is HCl step needed?

[bswartzwelder]

I have quite a bunch of cell phone boards which I am getting ready to process. Once I have removed everything which will come off with my heat gun, the question is: Do I soak the boards in HCl to remove the solder or just place them in AP? Is there any advantage to using the HCl twice or would just a dunk in AP do the same thing? Not looking to reinvent the wheel, just don't want to take a shortcut which may not work as planned.

 

[kronix]

I'm no expert, but I believe AP does remove solder. Although you may want to remove solder first with straight hcl so you can remove the solder mask with a lye solution in case there is any gold traces under the mask. I'm sure someone will correct me if I'm wrong, but that's how I would go about it.

-Ian

 

[nickvc]

Again I'm no expert but if I had a choice I'd remove tin before any other process, if it gets through to your gold solution you will understand why :twisted:

 

[Marcel]

If there are BMs you must do it.
Some BMs get dissolved by simple HCl, then PMs (such as copper the lowest) need oxydizing acids or acid plus oxidizer to dissolve them.
If you dunk you scrap into AP, the BMs will go into solution, blocking the copper or at least part of it to get dissolved.
It is as if you have a plane and you tell all passengers that they can use the First class. What will happen?
First class will be full, while noone wants to go into econmy for the same price.
You should treat your scrap with a non-oxidizing acid first, then remove the solution and therefore remove the basemetals. Then you go next step and remove the first precious metal (Copper) with an oxydizing solution such as AP or dilute nitric etc.
Then you advance and dissolve silver and up....

 

[Geo]

the best answer i can give you is this. if you plan on re-using your AP solution for other projects, you want to keep it as clean as possible. solder on cell phones contains several different metals including tin, lead and silver plus a couple of heavy metals in very small quantities. AP is re-usable forever if cared for and taken care of.the main cause of AP failure is contamination of the AP solution by metals other than copper. always start with the cleanest material you can as it will save you many headaches further down the line of processes.hcl is fairly cheap and for the purposes of removing solder a diluted solution will work just fine (especially if you add a little heat) i generally dilute with water to 1/3 hcl concentration. if you just put it in a bucket in the sunlight, it may take a couple of days. when you remove the boards, the gold traces will look dull and resemble copper color.this effect makes people think the gold has been removed in the hcl. dont worry, the gold will still be there. the color is due to the negative charge of the gold and the positive charge of the dissolving tin. when it dries, you can wipe it off with a dry rag. that is one way tin will follow your gold through the different processes and as Nick said, its a pain to deal with if it makes it that far.

 

[portalindo]

Hi all, i'm a newcomer seeking for a knowledge ,

the best answer i can give you is this. if you plan on re-using your AP solution for other projects, you want to keep it as clean as possible. solder on cell phones contains several different metals including tin, lead and silver plus a couple of heavy metals in very small quantities. AP is re-usable forever if cared for and taken care of.the main cause of AP failure is contamination of the AP solution by metals other than copper. always start with the cleanest material you can as it will save you many headaches further down the line of processes.hcl is fairly cheap and for the purposes of removing solder a diluted solution will work just fine (especially if you add a little heat) i generally dilute with water to 1/3 hcl concentration. if you just put it in a bucket in the sunlight, it may take a couple of days. when you remove the boards, the gold traces will look dull and resemble copper color.this effect makes people think the gold has been removed in the hcl. dont worry, the gold will still be there. the color is due to the negative charge of the gold and the positive charge of the dissolving tin. when it dries, you can wipe it off with a dry rag. that is one way tin will follow your gold through the different processes and as Nick said, its a pain to deal with if it makes it that far.

from hoke's book page 71 & 72 "If there are visible lumps of soft solder, cover the articles with full strength hydrochloric acid, and heat to boiling until the solder loosens and can be scraped off. Then pour off the acid and throw it away, and wash the metal thoroughly to get rid of all traces of this acid. Wash till the washings have no more sour taste, or fail to turn blue litmus paper red. (See Chapter IX.) Next, treat the metal with nitric acid and a little water, as usual. Since low grade scrap is mostly base metal, you will need much more acid than in Chapters V and VI, and there is much more chance that it will boil over, so add the acid slowly. This dissolves all the copper, silver, brass, zinc, iron, cadmium, and nickel, that the acid can reach. Tin is converted to the gelatinous tin paste. Lead turns into the scantily soluble lead nitrate; add a little more water, and all the lead nitrate will dissolve."

my question is :
how could we be sure that there's no trace of hcl left in the scrap after several washing with water before processing with nitric acid? i dont want to mix the tin and lead with the gold in the solution when the scrap process with aqua regia as i found in the forum it will be difficult to get the gold from solution if there's a presence of tin and lead. or should i wash over with hcl again to make sure that there's no trace of tin and lead, and incineration the scrap after that process it with aqua regia?. Btw the scrap is cell phones board

Thanks, and sorry for my bad english

 

[Geo]

it depends on what material your working with. ms. Hoke was referring to scrap jewelry i would assume as modern electronics had not been invented when she wrote the book.if you are talking about scrap karat gold, incineration will remove all traces of organics and left over acid residues. electronics will be more problematic to remove all the acid so you should not concentrate your efforts towards this end or go to great lengths to do so.after a hcl bath to remove solder, simply rinse the material well with clean water. if you intend on using AP to remove gold foils from printed circuit boards, this is all you will need to do.keep in mind what metals react to which chemical before you start. aluminum and zinc reacts to hcl strongly so these metals need to be removed mechanically as well as any batteries before the hcl bath.