separating gold "dust" from firing flux

[jmelson]

I have crunched up the blobs of flux after firing some precipitated gold in the crucible, and picked out the larger beads of gold with tweezers. Is there any way to "sluice out" the gold from the flux, or should I pan it as best as I can and then put it back in the crucible and fire it again? I have used strong acid to dissolve as much of the flux as will burn up that way, but what is left is basically glass and crumbs from the crucible. I can see a fair bit of gold in there, but it is very sub-mm specks.

Thanks for any ideas!

 

[Noxx]

Wich kind of flux it is ?

 

[Noxx]

Hello Jon,
Try separating your powder in small groups... Wich kind of crucible are you using ? I think you have this problem because your torch isn't able to get the powder reach the melting point of gold (+1000°Celcius). Try melting it in smaller amounts. Also, just try using borax as flux for begginning if you think your gold is pure anough (if you got a bright brown powder when precipitation occured).
Wood Charcoal is a good for a one use crucible... it holds and reflects temperature very easily. Especially if you are using an hotter gas than propane.

 

[lazersteve]

Jon,
Noxx is right, lots of heat is required. Practice using the torch in a circular motion when melting, starting from the top lip of the cupel (small 1-2" shallow bowl) and working your way inward to the middle. The gold BB's will appear green thru the torch goggles as you chase them together with the torch. If you are not using small cupels you should obtain some to help focus the heat into a smaller area. A larger crucible (the size of a small styrofoam cup) absorbs a lot of heat and hinders the golds melting. I find that by working the BB's into the center of the cupel they sink to the bottom and merge into a button. At this point I can pour off some of the excess flux using a set of metal tongs while the cupel is still hot. Then I grab the button out with a set of dental tweezers before the flux turns to glass. I put the hot button into a fresh cupel and remelt to purge the last bit of flux into the cupel and to pour the gold into a rod mold.

Steve

 

[jmelson]

Hello Jon,
Try separating your powder in small groups... Wich kind of crucible are you using ? I think you have this problem because your torch isn't able to get the powder reach the melting point of gold (+1000°Celcius). Try melting it in smaller amounts. Also, just try using borax as flux for begginning if you think your gold is pure anough (if you got a bright brown powder when precipitation occured).
Wood Charcoal is a good for a one use crucible... it holds and reflects temperature very easily. Especially if you are using an hotter gas than propane.

Oh, it melts, all right! it gets white hot, and I have to use dark goggles or the light is blinding. I bought 10 little clay crucibles. I am using Oxy-Propylene, it gets as hot as acetylene, and transfers even more heat.

The problem with straight borax (or this "Anti-Borax" stuff I have) is that it is
so thick even when orange hot that I can't pour it out of the crucible. So, using a fire assay flux recipe I found on another site, I use a mixture of borax and washing soda, which pours much more easily. Sometimes I get one beautiful button, and no stray gold. Other times I get lots of tiny round beads that were not there before, so the gold IS melting, it just isn't coalescing into one button.

Jon

 

[jmelson]

Jon,
Noxx is right, lots of heat is required. Practice using the torch in a circular motion when melting, starting from the top lip of the cupel (small 1-2" shallow bowl) and working your way inward to the middle. The gold BB's will appear green thru the torch goggles as you chase them together with the torch. If you are not using small cupels you should obtain some to help focus the heat into a smaller area. A larger crucible (the size of a small styrofoam cup) absorbs a lot of heat and hinders the golds melting. I find that by working the BB's into the center of the cupel they sink to the bottom and merge into a button. At this point I can pour off some of the excess flux using a set of metal tongs while the cupel is still hot. Then I grab the button out with a set of dental tweezers before the flux turns to glass. I put the hot button into a fresh cupel and remelt to purge the last bit of flux into the cupel and to pour the gold into a rod mold.

Steve

I'm using these TINY clay crucibles. They are actually smaller than a cupel, but deeper. If you know what a 10 ml beaker looks like, the inside dimensions of these crucibles are about that size. I use a pair of pliers to
tilt and turn the crucible, and eventually pour it out. When I get the flux thin enough to move, I can usually pour the flux and gold out onto an aluminum plate. The gold and flux won't stick to it. I then crush the flux with the pliers to see if there are any glod beads inside. Sometimes there's a big one, other times I can't even see the gold dust. But, when I put the crunched flux in a vial and add a little acid and let it sit a while, the gold dust sinks to the bottom, and most of the flux dissolves.

I have some cupels here, I might have to try your two-step technique.

Jon

 

[Harold_V]

You guys are chasing your tails. This subject is a no-brainer.

Assuming you can get a reasonably clean melt, the entire mess, flux and all, should be poured into a small cone mold. Assayers used them routinely. If the flux has done its job, the gold will be one nice button in the bottom with the flux cover on top. You tip it over and the button drops out easily, and is then quickly cleaned of flux. Stubborn flux can be removed by boiling in sulfuric acid and water. If, by chance, the gold hasn't agglomerated totally, it's because your flux is too contaminated, or you didn't get the entire lot hot enough. Dark flux is an indicator of very dirty metal being melted. Pure gold won't discolor the flux aside from colloidal gold turning it purple.

There are some things you need to understand about fluxes before you get involved with some of these mixes. First off, soda ash is a reducer, so almost any oxidized element that is included with your gold will be reduced and included in the final product. Borax works the opposite, and absorbs oxides. When borax comes out thick and dark, it's because you are working with very dirty material---lots of crud for it to absorb. The addition of fluorspar will thin the flux, but it is very aggressive and destroys dishes, crucibles and furnace lining quickly. Don't breath the fumes if you use it.

I rose bud is very desirable for dish melting. If you're serious about refining, consider buying one. Jewelry supply houses sell a very nice one.

Rather than make additional posts, there's one more thing you all need to come to terms with. That's the purity of your metals.

The systems you are talking about are recovery systems, they are NOT purification systems. The cast bars, for example, have a terrible color. There is no doubt they are far from pure------and should have been refined before melting the extracted values. It's far easier and faster to dissolve the gold while it's finely separated-----and until you do so, your gold won't be marketable as pure. While it can be accomplished in an electrolytic cell, the aqua regia method works very well, and should be assimilated into your operations. You'll come to terms with it, just as I did when starting out. I had hoped to short circuit the entire operation, but soon came to realize that I wasn't getting pure gold.

Harold

 

[lazersteve]

Rather than make additional posts, there's one more thing you all need to come to terms with. That's the purity of your metals.

The systems you are talking about are recovery systems, they are NOT purification systems. The cast bars, for example, have a terrible color. There is no doubt they are far from pure------and should have been refined before melting the extracted values. It's far easier and faster to dissolve the gold while it's finely separated-----and until you do so, your gold won't be marketable as pure.

The 50 grams of gold in the rods was recovered from fingers about nine months ago and sold to a precious metals refinery for 98% of spot price at the time. The precious metals dealer contacted me with the results of a fire assay and stated the gold in the rods was greater than 99% pure. The color in the photo is not the way they looked in real life, they are actually very yellow. The photo makes them appear reddish. I've sold several ounces of gold to various buyers and all have been very pleased. I realize they are not 100% gold, but I'm very pleased with the fruits of my labor considering I'm only doing this for fun as a hobby. The main reason I recover gold is so that I'll have a retirement fund when I'm ready to quit working.

I've read about assayers using conical molds with gold using lead or litharge as the flux in the same fashion described by Harold.

On the subject of Aqua Regia, I started out using it and really don't want anything to do with all the hazards. The chemicals and methods I use now can be handled safely indoors and produce results that please me. Harold you are right, I may end up coming around full circle and start using AR as a final purification step to attain the fully refined gold you speak of.

Thanks for all the good advice,

Steve

 

[Noxx]

Wich method are you using steve ?
Renverse electroplating ?

 

[lazersteve]

For fingers I use an acid peroxide mix. For larger connectors and pins I use reverse electroplating.

 

[Noxx]

I never heard acid peroxide mix... It is made of what ?

 

[lazersteve]

It's a method I developed myself to get past the hazards of AR while still getting maximum yields with mimimal effort. I worked up the ratios by trial and error. After working out the details, I fine tuned the process buy researching college web sites. I've put together a pdf file of etchants from several of these sites. Email me and I'll send it to you. The acid is standard muratic acid (HCL) and the peroxide is just the household variety (3%).

 

[Noxx]

PM sent.

 

[NaNO3]

jmelson

Sounds like you need to add a little silica sand or smashed glass and some more Borax

 

[Noxx]

What does silica sand adds ? Never eared about it.

 

[NaNO3]

.....

 

[Noxx]

Where can I get Silicia ? And can I substitute Sodium Nitrate with Potassium Nitrate ? I have 25 lbs of kno3 lol. :lol:

 

[jmelson]

If, by chance, the gold hasn't agglomerated totally, it's because your flux is too contaminated, or you didn't get the entire lot hot enough. Dark flux is an indicator of very dirty metal being melted. Pure gold won't discolor the flux aside from colloidal gold turning it purple.

There are some things you need to understand about fluxes before you get involved with some of these mixes. First off, soda ash is a reducer, so almost any oxidized element that is included with your gold will be reduced and included in the final product. Borax works the opposite, and absorbs oxides. When borax comes out thick and dark, it's because you are working with very dirty material---lots of crud for it to absorb.

Thanks again, Harold! This sure is true, because I haven't done things right.
But, the gold IS coming out pretty clean in the end. So, when it doesn't all melt into one button, it was because there was too much base metal in the mix?

I rose bud is very desirable for dish melting. If you're serious about refining, consider buying one. Jewelry supply houses sell a very nice one.

I have one, but have not tried using it on the gold.

Rather than make additional posts, there's one more thing you all need to come to terms with. That's the purity of your metals.

OK, I know you are right about this. I haven't figured out how to get HNO3
without having a visit by homeland security, but I will have to find out how.

I'm still trying to get the precipitation step to work properly. I'm going to run another batch this weekend, I hope.

Thanks,

 

[NaNO3]

...

 

[Noxx]

Where do I buy it ?