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I have 4 liters of electrolysis waste that was used to process stainless steel cathodes.

About half of it was oxalic acid based and the other half was sodium bicarbonate based (currently stored separately, pH 1.7 and 8.4 respectively). It is all mostly liquid with some precipitates currently. My assumption is that all of it contains dissolved (?) chromate complexes/compounds or maybe other chromium compounds like oxalates, hydroxides, oxides, etc.

Since chromates are controlled hazmat here I have to take them to a disposal facility. It's straightforward enough for me to take the liquids there, but I'd rather find a way to get all of the chromates and chromium compounds out of solution so that I can neutralize and dispose of the liquids as household waste and just store the solids to take in one big trip to disposal services later.

Since my ultimate goal is to just dispose of them, I'm not trying to extract chromates with any sort of purity. It's more important that I just get them all out of the liquid phase.

Is there some process by which I can do this using other relatively safe and easy to obtain chemicals?

Currently on my shelf I have a decent collection of filter papers, a vacuum filter, a pH tester, oxalic acid, sodium bicarbonate, hydrogen peroxide, table salt, hydrochloric acid (muriatic), distilled water, and a wide range of various shop solvents (ethanol, isopropanol, xylene, acetone, mineral spirits, MEK, and I'm pretty sure there's some toluene somewhere). Also I have iron, mild steel, aluminum, and copper stock, and a DC power supply. Not sure if any of that is useful but, that's a list of stuff that I already own.

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    $\begingroup$ Simplest thing, which does not generate additional waste: let the 4 liters of solution evaporate down to dryness, or close to it, and take it to the hazardous waste folks. $\endgroup$
    – Ed V
    Nov 14, 2021 at 18:01
  • $\begingroup$ @EdV Sweet. That was my first thought too, and that's what I was hoping someone would suggest. I wasn't sure if there was any chromium stuff that liked to exist as a gas. Can I boil it down, or give it at least a little extra heat, instead of waiting for it to evaporate? $\endgroup$
    – Jason C
    Nov 14, 2021 at 18:08
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    $\begingroup$ Sure, but gently and with good ventilation. It will likely corrode or strongly stick to the vessel, which is why I would just let the solution evaporate in disposable plastic containers. The less you have to mess with it, the better. $\endgroup$
    – Ed V
    Nov 14, 2021 at 18:14
  • $\begingroup$ Sounds like a plan. I'll filter first to get the easy stuff out (or not if I'm lazy) then just stick the rest outside in a wide container in the sun. I can neutralize the acid with the bicarbonate solution too. Post it as an answer if you want some bonus points, heh. Thanks! $\endgroup$
    – Jason C
    Nov 14, 2021 at 18:17
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    $\begingroup$ One thing: if you put it outside, please ensure that critters cannot drink that toxic brew. A shed or such is ideal for this. $\endgroup$
    – Ed V
    Nov 14, 2021 at 18:20

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