[SteveE]

Hello All.

How would I go about dissolving 8 to 10 grams of quartz off a gold in quartz specimen? I'd like to use hydrofluoric acid but that's impossible for me to obtain.

Any help would appreciated.

Steve

[Corribus]

Realistically HF is the only way. There are some ways you cam generate HF in situ but ymmv.

[SteveE]

If you have some ideas on this, I'd like to know. You can PM if you want.

[SteveE]

I found another way
 Already have the sodium hydroxide so this should be a cinch.
https://youtu.be/_1yNfsYMy1A

[Enthalpy]

If you seek gold as a material, independently of its shape and initial alloying elements, gold might be easier to dissolve than quartz. It would also need less solvent than the more abundant quartz.

After crushing the gold-containing quartz, many liquid metals will dissolve gold but not quartz. Do not use mercury not lead as their vapours are toxic, but tin, bismuth or the galinstan alloy could be a choice.

[SteveE]

I certainly don't want to dissolve the gold. I simply want to remove some of the quartz to improve the aesthetics of the specimen.

I would post a picture of a finished specimen but doesn't look like I can do that.

[Borek]

I would post a picture of a finished specimen but doesn't look like I can do that.

Shouldn't be a problem if the image is not too large. Click on Additional Option... below the edit field, then select Attach/Choose file.

[SteveE]

I found another way
 Already have the sodium hydroxide so this should be a cinch.
https://youtu.be/_1yNfsYMy1A

After dissolving in sodium hydroxide I'm left with a brown residue on the bottom of the stainless steel beaker. I'm trying to figure out the safest way to dispose of it.. Does this process form another chemical or is it still sodium hydroxide and silicone dioxide ,plus some impurities?

[Borek]

In general SiO₂ dissolves in NaOH producing just colorless metasilicate. But I doubt the rock was just a pure SiO₂, so I would expect impurities. Could be what is left is not exactly what was present in the rock though, it could react with the NaOH as well.

I admit I am a bit surprised NaOH is that effective. While I would never keep NaOH in glass bottle to avoid etching and contamination, I would also never expect it to easily eat through.

[Corribus]

If you leave glassware in base bath (KOH and solvent) for weeks, it does get etched.. a little. But yeah I would not predict it to be effective at total digestion of silica. Although, my experience is at room temperature.

We've been trying to do zeolites lately with acid digestions and it doesn't work very well (not surprising at all). I've resisted going the HF route. Maybe I should try some KOH solution on our microwave digester.

[SteveE]

Hello

I have more specimens I'd like to dissolve quartz off of.

I'm having trouble trying find a corrosion resistant stainless steel 150 ml beaker with a lid. A crucible with a lid would work as well.

I've been looking at some of the scientific supply websites and haven't found anything. Just wondering if anyone knows off hand where I can find one. Not asking someone to do research on my behalf. Perhaps someone owns a scientific supply store here in this forum and has one for sale.

Thanks

[RisingEastStar17]

Quartz is almost entirely comprised of silicon oxides and trace elements such as berrylium, gold, copper and zinc. I would definitely use hydrofluoric acid or some super acid. So really, there is no other alternative.

[Borek]

I would definitely use hydrofluoric acid or some super acid.

Nope, super acids won't help. Hydrofluroic is effective not because it is an strong acid (actually it is quite weak), but because the reaction produces volatile SiF₄.