3 ms·

Speaking of which, does anyone know where (in the US) I can safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid? I used to etch my own board

by m0zg 7y ago

Speaking of which, does anyone know where (in the US) I can safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid? I used to etch my own boards years ago. And ever since then the spent stuff just sits in glass jars in a double plastic box in my garage. I don't etch anything anymore, and it's taking up space.

segfaultbuserr 7y ago
> safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid The first step is easy: neutralize them with any base, such as baking soda. You don't need precision, just add a lot of it, and make sure the pH is close to 7 (or beyond, baking soda is not corrosive) at the end. After this step, the solution is no longer acidic or corrosive and much safer to handle. Unfortunately, the next step is tricky. The solution is safe, but it still contains a lot of Cu+ ions, which is a heavy metal pollutant and poisonous. On the other hand, if your sulfuric or hydrochloric acid is unused for etching anything (clean without those nasty ions), you are good to go, just dump them in the sink after you've neutralized them (test with pH paper) it's perfectly safe.
- m0zg 7y ago
  Is this what people actually do? I mean I'm aware I could neutralize them, but Cu is still going to be in there and I still can't pour this stuff down the drain. Then there's ferric chloride which is just nasty stuff that will likely stain everything it comes in contact with. I just want to get rid of it in a fully environmentally safe way.
  - segfaultbuserr 7y ago
    Don't ask me, I don't know, as I'm asking the same question. I'm waiting for some answers to my question: https://news.ycombinator.com/item?id=20659004 https://news.ycombinator.com/item?id=20659004
  - parsimo2010 7y ago
    I'm not sure it is economical, but I had some Sodium Persulfate etchant that was full of copper and accidentally dropped a piece of steel in it. The copper plated onto the steel almost instantly. You could probably use iron filings (or some metal that won't dissolve in your acid) to pull most of the copper out of the acid, and then neutralize. I'm not sure what you would do with the solid copper after that. It might take some effort to get a system that was reliable and economical, but the basic idea of precipitating out the copper before neutralization should work.
    - marmaduke 7y ago
      I don't think it's hard. My high school chemistry teacher did this, reusing the same copper every year. (I dont remember the details though)
faissaloo 7y ago
There are usually reactions you can do to make them safe to dispose of in a regular manner, you should be able to find them with a decent amount of googling.
asynchronous13 7y ago
pretty easy really. Add acid to water, then add baking soda to the acidic water until it's neutralized. (no more bubbling), then pour it down the sink with more water. Use appropriate precautions, gloves, goggles, well-ventilated area, etc. Once the acid is neutral, it won't hurt anything in the pipes.
- muricula 7y ago
  The concern probably isn't the acidity, but the heavy metals and other toxins in the solutions. Pouring tpxins down the drain isn't a good idea.
  - hinkley 7y ago
    Yeah it's being talked around in this thread but I think most of the participants seem to get it. The solvents can be broken down to things that are compatible with the sewer system. The hard part to deal with is the material you dissolved with the solvent.
- segfaultbuserr 7y ago
  But is it acceptable to dump wastewater with Cu+/Cl- ions inside? I've read that according to some regulations in some areas, they are considered pollutants and should not be dumped directly to the drainage. Or is it something you can just ignore, because at the end of the day everything goes to a wastewater treatment plant, and your volume/concentration is too low to be considered hazardous, and actually not more harmful than the wastewater of commercial chemical cleaners, and well within the wastewater processing capabilities for small volumes? Can anyone give an authoritative answer to this question?
  - kragen 7y ago
    Cl ions are fine; dissolved table salt consists of them, plus some cations. The copper is more of a problem, and I don't know the official answer. I'd think that if you could oxidize it to copper monosulfide (covellite), cupric oxide (tenorite), or even fully hydrated copper carbonate (malachite) if you don't have acid rain, that would adequately protect it from weathering and thus allow you to dispose of it safely. But it might be more practical, as well as legally safer, to electrolytically reduce it back to copper and sell it for recycling. Copper, as a semi-precious and semi-noble metal, is recycled actively everywhere the humans live. I think the biggest problems for chip fabrication waste (not circuit board etching) are HF and nonpolar organic solvents. I'd think neutralizing HF with chalk would yield fluorspar, which is resistant to weathering even over geological timescales. But again I don't know what the official answer is. Maybe dumping fluorspar in your yard will get you arrested.

by m0zg 7y ago

segfaultbuserr 7y ago

> safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid The first step is easy: neutralize them with any base, such as baking soda. You don't need precision, just add a lot of it, and make sure the pH is close to 7 (or beyond, baking soda is not corrosive) at the end. After this step, the solution is no longer acidic or corrosive and much safer to handle. Unfortunately, the next step is tricky. The solution is safe, but it still contains a lot of Cu+ ions, which is a heavy metal pollutant and poisonous. On the other hand, if your sulfuric or hydrochloric acid is unused for etching anything (clean without those nasty ions), you are good to go, just dump them in the sink after you've neutralized them (test with pH paper) it's perfectly safe.

m0zg 7y ago
Is this what people actually do? I mean I'm aware I could neutralize them, but Cu is still going to be in there and I still can't pour this stuff down the drain. Then there's ferric chloride which is just nasty stuff that will likely stain everything it comes in contact with. I just want to get rid of it in a fully environmentally safe way.
- segfaultbuserr 7y ago
  Don't ask me, I don't know, as I'm asking the same question. I'm waiting for some answers to my question: https://news.ycombinator.com/item?id=20659004 https://news.ycombinator.com/item?id=20659004
- parsimo2010 7y ago
  I'm not sure it is economical, but I had some Sodium Persulfate etchant that was full of copper and accidentally dropped a piece of steel in it. The copper plated onto the steel almost instantly. You could probably use iron filings (or some metal that won't dissolve in your acid) to pull most of the copper out of the acid, and then neutralize. I'm not sure what you would do with the solid copper after that. It might take some effort to get a system that was reliable and economical, but the basic idea of precipitating out the copper before neutralization should work.
  - marmaduke 7y ago
    I don't think it's hard. My high school chemistry teacher did this, reusing the same copper every year. (I dont remember the details though)

faissaloo 7y ago

There are usually reactions you can do to make them safe to dispose of in a regular manner, you should be able to find them with a decent amount of googling.

asynchronous13 7y ago

pretty easy really. Add acid to water, then add baking soda to the acidic water until it's neutralized. (no more bubbling), then pour it down the sink with more water. Use appropriate precautions, gloves, goggles, well-ventilated area, etc. Once the acid is neutral, it won't hurt anything in the pipes.

muricula 7y ago
The concern probably isn't the acidity, but the heavy metals and other toxins in the solutions. Pouring tpxins down the drain isn't a good idea.
- hinkley 7y ago
  Yeah it's being talked around in this thread but I think most of the participants seem to get it. The solvents can be broken down to things that are compatible with the sewer system. The hard part to deal with is the material you dissolved with the solvent.
segfaultbuserr 7y ago
But is it acceptable to dump wastewater with Cu+/Cl- ions inside? I've read that according to some regulations in some areas, they are considered pollutants and should not be dumped directly to the drainage. Or is it something you can just ignore, because at the end of the day everything goes to a wastewater treatment plant, and your volume/concentration is too low to be considered hazardous, and actually not more harmful than the wastewater of commercial chemical cleaners, and well within the wastewater processing capabilities for small volumes? Can anyone give an authoritative answer to this question?
- kragen 7y ago
  Cl ions are fine; dissolved table salt consists of them, plus some cations. The copper is more of a problem, and I don't know the official answer. I'd think that if you could oxidize it to copper monosulfide (covellite), cupric oxide (tenorite), or even fully hydrated copper carbonate (malachite) if you don't have acid rain, that would adequately protect it from weathering and thus allow you to dispose of it safely. But it might be more practical, as well as legally safer, to electrolytically reduce it back to copper and sell it for recycling. Copper, as a semi-precious and semi-noble metal, is recycled actively everywhere the humans live. I think the biggest problems for chip fabrication waste (not circuit board etching) are HF and nonpolar organic solvents. I'd think neutralizing HF with chalk would yield fluorspar, which is resistant to weathering even over geological timescales. But again I don't know what the official answer is. Maybe dumping fluorspar in your yard will get you arrested.