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I am removing high phosphorous (5~10%) nickel electroless plating from alumina circuit boards using 125 ml concentrated nitric acid to 250 ml water and 60 ml 35% hydrogen peroxide, generally following a published recipe for this task. This works well at 60°C. (I need to re-use the ceramic boards)

I'm doing everything slowly and carefully in a hood with proper protective equipment in another group's laboratory.

They have a modest (50 liter?) acid disposal storage tank, but the container does not appear to be vented. There's just a screw cap that you close and tighten when done. I'm a little worried that even after my solution cools, it has the capacity to produce oxygen gas after disposal in their container.

From this Quora post I understand that one might be able to catalyze decomposition of peroxide using an iron (II) salt, but that suggestion does not apply to a nitric acid solution with added peroxide.

I also don't want to boil the solution to decompose the peroxide, for safety reasons.

Question: How might one go about decomposing hydrogen peroxide in a nitric acid solution so that it can be disposed of, with out generating oxygen gas later?

I suppose that leaving it at 60°C for a few days, loosely covered so that it doesn't evaporate too quickly might work, but I have no way to know.

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    $\begingroup$ You should highlight you ask about solution after reaction. I doubt there's much peroxide left. $\endgroup$ Commented yesterday
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    $\begingroup$ Ask your local haz waste specialist. Mine says don’t mix peroxide and acid, so no go for me… $\endgroup$ Commented yesterday
  • $\begingroup$ @JonCuster yep yep; my thinking is that if the peroxide is neutralized (i.e. returned to water and oxygen), then it's not peroxide any more. Unless your local haz waste specialist is also a homeopathic dilutionist they shouldn't care if the once was, but no longer is any peroxide. :-) $\endgroup$ Commented yesterday
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    $\begingroup$ Well, we aren’t (well, weren’t since I retired) allowed to ‘treat’ waste in our labs. So still no go. $\endgroup$ Commented yesterday
  • $\begingroup$ Maybe try a tiny bit of it in a test tube with some blood? Haemoglobin catalyses H2O2 nicely (in fact, violently!), the question is how long it could withstand the nitric acid. $\endgroup$ Commented yesterday

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Law depends on locale (OSHA and similar), but

I suppose that leaving it at 60°C for a few days, loosely covered so that it doesn't evaporate too quickly might work, but I have no way to know.

i.e. storage of an oxidizer at elevated temperatures does not sound good.

  • keep the solution cool, and don't tighten the lid yet (to prevent a pressure buildup). The bottles of pristine aqueous $\ce{H2O2}$ we use in the lab, beside their added inhibitor, have a lid designed to allow venting, are only $\pu{1 L}$ in capacity max, and we keep only one per lab in the fridge at about $\pu{8 ^\circ{}C}$, far away from anything which can be oxidized by it.
  • If by dilution into water the concentration of the peroxide is about 5% in weight, and the solution is not above room temperature, carefully decompose the peroxide with sodium thiosulfate, $\ce{NaS2O3}$. Then neutralize the excess of the acid (e.g., $\ce{Na2CO3}$ or $\ce{NaHCO3}$). Especially in the beginning, this creates some fizz and foam (but you already use a larger container anyway); on the other hand, it already is some indicator about how much acid is left.
  • Since you generated an aqueous solution of $\ce{Ni^{2+}}$, the remainder is for the bin «aqueous heavy metal».

In our school, the shop for the chemicals equally is in charge to coordinate the waste disposal. If you are organized in a similar way, it is worth to coordinate with them (e.g., schedule when waste is picked up, the right container/label for the container; hints if/when it is safe to concentrate the solution for a lesser volume -- which here would be after the desactivation of the peroxide and after neutralization of the excess of acid).

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  • $\begingroup$ OK I will give some thought to sodium thiosulfate - is the effect catalytic (i.e. a small amount goes a long way) or is there some proportion (e.g. M/M) that I should be thinking of? (btw by "loosely covered" I meant placing a watch glass (those concave things) over the beaker to minimize evaporation loss, anyway "neutralizing" the peroxide is preferred) $\endgroup$ Commented yesterday

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