PURPOSE: To efficiently recover high-purity iron oxide powder and hydrochloric acid, by adding iron to an aqueous solution of iron chloride generated in acid cleaning of steel with hydrochloric acid to insolubilize and remove impurities, such as Al, thermally concentrating the resultant solution with a roasting gas to insolubilize and remove Si and roasting the obtained purified solution.
CONSTITUTION: An aqueous solution of iron chloride generated in acid cleaning of steel with hydrochloric acid is introduced into a storage tank 1 and kept warm or heated. Iron 27 is then added to form an insolubilized substance 22 containing most of Al, Cr, Cu and P in the solution and part of Si. The resultant substance is then separated and removed in a separator 21. The aqueous solution of iron chloride 28 is then introduced into a contact column 2, brought into contact with a hot gas 3 produced in a roasting step in the latter stage and thermally concentrated to form an insolubilized substance containing most of Si. The obtained insolubilized substance is subsequently separated and removed in a separator 24. The resultant purified solution of the iron chloride 25 is then roasted in a roasting furnace 5 to recover both high- purity iron oxide powder from the produced hot gas 3 in an electric dust collector 7 and hydrochloric acid in a hydrochloric acid recovering column 8.