Helium
Chronus
That article says "Once it is released into the atmosphere it [helium] becomes uneconomical to recapture it". That is simply not true.
Helium is recovered from the atmosphere in industrial quantities as a by-product of cryogenic air separation plants whose main purpose is to produce gaseous or liquefied oxygen and nitrogen.
It is a high value by-product and far from unecomical. I worked with BOC in the 60s, and there was always a mini plant at each basic oxygen process steelworks to extract argon, helium, neon, xenon and krypton from the atmosphere. The atmospheric carbon dioxide though, was discharged as waste.