Landfill it, it's harmless. And since it's only ash that messes up the salt, the mass is tiny compared to the input. Plastics produce virtually no ash. Salt

Landfill it, it's harmless. And since it's only ash that messes up the salt, the mass is tiny compared to the input. Plastics produce virtually no ash. Salt disposal could be a problem if it contains heavy metals, or if it contains something you want to recover (possibly phosphorus). Either way, MSO ended up concentrating the material in question and transforming it into a simpler chemical form, reducing the disposal problem, or making the recycling easier.