Don't Dump Your Toxic Wastes
As a general rule, hazardous waste is not dumped, buried, or otherwise sequestered if it can be helped -- destroying the waste is by far the better option, and with the base Anima spell-set's Book of Destruction, quite feasible even without modern technology. Of course, there are technological approaches to the problem at hand as well if you'd rather keep your industry and your mages separate.
So, we have a big pile of water-reactive hazardous waste on our hands here. What fun!
Your lampyridae falls into a general class of materials known as water-reactive materials (WRMs); several real-life materials in this class are industrially important, including some that generate toxic gases on water contact:
- Alkali metal hydrosulfides (NaSH and friends) -- used in tanning, produce H2S on water contact
- Chlorosilanes (anything with a Si-Cl bond) -- used in the production of silicon, silicon coatings, and certain industrial silicones, produce HCl on water contact
- Phosphorus sulfides (P4S10, P2S3) -- used in the production of organosulfur compounds, produce H2S on water contact
- Phosphide salts (anything with a P(3-) anion) -- used in incendiary applications, produce PH3 on water contact
- Alkali metal amides (NaNH2 and friends) -- used for miscellaneous chemical purposes, produce NH3 on water contact
First, some bad news
However, unlike your lampyridae heap, these water-reactive materials react instantly with water to produce other compounds and the characteristic poisonous gas. This means that disposal doesn't take long -- the combination of flooding quantities of water with something that can neutralize the toxic gas can be used, while some of them can also be fed to an incinerator.
This means that lampyridae is actually more difficult to dispose of, partly because of its reduced acute hazards compared to the materials mentioned above, and also because unlike the materials above, lampyridae does not go away in the process of emitting the toxic gas. This leads us down a different path than what's normally done to get rid of noncombustible, water-reactive materials -- destroying the material itself.
Sticking a mage on the problem
Fortunately, the base Anima magic system does provide some arcane assistance with this topic. Cracking open the Book of Destruction is the easiest option -- Minor Destruction would likely suffice for getting rid of a few stray scraps of the stuff, and Aura of Destruction could be used to create a reactor setup equivalent in effect to the chemistry proposed above, although I doubt it will be much lower-maintenance than keeping something oxygen clean and fluoride passivated.
(There are options from the Book of Creation for minor work, and a nuclear option, if you will, in the top end of the Book of Earth, but neither of them are quite as practical as a straight-forward destruction technique.)
Destroying the stuff chemically (or how to get rid of a pile of it that showed up in your driveway IRL)
If hiring a mage to refresh an Aura of Destruction isn't an option, but reasonably modern technology is, all hope is not lost. Looking again to the industrial machinations of reality, one reagent leaps out as being able to destroy even the most stubborn of substance problems: chlorine trifluoride.
ClF3, despite being easily worse than anything lampyridae gives off, is a staple of the semiconductor industry for its unrivaled efficiency at getting pesky oxide residues off the walls of chemical vapor deposition chambers. Almost no mineral known to man, not even asbestos, can withstand the intense fluorinating and oxidizing power at play here.
So, assuming that ClF3 does react with lampyridae (a fairly safe assumption to make considering chlorine trifluoride's legendary reactivity), a no-mage-needed disposal procedure would go as follows:
- Charge a fully fluoride passivated steel pressure vessel with a load of solid (powdered) lampyridae. (Any contaminants introduced here will get incinerated by the ClF3 as well.)
- Seal the vessel tightly -- you might as well make the charging hatch a plug-hatch that is sealed by pressure.
- Introduce dry, oil free purge nitrogen to bring the vessel up to operating pressure and remove any moisture or other contaminants.
- Evacuate the vessel to remove the purge nitrogen, which also removes any contaminants the purge may have swept up.
- Slowly introduce the chlorine trifluoride to the system while monitoring the system for temperature rises -- any rise in temperature outside the reaction vessel is an indication of contamination, and cause for aborting the process and re-purging/re-evacuating.
- If no contamination in the lines is detected, continue introducing chlorine trifluoride vapor to the system until regulator pressure is reached.
- Pressure will continue to build as the reacting chlorine trifluoride produces acid gases and oxidized byproducts -- at this point, the acid gases should be vented to a wet caustic scrubber, and the vent maintained so that reactor pressure is constant while chlorine trifluoride is added
- The chlorine trifluoride addition process should continue until the exotherm ends and the reaction vessel begins to cool, indicating that all of the charge has reacted.
- A final dry nitrogen purge should then be used to scavenge acid gases and remnant chlorine trifluoride into the scrubber.
- Finally, the reactor can be opened to receive the next batch of lampyridae.
Bypassing this problem
Interestingly enough, the function lampyridae performs can be performed in other ways using the technological level of the setting -- fixed lighting can be performed using gaslamps instead, and portable kerosene lanterns can be used to provide some form of portable light, although the light quality in both cases would be less until gas mantles were developed.