Is Sodium hydroxide best solution to git rid of tin and lead?

[Ayham Hafez]

Recently, I read about using concentrated sodium hydroxide solution with hydrogen peroxide to dissolve tin and lead from e-waste, till now I use copper chloride to git rid of tin but I'm not satisfied cause after leaching pcb for more than 3 days with 30 c temperature in copper chloride solution, I still get about 40% of gold still on circuit boards and some times gold dissolved in the solution, so I repeat the copper chloride process with fresh HCl and also I don't get feasible results, so at the end I take the circuit board specially which contains gold plated pins and put them in Aquaregia.

Direct using of Aquaregia is the best way to make sure I will get all the gold dissolved, in case there is no tin, so is it better to leach pcb in sodium hydroxide with some peroxide to dissolve all tin and lead then directly use Aquaregia? Ater dissolving tin I will get all ic chips in the bottom of the pool so will seperate them, I'm just talking about circuit boards with gold plated tracks and pins.

 

[Yggdrasil]

Recently, I read about using concentrated sodium hydroxide solution with hydrogen peroxide to dissolve tin and lead from e-waste, till now I use copper chloride to git rid of tin but I'm not satisfied cause after leaching pcb for more than 3 days with 30 c temperature in copper chloride solution, I still get about 40% of gold still on circuit boards and some times gold dissolved in the solution, so I repeat the copper chloride process with fresh HCl and also I don't get feasible results, so at the end I take the circuit board specially which contains gold plated pins and put them in Aquaregia.

Direct using of Aquaregia is the best way to make sure I will get all the gold dissolved, in case there is no tin, so is it better to leach pcb in sodium hydroxide with some peroxide to dissolve all tin and lead then directly use Aquaregia? Ater dissolving tin I will get all ic chips in the bottom of the pool so will seperate them, I'm just talking about circuit boards with gold plated tracks and pins.

You will not get all Gold by AR, you will dissolve all Gold, but some to much will cement out inside the PCB.
Do you use an air bubbler in your AP?

 

[Ayham Hafez]

I use hydrogen peroxide, tried to use air bubbler before but its very slow so I stuck with using peroxide.

I think AR will dissolve all gold with cementing out if we use enough nitric acid in AR.

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[Yggdrasil]

I use hydrogen peroxide, tried to use air bubbler before but its very slow so I stuck with using peroxide.

I think AR will dissolve all gold with cementing out if we use enough nitric acid in AR.

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Gold will always cement out on less noble metals as long as they are available.
Even if they are hidden inside the traces of the PCBs at which time the Gold may be considered lost,
or at least impractical to recover.

If you do not have time for AP you can use Nitric first to release the foils and components from the boards.
Then a sieve/coarse filter to get rid of the Metastannic acid.
You will then be left with the components and the foils.

 

[Martijn]

You are dissolving gold with the H2O2. Use an air bubbler and add HCl.
If you need faster results, use nitric, but your profit will be smaller. AP takes time.
no need to refresh it, just rejuvenate with HCl and an air bubbler.

I think AR will dissolve all gold with cementing out if we use enough nitric acid in AR.

Then you'll have the challenge to precipitate out gold or your spending even more money on sulfamic acid and wasting an excess of HNO3.
for gold foils!!!

 

[Martijn]

and before you remove any nitric, remove all solder.
Now why are you treating whole boards in AP? Are they heavily plated for some reason?

 

[Ayham Hafez]

Gold will always cement out on less noble metals as long as they are available.
Even if they are hidden inside the traces of the PCBs at which time the Gold may be considered lost,
or at least impractical to recover.

If you do not have time for AP you can use Nitric first to release the foils and components from the boards.
Then a sieve/coarse filter to get rid of the Metastannic acid.
You will then be left with the components and the foils.

Nitric with tin will make tin paste and that is nightmare, most important thing is to git rid of tin from pcb.

What's your opinion about using sodium hydroxide with peroxide as a begining to dissolve tin and lead then use nitric then AR?

 

[Yggdrasil]

Nitric with tin will make tin paste and that is nightmare, most important thing is to git rid of tin from pcb.

What's your opinion about using sodium hydroxide with peroxide as a begining to dissolve tin and lead then use nitric then AR?

I hve never used Sodium Hydroxide that way, I always use HCl.
Then I put it in my AP system.

 

[Ayham Hafez]

and before you remove any nitric, remove all solder.
Now why are you treating whole boards in AP? Are they heavily plated for some reason?

I'm doing recovery process for big amounts of pcbs, minimum I leach 50 Kg per barrel, and batch is about 10 barrels so we are talking about 500 Kg of circuit boards per batch.

AP leaching will help me also to get all ic chips and other small components, much more better than seperating small components from circuit boards using mechanical methods

 

[Ayham Hafez]

I hve never used Sodium Hydroxide that way, I always use HCl.
Then I put it in my AP system.

Do you mean you leach in HCl only, then you leach in AP??

 

[Yggdrasil]

Do you mean you leach in HCl only, then you leach in AP??

Yes, HCl to take the Tin and then AP to remove the foils.
But I have never been in a hurry.

 

[Ayham Hafez]

Yes, HCl to take the Tin and then AP to remove the foils.
But I have never been in a hurry.

Hmmm, I think you wait more than week to make HCl dissolve tin.

 

[Yggdrasil]

Hmmm, I think you wait more than week to make HCl dissolve tin.

As I said, I have never been in a hurry.
There are other methods, but they are more costly and might be more toxic as well.

 

[Yggdrasil]

Hmmm, I think you wait more than week to make HCl dissolve tin.

If you are in a hurry, how about trying hot concentrated HCl?

 

[FrugalRefiner]

Search crockpot solder. Keep the heat low, and only when you're around. It will gas off a lot of the HCl.

Dave

 

[GoIdman]

I'm doing recovery process for big amounts of pcbs, minimum I leach 50 Kg per barrel, and batch is about 10 barrels so we are talking about 500 Kg of circuit boards per batch.

AP leaching will help me also to get all ic chips and other small components, much more better than seperating small components from circuit boards using mechanical methods

Hi,
If you are processing a lot of boards, no matter how hard it sounds, mechanical is the best way to separate. I am making a drum separator using an old washing mschine with which i want to reclaim the solder and components, since solder conteins silver and some dissolved gold from the soldered plated foils. It is not ecological and stnks like hell if you overheat the PCB's but the advantage is that it separates small MLCCs which go through the holes and can be easily collected afterwards , solder as well, larger IC will remain in the drum with the PCBs. Clean boards are resold for reclaiming copper.

It is lpg operated.

I don' like to process whole PCB's, i rather separate and sort stuff to lower the acid consumption thus lower the waste created.

Pete

 

[Ayham Hafez]

If you are in a hurry, how about trying hot concentrated HCl?

I process large quantities, I use plastic barrels, can't heat HCl

 

[Yggdrasil]

I process large quantities, I use plastic barrels, can't heat HCl

If you are processing large quantities, then Hydro-metallurgy is not your friend.
Pyro-metallurgy is the only viable way for large quantities in my mind.
Shred and smelt it all to bars.
Then electrolytic cell for copper or sell it directly based on assays.
Pick out any high value board and process them in small batches.

 

[Deano]

Tin and lead will dissolve in NaOH solution, around 20% NaOH by weight is needed for reasonable dissolution times and complete removal of these metals.
Reaction time depends on the relative proportions of the metals and what, if any, impurities are present.
Dissolving the NaOH in water will generate heat, use this free heat to speed up the leach.
Adding oxidants is not a requirement, the time determinants are temperature, agitation and caustic level.
Agitation is required, cap your barrels and put on a tumbler for best results.
Deano

 

[Ayham Hafez]

Tin and lead will dissolve in NaOH solution, around 20% NaOH by weight is needed for reasonable dissolution times and complete removal of these metals.
Reaction time depends on the relative proportions of the metals and what, if any, impurities are present.
Dissolving the NaOH in water will generate heat, use this free heat to speed up the leach.
Adding oxidants is not a requirement, the time determinants are temperature, agitation and caustic level.
Agitation is required, cap your barrels and put on a tumbler for best results.
Deano

What is the approximate time concentrated NaOH took to dissolve all tin and lead under 30 c temperature in addition to the generated heat from NaOH solution?