The invention relates to energy mechanical engineering and can be used in power installations involving a liquid-metal heat carrier. A mass transfer apparatus including a housing and, provided therein, a flow reaction chamber filled with a solid-phase granulated oxidation agent, and an electric heater positioned in the reaction chamber. The housing of the apparatus is equipped with a repository for reserves of the solid-state granulated oxidation agent, said repository being located below the reaction chamber and being made in the form of a cup having a bottom, said cup being connected to the re-action chamber. The technical result consists in extending the operational duration of the mass transfer apparatus.