# Skimming base metals



## madelyn (Apr 23, 2016)

Is it possible to skimm most or all base metals from the top of the melt until you are only left with silver alloy?
I am melting e waiste into bars with my induction furnace and was wondering if I could do this to reduce the bar size and then move to nitric acid.
I don't know if I will loose precious metal value when skimming of base metals.
Can anyone please advise if this is optional?


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## Barren Realms 007 (Apr 23, 2016)

No you will not be able to skim the base metals of the top of a melt to reduce the volume you are going to have to process. The molten metal will want to have a rolling action cause some stirring of the metals. It is not generally a good idea to melt your material like this into bars and then to process the material with nitric.


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## goldsilverpro (Apr 23, 2016)

madelyn said:


> Is it possible to skimm most or all base metals from the top of the melt until you are only left with silver alloy?
> I am melting e waiste into bars with my induction furnace and was wondering if I could do this to reduce the bar size and then move to nitric acid.
> I don't know if I will loose precious metal value when skimming of base metals.
> Can anyone please advise if this is optional?


No. It won"t work if the copper and other base metals are in a metallic form, as they would be as molten alloys. If you could provide a source of oxygen, the base metal oxides that form, being lighter than the molten metal, would float on top of the metal as a slag. Then, you could pour everything into a mold, let it cool, and break the copper bearing slag on the top away from the solidified metal which has settled in the bottom. 

Problems in doing this:
(1) Unfortunately, since copper is, by far, the main constituent, and since copper oxide is much lighter weight than copper metal, you would end up with a proportionately huge volume of slag, all of which is inclined to trap jillions of very small BB's of gold. I would guess that copper oxide will occupy at least 10 times more space than the copper metal.
(2) Probably, the most efficient way of doing this is to bubble bottled oxygen into the molten metal via a pipe which will not be wasted away by the molten metal. About the only other way would be to add, say, niter, as the oxidizing agent, Unfortunately, the niter reaction destroys expensive crucibles.
(3) With oxygen, considering the vast amount of copper to convert, it would probably take days, at best.
(4) You'll never be able to convert it all for reasons I won't go into.
(5) Considering everything, it would be overly expensive.

You might be able to add some other compound that would combine with the copper and report in the slag but I can't think of anything expect maybe a very controlled amount of sulfide. However, even if it worked, you would have the same problems.

To make a long story short, this is a bad idea. It's a dream. If there was any merit in it, it would have been done centuries ago and everybody would be doing it now. 

As Barren said, in general, it's a bad idea to melt everything together (unless you want to sell it on eBay and screw your buyers). You make a lot more work for yourself and lose more money than you normally would.

If you must refine that type of material, use a traditional method, like acid/peroxide (AP). It's been discussed 1000's of times of this forum.


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## patnor1011 (Apr 24, 2016)

AP is rather slow but fairly safe compared to other methods, not to mention it will be cheaper. Steve mentioned several times something in sense that this method is good in a way you do not need to be constantly present during course of action. It is like fire and forget. All other methods need your presence consuming not only chemicals and energy but your time which can be used for other things simultaneously while you use AP. You can also reclaim copper from saturated AP solutions and that is a plus too.


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## nickvc (Apr 24, 2016)

There is one method that could be used but it means making an even bigger bar.
You add more copper to achieve at least a 95% copper bar and then put that into a copper cell to refine the copper, the values are then left in the slimes to recover and refine.
It almost sounds wrong to look at that method but in honesty were I to start to refine e scrap in volume that's the way I would proceed as all the copper would be high grade and hence saleable and the values are condensed almost for free, eventually the initial cost of the extra copper to start would be repaid and then you profit from the copper as well as the values, the other really good thing is that copper refining is an old technology and very well documented.


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## madelyn (Apr 24, 2016)

It is not generally a good idea to melt your material like this into bars and then to process the material with nitric.[/quote]

I don't have any other choice with the material, these are all the small parts from 80kg cellphone boards.
Pyro, crushing and smelting is the only efficient way to get the metals.
I ussally use nitric acid. But it also takes a few days on large pieces.


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## nickvc (Apr 24, 2016)

If you must melt then pour the molten metal carefully into water to form cornflakes, as you then have a larger surface area it dissolves much quicker, do not add big quantities of acid to start the reaction it will react violently!
Cover the cornflakes with water and slowly add the acid, as it's an exothermic reaction do not add more acid until the reaction has slowed considerably or a boil over is a certainty.


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## madelyn (Apr 24, 2016)

I always start with a dilute nitric acid mixed with water to get the reaction going on a hot plate.
When I'm done smelting I will be having a 10 to 15 kg bar as I also need to add more copper to the smelt to get the stainless steel parts melted in the mix. 
You guys can calculate how much acid is needed for this, almost about 60 liters of 70% nitric acid. This is a lot of acid to work with.

Something else I also had in mind was cupellation.
Does the bone ash only work with the lead or will it absorb base metals also? And would this mean that I would have to add lead to the mix?
Ive seen guys that vaporize the lead from the gold, but this is very toxic and deadly if not done with good control.


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## 4metals (Apr 24, 2016)

Cupellation will not work without adding a considerable excess of lead into the melt. As Nickvc said your best bet will be smelting into copper base bullion and casting into anodes. Electrolytic copper cells will yield valuable copper and your precious metals in the slimes. We started a thread about this process called smelting.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=23680


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## madelyn (Apr 24, 2016)

This is a very informative post on smelting, just wish it was brought up little earlier as I have been smelting for a while and had to learn everything the hard way through trial and error.
I'm using a 20 kg graphite cruicible for my melts.

At the moment I'm not worried about loosing base metals like copper and the rest, I just want to speed things up to get to the gold and silver for refining.
Electrolytic refining is a good way to get your copper and break up the meterial, but it also takes a lot of time and energy.

If cupellation could work with adding more lead, than I could add more lead rather than copper in my melt and absorb everything out with bone ash and refine the silver alloy with nitric?


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## butcher (Apr 24, 2016)

Bone ash can only absorb so much oxidized metals, it would work with small lots, but as a way to recover large lots, you would need a lot of bone ash or one of the other materials that absorb metal oxides.
Oxidizing large lots of metal to oxides with heat can take a lot of fuel.

As a recovery method this could become expensive. I believe would be more trouble and more expensive than other methods of recovery.

Smelting would not be a refining method but a recovery method


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## nickvc (Apr 24, 2016)

There are rules of chemistry that apply when you try any process.
The truth is that you are chasing a dream if you think you can find a new way with what you are doing to process more quickly or cheaply.
If you want cheap then the copper cell is the way to go, if you want quick then use more chemicals, the truth is you have to make a choice between cost and speed there is no process I know of that fills both requirements.
Spend some time looking at what your doing or need to do, research any ideas and try to find the compromise solution to fit your circumstances, there is no one answer but multitudes, the trick is to find the one that suits your circumstances.
Good luck and keep us posted.


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## 4metals (Apr 24, 2016)

It comes down to a question of what chemicals you have available and how much of a pollution load is acceptable.

Nitric dissolves produce a lot of waste acid and a lot of red fumes. 

Cupellation uses a lot of lead and results in bone ash loaded with lead as well as 10% of the lead going off into your exhaust. 

Smelting and a copper cell probably is the best solution to conserve on chemistry and waste acids.


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## madelyn (Apr 25, 2016)

4metals said:


> It comes down to a question of what chemicals you have available and how much of a pollution load is acceptable.
> 
> Nitric dissolves produce a lot of waste acid and a lot of red fumes.
> 
> ...



Nitric acid is cheap here with me ,but it's just a pain to work with so much acid.
At the moment I have a lot of bone ash and lead from car wheels, but I'm not very experienced with the process.
I wil first try and test small samples with the induction furnace in small crucibles which I don't use anymore.
The induction heater is very fast and gets to melting temps in 5 to 10 minutes. You just need to line the graphite cruicible on the inside with some refractory to protect it from the air.
Copper sulphate for the cell is super expensive hear because it's not available and needs to be imported.


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## g_axelsson (Apr 25, 2016)

If you have sulfuric acid you could make your copper sulfate by yourself.
http://chemistry.about.com/od/makechemicalsyourself/a/make-copper-sulfate.htm

I don't see why you couldn't just start the cell with a bit of extra sulfuric acid and the copper sulfate will be created from your anode. After a while when most of the sulfuric acid is used up it turns into a copper cell.

Göran


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## madelyn (Apr 25, 2016)

I actually have a 20 liter 98% industrial sulphuric acid now that you mention it, I only remember now that you mention it Goran.
How much copper would I have to add to a 15kg bar to make it work for the cell and how much solution would I have to use?
Would I be able to start without the copper sulphate?
How long would this take more or less to plate it out depending on the currents?
How do I deal with the slimes after its settled?


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## nickvc (Apr 25, 2016)

With cells you need the metal you are after in the solution, the idea is that as the solution yields the metal you are after the bar will start to dissolve into the solution to replace it leaving behind the values as slimes.
If you have sulphuric then dissolve some copper into it to create your electrolyte, same as you would do with a silver cell where you dissolve silver into nitric.
The trick with cells is to only put high grade feedstock into it to avoid fouling your electrolyte too quickly so weigh the parts you are going to melt and then add enough copper to bring it to 95%+ copper.
As to time it depends on current and anode and cathode size.
As I have said this is an old technology and there are thousands of detailed breakdowns of how the system is used and how to keep it running. GSP might be able to give you a better idea on times and current etc to run this.
Treating the slimes is not easy they seem to go everywhere but you will have at least 50% of copper in them, I believe the best method is to heat them in sulphuric in an iron pan as this should remove most of the copper and a few other metals but leave any values such as Pd in the slimes.
Getting everything right in the running of the cell is important and don't try to speed up the process, once it up and running you can basically walk away and let it do the work for you.


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## g_axelsson (Apr 25, 2016)

Adding pure metal to an anode just to get the purity up is counterproductive and doesn't help. The only limit you need to be concerned with is to have it pure enough to not passivate, for example silver in gold.

The electrolyte is fouled when enough lesser base metals are dissolved, turning it from a copper sulfate solution to a nickel iron zinc sulfate solution.

If you can run 10 kg of a 90% pure copper alloy before needing to change the electrolyte, adding 10 kilo of pure copper let's you run 20 kilo of 95% copper until the electrolyte is fouled. You still only ran 10 kilo of the original material but it took twice as long time and energy.

The correct way of raising the purity is to oxidize off most of the base metals by adding air or oxygen via a clay pipe directly into the melt. Zinc, iron or aluminum will be oxidized and collected in the slag.

Göran


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## nickvc (Apr 25, 2016)

Goran you idea is fine if you have the necessary equipment and ability to use it safely but the reality is that most do not have the right equipment or experience to attempt this, I know normally we look to remove the base metals first but with e scrap it doesn't necessary make sense.
The method I posted is easily understood and fully documented as I said it is a very old process.
Far from been counterproductive it's actually productive as you can recover fine copper and the values in the slimes.
How do you think most e scrap is processed? The method I suggested is the method most big boys use, the dore bars they produce go to copper refiners.
The initial costs are for the extra copper needed but that is easily recovered and soon the copper is free as you have a large amount of copper in e scrap which you can then monetise and profit from.
This really is the simple way that is fully and comprehensibly documented, trying to force oxygen through molten metal seems a dangerous process to advocate to amateur refiners with few of the necessary pieces of equipment to ensure safety or success.


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## g_axelsson (Apr 25, 2016)

You are right, nickvc, oxygen sparging a copper melt isn't so easy to do and nothing for the inexperienced smelter. Blowing oxygen or air through molten metal is severely dangerous and nothing an amateur should try.
But this is the way the big copper refineries is doing raw copper refining. To raise the copper content in their anodes by oxidizing more reactive base metals.

But adding pure copper to a melt with the sole purpose to raise the copper content doesn't help keeping your copper electrolyte fresh, it only increases the time and energy it takes to process a certain amount of material.

The only use of added copper I can see is as a collector of values during the melt.

Göran


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## nickvc (Apr 26, 2016)

Goran I can see the logic of what you are saying about the additional copper as I ran loads of sterling scrap through a silver cell, kilos and kilos, and avoided the fouling with added increments of nitric to dissolve more silver back into the electrolyte, it eventually had to be changed and I did it all by judgement and luck.
I think I'm going back to the trials I know Harold did and I tried which was to run gold filled through a copper cell, that was a total failure for both of us, it worked somewhat better using an old flower poor as a membrane but I gave up after a while...
The OP could try my technique and add small additions of sulphuric after each day's running of the cell, if I remember correctly the cell should still produce fine metal so long as there is enough copper present in the electolyte, well it did with the sterling.
Perhaps you can comment on whether this might be a viable idea as the physics and chemistry theories are beyond me


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## g_axelsson (Apr 26, 2016)

nickvc, that's the way I would run a cell and close to what a larger refinery is doing, they constantly tap some of the copper sulfate from the cell while they add fresh copper sulfate to the solution so they could run the process under tight control. Removing some of the electrolyte while topping up on sulfuric should also work. It might not produce the cleanest copper but that is not what we are after.

In a commercial copper refiner the main contamination seems to be nickel and that is extracted as nickel sulfate after the copper is removed by electrowinning from the used electrolyte.

I'm sure there are a lot of other pitfalls that I'm not aware of, especially if you are running a smaller cell.

This is a project that I'm dying to test some day, I already got a suitable power supply, programmable +/- 10V at 100A. 8) 

Göran


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## nickvc (Apr 27, 2016)

Goran I think that experiment could prove to be very very interesting, especially as most members are running e scrap which has a large copper content in many cases.
If someone could find a way to run e scrap an a small scale using cells to do the recoveries I think that it would become the number one choice for many, less fumes and as sulphuric is used ease of getting the acid would make it highly appealing and with the potential that the copper produced could be sold on even if slightly contaminated, as we both know fouling of the electrolyte is the major problem and whether just by trial and error or experience we could work out the parameters of running the cell long enough to reduce 10 kilos of mixed metals to say 250 grams of slimes in one solution with just small additions of sulphuric would I feel be a Great Leap Forward.
I'm sure that certain metals will remain troublesome, even the big copper refineries have penalties for certain metals, but you could run any impure copper produced alongside your next scrap bar to increase the amount of copper going in the electrolyte against the amount of troublesome metals, not sure it would work but could be worth a trial.


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## madelyn (Apr 28, 2016)

Ok, so if I understand this correctly, I can run the bar as it is without adding copper to increase the purity, and just add small increments of nitric to keep on dissolving copper into the cell?
Wouldn't adding a clean copper bar next to the mixed bar also help with this?
Also,what happens when the solution gets contaminated with the other metals?


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## nickvc (Apr 29, 2016)

I think you mean sulphuric not nitric as copper refining is done using copper sulphate.
When I was running my silver cells I could tell by the colour of the solution when it needed more nitric to dissolve more silver into the electrolyte, I have never run a copper cell so you would have to run it on a trial and error basis, when you make up your electolyte note the colour and as the cell runs if the colour starts to change then add more sulphuric to consume more copper, I think that so long as you maintain the copper concentration you shouldn't have too much trouble with other metals plating out but do some research and check that that is true, you will also have to remove some of the acid as you add more at some stage.
As to adding a copper bar I think that might work but the downside is it will take longer to do, I'm not an expert on copper refining but as I said it's an old technology and there are loads of artcles available to read and learn from.
My suggestion would be to start small maybe do a kilo to start with to see how or if it works and how well, do some homework and try it and keep us informed as to your progress and good luck.


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## madelyn (Apr 29, 2016)

I finally finished smelting more than half of the 80kg cell scrap today and produced 2 large bars almost weighing 10kg.
I took a small sample from the melt and tested it with the cell and ran a 30gram just by plating it without the addition of copper sulphate.
I than took the copper sponge produced and dissolved it with nitric to test for values.
The slimes tested positive with gold.

My conclusion was, why not plate the bar directly like this , seeing that the copper produced is very clean with little contamination and than melt the sponge again and plate it out for the second time?
The first cell would leave most contamination in the slime and the second run should produce a very clean bar?


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## 4metals (Apr 29, 2016)

The one thing an electroplating cell needs is good electrical contact. That piece you have posted would perform horribly as an anode and wouldn't maintain enough electrical contact properly. The anode needs to have good electrical contact throughout the anode which requires it to be all metal, yours appears to be hmmmm.... well not all metal! It isn't even a bar.


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## madelyn (Apr 29, 2016)

I totally agree with you 4metals, but this is only one half. If you look close you will see there is a hole on top where the flux is still present. This is where I tried to place a thin copper tubing when it was casted and stil hot, unfortunately for this one it was freezed already, but on the other half it worked very good.
I will simply clean this one of and solder a wire to the bar for contact on the top.


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