Best method for used crucibles PM recovery?

[autumnwillow]

Let me state a few that I know.

1) From hoke's book, is to crush the crucibles until very fine, mixed with 3:1 ratio of flux to crucible weight, melted in a very large furnace, slags are poured off once in a while. Slags are checked for values before throwing.
-Costs too much fuel and time.

2) Panning. Crush the crucibles until very fine. Panned by miller table, pan bowl, or any other related panning which simply has the idea of PMs are heavier that most metals. Then the panned material is melted with flux.
-Silver is lost?
-Low alloyed gold is lost?

3) Cyanide leaching. Crucibles are crushed to fine powder then leached in a cyanide solution. Recovered thru various methods such as zinc cementation, carbon adsorption, electroplating, etc.
-GSP mentioned somewhere here in the forums that cyanide cannot dissolve low alloyed gold?

If you were to process such material what would you do? I believe these procedures are also applicable to most e-waste.

 

[nickvc]

I used to keep a silver bar to put into old crucibles which I then melted to recover any gold, I used the same bar many times, if it's a larger quantity of old crucibles I would have them crushed and milled and then use sieves to recover the tiny prills of values and then assay the remaining powders and if they showed reasonable values I stored along with old flux until I had a decent volume to sell on.
With very low grade materials it just doesn't pay to try and wet refine them by taking good samples you can make sure you get a decent return.

 

[4metals]

I agree with Nick. But in addition to the silver I would add a bit of thinning flux to etch into the side walls of the crucible and loosen any beads stuck in old hardened borax flux. I would pour the silver into a cone mold and use the same bar repeatedly to clean up crucibles.

When you think you have collected a worthwhile quantity, part the silver to recover any gold and cement the rest of the values to re-use doing the same "crucible wash" in the future.

I did this for years between melts of different customers. No sense giving the second customer the gold the first customer left behind!

 

[autumnwillow]

I think you guys are missing the tiny prills that goes inside the crucible, I'm talking about sand crucibles though as I usually use sand crucibles when my flux contains soda ash. I only use the fused silica crucible when there is no soda ash in the flux.

Say I decide to clean all my current crucibles using a flux and a collector metal wouldn't it consume too much time and fuel compared to other processes?

When I were not into refining, I had a refiner who processes such lots. For one 55 gallon drum I recovered about 1 troy oz of gold. They crushed the crucibles to fine powders and panned them in water. Paid about $300 for the job and it took one day to finish it.

I do believe that processing it in a cyanide leach would yield much better results. Similar to how ores are being processed. I'll give this a try on a small scale when budget and time permits.

 

[nickvc]

I still think that crushing milling and maybe use of a shaker table or similar from the mining world would work better and safer, you can build a simple version yourself, I think Patnor built one check his posts, it should work well with this material as the sand should wash away while the prills are caught in the riffles.
I'm not sure what you mean by sand crucibles, post a picture it might give us better ideas.

 

[autumnwillow]

Clay crucible sorry.

 

[nickvc]

I thought that was what you meant.
The best process is what I advised above, I think Patnors design was in one of his threads about running incinerated chips.
The nice thing is you just set it up and add a bit more powder to it when you have the time and run it until you have done it all.
Trying to use Kcn I fear will cause problems as the material may well absorb some of the solution which will be nearly impossible to filter out, I think you would be lucky to recover 70 percent of the values, perhaps 4metals may know better.

 

[Deano]

Gold losses into slag are always associated with the presence of base metals in the gold.

This is usually caused by smelting gold which has been precipitated from dirty solutions without taking precautions to eliminate the base metals from the drop.

Base metals may be eliminated by carrying out a multi stage digest and precipitate routine or by ensuring that the pH of the solution is between 1 and 2 when the drop is performed.

I usually adjust the pH to 1.5 with tech grade urea before precipitation.

The size of any gold beads in the slag is related to the type and level of base metal present.

It is also related to the crucible type in that graphite crucibles will slag much higher levels of gold from the same precipitates than will clay crucibles.

The beads which give the greatest problems in recovery are the ones with lead complexes on them, they tend to be ultrafine and resistant to leaching.

Unless you have been very casual about the purity of the precipitation, the beads in the slag are generally not worth the cost of a dedicated re-smelt or milling and leaching.

The most viable method of recovery is to fine hammer mill the slag and then table very slowly using minimal wash water.

The cons from this are dried and then slowly added into a pre melted layer of straight borax in a clay crucible.

The clay crucible is likely to be attacked enough by the borax that it will rupture, it is sensible to put the operational crucible inside a larger clay crucible as a retention measure.

Deano

 

[patnor1011]

Here. About 5 euro worth of hi tech equipment.

 

[patnor1011]

If you wonder about grinding I got this one even cheaper, I paid for just that screw-able cup at the end.

 

[autumnwillow]

I am still confused on which path to take, a miller table or a cyanide leach (after hammer milling).

A miller table is not used in large scale mining because of its low recovery rate?

A cyanide leach will probably take weeks to dissolve large prills of gold?

Or maybe the miller table path should work if I re-process the material three times?

 

[nickvc]

You can try up using silver or copper as I said before to leach most of the values out, what's left simply crush and sieve if you can't make a sluice or can't be bothere, this works fine on reasonably small quantities, 1-3 kilos, a bit messy but it will recover the prills, much easier than trying to dissolve them from all that powder.

 

[autumnwillow]

I have two 55 gallon drums of it. Now that would really take a lot of time. Also, some of the clay crucibles are already broken apart.

 

[nickvc]

With that quantity you would do well to crush and use water to float off as much of the light material away as possible, gravity will sort it you just need to give it a helping hand as in crushing the material as fine as possible to make the separation as easy as possible. It will take some time but you need to create a concentrate before trying to dissolve anything.

 

[Deano]

Let me put it all simply.

The prills are present in the slag because they are contaminated with base metals and so are resistant to coalescing (joining together).

This contamination also makes the prills resistant to leach solutions.

Resistant is not the same as totally unaffected, a percentage of the gold and other metals will always be leached, just usually not a high percentage.

The commercial approach to this problem is usually to do a leach and dump the residue as being resistant to leaching and having a value not worth further efforts.

Keep in mind that any assays on this material will always be low no matter what type of assay is used.

The best approach is fine milling followed by slimes tabling.

Yes this is slow and the slowness is why the commercial operators don't do it.

The concentrate from this processing can be treated by very slowly pouring the dried cons into molten borax in a clay crucible inside a catch graphite crucible.

Extensive testwork may show a chemical route to processing the table cons using various chelates such as acetate, citrate, EDTA etc. to clean them up before leaching for precious metals.

Factors involved will not only be the chelate but also time, temp, pH. Generally can only be done in glass or plastic containers.

Deano

 

[autumnwillow]

Would a ball mill outperform a hammer mill (pulverizer)? Or vice versa?

I think it is best to go for the table milling route.

Thank you Deano and nickv.

 

[Deano]

Single pass hammer mill will cause less deformation of the metal particles than ball milling.

For tabling you want the least deformation possible.

Deano

 

[nickvc]

Deano just a thought would adding soap to the water and simply keep a running stream going into one container and onto another one remove a lot of the light valueless material before trying to do a better separation with the table, I'm thinking the less junk to start the easier to recover the values, I'm thinking the water would need to disturb the material, make the water cloudy and then be poured into another container and so on.
This is not my area of expertise as you well know just trying to think of ways to make life easier cheaply.

 

[Deano]

Why you would want to try and get a separation off the table which will in no way be as good as using a table I have no idea.

The table will give you a mechanical repeatable separation which you cannot get by manual means.

Usually the feed is introduced to the table by a mechanical feeder to maintain a constant bed on the table.

If it is a choice between mechanical efficiency or a quick rough pre-sort, always go the mechanical route.

Deano

 

[autumnwillow]

Deano,

If most low grade ores are processed in a cyanide leach why cant crucibles be processed the same way as they are both mostly considered as low grade PMs?