Hydrogen sulfide is scrubbed from a gas stream to prepare dissolved alkali metal sulfide or hydrosulfide, which is used to prepare feed electrolyte solution for electrochemical processing to generate alkali metal hydroxide in catholyte and polysulfide in anolyte, which may be recovered from an electrochemical reactor and which may be subjected to further processing to precipitate elemental sulfur. Aqueous scrubbing solution may include alkali metal carbonate capture agent to capture hydrogen sulfide in alkali metal bicarbonate The gas stream may include carbon dioxide in addition to hydrogen sulfide, and a ratio of dissolved alkali metal carbonate to bicarbonate may be increased prior to electrochemical processing.