I've been hoarding circuit boards for some time now, I don't want to refine any precious metals myself, unless I can't sell it for a satisfactory price as is to a primary escrap buyer like BoardSort, a big part of my hoard is "low-grade" boards, that aren't bought at a price that justifies shipping to a buyer, but the ic chips, exotic metal capacitors, ect. Are. Which means desoldering. To avoid diversifying my inventory any further until I'm ready I haven't done any desoldering yet, and have put a lot of thought into into how to handle this stage, to reduce frustration and improve efficiency
The problems I see with heat based desoldering is "smearing" of solder onto components, with small components like mlccs stuck together into booger like granules, as well as not recovering any of the solder, at least not in an easy way. That's significant to me, it may not be a precious metal but tin is the costliest BASE metal, and is a much bigger portion of this material by weight than any precious metal, potentially making tin the largest contributor to value, plus I like it for the fact I can melt significant quantities with a hot plate for casting. In addition all the associated risks with fumes from burning board material with your heat source, I don't want to breath that, and I don't want the neighbors complain either.
Where I've landed with all this is a drafted process to chemically desoldering the boards, and then electrolytically reclaim the tin from the desoldering solution, i still have some uncertainties about this process, and was hoping the community here could answer some questions for me.
The following is the proposed process step by step with my associated questions regarding each stage.
0. At this time I'm only planning this process for boards which are predominantly thruhole mounted where all solder joints are accessible from one side that has little to no components on that side, from observation the "solder side" frequently has very small mlccs which will need to be dealt with later, smd components I think would be easier to remove with hot air, but I'll test it out at some point.
1. Prepare boards by removing any iron, aluminum, or other base metals below tin on the galvanic scale( I think fe and Al are the only ones which would be present in this material) particularly in the "contact zone"
2. Set boards "solder-side" down in a tray with hcl that does not crest above the boards top surface, I want them sitting in it, not immersed. Let them sit till components desoldering.
So, as I understand it, the tin should go into solution as tin(II)Chloride, while the lead will form it's insoluble chloride and remain as a solid in bottom of tray(along with any silver chloride, or antimony) and no copper should go into solution until the tin is depleted, also my math tells me that the hcl should be able to digest
487g of tin OR 875g of lead per liter, this was calculated by finding the Cl content per liter by weight and then calculated the Cl content by weight of sncl2 and pbcl2 so if sn and pb are present in a 50/50 alloy (common comp. For leaded solder) a liter of acid should digest half of each figure? I also suspect that the lead may wind up on the tray floor as metallic powder, similar to anode slime, as lead reacts more slowly than tin? That's fine by me it just means my acid is going to convert tin more efficiently by not donating cl to turn an insoluble metal to an insoluble salt
3. Pour pregnant solution into vacuum filter or settling vessel, whatever proves easier, rinsing off board and tray into filter
This is another point of uncertainty, if diluting sncl2 solutions forms insoluble tin hydroxychloride which I can find very little information on, so id rather avoid it's formation altogether, so I have to rinse with hcl ? What concentration is sufficient to prevent the dissasociation of sncl2?
3.place filtered sncl2 solution in electrolytic cell to reduce tin to metal form, ready to be rinsed and melted, likely at fairly high purity,
The only accounts of sncl2 electrolysis I've seen were aimed at producing visually appealing crystals and were operated at low concentrations, would producing "compact" cathode deposit be acheivable at or near saturation as in copper cells?
Handling the lead chloride heavy solids fraction is another bag of snakes, I'm too tired to think about it right now.
I look forward to your responses, and producing some high purity tin
The problems I see with heat based desoldering is "smearing" of solder onto components, with small components like mlccs stuck together into booger like granules, as well as not recovering any of the solder, at least not in an easy way. That's significant to me, it may not be a precious metal but tin is the costliest BASE metal, and is a much bigger portion of this material by weight than any precious metal, potentially making tin the largest contributor to value, plus I like it for the fact I can melt significant quantities with a hot plate for casting. In addition all the associated risks with fumes from burning board material with your heat source, I don't want to breath that, and I don't want the neighbors complain either.
Where I've landed with all this is a drafted process to chemically desoldering the boards, and then electrolytically reclaim the tin from the desoldering solution, i still have some uncertainties about this process, and was hoping the community here could answer some questions for me.
The following is the proposed process step by step with my associated questions regarding each stage.
0. At this time I'm only planning this process for boards which are predominantly thruhole mounted where all solder joints are accessible from one side that has little to no components on that side, from observation the "solder side" frequently has very small mlccs which will need to be dealt with later, smd components I think would be easier to remove with hot air, but I'll test it out at some point.
1. Prepare boards by removing any iron, aluminum, or other base metals below tin on the galvanic scale( I think fe and Al are the only ones which would be present in this material) particularly in the "contact zone"
2. Set boards "solder-side" down in a tray with hcl that does not crest above the boards top surface, I want them sitting in it, not immersed. Let them sit till components desoldering.
So, as I understand it, the tin should go into solution as tin(II)Chloride, while the lead will form it's insoluble chloride and remain as a solid in bottom of tray(along with any silver chloride, or antimony) and no copper should go into solution until the tin is depleted, also my math tells me that the hcl should be able to digest
487g of tin OR 875g of lead per liter, this was calculated by finding the Cl content per liter by weight and then calculated the Cl content by weight of sncl2 and pbcl2 so if sn and pb are present in a 50/50 alloy (common comp. For leaded solder) a liter of acid should digest half of each figure? I also suspect that the lead may wind up on the tray floor as metallic powder, similar to anode slime, as lead reacts more slowly than tin? That's fine by me it just means my acid is going to convert tin more efficiently by not donating cl to turn an insoluble metal to an insoluble salt
3. Pour pregnant solution into vacuum filter or settling vessel, whatever proves easier, rinsing off board and tray into filter
This is another point of uncertainty, if diluting sncl2 solutions forms insoluble tin hydroxychloride which I can find very little information on, so id rather avoid it's formation altogether, so I have to rinse with hcl ? What concentration is sufficient to prevent the dissasociation of sncl2?
3.place filtered sncl2 solution in electrolytic cell to reduce tin to metal form, ready to be rinsed and melted, likely at fairly high purity,
The only accounts of sncl2 electrolysis I've seen were aimed at producing visually appealing crystals and were operated at low concentrations, would producing "compact" cathode deposit be acheivable at or near saturation as in copper cells?
Handling the lead chloride heavy solids fraction is another bag of snakes, I'm too tired to think about it right now.
I look forward to your responses, and producing some high purity tin
