A method and apparatus are disclosed for regenerating calcium oxide used in the production of hydrogen gas. The method includes steps of: (a) streaming a solid reactant into an inlet port of a contactor vessel; (b) streaming a purge oxidant into an oxidant port of the contactor vessel to reduce a partial pressure of a gas over the solid reactant; (c) venting the gas from a gas port of the contactor vessel; and (d) removing the solid reactant from a discharge port of the contactor vessel.