[asynchronous13]

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.

[segfaultbuserr]

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?

[joshvm]

The official advice is to keep neutralising it, collect the sludge and pour the waste water away.

https://www.mgchemicals.com/products/prototyping-and-circuit...

> The solution must not be put down the drain because of residual copper ions left in it. To make it safe for disposal, you can add sodium carbonate (washing soda) or sodium hydroxide to it to neutralize it, until the pH value goes up to between 7.0 and 8.0, testing it with indicator paper. Copper will be deposited as a sludge. Allow the sludge to settle, pour off the liquid, further dilute it with water and then it can be poured down the drain. Collect the sludge in plastic bags and dispose of it as required by your local waste authority.

[kragen]

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.

[hinkley]

First warning with neutralizing acids: You're going to release a lot of heat, make sure you have a large thermal mass to absorb it. Someone else mentioned mixing your ingredients with water first. This is why.

From what I understand the last thing you want to experience is an explosion of hydrofluoric acid.

The internet seems to suggest lime (->fluorspar) or soda lye (->NaF, used for fluoridating water) to neutralize HF, but that's two other substances you wouldn't want raining on your head... be careful out there.

[droithomme]

Yeah if you just dump a base into these strong acids things go foom! and you end up with dead makers.

Don't mix this stuff in dilution in an enclosed space either as the H2 gas can create another explosion hazard.

[kragen]

HF is technically a weak acid, but I wouldn't venture to neutralize it quickly; it's very reactive even if it doesn't fully dissociate in water.

As for hydrogen, neutralizing acids with bases doesn't generally produce it, but ventilation is still a good idea.

[kragen]

Why wouldn't you want fluorspar raining on your head? Just because it's heavy and hard?

I suggested fluorspar rather than NaF because a backyard full of fluorspar is a pretty rock garden, while a backyard full of NaF is a toxic waste dump.

[droithomme]

Cl's in toilet cleaner. Dilute is not a problem.

Cu though is an aquatic herbicide (used to rid decorative ponds of all plant life including algae) and can mess up things.

> at the end of the day everything goes to a wastewater treatment plant

Some of these things, especially the photosensitive chemicals in particular ammonium dichromate will annihilate the wastewater treatment plant. Experienced this problem in an industrial context once, resulting in tens of millions of dollars in damages to taxpayers and a giant fiasco. As a result our privileges to use the municipal sewage system were withdrawn and we had to spend tens of millions in evaporation towers since no water could leave our facility ever again.

[muricula]

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]

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.