100 lbs of lead free solder

[DNIndustry]

Been a while.

I have around 100 pounds of supposedly lead free solder
Some has a gold sheen to it. I don't know if they make gold solder alloys but what the best way to start biting this whale without wasting too much time if material is useless.

 

[ssabovic]

send us some pictures.
thank you

 

[FrugalRefiner]

A small test would be a good start. Dissolve a small bit in aqua regia, then test the solution.

Dave

 

[g_axelsson]

Better start with pure hydrochloric on a sample, then filter / decant off the stannous chloride and work with what's left. There shouldn't be any precious metals in the liquid. Any silver will stay behind as silver chloride and if it's used solder with gold dissolved it will also stay behind in the sediments.

My question is where the value lies. If the tin is worth more than the silver content and what the cost of processing would be, to dissolve all that tin seems to be wasteful, not to mention the cost of treating the wastes. I think I would look into electrolytic methods.

If the solder is unused I would do an XRF on it to get the composition and try to sell it on eBay, that would probably give the least amount of waste and work for most return.

Göran

 

[DNIndustry]

Thank you. Good advise.

 

[72chevel]

I get Lead free solder from my work from time to time. They send out a puck size sample to make sure it is still Lead free. If something is out of speck they drain it and put new in. The gold color is probably not what you think it is, I have seen that to.... I attached the paper work of what we get back from the sample sent in for analysis. This is Solder used in the last year or so, yours maybe different if it is from a decade ago. The sample was taken from 50lbs of solder


Solder Analysis Report
J-STD-001-E Sample in or out of
Sample results Wave soldering J-STD-001-E
Weight percent Specifications Specification
Tin................. 96.14 97.500% max. In-range
Arsenic........... < 0.0010 0.030% max. In-range
Antimony....... 0.0150 0.200% max. In-range
Gold.............. 0.0082 0.200% max. In-range
Iron................ 0.0021 0.020% max. In-range
Nickel............. 0.0740 0.050% max. Out-of-range
Bismuth.......... 0.0110 0.250% max. In-range
Aluminum....... 0.0005 0.006% max. In-range
Copper(1)....... 0.6300 1.100% max. In-range
Silver.............. 3.0900 4.000% max. In-range
Zinc............... 0.0004 0.005% max. In-range
Cadmium........ 0.0008 0.005% max. In-range
Indium............ 0.0027 0.100% max. In-range
Sulphur.......... 0.0005 Not Applicable Not Applicable
Phosphorous.. < 0.0100 Not Applicable Not Applicable
Lead............... 0.0239 0.100% max. In-range
1 Copper: When concentrations reach 1.0%, MRI recommends monitoring the solder bath more

 

[FrugalRefiner]

72chevel, that's a very interesting analysis. Do you have any information on the starting analysis? In other words, how much of that contamination is in the starting material, and how much is dissolved in the process of the soldering operation?

Dave

 

[72chevel]

I do not think we ever send in samples when new but I will look and see if the data sheet shows anything. This is about all I could find about initial ingredients:

Metallic Resources’ SAC305 Lead-free solder
alloy is manufactured from electrolytically
processed tin and other elements to create solder
so pure it far exceeds the most common
specifications. It has been independently tested
to meet all restrictions on hazardous substances.
It is RoHS compliant. The specific
alloy is Sn96.5/Ag3.0/Cu0.5 (commonly
referred to as SAC305 alloy). The melt point
is 217˚C and recommended operating temperature
ranges are between 250-275˚C.
Other variations on the tin/copper, tin/silver
and tin/silver/copper combination alloys are
also available, depending upon customer preference.
Standard packaging includes 50
pound boxes containing cast bars, ingots, or
feeder bars.
When copper content approaches 1.0%,
Metallic Resources offers a replenishment
alloy, SAC305-R to lower the copper content
of the solder bath.
Versatile Uses

 

[Geo]

Since it is lead free, I would think the majority would be tin. Melt the metal and cast into anode bars and part the tin out using stannous chloride as the electrolyte. You should get back relatively pure tin with any values being left in the anode slimes. If it were mine, that's exactly how I would deal with it.

 

[rickbb]

Typical lead free for electronics use is advertised as 96% tin, 4% silver, which is what 72chevel's report shows, with a trace of antimony. But there are many variations on that. If it was for plumbing use, may not have silver at all and be mostly tin and antimony.

So out of 100 lbs., you have 96 pounds of tin and 4 pounds of silver, maybe.

 

[kurtak]

Since it is lead free, I would think the majority would be tin. Melt the metal and cast into anode bars and part the tin out using stannous chloride as the electrolyte. You should get back relatively pure tin with any values being left in the anode slimes. If it were mine, that's exactly how I would deal with it.

One of the problems with electro refining tin is that the tin grows as "long" whiskers & they grow very fast so you have to keep a "close eye" on the cell to keep the growth knocked down & prevent bridge short out between anode & cathode

I watched a video a couple years ago (can't find it now) where a couple guys at a university made a cell with an automated roller that would every so often roll over the cathode to knock down the growth as a way of dealing with the problem so that the cell could run longer without need to continually attend it

Kurt

 

[Geo]

Couldn't you control the growth rate of crystals by adjusting the amps? From what I've seen, the faster the crystal grows, the longer and less dense they are. Perhaps adding some sort of buffer to the electrolyte to make the crystals more dense.

 

[kurtak]

Couldn't you control the growth rate of crystals by adjusting the amps? From what I've seen, the faster the crystal grows, the longer and less dense they are. Perhaps adding some sort of buffer to the electrolyte to make the crystals more dense.

Geo - I can't say for sure as I have never actually tried it only looked into it a couple years ago & learned that the long whisker growth is a problem

To a point - amp/volts settings would certainly play a part as well as buffers &/or inhibitors - in other words (at least as I understand it) proper volt/amp setting along with additives all help with getting a nice dense & even deposit on the cathode surface as a "surface plating"

The problem (again as I understand it) comes when the tin growth starts to get beyond that of a surface plating - as more metal (tin) gets deposited on the cathode the surface begins to become uneven (bumpy - highs & lows) & metal starts depositing more on the highs then on the lows which in turn becomes more uneven to the point of forming a rough surface with "many" little points & its from these little points that the tin starts to deposit at a rapid rate causing the growth of the whiskers

Tin is a much more reactive metal then silver so it parts from the anode & deposits at the cathode at a much faster rate - part of why it grows in long fast growing whiskers rather the dense crystals

Also - additives can cause a problem with co-depositing in electro refining (not a problem when using pure tin in a plating bath)

Also - I believe sulfuric is preferred over HCl for making the electrolyte (stannous sulfate) 40g tin/liter & 120g sulfuric/liter --- I believe the whisker growth is increased when HCl is used as electrolyte

Kurt

 

[MarcoP]

Would be a great way to process all solder coming from depopulated boards, including BGA solder. Would lead cause any issue?

Marco

 

[g_axelsson]

Would be a great way to process all solder coming from depopulated boards, including BGA solder. Would lead cause any issue?

Marco

If the electrolyte contains sulfuric acid the lead would create undissolvable lead sulfate, possibly cover up the anode and passivate it.

The refining of tin-led solder is discussed in Ammen, second edition page 277. The method recommended is to do electrolysis in a molten chloride electrolyte, made up of potassium chloride, lead chloride and tin chloride. Copper, gold, silver and other contaminants are concentrated at the anode. The anode and cathode leads are made up of tungsten.

The method is described in this article.
https://books.google.com/books?hl=en&id=NpqjY-AvX1kC
Can someone access this and download it? I can only see small fragments of the text, probably since I'm in Sweden.
Oh, I found it viewable here http://babel.hathitrust.org/cgi/pt?id=mdp.39015077584053;view=1up;seq=1 and it is possible to download one page at a time.

Happy reading! :mrgreen:

By the way, here is an article on wet chemistry refining of lead free solder. I just wonder about the cost of this process, a lot of acid is used.
https://www.jim.or.jp/journal/e/pdf3/53/12/2175.pdf

Göran

 

[FrugalRefiner]

The first link is in a language I'm afraid I don't recognize.

The second and third are good. You're a research master!

Dave

 

[Geraldo]

I know this is a refining forum, and my own background is refining on a very large commercial scale, but...why do you want to refine this?

If it is for fun - have at it.

If it is for money - I guarantee you won't make any.

If it is to build your stockpile of chemicals (e.g. stannous chloride) you could make that and just deal with the silver loss - if there is any silver. Well, you could recover a slime containing silver that you could then do something else with. But - who exactly needs hundreds of pounds of stannous chloride? It is also worth less than metallic tin and much less than lead-free solder e.g. you are reducing the value of your scrap, rather than moving UP the value chain.

If you want to turn this around for $$ the easy way - sell it to home ammunition reloaders. A proportion of them who cast their own bullets want tin and silver in a convenient form in order to harden lead bullets. There is a significant premium if you are selling by the pound. Craigslist and similar sites would get you plenty of customers. People in my area are endlessly scrounging for exactly this type of material because they don't like paying the exhorbitant prices for solder at the hardware store.

Just a thought.

 

[g_axelsson]

The first link is in a language I'm afraid I don't recognize.

The second and third are good. You're a research master!

Dave

That, my friend, was Swedish... sorry about that, didn't realize google had switched to the local Swedish site. I've changed the link now to point to the English site instead.

Now I'm just waiting for kadriver to build a system and make a nice video about it. 8)

Göran

 

[kurtak]

Now I'm just waiting for kadriver to build a system and make a nice video about it. 8)

Göran

:lol: :lol: :lol: - I to love kadriver's videos :mrgreen:

I think there should be a (single) post in the library that has a link to all of his videos & each time he ad a video ad it to the post 8) (hint, hint)

Kurt

 

[kurtak]

I know this is a refining forum, and my own background is refining on a very large commercial scale, but...why do you want to refine this?

If it is for fun - have at it.

If it is for money - I guarantee you won't make any.

That was kinda the point of my posting the problem with trying to home refine tin

Why tie up a cell that can be running silver (with less problems) when you can sell the (slight) corrupted tin for a fair price

Kurt