# Best method for used crucibles PM recovery?



## autumnwillow (May 29, 2016)

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.


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## nickvc (May 29, 2016)

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.


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## 4metals (May 29, 2016)

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!


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## autumnwillow (May 31, 2016)

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.


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## nickvc (May 31, 2016)

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.


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## autumnwillow (Jun 1, 2016)

Clay crucible sorry.


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## nickvc (Jun 1, 2016)

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.


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## Deano (Jun 19, 2016)

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


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## patnor1011 (Jun 19, 2016)

Here. About 5 euro worth of hi tech equipment.


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## patnor1011 (Jun 19, 2016)

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


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## autumnwillow (Oct 10, 2016)

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?


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## nickvc (Oct 10, 2016)

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.


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## autumnwillow (Oct 10, 2016)

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.


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## nickvc (Oct 10, 2016)

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.


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## Deano (Oct 10, 2016)

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


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## autumnwillow (Oct 10, 2016)

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.


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## Deano (Oct 11, 2016)

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

For tabling you want the least deformation possible.

Deano


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## nickvc (Oct 12, 2016)

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.


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## Deano (Oct 12, 2016)

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


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## autumnwillow (Oct 12, 2016)

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?


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## nickvc (Oct 13, 2016)

Deano my thoughts were towards cheapness and the fact this will not be an ongoing process once done the job is finished until the OP collects enough crucibles to make it worthwhile to run again so I was trying to find cheap and easy ways for him to process his material without spending large amounts of money.

If you are going to mill and separate the concentrates down to metallic prills then it makes more sense to use acids, it's quicker and more efficient as it will dissolve everything regardless of size which cyanide will struggle to do.


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## kurtak (Oct 13, 2016)

nickvc said:


> 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.



Nick 

I am not sure how well that would work for crucibles milled to a fine powder (as milled crucible powder would be heavier then prolized/incinerated IC chip ash/carbon) but it works very well for IC chip ash/carbon

I have a 5 gallon bucket set up just for this purpose - its very simple to make (as shown in the pic) its just a matter of cutting a piece of the bucket lid out & putting it back on the bucket to create a lip on the bucket

The lip on the bucket allows you to make a faster & more complete pour off of the water as it holds back the heaver material 

using this bucket to "pre" concentrate my IC chip ash/carbon reduces the amount of material I then take to my concentrator table in about half - AND - cuts my total time concentrating in at "least" half if not more then half

Like I said - I am not sure how well this would work on "fine" milled crucible material - so I don't want to hi jack this thread with details - so will try to post a new detailed thread on the process in a couple days (as I am going to be busy with some smelting for the next couple days)

Kurt


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## nickvc (Oct 13, 2016)

Kurt I think that you would need a heavier flow than with ash but I have never followed this procedure so I'm just thinking out loud, if my thinking is wrong then I'm happy to have it pointed out, I know Deano is the expert with mining materials so if he says it's a no no then that's good enough for me, like you Kurt I was hoping to reduce the time needed on the table which needs watching whereas the set up I had in mind could be set up and left to its own devices to a large extent.


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## autumnwillow (Oct 13, 2016)

Of course with Deano's table in mind you wouldn't have to separate the ash. With a common sluice box that will really take up a lot of time.


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## kurtak (Oct 13, 2016)

autumnwillow

Correct - with the shaker table there is no need to do the bucket "pre concentrate" as it is so much more efficient then a sluice box/miller table (when it comes to IC chip ash/carbon)

What size is your shaker table ? --- one of these days I want to get the 2' X 4' table - just haven't "quite" been able to justify it yet  

Kurt


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## autumnwillow (Oct 13, 2016)

How I wish I already have one, can't even find a local supplier yet. I think I may need to import.

Edit to add: Come to think of it, why not build one? Only the grooves seem to be the hardest part of it. Not sure what they are made of, the rest is just a pump, 2 catch basins, a vibratory motor, etc.


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## Deano (Oct 13, 2016)

Yes I was referring to the Wilfley type table.

They are available quite cheaply from China but the tops have top be replaced before using, they are very crudely made.

Do not get one as shown in the photo with a bend in the top side half way along.

This form is almost impossible to run for a clean concentrate line, at the discharge end there is no room for either a dedicated concentrate discharge or a splitter, you need both.

The spray bars as fitted are good but a feed box needs to be fitted in the top right hand corner.

A water supply is fed into this feed box and the spray bar is correspondingly shortened.

This ensures that the feed is fully wetted before it is subjected to the table action.

Read my post on Oct 10 in this thread for why you do not want to leach the pulverised material.

The prills are resistant to strong oxidising leaches (aqua regia) as well as cyanide.

Deano


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## nickvc (Oct 14, 2016)

Autumnwillow am I correct in thinking that most of the crucibles are from jewellery manufacturing rather than refining and recovery, the reason I'm asking relates to Deanos worries about the prills and residues been resistant to leaching, in my mind if the values are basically carat alloys you should be able to leach or fully dissolve the resultant material with AR, dependant on whether you work with large amounts of silver a nitric digest first may pay dividends also whether you use the crucibles for only gold or silver, if this is the case then melting the residues with more silver or copper and cornflaking before leaching with nitric would be advisable.
If the material is all from recovery and refining them follow Deanos advice to the word.


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## autumnwillow (Oct 14, 2016)

nickvc said:


> Autumnwillow am I correct in thinking that most of the crucibles are from jewellery manufacturing rather than refining and recovery, the reason I'm asking relates to Deanos worries about the prills and residues been resistant to leaching, in my mind if the values are basically carat alloys you should be able to leach or fully dissolve the resultant material with AR, dependant on whether you work with large amounts of silver a nitric digest first may pay dividends also whether you use the crucibles for only gold or silver, if this is the case then melting the residues with more silver or copper and cornflaking before leaching with nitric would be advisable.
> If the material is all from recovery and refining them follow Deanos advice to the word.



A mixture of both actually.
I would use silver as a collector after recovery to smelt. Assay, inquart, nitric digest then AR.

You aren't referring to the whole crucible being digested in AR right? What you are referring to is the recovered material after milling and using a concentrator table?

With what Deano said, crucible prills/slag whether milled or not will not be properly leached in AR and/or cyanide due to contamination of base metals.
While most ores are usually high karat gold, they should work fine in a cyanide/AR leach.


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## nickvc (Oct 14, 2016)

In this case with mixed material I would follow Deanos suggestions, his knowledge on this sort of material is far greater than mine.


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