# Question to the expert smelters



## alexxx (Aug 12, 2014)

Hello all,

I have a few tons of powder from incinerated circuit boards that was ball milled to 120 mesh. Most of the magnetic fractions were removed.
The non magnetic oversize was also separated.

PM / Cu content

Copper 28.1712 %
Silver 0.0842 %
Gold 0.0167%
Palladium 0.0155%

Fire assay made at Ledoux & Company.

The powder also contains C, Fe, Al, Ni, Zn, Sn, Pb, Ti, Be, Si, K, S, Na, and many other trace elements.

Sending the powder, as is, to a refiner is not an option.
Sending doré bars instead is way more interesting and profitable after checking all my costs.

I have my gas furnace and access to tons of copper to use as a collector metal.

Any idea of the perfect flux recipe to smelt properly this powder?
I would like to remove as much C, Fe, Al, Pb & Sn as possible.
Any tricks to prevent melt losses or losses of values?

I have very little knowledge of the use of fluxes, I mainly use my furnace to melt already refined metals.

Any insight, techniques or external resources on smelting would be greatly appreciated.

thanks in advance,

Alex


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## butcher (Aug 12, 2014)

alexxx, 
You make it a bit hard to help with your question.

Copper can oxidize in a melt, to make the Copper Dore bars for a copper refiner, you will want a reducing flux one with a carbon source so that the carbon can take the oxides from copper in the melt and to produce CO2 gas, which reduces the copper to metal in the melt.

To get many of the other base metals listed to oxidize, and to report into the slag glass as silicates, you would want to use an oxidizing flux, one that will give oxygen to many of the base metals listed, to oxidize them so they will make an metal oxide, or metal silicate slag glass.

You really cannot have a flux that will do both.

You could do a two step melt, one to oxidize the metals and collect many of them in the slag, (which would also reduce the copper content you have now in the material), and then re-melt the remaining metal, with more added copper in a reducing melt, but that would bring up the cost considerably.

You could also try and use a chemical process to remove some of the listed reactive base metals, cementing the copper and the values (along with a few of the uncreative metals and elements like carbon and silica...) and then take this cemented and washed copper powders and melt it with a reducing flux with more copper metal, one problem is working with the fine powders and ash from the crushed incinerated circuit boards, and all of this would also add to the cost, and problems with some possible lost values in the waste, and dealing with the waste...

You gave percentage of copper at about 28% with traces of values, but you did not give percentages of the remaining 60 something percent, beside the list of metals and elements, you did not give us the chemical state of these either, I would think several of these would be oxides, or compounds in your material, or even possibly salts of metals from the components involved in the circuit boards as these were burned an produced many of the gases the circuit board materials would release in the process you say they went through.
Having a better understanding of that other 60% may help in trying to make a decision.

Without knowing more of what you have now it is hard to say if you could just add a whole lot more copper in a reducing melt, to get the percentage of copper high enough in copper and the other metals low enough in percentage for the copper refiner, who may also penalize you for some of the metals you listed that may contaminate his electrolyte if he did by your copper bars.

In your list I see some metals, which can become dangerous as fine powders, and also as gases in an incineration or melting process and from the circuit boards.

In fact I hope you had the circuit boards burned properly (and professionally) to begin with, with proper after burners, multi cone ash separator, electrostatic fine ash precipitators, and toxic gas scrubbers, there are a trainload of toxic and very dangerous gases and particulate matter that comes from powdering and burning circuit board materials, which could make a toxic dump site of the area it is done in, if not done properly.

I do not see an easy solution here, what I do see is the dangers involved, I cannot see this being done at a profit on a small scale by anything but a very large company who are set up to do this work with many tons of circuit boards safely, and with all of the proper equipment and who have deep pockets, plus a few lawyers to keep them out of trouble.

I think the best bet at this point is to sell this ash to someone who can deal with it properly, cut your loses in the project, and forget trying to go any further with this dangerous idea, that is just my opinion, that may or may not be worth two cents.

I have studied just enough about this to know it is not something I would try, but not enough to know how to do it, but then again, I have no intentions of trying to do it.


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## Palladium (Aug 12, 2014)

Thank you for all you do to help others butcher. Someday god will reward you for your acts of kindness and generosity. You are a great moderator and teacher.


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## alexxx (Aug 12, 2014)

butcher said:


> alexxx,
> You make it a bit hard to help with your question.
> 
> Copper can oxidize in a melt, to make the Copper Dore bars for a copper refiner, you will want a reducing flux one with a carbon source so that the carbon can take the oxides from copper in the melt and to produce CO2 gas, which reduces the copper to metal in the melt.
> ...



Ok, that's a good start for me.
I don't mind loosing little copper in the melt... Well, always depends what "little" might be in terms of %... Any idea of what would be a fair % of lost copper in the process? 
2% ? 
5% ?
Do you believe that the carbon already mixed within the pulp can be enough ? What would be a decent % of C for a reducing flux like the one you mentioned ?

Regarding the oxidizing flux, which looks like the more interesting one for what I'm trying to achieve. I will search a bit more to find recipes.
Feel free to comment any interesting reading on the subject that you might have in mind. I would be really curious




butcher said:


> You could do a two step melt, one to oxidize the metals and collect many of them in the slag, (which would also reduce the copper content you have now in the material), and then re-melt the remaining metal, with more added copper in a reducing melt, but that would bring up the cost considerably.



Might be an option, just need to calculate if it's worth it at the end...



butcher said:


> You could also try and use a chemical process to remove some of the listed reactive base metals, cementing the copper and the values (along with a few of the uncreative metals and elements like carbon and silica...) and then take this cemented and washed copper powders and melt it with a reducing flux with more copper metal, one problem is working with the fine powders and ash from the crushed incinerated circuit boards, and all of this would also add to the cost, and problems with some possible lost values in the waste, and dealing with the waste...



I've tried this road before... takes too much time and generates way too much waste to deal with at the end.
I might try a selective leach of Sn, Pb & Ni, just after shredding. I'll have to try... But more reading is needed before trying that step



butcher said:


> You gave percentage of copper at about 28% with traces of values, but you did not give percentages of the remaining 60 something percent, beside the list of metals and elements, you did not give us the chemical state of these either, I would think several of these would be oxides, or compounds in your material, or even possibly salts of metals from the components involved in the circuit boards as these were burned an produced many of the gases the circuit board materials would release in the process you say they went through.
> Having a better understanding of that other 60% may help in trying to make a decision.



I'll have another sample assayed completely to know what % of other elements are exactly in there... It's expensive, but it looks like it's necessary.
I think C and Fe accounts for the biggest part of what remains, but it needs to be verified.



butcher said:


> Without knowing more of what you have now it is hard to say if you could just add a whole lot more copper in a reducing melt, to get the percentage of copper high enough in copper and the other metals low enough in percentage for the copper refiner, who may also penalize you for some of the metals you listed that may contaminate his electrolyte if he did by your copper bars.



Yes, there's a penalty for a whole bunch of unwanted elements in the doré bars. I'll post the exact figures of the company who wants to buy the prepared material.



butcher said:


> In your list I see some metals, which can become dangerous as fine powders, and also as gases in an incineration or melting process and from the circuit boards.
> 
> In fact I hope you had the circuit boards burned properly (and professionally) to begin with, with proper after burners, multi cone ash separator, electrostatic fine ash precipitators, and toxic gas scrubbers, there are a trainload of toxic and very dangerous gases and particulate matter that comes from powdering and burning circuit board materials, which could make a toxic dump site of the area it is done in, if not done properly.



The pyrolysis of the boards is conducted according all local environmental laws of my country, province & city. All this within a professional installation (not mine, I am paying a company to do so).
I know that the after burners are burning the gases and fumes during 3 seconds at (I don't remember what temperature) , instead of the regulated 1.5 seconds in Quebec province.
There's a couple of cyclone separators and a scrubber for dioxins and some other gases I am not familiar with.
I am not sure about the electrostatic fine ash separator, but I don't believe it's a requirement in Canada, never heard of it. If it's a requirement, the company I'm dealing with has probably one installed as they are checked constantly with those "surprise visits" & spot checks.

I want to make money, no doubt, but I am not ready to dump wastes or pollute the environment for a few bucks.



butcher said:


> I do not see an easy solution here, what I do see is the dangers involved, I cannot see this being done at a profit on a small scale by anything but a very large company who are set up to do this work with many tons of circuit boards safely, and with all of the proper equipment and who have deep pockets, plus a few lawyers to keep them out of trouble.



There's never an easy solution, otherwise everybody would be doing it...
It's not a small scale, I believe I'm the biggest buyer of scrap boards in my province, way ahead any of the big boys such as GEEP, FCM, SIMS or any other big electronic recycler based in my area...
My pockets are ok, can't complain... and my lawyers, well, fortunately for me and my pockets, I don't have to see them very often...



butcher said:


> I think the best bet at this point is to sell this ash to someone who can deal with it properly, cut your loses in the project, and forget trying to go any further with this dangerous idea, that is just my opinion, that may or may not be worth two cents.
> 
> I have studied just enough about this to know it is not something I would try, but not enough to know how to do it, but then again, I have no intentions of trying to do it.



Like any aspect of recycling or refining, I always started small, with a very very small idea and tried to scale it up.
If smelting pulp from boards is a scalable project, why not. I'm giving away way too much to the refiners now for something that could be achieved in house for a small fraction of what they are taking.

I know that I wont do any further processing like electrorefining. 
Processing the material up to doré bars is the final reasonable step one could achieve in order to get the most out of his buck if running a medium / large scale operation.
A few board members are trying to reach that goal, and I am sure they will. As I am very confident I will. There's simply too much money left on the table.

Butcher, thanks a lot for the reply, greatly appreciated. I'm sure many others will also benefit from it.
Some more reading ahead of me, love it...

cheers,

Alex


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## Geo (Aug 13, 2014)

Some fluxes can be, carbonate of soda, potash, charcoal, coke, borax, lime, lead sulfide, fluorite, silica sand, sodium nitrate not to mention a few others. Even some gasses are considered a type of flux. Molten metal will absorb oxygen from the air. Some metals are cast in an inert atmosphere or in a vacuum. As butcher said, some flux is meant to oxidize unwanted metals and minerals and trap the oxides in the slag. If you were working with large amounts of oxides to begin with, you would use a flux with a large amount of carbon in it to convert the oxygen and carbon into carbon dioxide (for people like me, I had to look it up) that's two oxygen for every one carbon. That's a pretty good trade off. Prospectors would roast their black sands and concentrates in big cast iron kettles and they would add wheat flour to it. Don't really know why but many did it for a long time so it must have been beneficial in some way.


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## butcher (Aug 13, 2014)

Alex,
It is good to hear you are having the circuit boards processed professionally,
And responsibly, by a company with the proper equipment, I really wasn’t sure if you were trying to do this yourself or not, and we sure would not want some one to get the idea they could burn a bunch of circuit boards in their yard and get some gold. If you read of the dangers and toxins from burning circuit boards, you will have a better understanding of how much of a pollutant, and how extremely dangerous it would be if not done properly, with the proper equipment, with several of the gases formed from that process, I just have to wonder if most of the gold in the process is not just going up the flue.

GSP has posted some great books, in the book section that can help you learn more about flux, and how it reacts with metals and the gangue in the melt, in some ways studying how flux is used in an assay, and how, the assay works, is also useful and will help you get a better understanding. As far as I can see, smelting and a fire assay have a lot in common, just on different scales.


You may also find C.W. Ammen's book handy.

Palladium, 
Thank you my friend, for the kind thoughts, I am only sharing what I have learned from you, and others here on the forum.
Many times when I try and make a post, I have no idea if I say anything someone else could understand, I can barley understand the way my own mind thinks, and trying to get it written down in a post with two fingers, punching buttons on a key board, it would be a miracle if it would make any sense to anyone else.

Geo, 
The burning flour is a good source for carbon in a flux, sugar can be another, as well as charcoal, and there are other materials that could be used to supply the carbon as well.
(even our pile of filter papers could be a source)...


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## maynman1751 (Aug 13, 2014)

Palladium said:


> Thank you for all you do to help others butcher. Someday god will reward you for your acts of kindness and generosity. You are a great moderator and teacher.



8) 8) 8)


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## Anonymous (Aug 13, 2014)

Palladium said:


> Thank you for all you do to help others butcher. Someday god will reward you for your acts of kindness and generosity. You are a great moderator and teacher.



More likely something far more mundane than God. What goes around comes around and I agree whole heartedly with the sentiment of your post Palladium but don't bring God into it mate.


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## Palladium (Aug 13, 2014)

I'm going to assume I'm missing something in the translation of the god part.


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## kurtak (Aug 14, 2014)

Geo said:


> . Prospectors would roast their black sands and concentrates in big cast iron kettles and they would add wheat flour to it. Don't really know why but many did it for a long time so it must have been beneficial in some way.



Geo - flour (or sugar) turns to carbon & thereby becomes the reducing agent

Kurt


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## butcher (Aug 14, 2014)

Normally roasting gold ore, or in incineration we want to oxidize the materials, bringing the materials heat up to red hot, which will help to drive off the ores Anionic component (like sulfides), as gases, this heat has to be kept high enough for a long enough time to force these out of the crushed material, stirring helps to distribute heat and will help to expose the red hot ore to air, which can give the ore enough oxygen to oxidize the metals in the ore that will oxidize at this high heat, like many of the more reactive metals, normally metals below copper, metals like gold will not oxidize in this process.

Crushing the material as fine as possible, keeping the material stirred well, controlling the temperature (sometimes at different settings, the latter being red hot), and raking or stirring to get good contact to air while red hot, wash important to proper roasting.

There are times where a pretreatment of the gold ore was also used in the roasting process, where an oxidizer or a reducer may be added to pretreat the ore in the roasting step.

I have not heard of flour being used with a pretreatment roasting process for gold ore,.
But I can see where it would be beneficial if you were trying to recover a metal like copper, or a base metal from an ore.

Salt NaCl (sodium chloride) for example has been used in some roasting processes with some types of gold ore (one that may not leach well in a chloride leach without this pretreatment). 
The salt was used to help to oxidize some of the gold in the roast to help put the gold in to a state that would help the gold dissolve easier in a latter chloride leaching process.
Gold in the form of chlorides being volatile at these red hot temperatures, this had to be done with only certain types of ore, and had to be done carefully, so they did not loose too much of the gold in the vapors of this roasting process. Here also keeping control over the temperature in steps during the roasting process was an important step. Salt has a high melting point, (very close to the melting point of some of the valuable metals like silver), and they needed good temperature control, and to bring the temperature up in steps to help the salt fuse with the gold, and not just burn the gold away in the fumes.


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## kurtak (Aug 15, 2014)

butcher said:


> I have not heard of flour being used with a pretreatment roasting process for gold ore,.
> But I can see where it would be beneficial if you were trying to recover a metal like copper, or a base metal from an ore.
> 
> .



Correct - my other post was meant to point out the purpose flour (or sugar) serves - not which step in the process it is used

The old timers used it in the smelting process - not the roasting process

I should have clarified that - my bad  

Kurt


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## Geo (Aug 15, 2014)

Me too. Like I said, I don't know what the purpose of it was. I asked what the cast iron kettles was for and that's what they told me. It was nearly thirty years ago so they may have been adding most anything trying to free the locked up gold.


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