32% HCL Dissolves Copper???

[Scott2357]

I read HCL alone would not dissolve copper without an oxidizer like H2O2. This link I picked up from here also shows this although there's no mention of temperature or concentration being a factor. http://www.teachersdomain.org/asset/lsps07_int_metalshcl/

I was trying an experiment to selectively dissolve solder from a memory stick PCB. It was old so I would assume it was tin/lead and not the Rohs solder used today. This was an unpopulated blank board but was pre tinned with solder. It was cold out so I warmed the solution to about 90-100' F with a crock pot to speed things up. After a while the solder dissolved away making the solution a light green color and began to show the copper pads. About 50% of the pads still had solder so I let it sit a bit longer but when I came back most of the copper had dissolved too and it had become a darker green? I decided that even though this was not supposed to happen that possibly the concentration was too high and so diluted with water to about 15% HCL. This stopped the process on the remaining copper but also precipitated the copper from solution onto all the remaining metal surfaces making the solution clear again. The precipitant had an affinity to the metal surfaces but didn't actually stick to it. It continued to slowly dissolve the remaining solder but not any more copper.

What did I miss, can someone explain? :?:

 

[Irons]

Air contains oxygen.

I have some copper wire that has been sitting in HCL for over a year and there is no color to the solution. I added Sodium Sulfite to scavenge the Oxygen, thus, no reaction. The Copper is still as pink as a Baby's butt.

Try it yourself and see.

 

[Scott2357]

Thanks Irons, that makes sense. Just added Sodium Sulfite to my grocery list. :lol: I wondered about exposure to the air but thought there wasn't enough time for that much to be absorbed. So is the tin/lead still in solution or did it drop out with the copper when I diluted and I just can't see it?

 

[goldsilverpro]

As I understand it, it seems that, once the HCl + oxygen dissolves a little copper, it becomes self-perpetuating, from the action of the copper chloride that is produced.

 

[Sodbuster]

Hi guys:
I'm still here. Just wanted to say that I have six 500 ml beakers on an old food warmer that heats up to about the temp of hot coffee.

I been using 50/50 hcl and tap water (no proxide) to remove base metals from some of the ronchy yeald stuff like the wiskers from the card slots on PC main boards, solder and all. This stuff is so low on gold content that I don't want to waste my nitric on it.

I start with 400 ml of solution and an exact 10 grams of identical material in each of the six beakers. It will sit for 3 days and fizz, but the solution stays clear. On day 3-4 it turns a tea color and soon turns very dark and you can't see through the beaker. After a week I had complete disolution of all base metals in all six beakers, 4 of the 6 were complete at 5 days.

At this point I filtered off mixing all solution to the same container. I put that same solution back in the 6 beakers with another 10 grams of same material. This time around I had complete disolution in 5 of the 6 after 3 days, with the last one still on going.

Soon I'll try another 10 grams in the same solution. I'm trying to find out how much material in X amount of solution befor I get that cloride bildup. Thats the only reason for filtering between batches at this point. I don't want those minute specks cought up in the sludge. I expect the 3rd round to finish in 2 days or less.

Like GSP said "it becomes self-perpetuating".
It is slow but I does disolve most all base metals if you got the time.
Lets not even talk about the yeald on this stuff :lol:
Ray

 

[creth]

So im still a noob at this and wanted to make sure i read this right. By putting the Sodium Sulfate into the %32 HCL then the copper on the chips, boards, ETC should not be dissolved. However, what about the silver? and how well would this work for preping flatpacks for further refining?