Sciencemadness Discussion Board

Silica dust

Phosphor-ing - 19-1-2024 at 08:42

There is a white/grey powder on the floor of a new warehouse we are converting. No work has been done inside yet. I think this powder is silica dust left over from the original build (saw cuts in the concrete floor). Is there a test I can do at to determine if silica is present/how much of the dust is silica? I don’t have analytical instruments. I do have glassware and access to basic chemicals.
I am not trying to do an analysis for the job/OSHA requirements. I just want to do a little chemistry and learn a new test or two.

Rainwater - 19-1-2024 at 15:37

SiO2 is basicly glass. Concrete is a complex mixture with lots of carbonates and oxides.
Most the components react with mineral acids.
If you dry and weigh a sample, aqua regia should remove almost everything but the silica.

A safer method would be HCl + hydrogen peroxide
This mixture is almost as powerful as aqua regia and will disolive most metals

If its new concrete, unsealed, then the slab will 'dust' CaCO3 for a few months. Apply a sealent or keep it mopped/wet.

Concrete dust is dangerous because it has to be coughed up, your body has no other way to get rid of it.

All this goes without saying anything about the dangers of exposing a mystery dust to strong acids and oxidizers. Stay safe

Bedlasky - 20-1-2024 at 06:26

Silica dissolves in molten NaOH. You can then dissolve sodium silicate in the water and precipitate hydrated SiO2 by adding HCl. Or slightly better test is when you add molybdate in to the sodium silicate solution before you add HCl. Molybdate forms with silicate yellow complex in acidic solution (silicomolybdate [SiMo12O40]4-). Ammonium and potassium silicomolybdates are insoluble, so you can precipitate them.

Phosphor-ing - 21-1-2024 at 06:07

I will get a sample tomorrow while I am at work. The HCl/peroxide seems doable.

I read an article about testing for it, but they used infrared spectroscopy. They mentioned the “pyrophosphoric acid method”. I found an article about that but it’s in Chinese.

Anyone know anything about the pyrophosphoric method? Or could possibly translate what I assume to be Chinese? I don’t have access to a computer right now so translation is unfortunately outside my abilities.