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Comment by fencepost | Hacker News Reader

For people talking about glass recycling, it's not NEARLY as simple as you might think because of input issues. Along with CoE (Coefficient of Expansion) concerns that may arise depending on the exact input materials, recycling ends up with grit and contaminants in the material, and those end up as inclusions in final products. That might not be a concern for glass blocks, but for anything where you care about the end quality (food containers, large sheets of glass for windows, etc.) inclusions can result in a lot of production loss. It's also not like you can just melt it and let the inclusions float or sink out - molten glass doesn't flow like water, and particles don't just move through it.

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And long, long before recycling glass, people just reused the bottle as a bottle. Which is IMHO the better approach.

This is why they have green and brown bottles in beverage industries, they're typically lower down the recycling chain so impurities and mixed silicates can be used without affecting the end use.

I don't think this glass is any less prone to recycling than standard sodium glass since it looks to be a post process with largely the same input materials.

Green, but especially brown, also protects photosensitive contents (eg beer).

One of the major products made out of recycled glass is Fiberglass (yes, it's literally glass) - sold in rolls for insulation.

And why would this contamination not happen with non-recycled glass, which is made from sand?

They use sand from deposits that are quite pure.

As another commenter said, they use very clean sources.

Even then, the sources are very at the very least consistent in their makeup. It's a lot easier to deal with a consistent type of contamination than a varying one.

Complicated, but routinely done? Glass recycling seems to be routine and widespread. Glass containers and jars, that is, not drinking glasses.

It's absolutely routinely done and there's a lot of PCR glass used, but there's also a significant amount of cleaning needed. I'm not involved in the industry beyond past interest in glasswork, but I wouldn't be surprised if there were packaging changes happening all along that improve the simplify cleaning - eg chemically soluble ink printing on containers instead of glued paper or composite labels.

Maybe a better approach would be to purify it by chemically dissolving the old glass in eg sodium hydroxide and reprecipitating it out.

I'm sure people have tried that though and it doesn't work for some reason.

There are a bunch of cleaning and separating steps that happen for removal of organics, metals, plastics, different colors of glass, etc.

Pretty sure the chemical reaction to actually dissolve glass is not particularly fast and I have no idea what you'd do to later precipitate it out, but it may not be an economically viable approach.

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