Separating precious metal powder from porous silica

[inspector071]

I have about a gallon or two of porous silica oil absorbent mixed with gold and perhaps platinum containing metal powder. I have some qualms about trying to just dissolve all of the metal using aqua regia, as it would require a very large volume to cover everything, and I'm worried that it might absorb into the silica, making removal even more difficult. The absorbent is contaminated with oil, so before I do anything else, I assume it would be wise to burn off the oil, leaving behind clean(er) silica and metal powder. I have considered using vibration to physically separate the metals from the porous silica, using the difference in densities, but a small scale test doesn't seem to do anything. I had placed a bottle of the stuff on a vibratory case tumbler used in reloading ammunition. Left overnight, no distinct layers were formed. My next thought is to try and pan the debris out using a gold pan. If that doesn't work, perhaps the best process will be to dissolve the metal in the minimum volume of aqua regia, filter, then do several rinses with HCl to try and remove as much gold containing AR from the silica as possible. Any thoughts?

 

[butcher]

I am not sure what material you are calling porous silica so my thoughts here may not apply.

Incineration would be a must,.

I think it would be hard separating by gravity, unless maybe the precious metal powder was finer than the silica or sands, and these could be somewhat separated by screening...

The silica I am assuming is sand, this may contain other metals depending on the source of sand or silica, so the leaching process may dissolve metal from the sand in a preleach, if so you could do a preleach that will not put precious metals into solution before leaching for the precious metal.

You are correct it make take more solution to wet powders and leach silica, and the sands can absorb some of the liquid (if the silica itself is actually porous these pore may hold liquid make what i am thinking here useless), although these can also be rinsed as the leach becomes water soluble, this could leave you with more solution for the amount of metal, but this solution can normally be concentrated later.

Maybe if you can give us a better idea of what this porous silica is and how it it mixed with oil, and what state you values are in and how all of this come to be combined someone here could give you a little better help.

In a way this almost sounds like a dirty catalytic converter, is that what you have? But that would not contain gold so that does not make sense.

Was this a solution spilled and cleaned up with some absorbent material?

Its hard answering questions when we cannot really tell what you have there.

 

[Gratilla]

Personally, I'd try cleaning out the oil with an organic solvent first - hexane, ethanol, etc.

Attempting incineration could leave you with a black carbonized gunk and more problems than you started with.

Just my opinion, FWIW.

 

[Westerngs]

I agree with Butcher. Incineration followed by smelting would be the way to go.

Incineration would indeed reduce everything to a mass of carbon, which would be easily smelted with flux.

 

[inspector071]

I talked to my friend who has the material, and he believes the absorbent is this stuff, which cellulose/kaolin based. Burning some of it reduces it's volume by more than half, so I think it's safe to say that is what it is. The oil that is contaminating it is hydrocarbon based vacuum pump oil and burns cleanly. Because it is not a porous silica like I had first assumed, perhaps aqua regia will be the best, followed by careful rinsing and filtering of the clay that is left behind. Because there will be a lot more clay than metal, should I use a different ratio than 4:1 aqua regia? Perhaps something as high as 8:1?

 

[butcher]

I agree with Westerngs, smelting may be the best way to go.

It looks like the absorbent clay does not have much free silica in it, you may want to add some glass or quartz sand with the flux.

kaolin Clay Al2Si2(OH)4 (looks like an aluminum silicate hydroxide powder clay). fiber material that should burn off fairly easy with the oils, and calcium carbonate (which would also act act a reducing agent).

Looks like the mix is a reducing (ore), maybe just a stock flux and some metal as a collector may do the trick.

I am just not sure how aluminum silicate would react with the other metals (or in the reducing environment), you may need an oxidizer to help slag it out, or possibly some fluorspar to help liquify it better which would also act on the crucible?

The other option incinerate (cook the heck out), of it to burn off oils, fibers, and carbonate (which would reduce acid quickly), and leach the remaining material.