METHOD AND APPARATUS FOR PRODUCING VANADIUM COMPOUND, AND METHOD AND APPARATUS FOR PRODUCING REDOX-FLOW BATTERY ELECTROLYTE

A production method comprises an alkali extraction step (step 12) for obtaining an alkaline leachate by adding an alkali and water or an alkaline solution to raw material ash, which contains ammonium sulfate, sulfuric acid, vanadium, and at least one other metal selected from among nickel, iron, and magnesium, until a pH of 13 or higher is reached; a solid-liquid separation step (step 13) for separating the alkaline leachate into solid and liquid phases to obtain a vanadium-containing leached filtrate; an evaporation/concentration step (step 14) for evaporating and concentrating the leached filtrate to obtain a concentrate; and a crystallization/solid-liquid separation step (step 15) for cooling the concentrate to cause crystallization and recovering a vanadium compound-containing precipitate. The other production method comprises an alkali extraction step (step 32); a solid-liquid separation step (step 4); an evaporation/concentration step (step 36); an alkali concentration adjustment step (step 37) for obta