How to refine gold jewellery with stones

[erinda]

Hello,

I'm interested in the refining gold jewellery with stones. Normally i use the aqua regia method and after the gold dissolves i filtre the solution and i use Sodium metabisulfite to precipitate the gold. Actually during this process the stones goes all in the inner surface of the reactor and it is a little difficult for me to put them out of the reactor. Can anyone help me with a more efficient method?


Thank you in advance

 

[snoman701]

Get a pair of long dressing forceps.


Sent from my iPhone using Tapatalk

 

[erinda]

To remove the stones mechanically needs time and during this process the stones can be damaged. I'm thinking to make a half process of gold dissolve in aqua regia (outside of the reactor) just to free the stones from their socket and after the stones separating to continue the reaction normally in the reactor.
Is it possible to do, or it's just a crazy idea?

Thnx

 

[FrugalRefiner]

It might help to know the scale you're working on and to see a picture or two of your equipment and set up. Are you processing ounces at a time or kilograms? Is your reactor so large that it can not be conveniently lifted to pour out the stones?

Dave

 

[4metals]

The most difficult stones to remove are the tiny melee that are channel set and cast in place, the larger stones are not the problem. And since you are having issues with the stones clinging to the inside of the reactor, I assume you are also dealing with the tiny stones.

These tiny stones are all but impossible to remove profitably by hand. Even by a partial reaction followed by manual extraction will be tough on the small stones.

I suggest you clean your reactor. I assume it is a glass vessel? I had similar issues and made the situation much better by a good glass cleaning, followed by a degreasing with acetone or alcohol every time the reactor was used. I still had some stones clinging to the sides but it was much better.

And the stones that remained were picked off with a pair of long forceps as snoman suggested.

To clean the glass mix up some Nochromix
http://godax.com/wp-content/uploads/2015/04/MSDS_4-2015.pdf
This is a great product for cleaning glassware.

 

[erinda]

The capacity of the reactor is 2 Kg but I use no more then 1 kg.If it is necessary i'm going to use less quantities. My reactor is not made of glass it is a resistant plastic (may be PVC, sorry i'm not sure for this).
It's true that the most difficult part is with the tiny stones.
Can you suggest me sth for cleaning the plastic reactor in order to get out all the stones?

In fact i'm looking for all the possibilities because i'm not sure to realise a half process out of the reactor because of poison gas and i'm not sure if a can control the reaction to stop it in the moment i need.


Thanks a lot

 

[4metals]

I have never seen a reactor made of anything but glass except for a closed automated system for aqua regia refining of diamond containing material. This system was set up in New York City and had no problems with stones sticking. However the unit was brand new when I worked with it and the plastic was smooth, I suspect it may have the same issues when the plastic becomes scratched from use.

This is the system I mentioned above;


I always use glass vessels for stone removal. Glass doesn't scratch as easily but when it does get scratched and worn, cleaning may help, otherwise it is replaced or just used for karat refining where no stones are involved.

These are the vessels I use;

These particular vessels will hold 100 ounces, or just over 3 kg.

Can you post a photo of your reactor?

 

[erinda]

This is a photo of the reactor.
Actually this is created for refining only karat gold (without stones)but i'm looking for any possibility to adopt it even for refining with stones involved.
If anyone can help me with any suggestion or advice for me will be very useful.

thnx

 

[g_axelsson]

My suggestion is to use preview... there's no picture there.

Göran

 

[erinda]

http://goldrefiningforum.com/phpBB3/download/file.php?mode=view&id=35516

 

[4metals]

Your reactor is, as you said, a setup made for refining karat or doré gold. Generally high grade. I actually did set up one of these, albeit larger, which was intended for karat and stone removal. This is that plant.

The refining capacity is 20kg per reaction. The digestion went well but the problems we had were when emptying the reactor through the valve. The stones clogged in the draining process which resulted in having to remove the access port, which like in yours is directly opposite the drain valve. Then a long rod was used to clear the drain path and all of the stones were hosed out.

One problem they had was the stones got caught in the ball of the valve and wore the seat until it no longer functioned to shut off the flow. Eventually they stopped using the machine for stones and did them in a 22 liter vessel like the one I showed you. The filtering system we set up for the stones was still used and the gold was processed in the equipment used by the machine after the digestion. To separate the stones from the silver chloride, we built a simple screen like this;


The screen is a polypropylene paint screen with a 100 mesh screening placed in a cut off bucket that supported the screen and allowed the solution to flow through the screen and be filtered in the manufacturer supplied filter. If you need more details and pictures of the screen I can post them.

As far as your continued use of this equipment for stone removal, I think you could position the vessel so the access port is above the center and the drain valve is not at the bottom in a position where the liquid is below the access port. Then remove the access port cover and siphon the liquid out of the chamber, rinse with water and siphon that as well, the rinse water should be aimed at the drain valve so any stones in the valve can be rinsed free. Now you can open the valve without fear of ruining the ball valve and rotate it into position so it is down and can act as a drain. Then you can wash out the stones through the screen I showed you above by adding water through the access port.

The benefit of this machine is the tumbling action does continually break off any encrusting silver chloride so there are relatively few encrusted chunks of gold when the process is complete.

 

[Topher_osAUrus]

8)

I swear, I will never grow tired of your show and tell time, 4metals.

I have seen you mention a couple times that you use sodium thiosulfate sometimes after stone removal with ar. Also where you mentioned using the cast iron pan and dilute sulfuric for AgCl from stone removal.

I assume that the chloride crust that remains on the karat gold itself after removal is treated with the former, and the loose stuff caught in a filter for the latter.?

For recovery from thiosulfate, is steel wool or electrolysis a better route?

I also recall the hypo solution will dissolve some gold as well? Is the extent substantial, or trace? And can its recovery be limited by either of the two methods for silver reclamation from the thiosulfate?

 

[4metals]

The tumbler method of digesting karat gold has a wonderful advantage of breaking off any silver chloride into nice small pieces leaving nothing but stones and any platinum findings. The silver chloride falls through the screen (or occasionally needs to be rinsed through) and that silver chloride can be recovered by whatever method you prefer.

The silver that encrusts karat gold without the benefit of tumbling is similarly poured through a screen to separate any silver chloride that is small enough to pass the screen and all of the chunks are tumbled in thiosulfate, resulting in nice yellow gold and loose stones, and an occasional stone still set in the remaining gold. The thiosulfate liquid can be recovered by passing through a steel wool column or some refiners, usually the ones who ship prepared sweeps, evaporate the thio liquid to crust and crush and sift it to ship co-mingled with their other powders.

The thiosulfate will dissolve some gold but it is recovered with the steel wool or from the powdered sweeps. It is negligible but it would be a lie to say it doesn't exist.

 

[erinda]

Thank you 4metals , i appreciate very much your help!!


So if I'm right you suggest :

to digest the gold (with stones) in AR in a glass vessel and after the complete digestion i can transfer the liquid in the gold precipitation tank, , and let in the glass vessel the undissolved alloy( any pieces), the silver (in complex salts form) and the stones.

After separation of the gold i have to add in the vessel NH4OH to dissolve the Ag and after Ag transfer from the glass vessel to another tank in the vessel stay only the undissolved alloy and the stones, which after the washing with water can go out very simply.

Can you please post some other photos especially glass vessel and how do you realize the connection between the vessel and the collector tank (in which precipitate the elementary gold / silver)

thnx

 

[4metals]

Ideally we are looking to integrate any process steps you add to refine jewelry with stones so you can utilize the most of your existing system. Specifically filtration and precipitation of the gold.

From the photo you attached of your system I see that the filtration system is not in place. Can you post a photo of the filter that slides under the tumbler?

Most systems, including the system in New York City I posted the photo of above, have what is usually called a filter trolley because it rolls around on wheels and easily slips into place.

This is a filter trolley standing alone.

The way the filters I am familiar with work is the double diaphragm pump creates suction under the filter paper to pull the liquid through and it pumps the liquid to the next step in the process. They are nice because they minimize pouring and handling of acids. They come in all sizes although for a system capable of refining 2 kilograms, I have never personally seen one sized for an acid usage of 10 or less liters, which is why I ask for a photo.

If you do digest the diamond containing gold in a glass vessel, you will need a hood to accommodate the vessel and the mantle to heat it. Do you have a separate lab hood to do the digestion in? I use spherical vessels which have capacities of 5 liters, 12, liters and 22 liters. These are the small reactors which are small enough to be lifted and poured manually. The 5 liter flask will process 20 ounces of karat gold, the 12 liter 50 ounces, and the 22 liter 100 ounces. It was my thought that you could digest in a glass vessel and manually pour the digested material into your existing filter system and process from there with your existing equipment. So your question about the connection between the vessel and the collection tank is simple, there is no connection, the completed reaction is removed from the mantle after disconnecting the reactor head, (which connects to a scrubber), and manually poured into the filter. Smaller stone removal lots can be processed in 4 liter beakers which have a capacity of 1/2 kilo per vessel. They are exhausted into a manifold that is scrubbed with a simple vented cover.


The encrusted silver chloride can be dissolved with Ammonia NH₄OH but this must be done in a hood as the ammonia and hydrochloric produce dense white (ammonium chloride) fumes. Please note, do not leave the ammonia loaded with silver sitting around, it can form explosive compounds if it dries out. Always acidify the ammonium hydroxide liquid after you are done with it. Hydrochloric acid will precipitate silver chlorides which can be filtered and processed with any silver chlorides that came from the aqua regia process.

If you would please post any photo's you have of your filtration and precipitation (cementation) setup that is used with the tumbler system, we may be able to come up with a method to utilize as much of the existing equipment you have. So if we can look at what you are looking at it will be helpful.

 

[Palladium]

I made a top to fit my beakers for a scrubber designed system back on the farm. I used the top from a Hamilton juicer and the hose from a Bissel vacuum cleaner.

I know right! I didn't like having the lip on the lid because if you happen to be moving things around in the hood and bump the hose it has a tendency to knock the beaker around or worse yet knock it over! I wound up making a flat top that just rest on the top of the beaker and if you bump something it just slides right off.

 

[erinda]

I'm very grateful for all this precious information that you have given to me, thank you a lot

This is the collector tank (in which i precipitate the elementary gold )and the filter trolley .

I actually have a separate lab hood and i will try to integrate my existing system to adopt it for refining gold with stones.

Can you suggest me a better way to dissolve the silver chloride than NH4OH (actually it is not only silver chloride, isn't it?) and to separate it from the undissolved alloy.

Thnx

 

[Lou]

He suggested thiosulfate with electrowinning to get the silver chloride dissolved.

I HEARTILY recommend the use of that procedure, and the use of the plastic mesh for separating the oversize stones/undissolved from the rest. That is the way to go.


You can also do small stone removals in the sonicator--10K works in nitric acid 30%, 14-18K work in aqua regia (glass in this case). Some girdle wear can occur on diamonds but most small melee aren't worth much more than $40-70/carat anyway.



Using ammonium hydroxide on karat gold from stone removal is a recipe for fulminating gold and should be avoided at all costs.

 

[4metals]

Thank you for posting the photo's.

So I went to the Koras website and looked at their tumbler systems to get a better idea about your system. http://www.en.koras-pmr.com/Gold_Refining_Tumbler_TB_I20822.whtml

The system they feature on their tumbler page is the same size as the system I posted a photo of which processes 20Kg per batch. Funny thing is the manufacturer does the same thing the sales people at Italimpianti do, they take the refining capacity per digestion and multiply it by the number of digestions that can be done in 8 hours. The folks at Koras claim that the new shape of the tumbler makes the digestion rate faster so they feel confident you can digest 20 kg in about 2 2/3 hours. Got to love those marketing guys!

The system you are using is the smallest I have seen so forgive me but to work out the way it works I need to make assumptions. So I can assume and make a point and you can correct me if my assumptions are wrong.

I am assuming the 90º elbow on top of the filter trolley is to connect a flex line to for fume exhaust. I am also assuming that under that top perforated plate with the 90º elbow is another plate that you set the filter paper on. The top plate catches all of the big chunks that don't dissolve. The pump on the right side, hidden under the flange, provides a vacuum and also pumps the container dry by pumping all of the liquid, and rinse water to the precipitation tank. I also assume the same filter setup slides under the precipitation tank and is used to filter the spent acid after precipitation. Is this correct so far or am I blowing smoke?

From what I see and assume, you can just empty the aqua regia and stones from a glass beaker into the filter and process from filtration on out with your existing equipment. The filter has the capacity to suck the fumes away from the operator which is a nice feature. I guess you could get fancy and cut a hole in your hood bottom so the filter can slide into place under your hood and you can transfer the liquids from the glass reactor into the filter in the hood.

The precipitation tank is very nice, do you know the liquid capacity of the unit. In addition to using it to drop your gold you can use it to cement silver from nitric solutions and for the cementation and iron precipitation in waste treatment as well. But you will have to clean it well if you want to continue to produce high purity gold. This is a larger cementation tank but as you can see it performs the same way.



As far as an alternative to Ammonia, Lou mentioned the thiosulphate method which has no odor or fume and is much more benign.

 

[autumnwillow]

Interesting.

As long as you keep tumbling and break the silver chloride layer you can go direct aqua regia on karat gold.

I wonder if there's a special magnetic bar that can go with my magnetic stirrer that is able to do such?

Edit to add:

Just to share, we process mostly karat golds and we remove the stones prior to refining. It takes a little bit more time but its worth it as you save the value of the stones and avoid any sort of etching from chemicals and heat. A little bit of stone setting skills, a hammer, cutter, a few engraver's bit and engraving block will do.