Bauxite, limestone and sodium hydroxide are mixed and wet-ground with a ball mill to produce a red pulp, which is then transported to a storage tank and then pumped out. The steel ball of the ball mill may be mixed into the storage tank with the slurry at this time. Therefore, the storage tank is equipped with an interception device at the feed port so that the steel ball will not fall into the tank. The level gauge above the storage tank ensures that the slurry pump does not idle, ensuring continuous operation of the production process.