that nitric you added is still in there, in the form of nitrates, in a soup of mainly H+, Cl-, NO3-, and metal ions.

At any temperature, the AgCl will be saturated, at equilibrium, in the concentrated HCl/AR. The higher the temperature, the more AgCl dissolves, and visa versa. At room temperature, the concentration of saturated AgCl in the conc HCl can be considerable and any amount of dilution from such as rinsing can cause small amounts of AgCl to precipitate.

I know quite a lot about this separate acid business because I've been doing it that way for 30 years and I introduced it to this forum. When I got here, everyone pre-mixed their AR. Lazersteve was the first to try my separate acid method and he liked it. For about a year, he was about the only one. Now, everyone does it. It's the only way to fly.

I don't know Chris... I don't think it's possible (without the proper machinery) to determine what will be the exact solubility of AgCl in a given AR and its products... What i do know is, we're talking trace amounts of AgCl in either cases... Thats why the ammonia and re-refining.

End result should be the same, isn't it?

No matter how you slice it there will remain a significant quantity of undissolved silver chloride. If your doing stone removal in test tubes it is quite easy to pick out the diamonds and leave the chlorides behind. The same does not apply when you are doing stone removal on hundreds of ounces of scrap at a time, you end up with a mud which is not easy to separate the diamonds from the chlorides and undissolved metal.

To remedy this there are 2 options, first I like to rinse the chloride mud though a fine polypropylene screen to separate the bulk of the chlorides from the diamonds and undissolved, silver chloride encrusted metal. The 2 options come in when handling the diamond and silver chloride encrusted pieces. One option is to use ammonium hydroxide to convert the silver chloride to silver nitrate and the other option is to use sodium thiosulfate to do the same. Each route has pro's and con's which we can discuss further if you would like.

I think i haven't made myself clear before, but i meant same as you. Anyway, i understand what you are saing about the later seperation of the encrusted metal + AgCl + stones and make sure to add it to the video. Though, will not be designated for a large refiner with hundreds of ounces to process at a time... someone like that don't need my humble advices.

 

[nickvc]

I have used the hot nitric boil first on all my stone set pieces for a while and even if it doesn't actually do the whole job I believe it gives the AR a better chance to penetrate further before the chloride build up stops the reaction, enough for the majority of the stones to be released after one AR treatment. The other advantage here in the UK is that the 9 k white is usually of high silver content that stops reacting in seconds in AR.
In truth I really don't think there is a one stop process for stone removal as the different alloys all react in various ways, some dissolve completely while others sit there stubbornly tittering at all attempts to dissolve them :evil:

 

[goldsilverpro]

Sam,

I downloaded a 1921 book on solubilities from Google books. At 25C, it said that about 3 grams per liter of AgCl are soluble in 34% (about 11M) HCl. For 5.5M HCl (about a 50/50 solution), the solubility is about .6g/l. As the strength of the HCl decreases, the solubility of AgCl decreases geometrically. When saturated (at any strength HCl), any rinsing will precipitate AgCl. However, the higher the strength of the HCl before dilution (rinsing), the greater the amount of AgCl precipitation.

When you chilled the strong HCl with ice, much of the AgCl that was dissolved precipitated. Then, when allowed to come back to room temperature overnight, the AgCl will tend to re-dissolve to the point of saturation. You will end up with about the same amount dissolved that you had before adding the ice. In other words, the way you are doing this, the ice is a totally wasted step.

If you want to eliminate as much AgCl as possible before dropping the gold (highly recommended, as far as I'm concerned), you will have to either filter while the solution is very cold or dilute 3 times with water and then filter. Maybe, then, you wouldn't have to double refine. The 3:1 dilution will theoretically precipitate at least 90% of the total AgCl dissolved in 34% HCl.

Since Ag is most always the prime contaminant in refined karat gold, even after using ammonia, I wonder how efficient the ammonia treatment is, especially when a large amount of AgCl is present in the gold powder? If you got rid of most of the AgCl first, the rinsing of the gold would precipitate only trace amounts.

Another thought. I've always wondered if, when dropping the gold, the sulfite (or, through some other mechanism) will precipitate small amounts of the dissolved AgCl in the HCl as Ag metal. If so, the ammonia wouldn't touch it. When I had my last refinery, I routinely leached the gold powder with nitric acid and found that I got better gold. I know that is considered heresy on the forum but, before doing so, I made sure all the chlorides were rinsed out with distilled water, by testing the rinse water with silver nitrate. If the nitric did improve the purity of the gold, it would be likely that it was dissolving metallic contaminants and maybe silver was one of these. Here again, if all this is true, it would be much better to eliminate the AgCl before dropping the gold.

Chris

 

[goldenchild]

Another thought. I've always wondered if, when dropping the gold, the sulfite (or, through some other mechanism) will precipitate small amounts of the dissolved AgCl in the HCl as Ag metal. If so, the ammonia wouldn't touch it. When I had my last refinery, I routinely leached the gold powder with nitric acid and found that I got better gold. I know that is considered heresy on the forum but, before doing so, I made sure all the chlorides were rinsed out with distilled water, by testing the rinse water with silver nitrate. If the nitric did improve the purity of the gold, it would be likely that it was dissolving metallic contaminants and maybe silver was one of these. Here again, if all this is true, it would be much better to eliminate the AgCl before dropping the gold.

Chris

I still think incinerating your dropped gold is a good idea to get rid of trace amounts of AgCl. In fact I think that will get rid of most of it if not all. You could then give it a nitric bath to get rid of any elemental silver. And finally you could do a second digestion of the gold (if necessary).

 

[4metals]

Why do you think incinerating will get rid of silver chloride?

Incineration temperatures are usually under 1000 F and that is not hot enough to drive off the chlorine but it is hot enough to melt the silver chloride. ( at about 850 F) Still you are not removing it.

The key to keeping the purity high is limiting the solubility of the chloride and filtering it out. Other steps are just band aids, you're not addressing the problem which is the presence of the silver in the solution.

 

[samuel-a]

I think you made me a believer, Chris.

Though there are some points that i feel the need to light:
Even if the solubility of AgCl drops by a big factor due to dilution or chilling, some does left behind as you said... therfore i still think a second refining is in order, both in terms of silver and maybe Cu+PGM's.

I remember that the ammonia washes did drop AgCl when HCl added on first refining, after seperated from the gold powder, so i guess the ammonia did dissolved something... I'm almost sure we are missing something here.
On the secund refining, there was no visible precipitation (if at all).

I've read somewhere that AgCl solubility in water is .89 ppm at room temp', where, when a cloride salt is added to produce 0.01 molar concentration of Cl^- ions, the solubility drops to near zero... from that concentration and above the solubility is rasing again...

I guess now we need to guess the impact on solubility derived from the different concentrations of the different ions constitutes the solution, such as water, free HCl, Au⁺, NOx^- etc'...

I guess this whole AgCl issue flew by without me noticing it. i know better now. And will update the video and article.

 

[goldsilverpro]

Another thought. I've always wondered if, when dropping the gold, the sulfite (or, through some other mechanism) will precipitate small amounts of the dissolved AgCl in the HCl as Ag metal. If so, the ammonia wouldn't touch it. When I had my last refinery, I routinely leached the gold powder with nitric acid and found that I got better gold. I know that is considered heresy on the forum but, before doing so, I made sure all the chlorides were rinsed out with distilled water, by testing the rinse water with silver nitrate. If the nitric did improve the purity of the gold, it would be likely that it was dissolving metallic contaminants and maybe silver was one of these. Here again, if all this is true, it would be much better to eliminate the AgCl before dropping the gold.

Chris

I still think incinerating your dropped gold is a good idea to get rid of trace amounts of AgCl. In fact I think that will get rid of most of it if not all. You could then give it a nitric bath to get rid of any elemental silver. And finally you could do a second digestion of the gold (if necessary).

I'm not well versed on the subject of the thermal decomposition and thermal volitalization of chemical compounds, but I spent an hour or two reading up on it and this is what I came up with. If my reasoning is faulty, please correct me.

Silver chloride melts at 451C (850F) and boils at 1550C (2822F). Several references said that AgCl started decomposing at 265C (509F). Decomposition entails the separation of Ag from the Cl. The Cl comes off as a gas and the metallic Ag stays with the gold powder. The higher the temperature, the greater the rate of decomposition. The metallic Ag produced could then be removed only by leaching (e.g., with nitric).

It is also possible to volitalize AgCl. This would be most evident at, or above, the boiling point, where the vapor pressure becomes equal or greater than the atmospheric pressure. Of course, the boiling point of AgCl is about 900 deg. F above the melting point of gold.

However, since the decomposition starts at a much lower temperature, I would think it would be mostly all decomposed to Ag metal before any substantial volitalization of AgCl took place. I might mention that the boiling point of silver is 2212C (4014F). Therefore, the removal of silver chloride from the gold powder, by incineration, won't work. You will end up with Ag metal in the gold, which can only be chemically removed.

 

[goldenchild]

...get rid of trace amounts of AgCl... You could then give it a nitric bath to get rid of any elemental silver. And finally you could do a second digestion of the gold (if necessary).

 

[goldsilverpro]

Something else I hadn't thought of. When Harold leaches the gold powder with hot HCl, he is very possibly dissolving the AgCl. Of course, the HCl couldn't be diluted or some of the AgCl would re-precipitate. Maybe best to add HCl, heat, leach, pour off, and repeat twice more. That way, the final HCl leach would have very little AgCl in it and rinsing would cause no AgCl to precipitate.