Hcl to dissolve tin

[kurtak]

I have a quick question about using Hcl to depopulate and dissolve tin, is it better to dilute 31%hcl when dissolving tin?

I may be wrong but doesn’t Hcl especially when hot just fume off Hcl vapor until it is 20%. Does the water play any roll in dissolving tin?

Getting back to the original question of this thread --- NO - it is not better to dilute HCl when dissolving tin - it will slow down the reaction AND if made to dilute it will actually cause the tin to precipitate out as stannic tin (the white paste)

if anything - when using heat (which is not needed when dissolving tin) which can/will vapor off HCl you would want to add "more" HCl to keep the HCl from becoming dilute

You "only" need to use hot HCl for dissolving solder IF the solder is an alloy of tin & lead --- that's because cold HCl does not react well with lead - but when lead is alloyed with tin the lead will dissolve along with the tin when the HCl is heated

Then - when the solution (tin/lead dissolved in hot HCl) is cooled - the lead will precipitate out as lead chloride crystals - which dissolve again when heated

Therefore - if the solder is tin solder (most if not all newer electronic scrap) - (mid 90s & newer) use HCl without heat & don't dilute it

older electronic (70s into early 90s) it is more likely the solder is lead/tin alloy therefore heat MAY need to be applied to dissolve the solder
Kurt

 

[butcher]

Thanks, Kurt, you explained that so very well.

Saying it another way.

HCl will only fume off if the concentration of the acid is above its azeotrope of around 20%.

Metals less reactive than hydrogen in the reactivity series like copper will not really react with HCl.

Now, the fact above can change if the copper has any copper oxidation, as the HCl would attack the oxidation products of the copper, making some cupric chloride in solution, which with oxygen absorbed from the air into the can also make the HCl more reactive towards copper metal, different metals ... but that is just nit-picking, HCl lone basically will not attack copper.

Base metals that are more reactive than hydrogen in the reactivity series like tin or lead will react or dissolve In HCl without the addition of an oxidizer.
In the reaction of HCl acid with these metals, we will have gases of that will evolve from the reaction, while HCl gas and its products may be carried off in the fumes of the other gases of the reaction it is not the HCl fuming off because of its azeotrope, or because of its concentration, as much as it is that some HCl fumes just getting carried along for the ride with the other gases evolving from the reaction such as hydrogen and the evolution of water vapors...

The HCl does not gas out of solution with the base metals it reacts with them to evolve hydrogen

solid Tin (Sn) metal or solid lead metal dissolves in hydrochloric acid (HCl) produces hydrogen gas (H2), it is the hydrogen gas that evolves from the reaction (and thus may carry some HCl fumes along for a ride) as the HCl is reduced to a chloride ion (Cl-), and the tin is oxidized to stannous chloride, or a lead chloride solution.

Sn(S) + HCl(aq) --> SnCl2(aq) +H2(g)
Pb(S) + 2HCl(aq) --PbCl2(aq) + H2(g)

Stannous chloride SnCl2 reacts ( or hydrolysis in the dilute solution) with water to form an insoluble basic salt called hydroxotin (II) Chloride Sn(OH)Cl(S) and hydrochloric acid in solution HCl(aq).

SnCl2(aq) + H2O(l) --> Sn(OH)Cl(s) + HCl(aq)

stannous chloride SnCl2and water H2O with oxygen O2 (oxygen absorbed into the solution from exposure to air...), we get a product of hydrolyzed stannic chloride SNCl4(aq) in solution and the insoluble salt called hydroxotin (II) Chloride Sn(OH)Cl(S).

6SnCl2(aq) + 2 H2O(l) + O2(g) --> 2SnCl4(aq) + 4Sn(OH)Cl(s)
6SnCl2(aq) + H2O + O2 --> Sn(OH)Cl + SnCl4

 

[kurtak]

You explain why hcl is better.

Because HCL has been the STANDARD method for removing solder (tin &/or tin/lead solder) by refiners (MAJOR refiners) around the world

Using NaOH is NOT the standard used by refiners

Does NaOH work --- yes

but there is a (good) reason why "experienced" refiners DON"T use it

Seems to me - as a NEW member here - you should be listening to them (the experienced refiners) instead of being combative with telling them how much wiser you are in your total lack of real knowledge &/or experience

Your experience - likely watching some "ill informed" you tube videos before joining this forum a few months ago with 44 post

The experience of those trying to help you ------

Butcher - member since 2008 with 8866 post - nickvc member since 2009 with 4343 post - Goran member since 2007 with 5007 post - Jon member since 2016 (under current user name) with 2743 post (was a member under another user name with MANY more post) - me member since 2014 (under current user name) with 1836 post (was a member under another user name with MANY more post)

Concerning "your" problem with Jon (& it is YOUR problem - because you don't like what &/or how he is telling you about refining) --- I recently just spent a week in his refining lab - Jon refines more gold "in one day" then you are likely to see in your life time (with your current attitude) --- on the other hand - if you gave him the "respect he deserves" as a "professional" refiner - you to may "someday" achieve the kilos of gold he refines

For what its worth (& as someone that has been at this for years) your "pushing" this idea of using NaOH to dissolve solder is a fools errand & continuing to "push it" you will soon rise to the level of being an idiot --- IMO
Kurt

 

[snoman701]

...but there is a (good) reason why "experienced" refiners DON"T use it

I understand that 95% of the reactions discussed on this forum are acid dissolutions...call it a hammer for your nail. But sometimes you need a screw, and I personally prefer screwing. :lol: :lol:

So what IS the reason experienced refiners don't use caustic?

Are there any, outside of the assumption that they are more accustomed to hammering instead of screwing?

 

[Shark]

To quote Kurt from this post...

Depopulated board in oil

And - don't forget - the FINE black powder from dissolving the tin away contains "gold" (and antimony) as well - so let that fine black powder from you HCl decant & the water washes settle out for processing as well

Kurt

Goods enough for me when I gain gold, even a tiny bit.

How would that tiny bit be gained using NaOH? Convince me it is better.

 

[Williamjf77]

I’m going to stick with the hcl, I didn’t try it without heat though. That would be good if it still strips tin solder without heat. I’ll keep it full strength.

 

[Jmk88]

Kurt,

That simply isn’t true. Refiners commonly use caustic. Particularly with jewellery.

Even Hoke mentions caustic.

And I don’t think I’ve once said I’m more experienced than others or know more; if anything I’ve repeatedly asked for input.

I believe I’ve expressed my gratitude for the people you’ve mentioned having input, as well as yourself.

The point is you don’t need to dissolve solder. You can simply remove it. Is that right or wrong? I believe right.

Why go to the trouble of dissolving when you can remove? That doesn’t make sense.

 

[Williamjf77]

I’m perfectly comfortable working with lye or acids, the precautions should be the same as far as respecting both. I get that some things are worse than others.

I’m just looking for practical means. I see now why some say the best way is to not process e scrap. Complete PITA compared to gold filled.

The education I got so far is invaluable though and the chemistry of it all is a huge learning curve but well worth learning.

 

[Jmk88]

Basically Kurts point was spot on; if you’re using modern e scrap yes, hcl.

If you’re using anything vintage, e scrap or jewellery I would definitely go with lye.

It’s a lot easier to remove in bulk on vintage things prior to removing any gold and lye will achieve this quite nicely.

But yes, if non lead containing solder (modern material) then I wouldn’t apply the same advice.

 

[kurtak]

Kurt,

(Point 1) --- That simply isn’t true. Refiners commonly use caustic. Particularly with jewellery.

(point 2) ---- Even Hoke mentions caustic. -----------



(point 3) --- The point is you don’t need to dissolve solder. You can simply remove it. Is that right or wrong? I believe right.

(point4) --- Why go to the trouble of dissolving when you can remove? That doesn’t make sense.

Point 1; - that simply is not true - there may be some you tube hobby "hacks" out there that commonly use NaOH to remove solder --- but not pro refiners - pro refiners ether use acid to "eliminate" solder - or in the case karat jewelry they simply melt it - pour it to shot - dissolve it in AR - Add a "bit" of sulfuric to precipitate the lead as lead sulfate - filter out any stannic tin &/or lead sulfate - precipitate the gold - put the gold through the proper washes - melt the gold

Point 2; - Hoke only mentions using NaOH in the final precipitated gold powder wash if you suspect "lead sulfate" followed your gold drop (page 73) --- other then that Hoke gives VERY CLEAR instruction to use hot HCl to "eliminate" tin/lead solder before taking the gold to AR (starting on page 70)

Point 3; - HCl "eliminate" the VAST majority of the solder when it "dissolves" the solder --- NaOH may "remove" much of the solder - but it's NOT going to eliminate all of it like acid does --- that means you are going to have more lead & tin follow you in the rest of your refining process. --- that is a fact & a period at the end of what I just said

Point 4 --- Because of what I just said above --- soooo - stop pushing what amounts to "misinformation" - you are coming very close to crossing the line of MANY that have come before you pushing such B.S. - & the don't last long here

Kurt

 

[Jmk88]

Kurt,

How is that misinformation?

Point 4 would be exactly the same as your point 1. If you remove the solder from vintage jewellery with lye, you would be able to dissolve the minor bits left and as you say, precipitate with sulphuric (or sulphamic).

There is nothing I have said factually incorrect; you may disagree with my opinion that lye is more effective on jewellery which is fine, you stick to you and I’ll do me.

I haven’t given any misinformation at all, I have simply pointed out another way of removing solder.

Why would someone be banned for expressing opinion? That’s not helpful to anyone, even if they are wrong there is enough people here that would point that out, which would result in valuable information.

I accept that you and others may not apply my approach, but to say it doesn’t work is not correct. Whether it’s better than hcl or not, I wouldn’t comment. I’ll just say I’ll stick to me.

Regards,

 

[Jmk88]

Kurt,

Another point, is that I don’t disagree hcl will dissolve solder. However, if you look at some posts here with the issue and I have had it myself, is that the rate of reaction across say 2kg of gold jewellery, would be tremendously slow, if simply placed in hcl and heated. You will also have other metals reacting with the hcl, particularly if heated.

You would be waiting a long time to have solder free gold. Even when incinerated, plus the amounts of solder (such as a 2k batch) would require a hell of a lot of hcl.

I think you need to calm down and stop attacking every point I make because I think its a debate worth having. Doesn’t need to become an argument.

My opinion, and it’s my opinion, is economically and environmentally you would be 1000 times better removing solder prior to gold recovery, IF APPLYING TO JEWELLERY.

This is the type of conversation that would benefit people looking to refine seriously.

 

[Lou]

...but there is a (good) reason why "experienced" refiners DON"T use it

I understand that 95% of the reactions discussed on this forum are acid dissolutions...call it a hammer for your nail. But sometimes you need a screw, and I personally prefer screwing. :lol: :lol:

So what IS the reason experienced refiners don't use caustic?

Are there any, outside of the assumption that they are more accustomed to hammering instead of screwing?

Maybe not caustic baths...but experienced refiners (i.e. places doing a truck load every 20 min...we all know who they are) do something similar. Moreover, caustic gets the masking and the tin and without fume. Is it more dangerous than muriatic acid? Absolutely. Is the waste somewhat more involved? Absolutely. Is it better? In my opinion, depends on the tin content. Stannate de-tinning is well established and used on loads of tinned copper since time immemorial. Higher tin, the better.

On the blister copper that contains the PMs poured from the converter/ shaft furnace, the slag contains hydroxide...which one I cannot say, but believe me, 'tis everything but the squeal and there's plenty of money in processing tin based solders. That tin slag also contains the Ta and Nb from caps. It also sucks to process :twisted:

Metallic Resources, really close by to us here in Ohio, has a process where they do very very large quantities of solder.

 

[Jmk88]

Lou,

That’s essentially all I was trying to say.

https://www.bairdmint.com

This is what I witnessed one of their refiners do last week (with my jewellery).

His advice was big batches are not economically viable if you are talking solely about solder removal (bit wordy) unless you have extreme patience and are not aiming to make money.

I have tried both and unless I’m placing the jewellery in hcl incorrectly, even with boiling and the horrendous fumes it generates, the results were not really comparable. That’s my personal experience and was reinforced by the chap at the above.

He said you just simply wouldn’t keep up with serious refiners, plus would generate fumes, a lot of acid and money expenditure.

I know butcher had provided the capacity of hcl for lead/tin but can’t find it. I believe it was around 82g per litre off the top of my head, which is a hell of a lot of acid consumption, in my opinion.

I’m beginning to fear saying anything out of not wanting to be publicly attacked and threatened with banning, so if any of the above is not right please do let me know. It will be hugely appreciated.

Kindest Regards,

 

[butcher]

Jmk88,
We do not ban members because they have a different opinion, we do expect them to keep any disagreement civil polite and without attacking the other member, or disrupting the forum...

Disagreements can be a good thing as long as we learn something from them and we all can come to some kind of agreement together if nothing else to agree to disagree with each other as gentlemen and ladies...

As far as stirring up a hornet nest and getting a lot of members to disagree with you on your first arrival to the forum, well sorry you are on your own on that one,

Looks like your holding your own and being a gentleman and putting your argument over effectively, so who knows you may survive the debate and maybe we will all learn something from it.

 

[Jmk88]

Thank you Butcher, very much appreciated.

Kindest Regards,

 

[snoman701]

It would also be helpful to note that those whose name is in green are moderators.

They have proven time and time again to be consistently level headed, well spoken, and value added assets to the community.

Everyone else is just a minion with an opinion.

Most of the problems in refining have more than one right answer...which answer is right for you depends on your individual situation, your education and your experience.

 

[anachronism]

It would also be helpful to note that those whose name is in green are moderators.

They have proven time and time again to be consistently level headed, well spoken, and value added assets to the community.

Everyone else is just a minion with an opinion.

Most of the problems in refining have more than one right answer...which answer is right for you depends on your individual situation, your education and your experience.

Hehe

 

[AuPure]

I just wanted to say as a new member with little experience with recovery and refining, I have found this debate quite interesting. I like to learn about all the different processes.

I can say that personally I have just started doing very small batches < 10 lb. Of ceramic ICs with some solder still on the pins and holding the tiny capacitors on the top. For batches this small using hot HCL has worked great for me. But I do this as a hobby and can let the parts soak in hot HCL for hours a day for multiple days if needed. I'm not doing this for a living, or for the $. I just like the whole chemistry/ mad scientist aspect of it. :lol: And having a beautiful little button of gold for my efforts at the end is just a good bonus.

Thank you all again for sharing this info freely.

 

[Williamjf77]

I agree, I love the heated debates. It ends up bringing out a lot of great info that is probably already somewhere on the forum but gives it a bump.

I was the OP. Guess I’m the instigator.

Back on to the hcl, I just put 4lbs of mixed cpus to remove pins in hcl. It’s 60 something degrees here in CT.

I want to see how long it takes without adding heat. If it goes over 24 hours I will abandon it and heat it. It is supposed to go down to like 15 tonight so we’ll see.