Help Needed (never seen this before)

[Harshrao]

so basically,
I smelted (with Pb0) and cupeled some mixed PCB scrap
Then I did a nitric treatment on the dore, after that i did aqua regia on the residue left from the nitric treatment.
I tested the AR solution it was strongly positive for gold. so I precipitated the gold with smb
Then I left the gold powder to settle for a few hours.
After the gold settled down there was some white precipitate on top of it. I decanted the solution and took the gold into a melting dish but it won't melt instead it formed chunks like this.

I also checked one golden looking chunk with AR and stannous it was positive.

thnks.

Pardon my mistakes, English is not my first language

 

[[email protected]]

I could be wrong but it looks like you have metallic gold. Thus meaning you successfully melted the gold. If it were me judging by the photo. I would put it in some HCl or nitric acid and dissolve the other base metals out. Then you can use auqa regia to dissolve the gold and drop it with SMB. That is my suggestion on how to fix it.

 

[orvi]

Lead form lead chloride, which is somewhat soluble in the hot solution, but upon cooling, it precipitates out as white crystals (often needle-like).
When something like this happens, never go straight to melting. Second refining is advised to make pure and properly dropped gold.

I (personally) will dissolve the remaining stuff in AR and used some H2SO4 or sulfate to drop any residual lead, which could be present. Properly filter the solution, rinse the filter and drop the gold again with sulfite. Then wash it and melt it. Should work

 

[Harshrao]

thnks @[email protected] & @orvi for your replies
problem is solved now, i smelted this with some silver powder & and some fluxes then i did a nitric treatment
and recovered 18.50gram of gold & 0.3gram of pd

 

[orvi]

thnks @[email protected] & @orvi for your replies
problem is solved now, i smelted this with some silver powder & and some fluxes then i did a nitric treatment
and recovered 18.50gram of gold & 0.3gram of pd

good results !

 

[Geo]

Smelting E-scrap is the least efficient process I can think of.
There are two major principles when refining. You are either removing the target metal from everything else, or you are removing everything else from the target metal. Either or both can be used but one or the other may be more efficient for the material you are working with. For me personally, removing the base metal first is my preferred process. I use copper(II) chloride (CuCl2) even though it is not the most cost effective. I have set up a system that I am oxidizing 200 gallons (757L) at one time. 10 - 14 days will dissolve about 20 Kg of base metal on average. The copper is reclaimed from the waste stream using scrap steel. I have recently discovered that CuCl2 is an effective way of concentrating Pd as CuCl2 will dissolve Pd fines with little problem. Any chloride solution with a low PH value will dissolve Pd foils or thin solids over time and faster if it's oxygenated.

.

 

[orvi]

Smelting E-scrap is the least efficient process I can think of.
There are two major principles when refining. You are either removing the target metal from everything else, or you are removing everything else from the target metal. Either or both can be used but one or the other may be more efficient for the material you are working with. For me personally, removing the base metal first is my preferred process. I use copper(II) chloride (CuCl2) even though it is not the most cost effective. I have set up a system that I am oxidizing 200 gallons (757L) at one time. 10 - 14 days will dissolve about 20 Kg of base metal on average. The copper is reclaimed from the waste stream using scrap steel. I have recently discovered that CuCl2 is an effective way of concentrating Pd as CuCl2 will dissolve Pd fines with little problem. Any chloride solution with a low PH value will dissolve Pd foils or thin solids over time and faster if it's oxygenated.

.

If I can ask, how do you reclaim the palladium from the vast ammount of solution ? Or you just cement it on the iron with copper and then electrorefine it ?

 

[Harshrao]

Hello Geo,
can you please elaborate why smelting is inefficient for E-waste?
i have seen many big refiners (informal sector) here in india following the smelting route, they process large quantities ic chips, mlcc & other type of high grade ewaste scrap
i understand that smelting is not very cost-effective and some losses of values are there
Thanks.

Smelting E-scrap is the least efficient process I can think of.
There are two major principles when refining. You are either removing the target metal from everything else, or you are removing everything else from the target metal. Either or both can be used but one or the other may be more efficient for the material you are working with. For me personally, removing the base metal first is my preferred process. I use copper(II) chloride (CuCl2) even though it is not the most cost effective. I have set up a system that I am oxidizing 200 gallons (757L) at one time. 10 - 14 days will dissolve about 20 Kg of base metal on average. The copper is reclaimed from the waste stream using scrap steel. I have recently discovered that CuCl2 is an effective way of concentrating Pd as CuCl2 will dissolve Pd fines with little problem. Any chloride solution with a low PH value will dissolve Pd foils or thin solids over time and faster if it's oxygenated.

.

/

 

[orvi]

Hello Geo,
can you please elaborate why smelting is inefficient for E-waste?
i have seen many big refiners (informal sector) here in india following the smelting route, they process large quantities ic chips, mlcc & other type of high grade ewaste scrap
i understand that smelting is not very cost-effective and some losses of values are there
Thanks.

/

Smelting does work. It is used a lot because of simplicity of the actual process. Incinerate, smelt, refine the metal dore... Or better fuel the whole furnance with flow of PCBs and gas, combined with flux to give you stream of molten metal and stream of slag. This is roughly what big guys are doing.
But it should be done properly to avoid messy situations. Pretreatment is key, but you cannot avoid metals like tin and iron completely to mix with your metal feed, making you hard time to separate the values from base metals. And these complicate things even further, when you try to reclaim the values from melted metal, let´s say with electrolysis.
Not mentioning the losses from incomplete separation of metals from slag (eg ceramics are notorious for difficult dissolution in common fluxes like borax/soda - they need high temperatures etc...)

Treating the dore after cupellation with nitric acid is not considered an good option because of vast ammount of spent acid, liquid waste which should be treated correctly, and also troubles with all kinds of mixed metals in it. In INDUSTRIAL scale. When you are located in country like India, where it is not a problem to obtain quantities of acid, create cloud of red fumes (and nobody is calling police and enviromental agencies on you), and dispose the spent metal/acid solution easily... Then I get it, and accept that for you it is a good option (aside of what would be the best in terms of reducing hazards and pollution). And you will recover all of the values in the dore, since cupellation and dissolving/precipitating techniques are more or less quantitative.

In my terms of effectivity, direct smeting and further reclamation of values from mixed metal dore is inefficient, as long as I cannot continue with hydrometallurgical treatment with it. Values are diluted with wide range of base metals, making the electrolytic separation ("cleaner" approach) tedious.
I would be happy to do so, but from enviromental and economical point, that wouldn´t work for me.

 

[Geo]

If I can ask, how do you reclaim the palladium from the vast ammount of solution ? Or you just cement it on the iron with copper and then electrorefine it ?

By dissolving copper until the solution is saturated and black. It is a balancing act of not dissolving so much copper that CuCl precipitates out and the cemented Pd can not redissolve. As a visual, if the solution is any shade of green, it will dissolve Pd fines. If the solution is black, it can't dissolve the Pd because the solution is saturated. It's not very scientific, but it is a low tech and low cost way of reclaiming the wayward Pd. You can always test the solution with stannous chloride to ensure that all has been removed. But be warned, it needs time to settle as the very fine Pd powder will stay suspended for some time. Adding magnesium sulfate, as a flocculant, helps the fines settle faster. I've tried just sulfuric acid but it tends to lower the Ph enough to cause the Pd to redissolve. I don't like to neutralize using a base like hydroxide because anything you do after is changed from what it would be if not used, like the cemented metal will make floating masses that stay suspended and will not settle completely. Not like a true colloid where you can't see the actual particles but more like a coarser grain and fluffy, larger volume cementation that shrinks to a fraction of the volume once dried. Instead, I adjust PH by dilution and just add more water.

 

[Geo]

Hello Geo,
can you please elaborate why smelting is inefficient for E-waste?
i have seen many big refiners (informal sector) here in india following the smelting route, they process large quantities ic chips, mlcc & other type of high grade ewaste scrap
i understand that smelting is not very cost-effective and some losses of values are there
Thanks.

/

A rough estimate of metal in PCB's is around 25% of the weight in total. Of that 25%, the copper content is around 90% with aluminum and steel being the next two majority metals. Leaving exotic metals and precious metal being around 5% or so. Of that 5%, gold makes up less than 1%. The higher reactive metals will be absorbed by the flux ideally. The enormous amount of copper (compared to gold) has to be remove at some point. Nitric acid leaching that amount of copper for that amount of gold would be foolhardy. You would come out better selling the bars for copper and leave it at that. The best that could be done is parting that copper out in an electrolytic cell. After having done some of the math on the subject, without huge equipment, copper doesn't dissolve and deposit very quickly. I would have to dig up the charts but the size of the anode and cathode, distance between the two, temperature, current density determines the amount of copper that can theoretically be deposited within a certain length of time. Not something that's going to happen in a short amount of time. "I'm going to part out this 20 kg's of copper bars RIGHT QUICK"

 

[Harshrao]

i have never seen anyone smelting the complete pcb boards
they dismantle, segregate, sort the components
and then smelt the high value material only like ic chips, mlcc, transistors etc.

bare pcb boards and other components are run through different machines to separate plastic/other junk from metal like crushers, pulverizer, air separators, eddy current, electrostatic separators
leached pins and other aluminium & pm free compo. are also processed in similar manner (these compo. makes high quality brass)

 

[The Devils Dog]

Lead form lead chloride, which is somewhat soluble in the hot solution, but upon cooling, it precipitates out as white crystals (often needle-like).
When something like this happens, never go straight to melting. Second refining is advised to make pure and properly dropped gold.

I (personally) will dissolve the remaining stuff in AR and used some H2SO4 or sulfate to drop any residual lead, which could be present. Properly filter the solution, rinse the filter and drop the gold again with sulfite. Then wash it and melt it. Should work

Smelting E-scrap is the least efficient process I can think of.
There are two major principles when refining. You are either removing the target metal from everything else, or you are removing everything else from the target metal. Either or both can be used but one or the other may be more efficient for the material you are working with. For me personally, removing the base metal first is my preferred process. I use copper(II) chloride (CuCl2) even though it is not the most cost effective. I have set up a system that I am oxidizing 200 gallons (757L) at one time. 10 - 14 days will dissolve about 20 Kg of base metal on average. The copper is reclaimed from the waste stream using scrap steel. I have recently discovered that CuCl2 is an effective way of concentrating Pd as CuCl2 will dissolve Pd fines with little problem. Any chloride solution with a low PH value will dissolve Pd foils or thin solids over time and faster if it's oxygenated.

.

Geo thank you for your extremely well worded description many thanks, I am having a very different problem but in a similar situation I am a hard rock miner working with a rather troublesome polymetallic Pegmatite vein matrix that is carrying just about as much mixed metals I have ever come in to contact with the materials generate elemental chlorine in Hcl and nitric is rendered useless almost instantly on the black sand cons the materials so far to my knowledge being Au,Ag,Pd,Pt,Mn,Fe,W,Cu,Ni,Zn,Zr,Si,S,Te, and somehow vastly more than I know how to test for I can collect the metallics with gravity means fine crush the heavies the second that fine materials have any form of Cl acids the Au passes through solution and seems that pgms and Mn are the problem but even after fusion with pyrometallurgy tactics and an odd alloy is created my yellow gold when hot looks great but as it continues to cool and rainbow of colors and a large percentage of the bead goes white this tone over powers the color tone of the Au and takes over when I try to dissolve the alloy it won’t go the pgms are covering the beads in an oxide layer protection phase and the beads that do partially dissolve stop dissolving at different colors when the fire fusion is done and a unfortunate happening of cup failure happened the metal that hit the ground was an array of colors that looked as if a basket of different colored metallic beads Ranging the full spectrum of metallic colors what could I be doing incorrectly that may aid in my attempts to separate the materials any form of success I’ve had in breaking up the alloy creates a mess of mixed salts any options would be greatly listened to and appreciated thanks

 

[Geo]

i have never seen anyone smelting the complete pcb boards
they dismantle, segregate, sort the components
and then smelt the high value material only like ic chips, mlcc, transistors etc.

bare pcb boards and other components are run through different machines to separate plastic/other junk from metal like crushers, pulverizer, air separators, eddy current, electrostatic separators
leached pins and other aluminium & pm free compo. are also processed in similar manner (these compo. makes high quality brass)

Even milspec connector pins are 0.001% gold. That is a very low percentage to work with when smelting. And you still have to remove the copper from the gold through electrolysis. Smelting is still the same as most other processes that are wet processes in that the flux is the solution, only it's done at high temps. Since you are working with cherry picked items, it makes smelting unnecessary. Smelting is for removing higher reactive metal. If you are working with just the gold bearing material, you have mechanically removed the higher reactive metals. You would achieve the same thing you are trying to do by simply melting everything and casting it into bars minus smelting.

 

[Geo]

Geo thank you for your extremely well worded description many thanks, I am having a very different problem but in a similar situation I am a hard rock miner working with a rather troublesome polymetallic Pegmatite vein matrix that is carrying just about as much mixed metals I have ever come in to contact with the materials generate elemental chlorine in Hcl and nitric is rendered useless almost instantly on the black sand cons the materials so far to my knowledge being Au,Ag,Pd,Pt,Mn,Fe,W,Cu,Ni,Zn,Zr,Si,S,Te, and somehow vastly more than I know how to test for I can collect the metallics with gravity means fine crush the heavies the second that fine materials have any form of Cl acids the Au passes through solution and seems that pgms and Mn are the problem but even after fusion with pyrometallurgy tactics and an odd alloy is created my yellow gold when hot looks great but as it continues to cool and rainbow of colors and a large percentage of the bead goes white this tone over powers the color tone of the Au and takes over when I try to dissolve the alloy it won’t go the pgms are covering the beads in an oxide layer protection phase and the beads that do partially dissolve stop dissolving at different colors when the fire fusion is done and a unfortunate happening of cup failure happened the metal that hit the ground was an array of colors that looked as if a basket of different colored metallic beads Ranging the full spectrum of metallic colors what could I be doing incorrectly that may aid in my attempts to separate the materials any form of success I’ve had in breaking up the alloy creates a mess of mixed salts any options would be greatly listened to and appreciated thanks

There are a few elements there that will not allow you to leach the precious metals in acidic solutions. Smelt using PbO as a collector. This will gather all of the metallics in the sample without the overburden. Zn boils at 1665°F and will boil away in the exhaust. Sulfur boils at 832°F. Te boils at 1810°F. Fe, Si, Zr, will report in the flux and the precious metals include Ni, Mn, W, Cu, will report in the metal bead. The bead then can be processed in acid without the troublesome elements.

 

[orvi]

Even milspec connector pins are 0.001% gold. That is a very low percentage to work with when smelting. And you still have to remove the copper from the gold through electrolysis. Smelting is still the same as most other processes that are wet processes in that the flux is the solution, only it's done at high temps. Since you are working with cherry picked items, it makes smelting unnecessary. Smelting is for removing higher reactive metal. If you are working with just the gold bearing material, you have mechanically removed the higher reactive metals. You would achieve the same thing you are trying to do by simply melting everything and casting it into bars minus smelting.

0,001% is too low, that would be 10 mg/kg. More likely you mean 1% or 10g/kg.
But agree with all your points.

 

[orvi]

By dissolving copper until the solution is saturated and black. It is a balancing act of not dissolving so much copper that CuCl precipitates out and the cemented Pd can not redissolve. As a visual, if the solution is any shade of green, it will dissolve Pd fines. If the solution is black, it can't dissolve the Pd because the solution is saturated. It's not very scientific, but it is a low tech and low cost way of reclaiming the wayward Pd. You can always test the solution with stannous chloride to ensure that all has been removed. But be warned, it needs time to settle as the very fine Pd powder will stay suspended for some time. Adding magnesium sulfate, as a flocculant, helps the fines settle faster. I've tried just sulfuric acid but it tends to lower the Ph enough to cause the Pd to redissolve. I don't like to neutralize using a base like hydroxide because anything you do after is changed from what it would be if not used, like the cemented metal will make floating masses that stay suspended and will not settle completely. Not like a true colloid where you can't see the actual particles but more like a coarser grain and fluffy, larger volume cementation that shrinks to a fraction of the volume once dried. Instead, I adjust PH by dilution and just add more water.

I think i get it. Thank you for response

 

[The Devils Dog]

There are a few elements there that will not allow you to leach the precious metals in acidic solutions. Smelt using PbO as a collector. This will gather all of the metallics in the sample without the overburden. Zn boils at 1665°F and will boil away in the exhaust. Sulfur boils at 832°F. Te boils at 1810°F. Fe, Si, Zr, will report in the flux and the precious metals include Ni, Mn, W, Cu, will report in the metal bead. The bead then can be processed in acid without the troublesome elements.

Thank you for your time Geo I will try again and be trying what I have learned today my many thank you

 

[Geo]

0,001% is too low, that would be 10 mg/kg. More likely you mean 1% or 10g/kg.
But agree with all your points.

Until it is refined, at least in the US, raw weights is in avoirdupois pounds of 453 grams. 1% would give you 4.53 grams per pound. I tend to get around 2g per pound on trimmed and fully plated pins and a solid 3g per pound of test (pogo) pins.
453 X 0.0045 = 2.03 So I was off a little. No where near 1%.

 

[Yggdrasil]

Until it is refined, at least in the US, raw weights is in avoirdupois pounds of 453 grams. 1% would give you 4.53 grams per pound. I tend to get around 2g per pound on trimmed and fully plated pins and a solid 3g per pound of test (pogo) pins.
453 X 0.0045 = 2.03 So I was off a little. No where near 1%.

I feel I need to arrest you a bit Geo

Percent is a measure without denomination.
So if it is kilos, tons or featherweight it do not matter.

It is a certain part per parts just like ppm and ppb.
1 % is one part per cent (100)
1 per mil (not used much in the US)
Is 1 part per 1000
1ppm is part per million
and so on.
They are all unit agnostic and can be used for grams, tons chicken or anything else for that matter.

So 1% is the original weight times 0.01
I have no idea where you find the 0.0045?

But anyway 0.001% of one metric ton is about 10 grams, good for industrial gold ore but not for pins