stripping cell acid stays black

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nickton

Well-known member
Joined
Dec 10, 2015
Messages
233
Location
Northern California
hello. I just finished a 5.5 kilo batch of assorted pins and other electroplated material, and have left my sulfuric acid sitting for over a week in order to separate black slime and save the acid for a later run. I read the tutorial which shows pictures of relatively clear liquid above black mud, to be decanted, but this won't happen for me. I have a jar full of opaquely black solution that hasn't cleared at all. I wonder what's going on and what to do next. There appears to be some accumulation at the bottom of my tall glass container, but I'm not sure since everything is so densely black. I guess my next step would be filtering in a fiberglass "charmin" plug but...

I wonder why the acid is still so black. :mrgreen:

thanks,
Nick

aspiring refiner.
 

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Have you diluted the acid at all? Concentrated sulfuric acid is very "thick". You can add the acid to some water to thin it out. Do it slowly and carefully, adding the acid to the water, not the water to the acid. Once the precipitate has settled, you can heat the acid to evaporate the water and reuse the acid.

Dave
 
Hmm. Hadn't thought of that. I was trying to avoid dilution, but I guess I could try it and like you say evaporate later. I don't love boiling sulfuric acid, but it isn't impossible. Do you think I should filter with fiberglass first?


thanks again,
Nick
 
Dilute just enough so the acid becomes more fluid. You don't need to approach boiling to reconcentrate the acid, just hot enough to evaporate water. If you filter first, it's one more thing to deal with. If you dilute and let it settle, it will all be in one place.

Dave
 
okay. I diluted it probably too much, and am filtering it through some fiberglass. Thanks for reminding me I didn't need to boil to evaporate water later.
It will take a while to filter and clean the sludge before I boil it in hot HCl. I also added some baking soda to help neutralize the remaining acid and was wondering if this does anything to the black solids (where does it go?)

One other thing I thought I'd share: I was just playing around with my little furnace and decided to melt down some of the de-plated pins and stuff. I think I could use some of this for later in quartation.

I cleaned and separated the more golden looking material, guessing it might be better quality than the rest. I figured trace amounts of gold left on pins would add to any in-quarted gold when I process it. I wonder how much there is actually in there. The yellow color surprised me since I figured it must be mostly copper, after removing magnetic material before smelting. My guess is it's some form of brass now.
 

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Be very careful when you decide to evaporate the water from the acid. While you don't need to approach the boiling point of sulfuric acid 337°C / 638.6°F, you do need to get it hot, and hot sulfuric is very unforgiving. Once you feel it's evaporated to the point you want, cover it and allow it to cool back down before handling it. Even cool, sulfuric is dangerous, but hot, it is a beast you don't want to come into contact with. Thick, long gloves, an apron, and a full face shield are a must.

Dave
 
FrugalRefiner said:
Be very careful when you decide to evaporate the water from the acid. While you don't need to approach the boiling point of sulfuric acid 337°C / 638.6°F, you do need to get it hot, and hot sulfuric is very unforgiving. Once you feel it's evaporated to the point you want, cover it and allow it to cool back down before handling it. Even cool, sulfuric is dangerous, but hot, it is a beast you don't want to come into contact with. Thick, long gloves, an apron, and a full face shield are a must.

Dave

Agreed hot concentrated sulphuric is in the same class as hydrofluoric as far as the danger it poses in my opinion, nasty stuff!
 
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