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

[Yggdrasil]

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?

That is easy to find out.
Do a small test, then you also can see when it looses effect and find out if can just replenish with new NaOH
or you need to change the whole batch.
It will also give you an idea on how to treat the waste.
The waste will probably be mostly solids after evaporating.

One Idea would be to see if you can use an electrolytic cell to strip the Tin out of solution.
It need to have wipers to break the Tin whiskers though.

How many tons of material per week/month do you expect to run?

 

[Yggdrasil]

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?

The formula is: Sn + 2NaOH + H₂O → Na₂SnO₃ + 2H₂
From this you see that one mole of Tin needs 2 moles of NaOH.
So one liter of 20% solution is approximately 200g of NaOH and can as such dissolve 100 grams Tin under ideal conditions.
Real world conditions, I'd expect more or less 50-75% of this to be achievable,
since there are other substances interfering with the process, namely Copper, other base metals and solder mask.
Only tests will show, and small scale test will not necessarily scale linearly to full size batches.

 

[Ayham Hafez]

That is easy to find out.
Do a small test, then you also can see when it looses effect and find out if can just replenish with new NaOH
or you need to change the whole batch.
It will also give you an idea on how to treat the waste.
The waste will probably be mostly solids after evaporating.

One Idea would be to see if you can use an electrolytic cell to strip the Tin out of solution.
It need to have wipers to break the Tin whiskers though.

How many tons of material per week/month do you expect to run?

Will make a test and feedback, right now I have 8 tons of PCB, usually I finish 3 tons per month.

 

[orvi]

What you plan to do with all of these drums of toxic Pb waste ? In my opinion, hydrometallurgical depopulation is not viable even on lower scale. Because you are losing significant portion of revenue by dissolving precious tin into the leach. And you need to deal with all of that liquid afterwards. Pouring such quantities down the river will wreck the enviroment pretty badly. And also children in your region will develop neurological problem, ADHD and lower IQ, because lead is potent neurotoxin. All proven facts. I hope you do not dispose the waste this way.

Heated de-soldering device is best for you. Rotating drum is only one of many designs. Vibrating conveyor type is also a possibility. If you are processing tons per month, you should be able to afford to build one and save a lot of time, chemistry, money on chemicals and also retrieve precious solder.

 

[GoIdman]

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

Can tin an lead be reclaimed afterwards from solution? Sound interesting since tin has good price nowadays...

Pete.

 

[Ayham Hafez]

What you plan to do with all of these drums of toxic Pb waste ? In my opinion, hydrometallurgical depopulation is not viable even on lower scale. Because you are losing significant portion of revenue by dissolving precious tin into the leach. And you need to deal with all of that liquid afterwards. Pouring such quantities down the river will wreck the enviroment pretty badly. And also children in your region will develop neurological problem, ADHD and lower IQ, because lead is potent neurotoxin. All proven facts. I hope you do not dispose the waste this way.

Heated de-soldering device is best for you. Rotating drum is only one of many designs. Vibrating conveyor type is also a possibility. If you are processing tons per month, you should be able to afford to build one and save a lot of time, chemistry, money on chemicals and also retrieve precious solder.

Always pouring solutions done after naturalization, so there is no harms.

 

[Ayham Hafez]

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.

I made an experiment, leached pcb in HCL 31% grade, it took about 12 hours to dissolve all tin with room temperature, I got a thick and a bit sticky white foam at the top of the solution, what it could be? And can I recover tin from the solution after filtering with using electrolysis method?

Another question, from your experience, regardless cost, stripping gold using nitric gives more gold recovery rate than using AP or the same, materials are PCB after HCl leaching.

 

[Yggdrasil]

I made an experiment, leached pcb in HCL 31% grade, it took about 12 hours to dissolve all tin with room temperature, I got a thick and a bit sticky white foam at the top of the solution, what it could be? And can I recover tin from the solution after filtering with using electrolysis method?

Another question, from your experience, regardless cost, stripping gold using nitric gives more gold recovery rate than using AP or the same, materials are PCB after HCl leaching.

I can not say from my experience.
Nitric is too costly for this use for me.
But both should give that same recovery if done properly, Metastannic may pose a challenge with Nitric though

 

[Ultrax]

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

Metallic lead won't dissolve even in the molten 100% NaOH, because it requires an additional (and powerful) source of oxygen to produce litharge first. Litharge will dissolve in NaOH readily.

We receive very clean lead from dirty lead alloys using this method - all impurities in lead (like antimony, tin, cadmium, etc.) are oxidizing in the melt of NaOH at 500C (except PMs, of course).

Perhaps thin films of oxidized lead (on PCBs) will dissolve slowly in the saturated NaOH solution, but I think you will have to boil it long enough.

 

[Ayham Hafez]

I have done a test for using NAOH to dissolve tin, used 50% NAOH concentrated solution, waited 24 hors, the results were negative since I didn't notice tin dissolved at all, only aluminum dissolved beside the resin layer of the boards, I think using HCL is much more effective since Concentrated HCL need about only 5 hours in room temperature to dissolve all tin.

 

[Ultrax]

I have done a test for using NAOH to dissolve tin, used 50% NAOH concentrated solution, waited 24 hors, the results were negative since I didn't notice tin dissolved at all, only aluminum dissolved beside the resin layer of the boards, I think using HCL is much more effective since Concentrated HCL need about only 5 hours in room temperature to dissolve all tin.

First of all, we are talking about 100% tin with no impurities. Tin dissolves slower than you are expected. Massive tin won't dissolve in a reasonable time so it needs to be powdered to increase reaction speed. You should use 70-90% NaOH and boil the solution to get acceptable results.
And do not try to compare acidic dissolution with basic Sn complexation speed.

 

[Ayham Hafez]

I have 3 types of boards, two of them high gold plated, and the other is high grade gold pins. As first stem I will leach them in HCl to eliminate tin and seperate components, but whats next?


I'm very confused about big boys advices of never use AR directly, I tested before the gold pins board in AP, more than week and I didn't get the gold foils, I think there is a thick Nickel layer under it.

Regard the gold plated boards, both types tested in AP, I got the gold foils but gold recovery rate was much less than using AR directly inspite of never used peroxide, I just add a little copper chloride to the batch and use bubbler.

I attached photos to get the right advice and try to process them in the right way, regard the pins board I have no chance to dismantle pins.

 

[Yggdrasil]

I have 3 types of boards, two of them high gold plated, and the other is high grade gold pins. As first stem I will leach them in HCl to eliminate tin and seperate components, but whats next?


I'm very confused about big boys advices of never use AR directly, I tested before the gold pins board in AP, more than week and I didn't get the gold foils, I think there is a thick Nickel layer under it.

Regard the gold plated boards, both types tested in AP, I got the gold foils but gold recovery rate was much less than using AR directly inspite of never used peroxide, I just add a little copper chloride to the batch and use bubbler.

I attached photos to get the right advice and try to process them in the right way, regard the pins board I have no chance to dismantle pins.

The professional companies do not process boards chemically.
Simple as that, they shred, pyrolize, incinerate and smelt.

 

[Ayham Hafez]

The professional companies do not process boards chemically.
Simple as that, they shred, pyrolize, incinerate and smelt.

Ok, but what if we want to process them by hydrometallurgy process?


By the way, I read that the gold recovery using hydrometallurgy process has higher recovery rate than pyrometallurgy process.

 

[Yggdrasil]

Ok, but what if we want to process them by hydrometallurgy process?


By the way, I read that the gold recovery using hydrometallurgy process has higher recovery rate than pyrometallurgy process.

That would depend entirely on the skills of the said processor.
In the scale of most moderate size processor, the upside of less waste will count significantly on the profitability in the end.
Do you think any professional big scale processor would select anything else than the most economical process?

 

[Ultrax]

Ok, but what if we want to process them by hydrometallurgy process?


By the way, I read that the gold recovery using hydrometallurgy process has higher recovery rate than pyrometallurgy process.

When you stated something like (I read ....), it is advisable to provide a link to the source of the facts.

 

[Ayham Hafez]

When you stated something like (I read ....), it is advisable to provide a link to the source of the facts.

https://sustainenvironres.biomedcen...yrometallurgical methods,management [12, 13].

 

[Ayham Hafez]

That would depend entirely on the skills of the said processor.
In the scale of most moderate size processor, the upside of less waste will count significantly on the profitability in the end.
Do you think any professional big scale processor would select anything else than the most economical process?

Sure, none like to pay 10 while he can pay only 9, but there are other circumstances, in my case I can't run pyrometallurgy process at this time.

I think I have to change my question to determine that I want to process the mentioned PCBs with hydrometallurgy techniques.

 

[Yggdrasil]

https://sustainenvironres.biomedcen...yrometallurgical methods,management [12, 13].

I just browsed this article.
It starts out with a statement that hydrometallurgical processing is better than pyrometallurgical processing due to the lower environmental impact, which is plain wrong.
There is however no comparison or other proofs presented.

They pyrolyze but do not ash the carbon????
This article seem worthless.

 

[Ultrax]

"For the processing of 1 t of waste PCBs, the costs would be approximately USD 34 for the energy consumption of microwave pyrolysis".

The absolute nonsense in this article, as for me. Have you ever tried to burn 1 ton of PCB for $34? How much money will you pay for the facility for pyrolysis and toxic fumes scrubbing in real life?