A method for recovering helium from a feed gas mixture comprising helium, carbon dioxide and at least one of methane and nitrogen, and wherein at least a part of the feed gas mixture is subjected to a separation sequence including a membrane-based separation and an adsorption-based separation forming a helium product, wherein the the membrane based separation is performed using a first membrane separation step and a second membrane separation step, the membrane based separation and the separation sequence includes no further membrane separation steps, the adsorption based separation is performed using a pressure swing adsorption step, at least a part of the feed gas mixture is subjected to the first membrane separation step forming a first retentate and a first permeate. A corresponding arrangement is also provided.

Disclosed is a purification method for removing a metal component from a fluorine gas containing hydrogen fluoride and a metal component. This method includes a removing step for removing the hydrogen fluoride and the metal component therefrom by bringing the fluorine gas into contact with a solid metal fluoride to adsorb the hydrogen fluoride and the metal component on the metal fluoride. The content of the hydrogen fluoride in the fluorine gas before the removing step is 50 volume ppm to 1 volume %, relative to the total volume of the fluorine gas, the hydrogen fluoride and the metal component. The metal fluoride is preferably an alkali metal fluoride or an alkali earth metal fluoride. Surprisingly, the presence of hydrogen fluoride in a fluorine gas makes it possible to remove a metal component therefrom as an impurity as a result of adsorption thereof by a metal fluoride.

The present invention relates to a hydrogen sulfide purification method including removing a lithium raw material from a mixed gas which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and the lithium raw material and which includes unreacted hydrogen sulfide and the lithium raw material.