[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.